Merge branch 'master' of https://github.com/iotbzh/afb-daemon

10 files changed, 2945 insertions, 1004 deletions

diff --git a/doc/FAQ.html b/doc/FAQ.html
index 4ebefaa3..98337815 100644
--- a/doc/FAQ.html
+++ b/doc/FAQ.html
@@ -8,7 +8,7 @@
 <h1>Frequently Asked Question about AFB-DAEMON</h1>
 
 <pre><code>version: 1
-Date:    24 mai 2016
+Date:    27 mai 2016
 Author:  José Bollo
 </code></pre>
 
diff --git a/doc/FAQ.md b/doc/FAQ.md
index 32ef2789..61105823 100644
--- a/doc/FAQ.md
+++ b/doc/FAQ.md
@@ -1,7 +1,7 @@
 Frequently Asked Question about AFB-DAEMON
 ==========================================
     version: 1
-    Date:    24 mai 2016
+    Date:    27 mai 2016
     Author:  José Bollo
 
 TABLE-OF-CONTENT-HERE
diff --git a/doc/afb-daemon-vocabulary.html b/doc/afb-daemon-vocabulary.html
index b398aa33..fadd1dee 100644
--- a/doc/afb-daemon-vocabulary.html
+++ b/doc/afb-daemon-vocabulary.html
@@ -8,16 +8,15 @@
 <h1>Vocabulary for AFB-DAEMON</h1>
 
 <pre><code>version: 1
-Date:    24 mai 2016
+Date:    27 mai 2016
 Author:  José Bollo
 </code></pre>
 
 <p><ul>
  <li><a href="#Vocabulary.for.AFB-DAEMON">Vocabulary for AFB-DAEMON</a>
  <ul>
-  <li><a href="#Authentification">Authentification</a></li>
-  <li><a href="#Context">Context</a></li>
-  <li><a href="#Level.of.authorisation..LOA.">Level of authorisation (LOA)</a></li>
+  <li><a href="#Event">Event</a></li>
+  <li><a href="#Level.of.assurance..LOA.">Level of assurance (LOA)</a></li>
   <li><a href="#Plugin">Plugin</a></li>
   <li><a href="#Request">Request</a></li>
   <li><a href="#Reply.Response">Reply/Response</a></li>
@@ -25,41 +24,83 @@ Author:  José Bollo
   <li><a href="#Session">Session</a></li>
   <li><a href="#Token">Token</a></li>
   <li><a href="#UUID">UUID</a></li>
+  <li><a href="#x-afb-reqid">x-afb-reqid</a></li>
   <li><a href="#x-afb-token">x-afb-token</a></li>
   <li><a href="#x-afb-uuid">x-afb-uuid</a></li>
  </ul>
  </li>
 </ul></p>
 
-<a name="Authentification"></a>
-<h2>Authentification</h2>
+<a name="Event"></a>
+<h2>Event</h2>
 
-<a name="Context"></a>
-<h2>Context</h2>
+<p>Message with data propagated from the services to the client and not expecting
+any reply.</p>
 
-<a name="Level.of.authorisation..LOA."></a>
-<h2>Level of authorisation (LOA)</h2>
+<p>The current implementation allows to widely broadcast events to all clients.</p>
+
+<a name="Level.of.assurance..LOA."></a>
+<h2>Level of assurance (LOA)</h2>
+
+<p>This level that can be from 0 to 3 represent the level of
+assurance that the services can expect from the session.</p>
+
+<p>The exact definition of the meaning of this levels and of
+how to use it remains to be achived.</p>
 
 <a name="Plugin"></a>
 <h2>Plugin</h2>
 
+<p>A shared library object intended to be plug to an afb-daemon instance
+to implement an API.</p>
+
 <a name="Request"></a>
 <h2>Request</h2>
 
+<p>A request is an invocation by a client to a method of a plugin using a message
+transfered through some protocol: HTTP, WebSocket, DBUS&hellip; served by afb-daemon</p>
+
 <a name="Reply.Response"></a>
 <h2>Reply/Response</h2>
 
+<p>This is a message sent to client as the result of the request.</p>
+
 <a name="Service"></a>
 <h2>Service</h2>
 
+<p>Service are made of plugins runnning by their side on their binder.
+It can serve many client. Each one being attached to one session.</p>
+
+<p>The framework establishes the connection between the services and
+the clients. Using DBus currently.</p>
+
 <a name="Session"></a>
 <h2>Session</h2>
 
-<p>A session records data as</p>
+<p>A session is meant to be the unic context of an instance of client,
+identifying that instance across requests.</p>
+
+<p>Each session has an identifier. Session identifier generated by afb-daemon are UUIDs.</p>
+
+<p>Internally, afb-daemon offers a mechanism to attach data to sessions.
+When the session is closed or disappears, the data attached to that session
+are freed.</p>
 
 <a name="Token"></a>
 <h2>Token</h2>
 
+<p>The token is an identifier that the the client must give to be authentificated.</p>
+
+<p>At start, afb-daemon get an initial token. This initial token must be presented
+incoming client to be authentificated.</p>
+
+<p>A token is valid only for a period.</p>
+
+<p>The token must be renewed periodically. When the token is renewed, afb-daemon
+sends the new token to the client.</p>
+
+<p>Tokens generated by afb-daemon are UUIDs.</p>
+
 <a name="UUID"></a>
 <h2>UUID</h2>
 
@@ -68,10 +109,23 @@ Author:  José Bollo
 <p>Its is designed to create identifier in a way that avoid has much as possible conflicts.
 It means that if two differents instance create a UUID, the probability that they create the same UUID is very low, near to zero.</p>
 
+<a name="x-afb-reqid"></a>
+<h2>x-afb-reqid</h2>
+
+<p>Argument name that can be used with HTTP request.
+When this argument is given, it is automatically added to the &ldquo;request&rdquo; object of the
+answer.</p>
+
 <a name="x-afb-token"></a>
 <h2>x-afb-token</h2>
 
+<p>Argument name for giving the token without ambiguity.
+You can also use the name <strong>token</strong> but it may conflicts with other arguments.</p>
+
 <a name="x-afb-uuid"></a>
 <h2>x-afb-uuid</h2>
+
+<p>Argument name for giving explicitely the session identifier without ambiguity.
+You can also use the name <strong>uuid</strong> but it may conflicts with other arguments.</p>
 </body>
 </html>
diff --git a/doc/afb-daemon-vocabulary.md b/doc/afb-daemon-vocabulary.md
index 7a4b6537..8427b736 100644
--- a/doc/afb-daemon-vocabulary.md
+++ b/doc/afb-daemon-vocabulary.md
@@ -1,31 +1,72 @@
 Vocabulary for AFB-DAEMON
 =========================
     version: 1
-    Date:    24 mai 2016
+    Date:    27 mai 2016
     Author:  José Bollo
 
 TABLE-OF-CONTENT-HERE
 
-## Authentification
+## Event
 
-## Context
+Message with data propagated from the services to the client and not expecting
+any reply.
 
-## Level of authorisation (LOA)
+The current implementation allows to widely broadcast events to all clients.
+
+## Level of assurance (LOA)
+
+This level that can be from 0 to 3 represent the level of
+assurance that the services can expect from the session.
+
+The exact definition of the meaning of this levels and of
+how to use it remains to be achived.
 
 ## Plugin
 
+A shared library object intended to be plug to an afb-daemon instance
+to implement an API.
+
 ## Request
 
+A request is an invocation by a client to a method of a plugin using a message
+transfered through some protocol: HTTP, WebSocket, DBUS... served by afb-daemon
+
 ## Reply/Response
 
+This is a message sent to client as the result of the request.
+
 ## Service
 
+Service are made of plugins runnning by their side on their binder.
+It can serve many client. Each one being attached to one session.
+
+The framework establishes the connection between the services and
+the clients. Using DBus currently.
+
 ## Session
 
-A session records data as
+A session is meant to be the unic context of an instance of client, 
+identifying that instance across requests.
+
+Each session has an identifier. Session identifier generated by afb-daemon are UUIDs.
+
+Internally, afb-daemon offers a mechanism to attach data to sessions.
+When the session is closed or disappears, the data attached to that session
+are freed.
 
 ## Token
 
+The token is an identifier that the the client must give to be authentificated.
+
+At start, afb-daemon get an initial token. This initial token must be presented
+incoming client to be authentificated.
+
+A token is valid only for a period.
+
+The token must be renewed periodically. When the token is renewed, afb-daemon
+sends the new token to the client.
+
+Tokens generated by afb-daemon are UUIDs.
 
 ## UUID
 
@@ -34,6 +75,19 @@ It stand for Universal Unic IDentifier.
 Its is designed to create identifier in a way that avoid has much as possible conflicts.
 It means that if two differents instance create a UUID, the probability that they create the same UUID is very low, near to zero.
 
+## x-afb-reqid
+
+Argument name that can be used with HTTP request.
+When this argument is given, it is automatically added to the "request" object of the
+answer.
+
 ## x-afb-token
 
+Argument name for giving the token without ambiguity.
+You can also use the name **token** but it may conflicts with other arguments.
+
 ## x-afb-uuid
+
+Argument name for giving explicitely the session identifier without ambiguity.
+You can also use the name **uuid** but it may conflicts with other arguments.
+
diff --git a/doc/afb-plugin-writing.html b/doc/afb-plugin-writing.html
new file mode 100644
index 00000000..20e25972
--- /dev/null
+++ b/doc/afb-plugin-writing.html
@@ -0,0 +1,1542 @@
+<html>
+<head>
+  <link rel="stylesheet" type="text/css" href="doc.css">
+  <meta charset="UTF-8">
+</head>
+<body>
+<a name="HOWTO.WRITE.a.PLUGIN.for.AFB-DAEMON"></a>
+<h1>HOWTO WRITE a PLUGIN for AFB-DAEMON</h1>
+
+<pre><code>version: 1
+Date:    27 mai 2016
+Author:  José Bollo
+</code></pre>
+
+<p><ul>
+ <li><a href="#HOWTO.WRITE.a.PLUGIN.for.AFB-DAEMON">HOWTO WRITE a PLUGIN for AFB-DAEMON</a>
+ <ul>
+  <li><a href="#Summary">Summary</a>
+  <ul>
+   <li><a href="#Nature.of.a.plugin">Nature of a plugin</a></li>
+   <li><a href="#Kinds.of.plugins">Kinds of plugins</a>
+   <ul>
+    <li><a href="#Application.plugins">Application plugins</a></li>
+    <li><a href="#Service.plugins">Service plugins</a></li>
+   </ul>
+   </li>
+   <li><a href="#Live.cycle.of.a.plugin.within.afb-daemon">Live cycle of a plugin within afb-daemon</a></li>
+   <li><a href="#Content.of.a.plugin">Content of a plugin</a>
+   <ul>
+    <li><a href="#The.name.of.the.plugin">The name of the plugin</a></li>
+    <li><a href="#Names.of.verbs">Names of verbs</a></li>
+    <li><a href="#The.initialisation.function">The initialisation function</a></li>
+    <li><a href="#Functions.implementing.verbs">Functions implementing verbs</a>
+</li>
+   </ul>
+   </li>
+  </ul>
+  </li>
+  <li><a href="#The.Tic-Tac-Toe.example">The Tic-Tac-Toe example</a></li>
+  <li><a href="#Dependencies.when.compiling">Dependencies when compiling</a></li>
+  <li><a href="#Header.files.to.include">Header files to include</a></li>
+  <li><a href="#Choosing.names">Choosing names</a>
+  <ul>
+   <li><a href="#Names.for.API..plugin.">Names for API (plugin)</a></li>
+   <li><a href="#Names.for.verbs">Names for verbs</a></li>
+   <li><a href="#Names.for.arguments">Names for arguments</a></li>
+   <li><a href="#Forging.names.widely.available">Forging names widely available</a></li>
+  </ul>
+  </li>
+  <li><a href="#Writing.a.synchronous.verb.implementation">Writing a synchronous verb implementation</a>
+  <ul>
+   <li><a href="#The.incoming.request">The incoming request</a></li>
+   <li><a href="#Associating.a.context.to.the.session">Associating a context to the session</a></li>
+   <li><a href="#Sending.the.reply.to.a.request">Sending the reply to a request</a></li>
+  </ul>
+  </li>
+  <li><a href="#Getting.argument.of.invocation">Getting argument of invocation</a>
+  <ul>
+   <li><a href="#Basic.functions.for.querying.arguments">Basic functions for querying arguments</a></li>
+   <li><a href="#Arguments.for.received.files">Arguments for received files</a></li>
+   <li><a href="#Arguments.as.a.JSON.object">Arguments as a JSON object</a></li>
+  </ul>
+  </li>
+  <li><a href="#Initialisation.of.the.plugin.and.declaration.of.verbs">Initialisation of the plugin and declaration of verbs</a></li>
+  <li><a href="#Sending.messages.to.the.log.system">Sending messages to the log system</a>
+  <ul>
+   <li><a href="#Verbs.for.logging.messages">Verbs for logging messages</a></li>
+   <li><a href="#Managing.verbosity">Managing verbosity</a></li>
+   <li><a href="#Output.format.and.destination">Output format and destination</a></li>
+  </ul>
+  </li>
+  <li><a href="#Sending.events">Sending events</a></li>
+  <li><a href="#Writing.an.asynchronous.verb.implementation">Writing an asynchronous verb implementation</a></li>
+  <li><a href="#How.to.build.a.plugin">How to build a plugin</a>
+  <ul>
+   <li><a href="#Example.for.cmake.meta.build.system">Example for cmake meta build system</a></li>
+   <li><a href="#Exporting.the.function.pluginAfbV1Register">Exporting the function pluginAfbV1Register</a></li>
+   <li><a href="#Building.within.yocto">Building within yocto</a></li>
+  </ul>
+  </li>
+ </ul>
+ </li>
+</ul></p>
+
+<a name="Summary"></a>
+<h2>Summary</h2>
+
+<p>The binder afb-daemon serves files through
+the HTTP protocol and offers access to API&rsquo;s through
+HTTP or WebSocket protocol.</p>
+
+<p>The plugins are used to add API&rsquo;s to afb-daemon.
+This part describes how to write a plugin for afb-daemon.
+Excepting this summary, this part is intended to be read
+by developpers.</p>
+
+<p>Before going into details, through a tiny example,
+a short overview plugins basis is needed.</p>
+
+<a name="Nature.of.a.plugin"></a>
+<h3>Nature of a plugin</h3>
+
+<p>A plugin is a separate piece of code made of a shared library.
+The plugin is loaded and activated by afb-daemon when afb-daemon
+starts.</p>
+
+<p>Technically, a plugin is not linked to any library of afb-daemon.</p>
+
+<a name="Kinds.of.plugins"></a>
+<h3>Kinds of plugins</h3>
+
+<p>There is two kinds of plugins: application plugins and service
+plugins.</p>
+
+<a name="Application.plugins"></a>
+<h4>Application plugins</h4>
+
+<p>Application plugins are intended to be instanciated for each
+application: when an application using that plugin is started,
+its binder starts a new instance of the plugin.</p>
+
+<p>It means that the application plugins mainly have only one
+context to manage for one client.</p>
+
+<a name="Service.plugins"></a>
+<h4>Service plugins</h4>
+
+<p>Service plugins are intended to be instanciated only one time
+only and connected to many clients.</p>
+
+<p>So either it does not manage context at all or otherwise,
+if it manages context, it should be able to manage one context
+per client.</p>
+
+<p>In details, it may be useful to have service plugins at a user
+level.</p>
+
+<a name="Live.cycle.of.a.plugin.within.afb-daemon"></a>
+<h3>Live cycle of a plugin within afb-daemon</h3>
+
+<p>The plugins are loaded and activated when afb-daemon starts.</p>
+
+<p>At start, the plugin initialise itself.
+If it fails to initialise then afb-daemon stops.</p>
+
+<p>Conversely, if it success to initialize, it must declare
+a name, that must be unique, and a list of API&rsquo;s verbs.</p>
+
+<p>When initialized, the functions implementing the API&rsquo;s verbs
+of the plugin are activated on call.</p>
+
+<p>At the end, nothing special is done by afb-daemon.
+Consequently, developpers of plugins should use &lsquo;atexit&rsquo;
+or &lsquo;on_exit&rsquo; during initialisation if they need to
+perform specific actions when stopping.</p>
+
+<a name="Content.of.a.plugin"></a>
+<h3>Content of a plugin</h3>
+
+<p>For afb-daemon, a plugin contains 2 different
+things: names and functions.</p>
+
+<p>There is two kind of names:
+ - the name of the plugin,
+ - the names of the verbs.</p>
+
+<p>There is two kind of functions:
+ - the initialisation function
+ - functions implementing verbs</p>
+
+<p>Afb-daemon translates the name of the method that is
+invoked to a pair of API and verb names. For example,
+the method named <strong>foo/bar</strong> translated to the API
+name <strong>foo</strong> and the verb name <strong>bar</strong>.
+To serve it, afb-daemon search the plugin that record
+the name <strong>foo</strong> and if it also recorded the verb <strong>bar</strong>,
+it calls the implementation function declared for this verb.</p>
+
+<p>Afb-daemon make no distinction between lower case
+and upper case when searching for a method.
+Thus, The names <strong>TicTacToe/Board</strong> and <strong>tictactoe/borad</strong>
+are equals.</p>
+
+<a name="The.name.of.the.plugin"></a>
+<h4>The name of the plugin</h4>
+
+<p>The name of the plugin is also known as the name
+of the API that defines the plugin.</p>
+
+<p>This name is also known as the prefix.</p>
+
+<p>The name of a plugin MUST be unique within afb-daemon.</p>
+
+<p>For example, when a client of afb-daemon
+calls a method named <strong>foo/bar</strong>. Afb-daemon
+extracts the prefix <strong>foo</strong> and the suffix <strong>bar</strong>.
+<strong>foo</strong> is the API name and must match a plugin name,
+the plugin that implements the verb <strong>bar</strong>.</p>
+
+<a name="Names.of.verbs"></a>
+<h4>Names of verbs</h4>
+
+<p>Each plugin exposes a set of verbs that can be called
+by client of afb-daemon.</p>
+
+<p>The name of a verb MUST be unique within a plugin.</p>
+
+<p>Plugins link verbs to functions that are called
+when clients emit requests for that verb.</p>
+
+<p>For example, when a client of afb-daemon
+calls a method named <strong>foo/bar</strong>.</p>
+
+<a name="The.initialisation.function"></a>
+<h4>The initialisation function</h4>
+
+<p>The initialisation function serves several purposes.</p>
+
+<ol>
+<li><p>It allows afb-daemon to check the version
+of the plugin using the name of the initialisation
+functions that it found. Currently, the initialisation
+function is named <strong>pluginAfbV1Register</strong>. It identifies
+the first version of plugins.</p></li>
+<li><p>It allows the plugin to initialise itself.</p></li>
+<li><p>It serves to the plugin to declare names, descriptions,
+requirements and implmentations of the verbs that it exposes.</p></li>
+</ol>
+
+
+<a name="Functions.implementing.verbs"></a>
+<h4>Functions implementing verbs</h4>
+
+<p>When a method is called, afb-daemon constructs a request
+object and pass it to the implementation function for verb
+within the plugin of the API.</p>
+
+<p>An implementation function receives a request object that
+is used to get arguments of the request, to send
+answer, to store session data.</p>
+
+<p>A plugin MUST send an answer to the request.</p>
+
+<p>But it is not mandatory to send the answer
+before to return from the implementing function.
+This behaviour is important for implementing
+asynchronous actions.</p>
+
+<p>Implementation functions that always reply to the request
+before returning are named <em>synchronous implementations</em>.
+Those that don&rsquo;t always reply to the request before
+returning are named <em>asynchronous implementations</em>.</p>
+
+<p>Asynchronous implementations typically initiate an
+asynchronous action and record to send the reply
+on completion of this action.</p>
+
+<a name="The.Tic-Tac-Toe.example"></a>
+<h2>The Tic-Tac-Toe example</h2>
+
+<p>This part explains how to write an afb-plugin.
+For the sake of being practical we will use many
+examples from the tic-tac-toe example.
+This plugin example is in <em>plugins/samples/tic-tac-toe.c</em>.</p>
+
+<p>This plugin is named <strong><em>tictactoe</em></strong>.</p>
+
+<a name="Dependencies.when.compiling"></a>
+<h2>Dependencies when compiling</h2>
+
+<p>Afb-daemon provides a configuration file for <em>pkg-config</em>.
+Typing the command</p>
+
+<pre><code>pkg-config --cflags afb-daemon
+</code></pre>
+
+<p>will print the flags to use for compiling, like this:</p>
+
+<pre><code>$ pkg-config --cflags afb-daemon
+-I/opt/local/include -I/usr/include/json-c 
+</code></pre>
+
+<p>For linking, you should use</p>
+
+<pre><code>$ pkg-config --libs afb-daemon
+-ljson-c
+</code></pre>
+
+<p>As you see, afb-daemon automatically includes dependency to json-c.
+This is done through the <strong>Requires</strong> keyword of pkg-config
+because almost all plugin will use <strong>json-c</strong>.</p>
+
+<p>If this behaviour is a problem, let us know.</p>
+
+<p>Internally, afb-daemon uses <strong>libsystemd</strong> for its event loop
+and for its binding to D-Bus.
+Plugins developpers are encouraged to also use this library.
+But it is a matter of choice.
+Thus there is no dependency to <strong>libsystemd</strong>.</p>
+
+<blockquote><p>Afb-daemon provides no library for plugins.
+The functions that the plugin need to have are given
+to the plugin at runtime through pointer using read-only
+memory.</p></blockquote>
+
+<a name="Header.files.to.include"></a>
+<h2>Header files to include</h2>
+
+<p>The plugin <em>tictactoe</em> has the following lines for its includes:</p>
+
+<pre><code>#define _GNU_SOURCE
+#include &lt;stdio.h&gt;
+#include &lt;string.h&gt;
+#include &lt;json-c/json.h&gt;
+#include &lt;afb/afb-plugin.h&gt;
+</code></pre>
+
+<p>The header <em>afb/afb-plugin.h</em> includes all the features that a plugin
+needs except two foreign header that must be included by the plugin
+if it needs it:</p>
+
+<ul>
+<li><em>json-c/json.h</em>: this header must be include to handle json objects;</li>
+<li><em>systemd/sd-event.h</em>: this must be include to access the main loop;</li>
+<li><em>systemd/sd-bus.h</em>: this may be include to use dbus connections.</li>
+</ul>
+
+
+<p>The <em>tictactoe</em> plugin does not use systemd features so it is not included.</p>
+
+<p>When including <em>afb/afb-plugin.h</em>, the macro <strong>_GNU_SOURCE</strong> must be
+defined.</p>
+
+<a name="Choosing.names"></a>
+<h2>Choosing names</h2>
+
+<p>The designer of a plugin must defines names for its plugin
+(or its API) and for the verbs of its API. He also
+must defines names for arguments given by name.</p>
+
+<p>While forging names, the designer should take into account
+the rules for making valid names and some rules that make
+the names easy to use across plaforms.</p>
+
+<p>The names and strings used ALL are UTF-8 encoded.</p>
+
+<a name="Names.for.API..plugin."></a>
+<h3>Names for API (plugin)</h3>
+
+<p>The names of the API are checked.
+All characters are authorised except:</p>
+
+<ul>
+<li>the control characters (\u0000 .. \u001f)</li>
+<li>the characters of the set { &lsquo; &rsquo;, &lsquo;&ldquo;&rsquo;, &lsquo;#&rsquo;, &lsquo;%&rsquo;, &lsquo;&amp;&rsquo;,
+&lsquo;&rsquo;&lsquo;, &rsquo;/&lsquo;, &rsquo;?&lsquo;, &rsquo;`&lsquo;, &rsquo;\x7f' }</li>
+</ul>
+
+
+<p>In other words the set of forbidden characters is
+{ \u0000..\u0020, \u0022, \u0023, \u0025..\u0027,
+  \u002f, \u003f, \u0060, \u007f }.</p>
+
+<p>Afb-daemon make no distinction between lower case
+and upper case when searching for an API by its name.</p>
+
+<a name="Names.for.verbs"></a>
+<h3>Names for verbs</h3>
+
+<p>The names of the verbs are not checked.</p>
+
+<p>However, the validity rules for verb&rsquo;s names are the
+same as for API&rsquo;s names except that the dot (.) character
+is forbidden.</p>
+
+<p>Afb-daemon make no distinction between lower case
+and upper case when searching for an API by its name.</p>
+
+<a name="Names.for.arguments"></a>
+<h3>Names for arguments</h3>
+
+<p>The names for arguments are not restricted and can be
+anything.</p>
+
+<p>The arguments are searched with the case sensitive
+string comparison. Thus the names &ldquo;index&rdquo; and &ldquo;Index&rdquo;
+are not the same.</p>
+
+<a name="Forging.names.widely.available"></a>
+<h3>Forging names widely available</h3>
+
+<p>The key names of javascript object can be almost
+anything using the arrayed notation:</p>
+
+<pre><code>object[key] = value
+</code></pre>
+
+<p>That is not the case with the dot notation:</p>
+
+<pre><code>object.key = value
+</code></pre>
+
+<p>Using the dot notation, the key must be a valid javascript
+identifier.</p>
+
+<p>For this reason, the chosen names should better be
+valid javascript identifier.</p>
+
+<p>It is also a good practice, even for arguments, to not
+rely on the case sensitivity and to avoid the use of
+names different only by the case.</p>
+
+<a name="Writing.a.synchronous.verb.implementation"></a>
+<h2>Writing a synchronous verb implementation</h2>
+
+<p>The verb <strong>tictactoe/board</strong> is a synchronous implementation.
+Here is its listing:</p>
+
+<pre><code>/*
+ * get the board
+ */
+static void board(struct afb_req req)
+{
+        struct board *board;
+        struct json_object *description;
+
+        /* retrieves the context for the session */
+        board = board_of_req(req);
+        INFO(afbitf, "method 'board' called for boardid %d", board-&gt;id);
+
+        /* describe the board */
+        description = describe(board);
+
+        /* send the board's description */
+        afb_req_success(req, description, NULL);
+}
+</code></pre>
+
+<p>This examples show many aspects of writing a synchronous
+verb implementation. Let summarize it:</p>
+
+<ol>
+<li><p>The function <strong>board_of_req</strong> retrieves the context stored
+for the plugin: the board.</p></li>
+<li><p>The macro <strong>INFO</strong> sends a message of kind <em>INFO</em>
+to the logging system. The global variable named <strong>afbitf</strong>
+used represents the interface to afb-daemon.</p></li>
+<li><p>The function <strong>describe</strong> creates a json_object representing
+the board.</p></li>
+<li><p>The function <strong>afb_req_success</strong> sends the reply, attaching to
+it the object <em>description</em>.</p></li>
+</ol>
+
+
+<a name="The.incoming.request"></a>
+<h3>The incoming request</h3>
+
+<p>For any implementation, the request is received by a structure of type
+<strong>struct afb_req</strong>.</p>
+
+<blockquote><p>Note that this is a PLAIN structure, not a pointer to a structure.</p></blockquote>
+
+<p>The definition of <strong>struct afb_req</strong> is:</p>
+
+<pre><code>/*
+ * Describes the request by plugins from afb-daemon
+ */
+struct afb_req {
+        const struct afb_req_itf *itf;  /* the interfacing functions */
+        void *closure;          /* the closure for functions */
+};
+</code></pre>
+
+<p>It contains two pointers: one, <em>itf</em>, points to the functions needed
+to handle the internal request represented by the second pointer, <em>closure</em>.</p>
+
+<blockquote><p>The structure must never be used directly.
+Insted, use the intended functions provided
+by afb-daemon and described here.</p></blockquote>
+
+<p><em>req</em> is used to get arguments of the request, to send
+answer, to store session data.</p>
+
+<p>This object and its interface is defined and documented
+in the file names <em>afb/afb-req-itf.h</em></p>
+
+<p>The above example uses 2 times the request object <em>req</em>.</p>
+
+<p>The first time, it is used for retrieving the board attached to
+the session of the request.</p>
+
+<p>The second time, it is used to send the reply: an object that
+describes the current board.</p>
+
+<a name="Associating.a.context.to.the.session"></a>
+<h3>Associating a context to the session</h3>
+
+<p>When the plugin <em>tic-tac-toe</em> receives a request, it musts regain
+the board that describes the game associated to the session.</p>
+
+<p>For a plugin, having data associated to a session is a common case.
+This data is called the context of the plugin for the session.
+For the plugin <em>tic-tac-toe</em>, the context is the board.</p>
+
+<p>The requests <em>afb_req</em> offer four functions for
+storing and retrieving the context associated to the session.</p>
+
+<p>These functions are:</p>
+
+<ul>
+<li><p><strong>afb_req_context_get</strong>:
+retrieves the context data stored for the plugin.</p></li>
+<li><p><strong>afb_req_context_set</strong>:
+store the context data of the plugin.</p></li>
+<li><p><strong>afb_req_context</strong>:
+retrieves the context data of the plugin,
+if needed, creates the context and store it.</p></li>
+<li><p><strong>afb_req_context_clear</strong>:
+reset the stored data.</p></li>
+</ul>
+
+
+<p>The plugin <em>tictactoe</em> use a convenient function to retrieve
+its context: the board. This function is <em>board_of_req</em>:</p>
+
+<pre><code>/*
+ * retrieves the board of the request
+ */
+static inline struct board *board_of_req(struct afb_req req)
+{
+        return afb_req_context(req, (void*)get_new_board, (void*)release_board);
+}
+</code></pre>
+
+<p>The function <strong>afb_req_context</strong> ensure an existing context
+for the session of the request.
+Its two last arguments are functions. Here, the casts are required
+to avoid a warning when compiling.</p>
+
+<p>Here is the definition of the function <strong>afb_req_context</strong></p>
+
+<pre><code>/*
+ * Gets the pointer stored by the plugin for the session of 'req'.
+ * If the stored pointer is NULL, indicating that no pointer was
+ * already stored, afb_req_context creates a new context by calling
+ * the function 'create_context' and stores it with the freeing function
+ * 'free_context'.
+ */
+static inline void *afb_req_context(struct afb_req req, void *(*create_context)(), void (*free_context)(void*))
+{
+        void *result = afb_req_context_get(req);
+        if (result == NULL) {
+                result = create_context();
+                afb_req_context_set(req, result, free_context);
+        }
+        return result;
+}
+</code></pre>
+
+<p>The second argument if the function that creates the context.
+For the plugin <em>tic-tac-toe</em> it is the function <strong>get_new_board</strong>.
+The function <strong>get_new_board</strong> creates a new board and set its
+count of use to 1. The boards are counting their count of use
+to free there ressources when no more used.</p>
+
+<p>The third argument if the function that frees the context.
+For the plugin <em>tic-tac-toe</em> it is the function <strong>release_board</strong>.
+The function <strong>release_board</strong> decrease the the count of use of
+the board given as argument. If the use count decrease to zero,
+the board data are freed.</p>
+
+<p>The definition of the other functions for dealing with contexts are:</p>
+
+<pre><code>/*
+ * Gets the pointer stored by the plugin for the session of 'req'.
+ * When the plugin has not yet recorded a pointer, NULL is returned.
+ */
+void *afb_req_context_get(struct afb_req req);
+
+/*
+ * Stores for the plugin the pointer 'context' to the session of 'req'.
+ * The function 'free_context' will be called when the session is closed
+ * or if plugin stores an other pointer.
+ */
+void afb_req_context_set(struct afb_req req, void *context, void (*free_context)(void*));
+
+/*
+ * Frees the pointer stored by the plugin for the session of 'req'
+ * and sets it to NULL.
+ *
+ * Shortcut for: afb_req_context_set(req, NULL, NULL)
+ */
+static inline void afb_req_context_clear(struct afb_req req)
+{
+        afb_req_context_set(req, NULL, NULL);
+}
+</code></pre>
+
+<a name="Sending.the.reply.to.a.request"></a>
+<h3>Sending the reply to a request</h3>
+
+<p>Two kinds of replies can be made: successful replies and
+failure replies.</p>
+
+<blockquote><p>Sending a reply to a request must be done at most one time.</p></blockquote>
+
+<p>The two functions to send a reply of kind &ldquo;success&rdquo; are
+<strong>afb_req_success</strong> and <strong>afb_req_success_f</strong>.</p>
+
+<pre><code>/*
+ * Sends a reply of kind success to the request 'req'.
+ * The status of the reply is automatically set to "success".
+ * Its send the object 'obj' (can be NULL) with an
+ * informationnal comment 'info (can also be NULL).
+ *
+ * For conveniency, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_success(struct afb_req req, struct json_object *obj, const char *info);
+
+/*
+ * Same as 'afb_req_success' but the 'info' is a formatting
+ * string followed by arguments.
+ *
+ * For conveniency, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_success_f(struct afb_req req, struct json_object *obj, const char *info, ...);
+</code></pre>
+
+<p>The two functions to send a reply of kind &ldquo;failure&rdquo; are
+<strong>afb_req_fail</strong> and <strong>afb_req_fail_f</strong>.</p>
+
+<pre><code>/*
+ * Sends a reply of kind failure to the request 'req'.
+ * The status of the reply is set to 'status' and an
+ * informationnal comment 'info' (can also be NULL) can be added.
+ *
+ * Note that calling afb_req_fail("success", info) is equivalent
+ * to call afb_req_success(NULL, info). Thus even if possible it
+ * is strongly recommanded to NEVER use "success" for status.
+ *
+ * For conveniency, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_fail(struct afb_req req, const char *status, const char *info);
+
+/*
+ * Same as 'afb_req_fail' but the 'info' is a formatting
+ * string followed by arguments.
+ *
+ * For conveniency, the function calls 'json_object_put' for 'obj'.
+ * Thus, in the case where 'obj' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_req_fail_f(struct afb_req req, const char *status, const char *info, ...);
+</code></pre>
+
+<blockquote><p>For conveniency, these functions call <strong>json_object_put</strong> to release the object <strong>obj</strong>
+that they send. Then <strong>obj</strong> can not be used after calling one of these reply functions.
+When it is not the expected behaviour, calling the function <strong>json_object_get</strong> on the object <strong>obj</strong>
+before cancels the effect of <strong>json_object_put</strong>.</p></blockquote>
+
+<a name="Getting.argument.of.invocation"></a>
+<h2>Getting argument of invocation</h2>
+
+<p>Many verbs expect arguments. Afb-daemon let plugins
+retrieve their arguments by name not by position.</p>
+
+<p>Arguments are given by the requests either through HTTP
+or through WebSockets.</p>
+
+<p>For example, the verb <strong>join</strong> of the plugin <strong>tic-tac-toe</strong>
+expects one argument: the <em>boardid</em> to join. Here is an extract:</p>
+
+<pre><code>/*
+ * Join a board
+ */
+static void join(struct afb_req req)
+{
+        struct board *board, *new_board;
+        const char *id;
+
+        /* retrieves the context for the session */
+        board = board_of_req(req);
+        INFO(afbitf, "method 'join' called for boardid %d", board-&gt;id);
+
+        /* retrieves the argument */
+        id = afb_req_value(req, "boardid");
+        if (id == NULL)
+                goto bad_request;
+        ...
+</code></pre>
+
+<p>The function <strong>afb_req_value</strong> search in the request <em>req</em>
+for an argument whose name is given. When no argument of the
+given name was passed, <strong>afb_req_value</strong> returns NULL.</p>
+
+<blockquote><p>The search is case sensitive. So the name <em>boardid</em> is not the
+same name than <em>BoardId</em>. But this must not be assumed so two
+expected names of argument should not differ only by case.</p></blockquote>
+
+<a name="Basic.functions.for.querying.arguments"></a>
+<h3>Basic functions for querying arguments</h3>
+
+<p>The function <strong>afb_req_value</strong> is defined as below:</p>
+
+<pre><code>/*
+ * Gets from the request 'req' the string value of the argument of 'name'.
+ * Returns NULL if when there is no argument of 'name'.
+ * Returns the value of the argument of 'name' otherwise.
+ *
+ * Shortcut for: afb_req_get(req, name).value
+ */
+static inline const char *afb_req_value(struct afb_req req, const char *name)
+{
+        return afb_req_get(req, name).value;
+}
+</code></pre>
+
+<p>It is defined as a shortcut to call the function <strong>afb_req_get</strong>.
+That function is defined as below:</p>
+
+<pre><code>/*
+ * Gets from the request 'req' the argument of 'name'.
+ * Returns a PLAIN structure of type 'struct afb_arg'.
+ * When the argument of 'name' is not found, all fields of result are set to NULL.
+ * When the argument of 'name' is found, the fields are filled,
+ * in particular, the field 'result.name' is set to 'name'.
+ *
+ * There is a special name value: the empty string.
+ * The argument of name "" is defined only if the request was made using
+ * an HTTP POST of Content-Type "application/json". In that case, the
+ * argument of name "" receives the value of the body of the HTTP request.
+ */
+struct afb_arg afb_req_get(struct afb_req req, const char *name);
+</code></pre>
+
+<p>That function takes 2 parameters: the request and the name
+of the argument to retrieve. It returns a PLAIN structure of
+type <strong>struct afb_arg</strong>.</p>
+
+<p>There is a special name that is defined when the request is
+of type HTTP/POST with a Content-Type being application/json.
+This name is <strong>&ldquo;&rdquo;</strong> (the empty string). In that case, the value
+of this argument of empty name is the string received as a body
+of the post and is supposed to be a JSON string.</p>
+
+<p>The definition of <strong>struct afb_arg</strong> is:</p>
+
+<pre><code>/*
+ * Describes an argument (or parameter) of a request
+ */
+struct afb_arg {
+        const char *name;   /* name of the argument or NULL if invalid */
+        const char *value;  /* string representation of the value of the argument */
+                                /* original filename of the argument if path != NULL */
+        const char *path;   /* if not NULL, path of the received file for the argument */
+                                /* when the request is finalized this file is removed */
+};
+</code></pre>
+
+<p>The structure returns the data arguments that are known for the
+request. This data include a field named <strong>path</strong>. This <strong>path</strong>
+can be accessed using the function <strong>afb_req_path</strong> defined as
+below:</p>
+
+<pre><code>/*
+ * Gets from the request 'req' the path for file attached to the argument of 'name'.
+ * Returns NULL if when there is no argument of 'name' or when there is no file.
+ * Returns the path of the argument of 'name' otherwise.
+ *
+ * Shortcut for: afb_req_get(req, name).path
+ */
+static inline const char *afb_req_path(struct afb_req req, const char *name)
+{
+        return afb_req_get(req, name).path;
+}
+</code></pre>
+
+<p>The path is only defined for HTTP/POST requests that send file.</p>
+
+<a name="Arguments.for.received.files"></a>
+<h3>Arguments for received files</h3>
+
+<p>As it is explained just above, clients can send files using
+HTTP/POST requests.</p>
+
+<p>Received files are attached to a arguments. For example, the
+following HTTP fragment (from test/sample-post.html)
+will send an HTTP/POST request to the method
+<strong>post/upload-image</strong> with 2 arguments named <em>file</em> and
+<em>hidden</em>.</p>
+
+<pre><code>&lt;h2&gt;Sample Post File&lt;/h2&gt;
+&lt;form enctype="multipart/form-data"&gt;
+    &lt;input type="file" name="file" /&gt;
+    &lt;input type="hidden" name="hidden" value="bollobollo" /&gt;
+    &lt;br&gt;
+    &lt;button formmethod="POST" formaction="api/post/upload-image"&gt;Post File&lt;/button&gt;
+&lt;/form&gt;
+</code></pre>
+
+<p>In that case, the argument named <strong>file</strong> has its value and its
+path defined and not NULL.</p>
+
+<p>The value is the name of the file as it was
+set by the HTTP client and is generally the filename on the
+client side.</p>
+
+<p>The path is the path of the file saved on the temporary local storage
+area of the application. This is a randomly generated and unic filename
+not linked in any way with the original filename on the client.</p>
+
+<p>The plugin can use the file at the given path the way that it wants:
+read, write, remove, copy, rename&hellip;
+But when the reply is sent and the query is terminated, the file at
+this path is destroyed if it still exist.</p>
+
+<a name="Arguments.as.a.JSON.object"></a>
+<h3>Arguments as a JSON object</h3>
+
+<p>Plugins can get all the arguments as one single object.
+This feature is provided by the function <strong>afb_req_json</strong>
+that is defined as below:</p>
+
+<pre><code>/*
+ * Gets from the request 'req' the json object hashing the arguments.
+ * The returned object must not be released using 'json_object_put'.
+ */
+struct json_object *afb_req_json(struct afb_req req);
+</code></pre>
+
+<p>It returns a json object. This object depends on how the request was
+made:</p>
+
+<ul>
+<li><p>For HTTP requests, this is an object whose keys are the names of the
+arguments and whose values are either a string for common arguments or
+an object like { &ldquo;file&rdquo;: &ldquo;&hellip;&rdquo;, &ldquo;path&rdquo;: &ldquo;&hellip;&rdquo; }</p></li>
+<li><p>For WebSockets requests, the returned object is the object
+given by the client transparently transported.</p></li>
+</ul>
+
+
+<blockquote><p>In fact, for Websockets requests, the function <strong>afb_req_value</strong>
+can be seen as a shortcut to
+<strong><em>json_object_get_string(json_object_object_get(afb_req_json(req), name))</em></strong></p></blockquote>
+
+<a name="Initialisation.of.the.plugin.and.declaration.of.verbs"></a>
+<h2>Initialisation of the plugin and declaration of verbs</h2>
+
+<p>To be active, the verbs of the plugin should be declared to
+afb-daemon. And even more, the plugin itself must be recorded.</p>
+
+<p>The mechanism for doing this is very simple: when afb-need starts,
+it loads the plugins that are listed in its argument or configuration.</p>
+
+<p>Loading a plugin follows the following steps:</p>
+
+<ol>
+<li><p>It loads the plugin using <em>dlopen</em>.</p></li>
+<li><p>It searchs for the symbol named <strong>pluginAfbV1Register</strong> using <em>dlsym</em>.
+This symbol is assumed to be the exported initialisation function of the plugin.</p></li>
+<li><p>It build an interface object for the plugin.</p></li>
+<li><p>It calls the found function <strong>pluginAfbV1Register</strong> and pass it the pointer
+to its interface.</p></li>
+<li><p>The function <strong>pluginAfbV1Register</strong> setup the plugin, initialize it.</p></li>
+<li><p>The function <strong>pluginAfbV1Register</strong> returns the pointer to a structure
+that describes the plugin: its version, its name (prefix or API name), and the
+list of its verbs.</p></li>
+<li><p>Afb-daemon checks that the returned version and name can be managed.
+If it can manage it, the plugin and its verbs are recorded and can be used
+when afb-daemon finishes it initialisation.</p></li>
+</ol>
+
+
+<p>Here is the listing of the function <strong>pluginAfbV1Register</strong> of the plugin
+<em>tic-tac-toe</em>:</p>
+
+<pre><code>/*
+ * activation function for registering the plugin called by afb-daemon
+ */
+const struct AFB_plugin *pluginAfbV1Register(const struct AFB_interface *itf)
+{
+   afbitf = itf;         // records the interface for accessing afb-daemon
+   return &amp;plugin_description;  // returns the description of the plugin
+}
+</code></pre>
+
+<p>This is a very small function because the <em>tic-tac-toe</em> plugin doesn&rsquo;t have initialisation step.
+It merely record the daemon&rsquo;s interface and returns its descritption.</p>
+
+<p>The variable <strong>afbitf</strong> is a variable global to the plugin. It records the
+interface to afb-daemon and is used for logging and pushing events.
+Here is its declaration:</p>
+
+<pre><code>/*
+ * the interface to afb-daemon
+ */
+const struct AFB_interface *afbitf;
+</code></pre>
+
+<p>The description of the plugin is defined as below.</p>
+
+<pre><code>/*
+ * array of the verbs exported to afb-daemon
+ */
+static const struct AFB_verb_desc_v1 plugin_verbs[] = {
+   /* VERB'S NAME     SESSION MANAGEMENT          FUNCTION TO CALL  SHORT DESCRIPTION */
+   { .name= "new",   .session= AFB_SESSION_NONE, .callback= new,   .info= "Starts a new game" },
+   { .name= "play",  .session= AFB_SESSION_NONE, .callback= play,  .info= "Asks the server to play" },
+   { .name= "move",  .session= AFB_SESSION_NONE, .callback= move,  .info= "Tells the client move" },
+   { .name= "board", .session= AFB_SESSION_NONE, .callback= board, .info= "Get the current board" },
+   { .name= "level", .session= AFB_SESSION_NONE, .callback= level, .info= "Set the server level" },
+   { .name= "join",  .session= AFB_SESSION_CHECK,.callback= join,  .info= "Join a board" },
+   { .name= "undo",  .session= AFB_SESSION_NONE, .callback= undo,  .info= "Undo the last move" },
+   { .name= "wait",  .session= AFB_SESSION_NONE, .callback= wait,  .info= "Wait for a change" },
+   { .name= NULL } /* marker for end of the array */
+};
+
+/*
+ * description of the plugin for afb-daemon
+ */
+static const struct AFB_plugin plugin_description =
+{
+   /* description conforms to VERSION 1 */
+   .type= AFB_PLUGIN_VERSION_1,
+   .v1= {               /* fills the v1 field of the union when AFB_PLUGIN_VERSION_1 */
+      .prefix= "tictactoe",     /* the API name (or plugin name or prefix) */
+      .info= "Sample tac-tac-toe game", /* short description of of the plugin */
+      .verbs = plugin_verbs     /* the array describing the verbs of the API */
+   }
+};
+</code></pre>
+
+<p>The structure <strong>plugin_description</strong> describes the plugin.
+It declares the type and version of the plugin, its name, a description
+and a list of its verbs.</p>
+
+<p>The list of verbs is an array of structures describing the verbs and terminated by a marker:
+a verb whose name is NULL.</p>
+
+<p>The description of the verbs for this version is made of 4 fields:</p>
+
+<ul>
+<li><p>the name of the verbs,</p></li>
+<li><p>the session management flags,</p></li>
+<li><p>the implementation function to be call for the verb,</p></li>
+<li><p>a short description.</p></li>
+</ul>
+
+
+<p>The structure describing verbs is defined as follows:</p>
+
+<pre><code>/*
+ * Description of one verb of the API provided by the plugin
+ * This enumeration is valid for plugins of type 1
+ */
+struct AFB_verb_desc_v1
+{
+       const char *name;                       /* name of the verb */
+       enum AFB_session_v1 session;            /* authorisation and session requirements of the verb */
+       void (*callback)(struct afb_req req);   /* callback function implementing the verb */
+       const char *info;                       /* textual description of the verb */
+};
+</code></pre>
+
+<p>For technical reasons, the enumeration <strong>enum AFB_session_v1</strong> is not exactly an
+enumeration but the wrapper of constant definitions that can be mixed using bitwise or
+(the C operator |).</p>
+
+<p>The constants that can bit mixed are:</p>
+
+<table>
+<thead>
+<tr>
+<th>Constant name        </th>
+<th> Meaning</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td><strong>AFB_SESSION_CREATE</strong>   </td>
+<td> Equals to AFB_SESSION_LOA_EQ_0|AFB_SESSION_RENEW</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_CLOSE</strong>    </td>
+<td> Closes the session after the reply and set the LOA to 0</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_RENEW</strong>    </td>
+<td> Refreshes the token of authentification</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_CHECK</strong>    </td>
+<td> Just requires the token authentification</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_LE_0</strong> </td>
+<td> Requires the current LOA to be lesser then or equal to 0</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_LE_1</strong> </td>
+<td> Requires the current LOA to be lesser then or equal to 1</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_LE_2</strong> </td>
+<td> Requires the current LOA to be lesser then or equal to 2</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_LE_3</strong> </td>
+<td> Requires the current LOA to be lesser then or equal to 3</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_GE_0</strong> </td>
+<td> Requires the current LOA to be greater then or equal to 0</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_GE_1</strong> </td>
+<td> Requires the current LOA to be greater then or equal to 1</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_GE_2</strong> </td>
+<td> Requires the current LOA to be greater then or equal to 2</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_GE_3</strong> </td>
+<td> Requires the current LOA to be greater then or equal to 3</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_EQ_0</strong> </td>
+<td> Requires the current LOA to be equal to 0</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_EQ_1</strong> </td>
+<td> Requires the current LOA to be equal to 1</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_EQ_2</strong> </td>
+<td> Requires the current LOA to be equal to 2</td>
+</tr>
+<tr>
+<td><strong>AFB_SESSION_LOA_EQ_3</strong> </td>
+<td> Requires the current LOA to be equal to 3</td>
+</tr>
+</tbody>
+</table>
+
+
+<p>If any of this flags is set, afb-daemon requires the token authentification
+as if the flag <strong>AFB_SESSION_CHECK</strong> had been set.</p>
+
+<p>The special value <strong>AFB_SESSION_NONE</strong> is zero and can be used to avoid any check.</p>
+
+<blockquote><p>Note that <strong>AFB_SESSION_CREATE</strong> and <strong>AFB_SESSION_CLOSE</strong> might be removed in later versions.</p></blockquote>
+
+<a name="Sending.messages.to.the.log.system"></a>
+<h2>Sending messages to the log system</h2>
+
+<p>Afb-daemon provides 4 levels of verbosity and 5 verbs for logging messages.</p>
+
+<p>The verbosity is managed. Options allow the change the verbosity of afb-daemon
+and the verbosity of the plugins can be set plugin by plugin.</p>
+
+<p>The verbs for logging messages are defined as macros that test the
+verbosity level and that call the real logging function only if the
+message must be output. This avoid evaluation of arguments of the
+formatting messages if the message must not be output.</p>
+
+<a name="Verbs.for.logging.messages"></a>
+<h3>Verbs for logging messages</h3>
+
+<p>The 5 logging verbs are:</p>
+
+<table>
+<thead>
+<tr>
+<th>Macro   </th>
+<th style="text-align:center;"> Verbosity </th>
+<th> Meaning                       </th>
+<th style="text-align:center;"> syslog level</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>ERROR   </td>
+<td style="text-align:center;">     0     </td>
+<td> Error conditions              </td>
+<td style="text-align:center;">     3</td>
+</tr>
+<tr>
+<td>WARNING </td>
+<td style="text-align:center;">     1     </td>
+<td> Warning conditions            </td>
+<td style="text-align:center;">     4</td>
+</tr>
+<tr>
+<td>NOTICE  </td>
+<td style="text-align:center;">     1     </td>
+<td> Normal but significant condition  </td>
+<td style="text-align:center;">     5</td>
+</tr>
+<tr>
+<td>INFO    </td>
+<td style="text-align:center;">     2     </td>
+<td> Informational                 </td>
+<td style="text-align:center;">     6</td>
+</tr>
+<tr>
+<td>DEBUG   </td>
+<td style="text-align:center;">     3     </td>
+<td> Debug-level messages          </td>
+<td style="text-align:center;">     7</td>
+</tr>
+</tbody>
+</table>
+
+
+<p>You can note that the 2 verbs <strong>WARNING</strong> and <strong>INFO</strong> have the same level
+of verbosity. But they don&rsquo;t have the same <em>syslog level</em>. It means that
+they are output with a different level on the logging system.</p>
+
+<p>All of these verbs have the same signature:</p>
+
+<pre><code>void ERROR(const struct AFB_interface *afbitf, const char *message, ...);
+</code></pre>
+
+<p>The first argument <strong>afbitf</strong> is the interface to afb daemon that the
+plugin received at its initialisation when <strong>pluginAfbV1Register</strong> was called.</p>
+
+<p>The second argument <strong>message</strong> is a formatting string compatible with printf/sprintf.</p>
+
+<p>The remaining arguments are arguments of the formating message like for printf.</p>
+
+<a name="Managing.verbosity"></a>
+<h3>Managing verbosity</h3>
+
+<p>Depending on the level of verbosity, the messages are output or not.
+The following table explains what messages will be output depending
+ont the verbosity level.</p>
+
+<table>
+<thead>
+<tr>
+<th style="text-align:center;">Level of verbosity </th>
+<th> Outputed macro</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td style="text-align:center;">0          </td>
+<td> ERROR</td>
+</tr>
+<tr>
+<td style="text-align:center;">1          </td>
+<td> ERROR + WARNING + NOTICE</td>
+</tr>
+<tr>
+<td style="text-align:center;">2          </td>
+<td> ERROR + WARNING + NOTICE + INFO</td>
+</tr>
+<tr>
+<td style="text-align:center;">3          </td>
+<td> ERROR + WARNING + NOTICE + INFO + DEBUG</td>
+</tr>
+</tbody>
+</table>
+
+
+<a name="Output.format.and.destination"></a>
+<h3>Output format and destination</h3>
+
+<p>The syslog level is used for forging a prefix to the message.
+The prefixes are:</p>
+
+<table>
+<thead>
+<tr>
+<th style="text-align:center;">syslog level </th>
+<th> prefix</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td style="text-align:center;">0      </td>
+<td> <0> EMERGENCY</td>
+</tr>
+<tr>
+<td style="text-align:center;">1      </td>
+<td> <1> ALERT</td>
+</tr>
+<tr>
+<td style="text-align:center;">2      </td>
+<td> <2> CRITICAL</td>
+</tr>
+<tr>
+<td style="text-align:center;">3      </td>
+<td> <3> ERROR</td>
+</tr>
+<tr>
+<td style="text-align:center;">4      </td>
+<td> <4> WARNING</td>
+</tr>
+<tr>
+<td style="text-align:center;">5      </td>
+<td> <5> NOTICE</td>
+</tr>
+<tr>
+<td style="text-align:center;">6      </td>
+<td> <6> INFO</td>
+</tr>
+<tr>
+<td style="text-align:center;">7      </td>
+<td> <7> DEBUG</td>
+</tr>
+</tbody>
+</table>
+
+
+<p>The message is issued to the standard error.
+The final destination of the message depends on how the systemd service
+was configured through the variable <strong>StandardError</strong>: It can be
+journal, syslog or kmsg. (See man sd-daemon).</p>
+
+<a name="Sending.events"></a>
+<h2>Sending events</h2>
+
+<p>Since version 0.5, plugins can broadcast events to any potential listener.
+This kind of bradcast is not targeted. Event targeted will come in a future
+version of afb-daemon.</p>
+
+<p>The plugin <em>tic-tac-toe</em> broadcasts events when the board changes.
+This is done in the function <strong>changed</strong>:</p>
+
+<pre><code>/*
+ * signals a change of the board
+ */
+static void changed(struct board *board, const char *reason)
+{
+        ...
+        struct json_object *description;
+
+        /* get the description */
+        description = describe(board);
+
+        ...
+
+        afb_daemon_broadcast_event(afbitf-&gt;daemon, reason, description);
+}
+</code></pre>
+
+<p>The description of the changed board is pushed via the daemon interface.</p>
+
+<p>Within the plugin <em>tic-tac-toe</em>, the <em>reason</em> indicates the origin of
+the change. For the function <strong>afb_daemon_broadcast_event</strong>, the second
+parameter is the name of the broadcasted event. The third argument is the
+object that is transmitted with the event.</p>
+
+<p>The function <strong>afb_daemon_broadcast_event</strong> is defined as below:</p>
+
+<pre><code>/*
+ * Broadcasts widely the event of 'name' with the data 'object'.
+ * 'object' can be NULL.
+ * 'daemon' MUST be the daemon given in interface when activating the plugin.
+ *
+ * For conveniency, the function calls 'json_object_put' for 'object'.
+ * Thus, in the case where 'object' should remain available after
+ * the function returns, the function 'json_object_get' shall be used.
+ */
+void afb_daemon_broadcast_event(struct afb_daemon daemon, const char *name, struct json_object *object);
+</code></pre>
+
+<blockquote><p>Be aware, as for reply functions, the <strong>object</strong> is automatically released using
+<strong>json_object_put</strong> by the function. Then call <strong>json_object_get</strong> before
+calling <strong>afb_daemon_broadcast_event</strong> to keep <strong>object</strong> available
+after the returning of the function.</p></blockquote>
+
+<p>In fact the event name received by the listener is prefixed with
+the name of the plugin. So when the change occurs after a move, the
+reason is <strong>move</strong> and then the clients receive the event <strong>tictactoe/move</strong>.</p>
+
+<blockquote><p>Note that nothing is said about the case sensitivity of event names.
+However, the event is always prefixed with the name that the plugin
+declared, with the same case, followed with a slash /.
+Thus it is safe to compare event using a case sensitive comparison.</p></blockquote>
+
+<a name="Writing.an.asynchronous.verb.implementation"></a>
+<h2>Writing an asynchronous verb implementation</h2>
+
+<p>The <em>tic-tac-toe</em> example allows two clients or more to share the same board.
+This is implemented by the verb <strong>join</strong> that illustrated partly the how to
+retrieve arguments.</p>
+
+<p>When two or more clients are sharing a same board, one of them can wait
+until the state of the board changes. (This coulded also be implemented using
+events because an even is generated each time the board changes).</p>
+
+<p>In this case, the reply to the wait is sent only when the board changes.
+See the diagram below:</p>
+
+<pre><code>CLIENT A       CLIENT B         TIC-TAC-TOE
+   |              |                  |
+   +--------------|-----------------&gt;| wait . . . . . . . .
+   |              |                  |                     .
+   :              :                  :                      .
+   :              :                  :                      .
+   |              |                  |                      .
+   |              +-----------------&gt;| move . . .           .
+   |              |                  |          V           .
+   |              |&lt;-----------------+ success of move      .
+   |              |                  |                    .
+   |&lt;-------------|------------------+ success of wait  &lt;
+</code></pre>
+
+<p>Here, this is an invocation of the plugin by an other client that
+unblock the suspended <em>wait</em> call.
+But in general, this will be a timer, a hardware event, the sync with
+a concurrent process or thread, &hellip;</p>
+
+<p>So the case is common, this is an asynchronous implementation.</p>
+
+<p>Here is the listing of the function <strong>wait</strong>:</p>
+
+<pre><code>static void wait(struct afb_req req)
+{
+        struct board *board;
+        struct waiter *waiter;
+
+        /* retrieves the context for the session */
+        board = board_of_req(req);
+        INFO(afbitf, "method 'wait' called for boardid %d", board-&gt;id);
+
+        /* creates the waiter and enqueues it */
+        waiter = calloc(1, sizeof *waiter);
+        waiter-&gt;req = req;
+        waiter-&gt;next = board-&gt;waiters;
+        afb_req_addref(req);
+        board-&gt;waiters = waiter;
+}
+</code></pre>
+
+<p>After retrieving the board, the function adds a new waiter to the
+current list of waiters and returns without sending a reply.</p>
+
+<p>Before returning, it increases the reference count of the
+request <strong>req</strong> using the function <strong>afb_req_addref</strong>.</p>
+
+<blockquote><p>When the implentation of a verb returns without sending a reply,
+it <strong>MUST</strong> increment the reference count of the request
+using <strong>afb_req_addref</strong>. If it doesn&rsquo;t bad things can happen.</p></blockquote>
+
+<p>Later, when the board changes, it calls the function <strong>changed</strong>
+of <em>tic-tac-toe</em> with the reason of the change.</p>
+
+<p>Here is the full listing of the function <strong>changed</strong>:</p>
+
+<pre><code>/*
+ * signals a change of the board
+ */
+static void changed(struct board *board, const char *reason)
+{
+        struct waiter *waiter, *next;
+        struct json_object *description;
+
+        /* get the description */
+        description = describe(board);
+
+        waiter = board-&gt;waiters;
+        board-&gt;waiters = NULL;
+        while (waiter != NULL) {
+                next = waiter-&gt;next;
+                afb_req_success(waiter-&gt;req, json_object_get(description), reason);
+                afb_req_unref(waiter-&gt;req);
+                free(waiter);
+                waiter = next;
+        }
+
+        afb_event_sender_push(afb_daemon_get_event_sender(afbitf-&gt;daemon), reason, description);
+}
+</code></pre>
+
+<p>The list of waiters is walked and a reply is sent to each waiter.
+After the sending the reply, the reference count of the request
+is decremented using <strong>afb_req_unref</strong> to allow its resources to be freed.</p>
+
+<blockquote><p>The reference count <strong>MUST</strong> be decremented using <strong>afb_req_unref</strong> because,
+otherwise, there is a leak of resources.
+It must be decremented <strong>AFTER</strong> the sending of the reply, because, otherwise,
+bad things may happen.</p></blockquote>
+
+<a name="How.to.build.a.plugin"></a>
+<h2>How to build a plugin</h2>
+
+<p>Afb-daemon provides a <em>pkg-config</em> configuration file that can be
+queried by the name <strong>afb-daemon</strong>.
+This configuration file provides data that should be used
+for compiling plugins. Examples:</p>
+
+<pre><code>$ pkg-config --cflags afb-daemon
+$ pkg-config --libs afb-daemon
+</code></pre>
+
+<a name="Example.for.cmake.meta.build.system"></a>
+<h3>Example for cmake meta build system</h3>
+
+<p>This example is the extract for building the plugin <em>afm-main</em> using <em>CMAKE</em>.</p>
+
+<pre><code>pkg_check_modules(afb afb-daemon)
+if(afb_FOUND)
+        message(STATUS "Creation afm-main-plugin for AFB-DAEMON")
+        add_library(afm-main-plugin MODULE afm-main-plugin.c)
+        target_compile_options(afm-main-plugin PRIVATE ${afb_CFLAGS})
+        target_include_directories(afm-main-plugin PRIVATE ${afb_INCLUDE_DIRS})
+        target_link_libraries(afm-main-plugin utils ${afb_LIBRARIES})
+        set_target_properties(afm-main-plugin PROPERTIES
+                PREFIX ""
+                LINK_FLAGS "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/afm-main-plugin.export-map"
+        )
+        install(TARGETS afm-main-plugin LIBRARY DESTINATION ${plugin_dir})
+else()
+        message(STATUS "Not creating the plugin for AFB-DAEMON")
+endif()
+</code></pre>
+
+<p>Let now describe some of these lines.</p>
+
+<pre><code>pkg_check_modules(afb afb-daemon)
+</code></pre>
+
+<p>This first lines searches to the <em>pkg-config</em> configuration file for
+<strong>afb-daemon</strong>. Resulting data are stored in the following variables:</p>
+
+<table>
+<thead>
+<tr>
+<th>Variable      </th>
+<th> Meaning</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>afb_FOUND     </td>
+<td> Set to 1 if afb-daemon plugin development files exist</td>
+</tr>
+<tr>
+<td>afb_LIBRARIES     </td>
+<td> Only the libraries (w/o the &lsquo;-l&rsquo;) for compiling afb-daemon plugins</td>
+</tr>
+<tr>
+<td>afb_LIBRARY_DIRS  </td>
+<td> The paths of the libraries (w/o the &lsquo;-L&rsquo;) for compiling afb-daemon plugins</td>
+</tr>
+<tr>
+<td>afb_LDFLAGS       </td>
+<td> All required linker flags for compiling afb-daemon plugins</td>
+</tr>
+<tr>
+<td>afb_INCLUDE_DIRS  </td>
+<td> The &lsquo;-I&rsquo; preprocessor flags (w/o the &lsquo;-I&rsquo;) for compiling afb-daemon plugins</td>
+</tr>
+<tr>
+<td>afb_CFLAGS    </td>
+<td> All required cflags for compiling afb-daemon plugins</td>
+</tr>
+</tbody>
+</table>
+
+
+<p>If development files are found, the plugin can be added to the set of
+target to build.</p>
+
+<pre><code>add_library(afm-main-plugin MODULE afm-main-plugin.c)
+</code></pre>
+
+<p>This line asks to create a shared library having only the
+source file afm-main-plugin.c (that is compiled).
+The default name of the created shared object is
+<strong>libafm-main-plugin.so</strong>.</p>
+
+<pre><code>set_target_properties(afm-main-plugin PROPERTIES
+        PREFIX ""
+        LINK_FLAGS "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/afm-main-plugin.export-map"
+)
+</code></pre>
+
+<p>This lines are doing two things:</p>
+
+<ol>
+<li><p>It renames the built library from <strong>libafm-main-plugin.so</strong> to <strong>afm-main-plugin.so</strong>
+by removing the implicitely added prefix <em>lib</em>. This step is not mandatory
+at all because afb-daemon doesn&rsquo;t check names of files when loading it.
+The only convention that use afb-daemon is that extension is <strong>.so</strong>
+but this convention is used only when afb-daemon discovers plugin
+from a directory hierarchy.</p></li>
+<li><p>It applies a version script at link to only export the conventional name
+of the entry point: <strong>pluginAfbV1Register</strong>. See below. By default, the linker
+that creates the shared object exports all the public symbols (C functions that
+are not <strong>static</strong>).</p></li>
+</ol>
+
+
+<p>Next line are:</p>
+
+<pre><code>target_include_directories(afm-main-plugin PRIVATE ${afb_INCLUDE_DIRS})
+target_link_libraries(afm-main-plugin utils ${afb_LIBRARIES})
+</code></pre>
+
+<p>As you can see it uses the variables computed by <strong><em>pkg_check_modules(afb afb-daemon)</em></strong>
+to configure the compiler and the linker.</p>
+
+<a name="Exporting.the.function.pluginAfbV1Register"></a>
+<h3>Exporting the function pluginAfbV1Register</h3>
+
+<p>The function <strong>pluginAfbV1Register</strong> must be exported. This can be achieved
+using a version script when linking. Here is the version script that is
+used for <em>tic-tac-toe</em> (plugins/samples/export.map).</p>
+
+<pre><code>{ global: pluginAfbV1Register; local: *; };
+</code></pre>
+
+<p>This sample <a href="https://sourceware.org/binutils/docs-2.26/ld/VERSION.html#VERSION">version script</a>
+exports as global the symbol <em>pluginAfbV1Register</em> and hides any
+other symbols.</p>
+
+<p>This version script is added to the link options using the
+option <strong>&ndash;version-script=export.map</strong> is given directly to the
+linker or using th option <strong>-Wl,&ndash;version-script=export.map</strong>
+when the option is given to the C compiler.</p>
+
+<a name="Building.within.yocto"></a>
+<h3>Building within yocto</h3>
+
+<p>Adding a dependency to afb-daemon is enough. See below:</p>
+
+<pre><code>DEPENDS += " afb-daemon "
+</code></pre>
+</body>
+</html>
diff --git a/doc/afb-plugin-writing.md b/doc/afb-plugin-writing.md
new file mode 100644
index 00000000..486b141d
--- /dev/null
+++ b/doc/afb-plugin-writing.md
@@ -0,0 +1,1222 @@
+HOWTO WRITE a PLUGIN for AFB-DAEMON
+===================================
+    version: 1
+    Date:    27 mai 2016
+    Author:  José Bollo
+
+TABLE-OF-CONTENT-HERE
+
+Summary
+-------
+
+The binder afb-daemon serves files through
+the HTTP protocol and offers access to API's through
+HTTP or WebSocket protocol.
+
+The plugins are used to add API's to afb-daemon.
+This part describes how to write a plugin for afb-daemon.
+Excepting this summary, this part is intended to be read
+by developpers.
+
+Before going into details, through a tiny example,
+a short overview plugins basis is needed.
+
+### Nature of a plugin
+
+A plugin is a separate piece of code made of a shared library.
+The plugin is loaded and activated by afb-daemon when afb-daemon
+starts.
+
+Technically, a plugin is not linked to any library of afb-daemon.
+
+### Kinds of plugins
+
+There is two kinds of plugins: application plugins and service
+plugins.
+
+#### Application plugins
+
+Application plugins are intended to be instanciated for each
+application: when an application using that plugin is started,
+its binder starts a new instance of the plugin.
+
+It means that the application plugins mainly have only one
+context to manage for one client.
+
+#### Service plugins
+
+Service plugins are intended to be instanciated only one time
+only and connected to many clients.
+
+So either it does not manage context at all or otherwise,
+if it manages context, it should be able to manage one context
+per client.
+
+In details, it may be useful to have service plugins at a user
+level.
+ 
+### Live cycle of a plugin within afb-daemon
+
+The plugins are loaded and activated when afb-daemon starts.
+
+At start, the plugin initialise itself.
+If it fails to initialise then afb-daemon stops.
+
+Conversely, if it success to initialize, it must declare
+a name, that must be unique, and a list of API's verbs.
+
+When initialized, the functions implementing the API's verbs
+of the plugin are activated on call.
+
+At the end, nothing special is done by afb-daemon.
+Consequently, developpers of plugins should use 'atexit'
+or 'on_exit' during initialisation if they need to
+perform specific actions when stopping.
+
+### Content of a plugin
+
+For afb-daemon, a plugin contains 2 different
+things: names and functions.
+
+There is two kind of names:
+ - the name of the plugin,
+ - the names of the verbs.
+
+There is two kind of functions:
+ - the initialisation function
+ - functions implementing verbs
+
+Afb-daemon translates the name of the method that is
+invoked to a pair of API and verb names. For example,
+the method named **foo/bar** translated to the API
+name **foo** and the verb name **bar**.
+To serve it, afb-daemon search the plugin that record
+the name **foo** and if it also recorded the verb **bar**,
+it calls the implementation function declared for this verb.
+
+Afb-daemon make no distinction between lower case
+and upper case when searching for a method.
+Thus, The names **TicTacToe/Board** and **tictactoe/borad**
+are equals.
+
+#### The name of the plugin
+
+The name of the plugin is also known as the name
+of the API that defines the plugin.
+
+This name is also known as the prefix.
+
+The name of a plugin MUST be unique within afb-daemon.
+
+For example, when a client of afb-daemon
+calls a method named **foo/bar**. Afb-daemon
+extracts the prefix **foo** and the suffix **bar**.
+**foo** is the API name and must match a plugin name,
+the plugin that implements the verb **bar**.
+
+#### Names of verbs
+
+Each plugin exposes a set of verbs that can be called
+by client of afb-daemon.
+
+The name of a verb MUST be unique within a plugin.
+
+Plugins link verbs to functions that are called
+when clients emit requests for that verb.
+
+For example, when a client of afb-daemon
+calls a method named **foo/bar**.
+
+#### The initialisation function
+
+The initialisation function serves several purposes.
+
+1. It allows afb-daemon to check the version
+of the plugin using the name of the initialisation
+functions that it found. Currently, the initialisation
+function is named **pluginAfbV1Register**. It identifies
+the first version of plugins.
+
+2. It allows the plugin to initialise itself.
+
+3. It serves to the plugin to declare names, descriptions,
+requirements and implmentations of the verbs that it exposes.
+
+#### Functions implementing verbs
+
+When a method is called, afb-daemon constructs a request
+object and pass it to the implementation function for verb
+within the plugin of the API.
+
+An implementation function receives a request object that
+is used to get arguments of the request, to send
+answer, to store session data.
+
+A plugin MUST send an answer to the request.
+
+But it is not mandatory to send the answer
+before to return from the implementing function.
+This behaviour is important for implementing
+asynchronous actions.
+
+Implementation functions that always reply to the request
+before returning are named *synchronous implementations*.
+Those that don't always reply to the request before
+returning are named *asynchronous implementations*.
+
+Asynchronous implementations typically initiate an
+asynchronous action and record to send the reply
+on completion of this action.
+
+The Tic-Tac-Toe example
+-----------------------
+
+This part explains how to write an afb-plugin.
+For the sake of being practical we will use many
+examples from the tic-tac-toe example.
+This plugin example is in *plugins/samples/tic-tac-toe.c*.
+
+This plugin is named ***tictactoe***.
+
+Dependencies when compiling
+---------------------------
+
+Afb-daemon provides a configuration file for *pkg-config*.
+Typing the command
+
+	pkg-config --cflags afb-daemon
+
+will print the flags to use for compiling, like this:
+
+	$ pkg-config --cflags afb-daemon
+	-I/opt/local/include -I/usr/include/json-c 
+
+For linking, you should use
+
+	$ pkg-config --libs afb-daemon
+	-ljson-c
+
+As you see, afb-daemon automatically includes dependency to json-c.
+This is done through the **Requires** keyword of pkg-config
+because almost all plugin will use **json-c**.
+
+If this behaviour is a problem, let us know.
+
+Internally, afb-daemon uses **libsystemd** for its event loop
+and for its binding to D-Bus.
+Plugins developpers are encouraged to also use this library.
+But it is a matter of choice.
+Thus there is no dependency to **libsystemd**.
+
+> Afb-daemon provides no library for plugins.
+> The functions that the plugin need to have are given
+> to the plugin at runtime through pointer using read-only
+> memory.
+
+Header files to include
+-----------------------
+
+The plugin *tictactoe* has the following lines for its includes:
+
+	#define _GNU_SOURCE
+	#include <stdio.h>
+	#include <string.h>
+	#include <json-c/json.h>
+	#include <afb/afb-plugin.h>
+
+The header *afb/afb-plugin.h* includes all the features that a plugin
+needs except two foreign header that must be included by the plugin
+if it needs it:
+
+- *json-c/json.h*: this header must be include to handle json objects;
+- *systemd/sd-event.h*: this must be include to access the main loop;
+- *systemd/sd-bus.h*: this may be include to use dbus connections.
+
+The *tictactoe* plugin does not use systemd features so it is not included.
+
+When including *afb/afb-plugin.h*, the macro **_GNU_SOURCE** must be
+defined.
+
+Choosing names
+--------------
+
+The designer of a plugin must defines names for its plugin
+(or its API) and for the verbs of its API. He also
+must defines names for arguments given by name.
+
+While forging names, the designer should take into account
+the rules for making valid names and some rules that make
+the names easy to use across plaforms.
+
+The names and strings used ALL are UTF-8 encoded.
+
+### Names for API (plugin)
+
+The names of the API are checked.
+All characters are authorised except:
+
+- the control characters (\u0000 .. \u001f)
+- the characters of the set { ' ', '"', '#', '%', '&',
+  '\'', '/', '?', '`', '\x7f' }
+
+In other words the set of forbidden characters is
+{ \u0000..\u0020, \u0022, \u0023, \u0025..\u0027,
+  \u002f, \u003f, \u0060, \u007f }.
+
+Afb-daemon make no distinction between lower case
+and upper case when searching for an API by its name.
+
+### Names for verbs
+
+The names of the verbs are not checked.
+
+However, the validity rules for verb's names are the
+same as for API's names except that the dot (.) character
+is forbidden.
+
+Afb-daemon make no distinction between lower case
+and upper case when searching for an API by its name.
+
+### Names for arguments
+
+The names for arguments are not restricted and can be
+anything.
+
+The arguments are searched with the case sensitive
+string comparison. Thus the names "index" and "Index"
+are not the same.
+
+### Forging names widely available
+
+The key names of javascript object can be almost
+anything using the arrayed notation:
+
+	object[key] = value
+
+That is not the case with the dot notation:
+
+	object.key = value
+
+Using the dot notation, the key must be a valid javascript
+identifier.
+
+For this reason, the chosen names should better be
+valid javascript identifier.
+
+It is also a good practice, even for arguments, to not
+rely on the case sensitivity and to avoid the use of
+names different only by the case.
+
+Writing a synchronous verb implementation
+-----------------------------------------
+
+The verb **tictactoe/board** is a synchronous implementation.
+Here is its listing:
+
+	/*
+	 * get the board
+	 */
+	static void board(struct afb_req req)
+	{
+		struct board *board;
+		struct json_object *description;
+
+		/* retrieves the context for the session */
+		board = board_of_req(req);
+		INFO(afbitf, "method 'board' called for boardid %d", board->id);
+
+		/* describe the board */
+		description = describe(board);
+
+		/* send the board's description */
+		afb_req_success(req, description, NULL);
+	}
+
+This examples show many aspects of writing a synchronous
+verb implementation. Let summarize it:
+
+1. The function **board_of_req** retrieves the context stored
+for the plugin: the board.
+
+2. The macro **INFO** sends a message of kind *INFO*
+to the logging system. The global variable named **afbitf**
+used represents the interface to afb-daemon.
+
+3. The function **describe** creates a json_object representing
+the board.
+
+4. The function **afb_req_success** sends the reply, attaching to
+it the object *description*.
+
+### The incoming request
+
+For any implementation, the request is received by a structure of type
+**struct afb_req**.
+
+> Note that this is a PLAIN structure, not a pointer to a structure.
+
+The definition of **struct afb_req** is:
+
+	/*
+	 * Describes the request by plugins from afb-daemon
+	 */
+	struct afb_req {
+		const struct afb_req_itf *itf;	/* the interfacing functions */
+		void *closure;			/* the closure for functions */
+	};
+
+It contains two pointers: one, *itf*, points to the functions needed
+to handle the internal request represented by the second pointer, *closure*.
+
+> The structure must never be used directly.
+> Insted, use the intended functions provided
+> by afb-daemon and described here.
+
+*req* is used to get arguments of the request, to send
+answer, to store session data.
+
+This object and its interface is defined and documented
+in the file names *afb/afb-req-itf.h*
+
+The above example uses 2 times the request object *req*.
+
+The first time, it is used for retrieving the board attached to
+the session of the request.
+
+The second time, it is used to send the reply: an object that
+describes the current board.
+
+### Associating a context to the session
+
+When the plugin *tic-tac-toe* receives a request, it musts regain
+the board that describes the game associated to the session.
+
+For a plugin, having data associated to a session is a common case.
+This data is called the context of the plugin for the session.
+For the plugin *tic-tac-toe*, the context is the board.
+
+The requests *afb_req* offer four functions for
+storing and retrieving the context associated to the session.
+
+These functions are:
+
+- **afb_req_context_get**:
+  retrieves the context data stored for the plugin.
+
+- **afb_req_context_set**:
+  store the context data of the plugin.
+
+- **afb_req_context**:
+  retrieves the context data of the plugin,
+  if needed, creates the context and store it.
+
+- **afb_req_context_clear**:
+  reset the stored data.
+
+The plugin *tictactoe* use a convenient function to retrieve
+its context: the board. This function is *board_of_req*:
+
+	/*
+	 * retrieves the board of the request
+	 */
+	static inline struct board *board_of_req(struct afb_req req)
+	{
+		return afb_req_context(req, (void*)get_new_board, (void*)release_board);
+	}
+
+The function **afb_req_context** ensure an existing context
+for the session of the request.
+Its two last arguments are functions. Here, the casts are required
+to avoid a warning when compiling.
+
+Here is the definition of the function **afb_req_context**
+
+	/*
+	 * Gets the pointer stored by the plugin for the session of 'req'.
+	 * If the stored pointer is NULL, indicating that no pointer was
+	 * already stored, afb_req_context creates a new context by calling
+	 * the function 'create_context' and stores it with the freeing function
+	 * 'free_context'.
+	 */
+	static inline void *afb_req_context(struct afb_req req, void *(*create_context)(), void (*free_context)(void*))
+	{
+		void *result = afb_req_context_get(req);
+		if (result == NULL) {
+			result = create_context();
+			afb_req_context_set(req, result, free_context);
+		}
+		return result;
+	}
+
+The second argument if the function that creates the context.
+For the plugin *tic-tac-toe* it is the function **get_new_board**.
+The function **get_new_board** creates a new board and set its
+count of use to 1. The boards are counting their count of use
+to free there ressources when no more used.
+
+The third argument if the function that frees the context.
+For the plugin *tic-tac-toe* it is the function **release_board**.
+The function **release_board** decrease the the count of use of
+the board given as argument. If the use count decrease to zero,
+the board data are freed.
+
+The definition of the other functions for dealing with contexts are:
+
+	/*
+	 * Gets the pointer stored by the plugin for the session of 'req'.
+	 * When the plugin has not yet recorded a pointer, NULL is returned.
+	 */
+	void *afb_req_context_get(struct afb_req req);
+
+	/*
+	 * Stores for the plugin the pointer 'context' to the session of 'req'.
+	 * The function 'free_context' will be called when the session is closed
+	 * or if plugin stores an other pointer.
+	 */
+	void afb_req_context_set(struct afb_req req, void *context, void (*free_context)(void*));
+
+	/*
+	 * Frees the pointer stored by the plugin for the session of 'req'
+	 * and sets it to NULL.
+	 *
+	 * Shortcut for: afb_req_context_set(req, NULL, NULL)
+	 */
+	static inline void afb_req_context_clear(struct afb_req req)
+	{
+		afb_req_context_set(req, NULL, NULL);
+	}
+
+### Sending the reply to a request
+
+Two kinds of replies can be made: successful replies and
+failure replies.
+
+> Sending a reply to a request must be done at most one time.
+
+The two functions to send a reply of kind "success" are
+**afb_req_success** and **afb_req_success_f**.
+
+	/*
+	 * Sends a reply of kind success to the request 'req'.
+	 * The status of the reply is automatically set to "success".
+	 * Its send the object 'obj' (can be NULL) with an
+	 * informationnal comment 'info (can also be NULL).
+	 *
+	 * For conveniency, the function calls 'json_object_put' for 'obj'.
+	 * Thus, in the case where 'obj' should remain available after
+	 * the function returns, the function 'json_object_get' shall be used.
+	 */
+	void afb_req_success(struct afb_req req, struct json_object *obj, const char *info);
+
+	/*
+	 * Same as 'afb_req_success' but the 'info' is a formatting
+	 * string followed by arguments.
+	 *
+	 * For conveniency, the function calls 'json_object_put' for 'obj'.
+	 * Thus, in the case where 'obj' should remain available after
+	 * the function returns, the function 'json_object_get' shall be used.
+	 */
+	void afb_req_success_f(struct afb_req req, struct json_object *obj, const char *info, ...);
+
+The two functions to send a reply of kind "failure" are
+**afb_req_fail** and **afb_req_fail_f**.
+
+	/*
+	 * Sends a reply of kind failure to the request 'req'.
+	 * The status of the reply is set to 'status' and an
+	 * informationnal comment 'info' (can also be NULL) can be added.
+	 *
+	 * Note that calling afb_req_fail("success", info) is equivalent
+	 * to call afb_req_success(NULL, info). Thus even if possible it
+	 * is strongly recommanded to NEVER use "success" for status.
+	 *
+	 * For conveniency, the function calls 'json_object_put' for 'obj'.
+	 * Thus, in the case where 'obj' should remain available after
+	 * the function returns, the function 'json_object_get' shall be used.
+	 */
+	void afb_req_fail(struct afb_req req, const char *status, const char *info);
+
+	/*
+	 * Same as 'afb_req_fail' but the 'info' is a formatting
+	 * string followed by arguments.
+	 *
+	 * For conveniency, the function calls 'json_object_put' for 'obj'.
+	 * Thus, in the case where 'obj' should remain available after
+	 * the function returns, the function 'json_object_get' shall be used.
+	 */
+	void afb_req_fail_f(struct afb_req req, const char *status, const char *info, ...);
+
+> For conveniency, these functions call **json_object_put** to release the object **obj**
+> that they send. Then **obj** can not be used after calling one of these reply functions.
+> When it is not the expected behaviour, calling the function **json_object_get** on the object **obj**
+> before cancels the effect of **json_object_put**.
+
+Getting argument of invocation
+------------------------------
+
+Many verbs expect arguments. Afb-daemon let plugins
+retrieve their arguments by name not by position.
+
+Arguments are given by the requests either through HTTP
+or through WebSockets.
+
+For example, the verb **join** of the plugin **tic-tac-toe**
+expects one argument: the *boardid* to join. Here is an extract:
+
+	/*
+	 * Join a board
+	 */
+	static void join(struct afb_req req)
+	{
+		struct board *board, *new_board;
+		const char *id;
+
+		/* retrieves the context for the session */
+		board = board_of_req(req);
+		INFO(afbitf, "method 'join' called for boardid %d", board->id);
+
+		/* retrieves the argument */
+		id = afb_req_value(req, "boardid");
+		if (id == NULL)
+			goto bad_request;
+		...
+
+The function **afb_req_value** search in the request *req*
+for an argument whose name is given. When no argument of the
+given name was passed, **afb_req_value** returns NULL.
+
+> The search is case sensitive. So the name *boardid* is not the
+> same name than *BoardId*. But this must not be assumed so two
+> expected names of argument should not differ only by case.
+
+### Basic functions for querying arguments
+
+The function **afb_req_value** is defined as below:
+
+	/*
+	 * Gets from the request 'req' the string value of the argument of 'name'.
+	 * Returns NULL if when there is no argument of 'name'.
+	 * Returns the value of the argument of 'name' otherwise.
+	 *
+	 * Shortcut for: afb_req_get(req, name).value
+	 */
+	static inline const char *afb_req_value(struct afb_req req, const char *name)
+	{
+		return afb_req_get(req, name).value;
+	}
+
+It is defined as a shortcut to call the function **afb_req_get**.
+That function is defined as below:
+
+	/*
+	 * Gets from the request 'req' the argument of 'name'.
+	 * Returns a PLAIN structure of type 'struct afb_arg'.
+	 * When the argument of 'name' is not found, all fields of result are set to NULL.
+	 * When the argument of 'name' is found, the fields are filled,
+	 * in particular, the field 'result.name' is set to 'name'.
+	 *
+	 * There is a special name value: the empty string.
+	 * The argument of name "" is defined only if the request was made using
+	 * an HTTP POST of Content-Type "application/json". In that case, the
+	 * argument of name "" receives the value of the body of the HTTP request.
+	 */
+	struct afb_arg afb_req_get(struct afb_req req, const char *name);
+
+That function takes 2 parameters: the request and the name
+of the argument to retrieve. It returns a PLAIN structure of
+type **struct afb_arg**.
+
+There is a special name that is defined when the request is
+of type HTTP/POST with a Content-Type being application/json.
+This name is **""** (the empty string). In that case, the value
+of this argument of empty name is the string received as a body
+of the post and is supposed to be a JSON string.
+
+The definition of **struct afb_arg** is:
+
+	/*
+	 * Describes an argument (or parameter) of a request
+	 */
+	struct afb_arg {
+		const char *name;	/* name of the argument or NULL if invalid */
+		const char *value;	/* string representation of the value of the argument */
+					/* original filename of the argument if path != NULL */
+		const char *path;	/* if not NULL, path of the received file for the argument */
+					/* when the request is finalized this file is removed */
+	};
+
+The structure returns the data arguments that are known for the
+request. This data include a field named **path**. This **path**
+can be accessed using the function **afb_req_path** defined as
+below:
+
+	/*
+	 * Gets from the request 'req' the path for file attached to the argument of 'name'.
+	 * Returns NULL if when there is no argument of 'name' or when there is no file.
+	 * Returns the path of the argument of 'name' otherwise.
+	 *
+	 * Shortcut for: afb_req_get(req, name).path
+	 */
+	static inline const char *afb_req_path(struct afb_req req, const char *name)
+	{
+		return afb_req_get(req, name).path;
+	}
+
+The path is only defined for HTTP/POST requests that send file.
+
+### Arguments for received files
+
+As it is explained just above, clients can send files using
+HTTP/POST requests.
+
+Received files are attached to a arguments. For example, the
+following HTTP fragment (from test/sample-post.html)
+will send an HTTP/POST request to the method
+**post/upload-image** with 2 arguments named *file* and
+*hidden*.
+
+	<h2>Sample Post File</h2>
+	<form enctype="multipart/form-data">
+	    <input type="file" name="file" />
+	    <input type="hidden" name="hidden" value="bollobollo" />
+	    <br>
+	    <button formmethod="POST" formaction="api/post/upload-image">Post File</button>
+	</form>
+
+In that case, the argument named **file** has its value and its
+path defined and not NULL.
+
+The value is the name of the file as it was
+set by the HTTP client and is generally the filename on the
+client side.
+
+The path is the path of the file saved on the temporary local storage
+area of the application. This is a randomly generated and unic filename
+not linked in any way with the original filename on the client.
+
+The plugin can use the file at the given path the way that it wants:
+read, write, remove, copy, rename...
+But when the reply is sent and the query is terminated, the file at
+this path is destroyed if it still exist.
+
+### Arguments as a JSON object
+
+Plugins can get all the arguments as one single object.
+This feature is provided by the function **afb_req_json**
+that is defined as below:
+
+	/*
+	 * Gets from the request 'req' the json object hashing the arguments.
+	 * The returned object must not be released using 'json_object_put'.
+	 */
+	struct json_object *afb_req_json(struct afb_req req);
+
+It returns a json object. This object depends on how the request was
+made:
+
+- For HTTP requests, this is an object whose keys are the names of the
+arguments and whose values are either a string for common arguments or
+an object like { "file": "...", "path": "..." }
+
+- For WebSockets requests, the returned object is the object
+given by the client transparently transported.
+
+> In fact, for Websockets requests, the function **afb_req_value**
+> can be seen as a shortcut to
+> ***json_object_get_string(json_object_object_get(afb_req_json(req), name))***
+
+Initialisation of the plugin and declaration of verbs
+-----------------------------------------------------
+
+To be active, the verbs of the plugin should be declared to
+afb-daemon. And even more, the plugin itself must be recorded.
+
+The mechanism for doing this is very simple: when afb-need starts,
+it loads the plugins that are listed in its argument or configuration.
+
+Loading a plugin follows the following steps:
+
+1. It loads the plugin using *dlopen*.
+
+2. It searchs for the symbol named **pluginAfbV1Register** using *dlsym*.
+This symbol is assumed to be the exported initialisation function of the plugin.
+
+3. It build an interface object for the plugin.
+
+4. It calls the found function **pluginAfbV1Register** and pass it the pointer
+to its interface.
+
+5. The function **pluginAfbV1Register** setup the plugin, initialize it.
+
+6. The function **pluginAfbV1Register** returns the pointer to a structure
+that describes the plugin: its version, its name (prefix or API name), and the
+list of its verbs.
+
+7. Afb-daemon checks that the returned version and name can be managed.
+If it can manage it, the plugin and its verbs are recorded and can be used
+when afb-daemon finishes it initialisation.
+
+Here is the listing of the function **pluginAfbV1Register** of the plugin
+*tic-tac-toe*:
+
+	/*
+	 * activation function for registering the plugin called by afb-daemon
+	 */
+	const struct AFB_plugin *pluginAfbV1Register(const struct AFB_interface *itf)
+	{
+	   afbitf = itf;         // records the interface for accessing afb-daemon
+	   return &plugin_description;  // returns the description of the plugin
+	}
+
+This is a very small function because the *tic-tac-toe* plugin doesn't have initialisation step.
+It merely record the daemon's interface and returns its descritption.
+
+The variable **afbitf** is a variable global to the plugin. It records the
+interface to afb-daemon and is used for logging and pushing events.
+Here is its declaration:
+
+	/*
+	 * the interface to afb-daemon
+	 */
+	const struct AFB_interface *afbitf;
+
+The description of the plugin is defined as below.
+
+	/*
+	 * array of the verbs exported to afb-daemon
+	 */
+	static const struct AFB_verb_desc_v1 plugin_verbs[] = {
+	   /* VERB'S NAME     SESSION MANAGEMENT          FUNCTION TO CALL  SHORT DESCRIPTION */
+	   { .name= "new",   .session= AFB_SESSION_NONE, .callback= new,   .info= "Starts a new game" },
+	   { .name= "play",  .session= AFB_SESSION_NONE, .callback= play,  .info= "Asks the server to play" },
+	   { .name= "move",  .session= AFB_SESSION_NONE, .callback= move,  .info= "Tells the client move" },
+	   { .name= "board", .session= AFB_SESSION_NONE, .callback= board, .info= "Get the current board" },
+	   { .name= "level", .session= AFB_SESSION_NONE, .callback= level, .info= "Set the server level" },
+	   { .name= "join",  .session= AFB_SESSION_CHECK,.callback= join,  .info= "Join a board" },
+	   { .name= "undo",  .session= AFB_SESSION_NONE, .callback= undo,  .info= "Undo the last move" },
+	   { .name= "wait",  .session= AFB_SESSION_NONE, .callback= wait,  .info= "Wait for a change" },
+	   { .name= NULL } /* marker for end of the array */
+	};
+
+	/*
+	 * description of the plugin for afb-daemon
+	 */
+	static const struct AFB_plugin plugin_description =
+	{
+	   /* description conforms to VERSION 1 */
+	   .type= AFB_PLUGIN_VERSION_1,
+	   .v1= {				/* fills the v1 field of the union when AFB_PLUGIN_VERSION_1 */
+	      .prefix= "tictactoe",		/* the API name (or plugin name or prefix) */
+	      .info= "Sample tac-tac-toe game",	/* short description of of the plugin */
+	      .verbs = plugin_verbs		/* the array describing the verbs of the API */
+	   }
+	};
+
+The structure **plugin_description** describes the plugin.
+It declares the type and version of the plugin, its name, a description
+and a list of its verbs.
+
+The list of verbs is an array of structures describing the verbs and terminated by a marker:
+a verb whose name is NULL.
+
+The description of the verbs for this version is made of 4 fields:
+
+- the name of the verbs,
+
+- the session management flags,
+
+- the implementation function to be call for the verb,
+
+- a short description.
+
+The structure describing verbs is defined as follows:
+
+	/*
+	 * Description of one verb of the API provided by the plugin
+	 * This enumeration is valid for plugins of type 1
+	 */
+	struct AFB_verb_desc_v1
+	{
+	       const char *name;                       /* name of the verb */
+	       enum AFB_session_v1 session;            /* authorisation and session requirements of the verb */
+	       void (*callback)(struct afb_req req);   /* callback function implementing the verb */
+	       const char *info;                       /* textual description of the verb */
+	};
+
+For technical reasons, the enumeration **enum AFB_session_v1** is not exactly an
+enumeration but the wrapper of constant definitions that can be mixed using bitwise or
+(the C operator |).
+
+The constants that can bit mixed are:
+
+Constant name            | Meaning
+-------------------------|-------------------------------------------------------------
+**AFB_SESSION_CREATE**   | Equals to AFB_SESSION_LOA_EQ_0|AFB_SESSION_RENEW
+**AFB_SESSION_CLOSE**    | Closes the session after the reply and set the LOA to 0
+**AFB_SESSION_RENEW**    | Refreshes the token of authentification
+**AFB_SESSION_CHECK**    | Just requires the token authentification
+**AFB_SESSION_LOA_LE_0** | Requires the current LOA to be lesser then or equal to 0
+**AFB_SESSION_LOA_LE_1** | Requires the current LOA to be lesser then or equal to 1
+**AFB_SESSION_LOA_LE_2** | Requires the current LOA to be lesser then or equal to 2
+**AFB_SESSION_LOA_LE_3** | Requires the current LOA to be lesser then or equal to 3
+**AFB_SESSION_LOA_GE_0** | Requires the current LOA to be greater then or equal to 0
+**AFB_SESSION_LOA_GE_1** | Requires the current LOA to be greater then or equal to 1
+**AFB_SESSION_LOA_GE_2** | Requires the current LOA to be greater then or equal to 2
+**AFB_SESSION_LOA_GE_3** | Requires the current LOA to be greater then or equal to 3
+**AFB_SESSION_LOA_EQ_0** | Requires the current LOA to be equal to 0
+**AFB_SESSION_LOA_EQ_1** | Requires the current LOA to be equal to 1
+**AFB_SESSION_LOA_EQ_2** | Requires the current LOA to be equal to 2
+**AFB_SESSION_LOA_EQ_3** | Requires the current LOA to be equal to 3
+
+If any of this flags is set, afb-daemon requires the token authentification
+as if the flag **AFB_SESSION_CHECK** had been set.
+
+The special value **AFB_SESSION_NONE** is zero and can be used to avoid any check.
+
+> Note that **AFB_SESSION_CREATE** and **AFB_SESSION_CLOSE** might be removed in later versions.
+
+Sending messages to the log system
+----------------------------------
+
+Afb-daemon provides 4 levels of verbosity and 5 verbs for logging messages.
+
+The verbosity is managed. Options allow the change the verbosity of afb-daemon
+and the verbosity of the plugins can be set plugin by plugin.
+
+The verbs for logging messages are defined as macros that test the
+verbosity level and that call the real logging function only if the
+message must be output. This avoid evaluation of arguments of the
+formatting messages if the message must not be output.
+
+### Verbs for logging messages
+
+The 5 logging verbs are:
+
+Macro   | Verbosity | Meaning                           | syslog level
+--------|:---------:|-----------------------------------|:-----------:
+ERROR   |     0     | Error conditions                  |     3
+WARNING |     1     | Warning conditions                |     4
+NOTICE  |     1     | Normal but significant condition  |     5
+INFO    |     2     | Informational                     |     6
+DEBUG   |     3     | Debug-level messages              |     7
+
+You can note that the 2 verbs **WARNING** and **INFO** have the same level
+of verbosity. But they don't have the same *syslog level*. It means that
+they are output with a different level on the logging system.
+
+All of these verbs have the same signature:
+
+	void ERROR(const struct AFB_interface *afbitf, const char *message, ...);
+
+The first argument **afbitf** is the interface to afb daemon that the
+plugin received at its initialisation when **pluginAfbV1Register** was called.
+
+The second argument **message** is a formatting string compatible with printf/sprintf.
+
+The remaining arguments are arguments of the formating message like for printf.
+
+### Managing verbosity
+
+Depending on the level of verbosity, the messages are output or not.
+The following table explains what messages will be output depending
+ont the verbosity level.
+
+Level of verbosity | Outputed macro
+:-----------------:|--------------------------
+        0          | ERROR
+        1          | ERROR + WARNING + NOTICE
+        2          | ERROR + WARNING + NOTICE + INFO
+        3          | ERROR + WARNING + NOTICE + INFO + DEBUG
+
+### Output format and destination
+
+The syslog level is used for forging a prefix to the message.
+The prefixes are:
+
+syslog level | prefix
+:-----------:|---------------
+      0      | <0> EMERGENCY
+      1      | <1> ALERT
+      2      | <2> CRITICAL
+      3      | <3> ERROR
+      4      | <4> WARNING
+      5      | <5> NOTICE
+      6      | <6> INFO
+      7      | <7> DEBUG
+
+
+The message is issued to the standard error.
+The final destination of the message depends on how the systemd service
+was configured through the variable **StandardError**: It can be
+journal, syslog or kmsg. (See man sd-daemon).
+
+Sending events
+--------------
+
+Since version 0.5, plugins can broadcast events to any potential listener.
+This kind of bradcast is not targeted. Event targeted will come in a future
+version of afb-daemon.
+
+The plugin *tic-tac-toe* broadcasts events when the board changes.
+This is done in the function **changed**:
+
+	/*
+	 * signals a change of the board
+	 */
+	static void changed(struct board *board, const char *reason)
+	{
+		...
+		struct json_object *description;
+
+		/* get the description */
+		description = describe(board);
+
+		...
+
+		afb_daemon_broadcast_event(afbitf->daemon, reason, description);
+	}
+
+The description of the changed board is pushed via the daemon interface.
+
+Within the plugin *tic-tac-toe*, the *reason* indicates the origin of
+the change. For the function **afb_daemon_broadcast_event**, the second
+parameter is the name of the broadcasted event. The third argument is the
+object that is transmitted with the event.
+
+The function **afb_daemon_broadcast_event** is defined as below:
+
+	/*
+	 * Broadcasts widely the event of 'name' with the data 'object'.
+	 * 'object' can be NULL.
+	 * 'daemon' MUST be the daemon given in interface when activating the plugin.
+	 *
+	 * For conveniency, the function calls 'json_object_put' for 'object'.
+	 * Thus, in the case where 'object' should remain available after
+	 * the function returns, the function 'json_object_get' shall be used.
+	 */
+	void afb_daemon_broadcast_event(struct afb_daemon daemon, const char *name, struct json_object *object);
+
+> Be aware, as for reply functions, the **object** is automatically released using
+> **json_object_put** by the function. Then call **json_object_get** before
+> calling **afb_daemon_broadcast_event** to keep **object** available
+> after the returning of the function.
+
+In fact the event name received by the listener is prefixed with
+the name of the plugin. So when the change occurs after a move, the
+reason is **move** and then the clients receive the event **tictactoe/move**.
+
+> Note that nothing is said about the case sensitivity of event names.
+> However, the event is always prefixed with the name that the plugin
+> declared, with the same case, followed with a slash /.
+> Thus it is safe to compare event using a case sensitive comparison.
+
+
+
+Writing an asynchronous verb implementation
+-------------------------------------------
+
+The *tic-tac-toe* example allows two clients or more to share the same board.
+This is implemented by the verb **join** that illustrated partly the how to
+retrieve arguments.
+
+When two or more clients are sharing a same board, one of them can wait
+until the state of the board changes. (This coulded also be implemented using
+events because an even is generated each time the board changes).
+
+In this case, the reply to the wait is sent only when the board changes.
+See the diagram below:
+
+	CLIENT A       CLIENT B         TIC-TAC-TOE
+	   |              |                  |
+	   +--------------|----------------->| wait . . . . . . . .
+	   |              |                  |                     .
+	   :              :                  :                      .
+	   :              :                  :                      .
+	   |              |                  |                      .
+	   |              +----------------->| move . . .           .
+	   |              |                  |          V           .
+	   |              |<-----------------+ success of move      .
+	   |              |                  |                    .
+	   |<-------------|------------------+ success of wait  <
+
+Here, this is an invocation of the plugin by an other client that
+unblock the suspended *wait* call.
+But in general, this will be a timer, a hardware event, the sync with
+a concurrent process or thread, ...
+
+So the case is common, this is an asynchronous implementation.
+
+Here is the listing of the function **wait**:
+
+	static void wait(struct afb_req req)
+	{
+		struct board *board;
+		struct waiter *waiter;
+
+		/* retrieves the context for the session */
+		board = board_of_req(req);
+		INFO(afbitf, "method 'wait' called for boardid %d", board->id);
+
+		/* creates the waiter and enqueues it */
+		waiter = calloc(1, sizeof *waiter);
+		waiter->req = req;
+		waiter->next = board->waiters;
+		afb_req_addref(req);
+		board->waiters = waiter;
+	}
+
+After retrieving the board, the function adds a new waiter to the
+current list of waiters and returns without sending a reply.
+
+Before returning, it increases the reference count of the
+request **req** using the function **afb_req_addref**.
+
+> When the implentation of a verb returns without sending a reply,
+> it **MUST** increment the reference count of the request
+> using **afb_req_addref**. If it doesn't bad things can happen.
+
+Later, when the board changes, it calls the function **changed**
+of *tic-tac-toe* with the reason of the change.
+
+Here is the full listing of the function **changed**:
+
+	/*
+	 * signals a change of the board
+	 */
+	static void changed(struct board *board, const char *reason)
+	{
+		struct waiter *waiter, *next;
+		struct json_object *description;
+
+		/* get the description */
+		description = describe(board);
+
+		waiter = board->waiters;
+		board->waiters = NULL;
+		while (waiter != NULL) {
+			next = waiter->next;
+			afb_req_success(waiter->req, json_object_get(description), reason);
+			afb_req_unref(waiter->req);
+			free(waiter);
+			waiter = next;
+		}
+
+		afb_event_sender_push(afb_daemon_get_event_sender(afbitf->daemon), reason, description);
+	}
+
+The list of waiters is walked and a reply is sent to each waiter.
+After the sending the reply, the reference count of the request
+is decremented using **afb_req_unref** to allow its resources to be freed.
+
+> The reference count **MUST** be decremented using **afb_req_unref** because,
+> otherwise, there is a leak of resources.
+> It must be decremented **AFTER** the sending of the reply, because, otherwise,
+> bad things may happen.
+
+How to build a plugin
+---------------------
+
+Afb-daemon provides a *pkg-config* configuration file that can be
+queried by the name **afb-daemon**.
+This configuration file provides data that should be used
+for compiling plugins. Examples:
+
+	$ pkg-config --cflags afb-daemon
+	$ pkg-config --libs afb-daemon
+
+### Example for cmake meta build system
+
+This example is the extract for building the plugin *afm-main* using *CMAKE*.
+
+	pkg_check_modules(afb afb-daemon)
+	if(afb_FOUND)
+		message(STATUS "Creation afm-main-plugin for AFB-DAEMON")
+		add_library(afm-main-plugin MODULE afm-main-plugin.c)
+		target_compile_options(afm-main-plugin PRIVATE ${afb_CFLAGS})
+		target_include_directories(afm-main-plugin PRIVATE ${afb_INCLUDE_DIRS})
+		target_link_libraries(afm-main-plugin utils ${afb_LIBRARIES})
+		set_target_properties(afm-main-plugin PROPERTIES
+			PREFIX ""
+			LINK_FLAGS "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/afm-main-plugin.export-map"
+		)
+		install(TARGETS afm-main-plugin LIBRARY DESTINATION ${plugin_dir})
+	else()
+		message(STATUS "Not creating the plugin for AFB-DAEMON")
+	endif()
+
+Let now describe some of these lines.
+
+	pkg_check_modules(afb afb-daemon)
+
+This first lines searches to the *pkg-config* configuration file for
+**afb-daemon**. Resulting data are stored in the following variables:
+
+Variable          | Meaning
+------------------|------------------------------------------------
+afb_FOUND         | Set to 1 if afb-daemon plugin development files exist
+afb_LIBRARIES     | Only the libraries (w/o the '-l') for compiling afb-daemon plugins
+afb_LIBRARY_DIRS  | The paths of the libraries (w/o the '-L') for compiling afb-daemon plugins
+afb_LDFLAGS       | All required linker flags for compiling afb-daemon plugins
+afb_INCLUDE_DIRS  | The '-I' preprocessor flags (w/o the '-I') for compiling afb-daemon plugins
+afb_CFLAGS        | All required cflags for compiling afb-daemon plugins
+
+If development files are found, the plugin can be added to the set of
+target to build.
+
+	add_library(afm-main-plugin MODULE afm-main-plugin.c)
+
+This line asks to create a shared library having only the
+source file afm-main-plugin.c (that is compiled).
+The default name of the created shared object is
+**libafm-main-plugin.so**.
+
+	set_target_properties(afm-main-plugin PROPERTIES
+		PREFIX ""
+		LINK_FLAGS "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/afm-main-plugin.export-map"
+	)
+
+This lines are doing two things:
+
+1. It renames the built library from **libafm-main-plugin.so** to **afm-main-plugin.so**
+by removing the implicitely added prefix *lib*. This step is not mandatory
+at all because afb-daemon doesn't check names of files when loading it.
+The only convention that use afb-daemon is that extension is **.so**
+but this convention is used only when afb-daemon discovers plugin
+from a directory hierarchy.
+
+2. It applies a version script at link to only export the conventional name
+of the entry point: **pluginAfbV1Register**. See below. By default, the linker
+that creates the shared object exports all the public symbols (C functions that
+are not **static**).
+
+Next line are:
+
+	target_include_directories(afm-main-plugin PRIVATE ${afb_INCLUDE_DIRS})
+	target_link_libraries(afm-main-plugin utils ${afb_LIBRARIES})
+
+As you can see it uses the variables computed by ***pkg_check_modules(afb afb-daemon)***
+to configure the compiler and the linker.
+
+### Exporting the function pluginAfbV1Register
+
+The function **pluginAfbV1Register** must be exported. This can be achieved
+using a version script when linking. Here is the version script that is
+used for *tic-tac-toe* (plugins/samples/export.map).
+
+	{ global: pluginAfbV1Register; local: *; };
+
+This sample [version script](https://sourceware.org/binutils/docs-2.26/ld/VERSION.html#VERSION)
+exports as global the symbol *pluginAfbV1Register* and hides any
+other symbols.
+
+This version script is added to the link options using the
+option **--version-script=export.map** is given directly to the
+linker or using th option **-Wl,--version-script=export.map**
+when the option is given to the C compiler.
+
+### Building within yocto
+
+Adding a dependency to afb-daemon is enough. See below:
+
+	DEPENDS += " afb-daemon "
+
diff --git a/doc/doc.css b/doc/doc.css
index c11082fd..27be9dc7 100644
--- a/doc/doc.css
+++ b/doc/doc.css
@@ -4,12 +4,36 @@ body {
 	color: #000;
 }
 
-h1, h2, h3 { color: #306; }
+h1, h2, h3, h4 {
+	color: #306;
+	text-decoration: underline;
+}
 
 pre {
 	border: medium dashed #306;
-	background: #ccc;
-	margin-left: 4em;
+	border-width: 0.1em;
+	background-color: #eee;
+	margin-left: 2em;
+	margin-right: 2em;
 	padding: 1em;
+	outline: #555;
 }
 
+pre:first-of-type { width: 20em; }
+
+blockquote {
+	border-left: solid thick black;
+	background-color: #ff8;
+	font: bolder;
+	padding: 0.7em 1.5em;
+}
+
+table  {
+	margin-left: 2em;
+	background-color: #dff;
+	outline: 0.25em solid #a6f;
+/*	padding: 0.25em;*/
+}
+thead {background-color: #a6f;}
+tr:nth-child(even) {background-color: #aee;}
+td { padding: 0.1em 0.5em; }
diff --git a/doc/updt.sh b/doc/updt.sh
index cd978e22..af64e31e 100755
--- a/doc/updt.sh
+++ b/doc/updt.sh
@@ -1,9 +1,6 @@
-#!/bin/sh
-
-subst() {
-  awk -v pat="$1" -v rep="$(sed 's:\\:\\\\:g' $2)" '{gsub(pat,rep);gsub(pat,"\\&");print}'
-}
+#!/bin/bash
 
+# the HTML template
 main='<html>
 <head>
   <link rel="stylesheet" type="text/css" href="doc.css">
@@ -14,18 +11,37 @@ GENERATED-MARKDOWN-HERE
 </body>
 </html>'
 
-for x in *.md; do
-  t=$(git log -n 1 --format=%ct $x)
+# substitute the pattern $1 by the content of the file $2
+subst() {
+  awk -v pat="$1" -v rep="$(sed 's:\\:\\\\:g' $2)" '{gsub(pat,rep);gsub(pat,"\\&");print}'
+}
+
+# update the date field of file $1
+updadate() {
+  local x=$1
+  local t=$(git log -n 1 --format=%ct $x)
   [[ -n "$t" ]] || t=$(stat -c %Y $x)
-  d=$(LANG= date -d @$t +"%d %B %Y")
+  local d=$(LANG= date -d @$t +"%d %B %Y")
   sed -i "s/^\(    Date: *\).*/\1$d/" $x
-  h=${x%%.md}.html
-  markdown -f toc,autolink $x > $h.toc.no
-  markdown -Tf toc,autolink $x > $h.toc.yes
+}
+
+# make the html file for $1
+mkhtml() {
+  local x=$1
+  local h=${x%%.md}.html
+  expand -i $x | sed 's:        :    :' > $h.pre
+  markdown -f toc,autolink $h.pre > $h.toc.no
+  markdown -Tf toc,autolink $h.pre > $h.toc.yes
   head --bytes=-$(stat -c %s $h.toc.no) $h.toc.yes > $h.toc
   echo "$main" |
   subst GENERATED-MARKDOWN-HERE $h.toc.no |
   subst TABLE-OF-CONTENT-HERE $h.toc > $h
-#  rm $h.toc*
+  rm $h.*
+}
+
+# apply
+for x in *.md; do
+  updadate $x
+  mkhtml $x
 done
 
diff --git a/doc/writing-afb-plugins.html b/doc/writing-afb-plugins.html
deleted file mode 100644
index 5aeca0a5..00000000
--- a/doc/writing-afb-plugins.html
+++ /dev/null
@@ -1,482 +0,0 @@
-<html>
-<head>
-  <link rel="stylesheet" type="text/css" href="doc.css">
-  <meta charset="UTF-8">
-</head>
-<body>
-<a name="HOWTO.WRITE.a.PLUGIN.for.AFB-DAEMON"></a>
-<h1>HOWTO WRITE a PLUGIN for AFB-DAEMON</h1>
-
-<pre><code>version: 1
-Date:    24 mai 2016
-Author:  José Bollo
-</code></pre>
-
-<p><ul>
- <li><a href="#HOWTO.WRITE.a.PLUGIN.for.AFB-DAEMON">HOWTO WRITE a PLUGIN for AFB-DAEMON</a>
- <ul>
-  <li><a href="#Summary">Summary</a>
-  <ul>
-   <li><a href="#Nature.of.a.plugin">Nature of a plugin</a></li>
-   <li><a href="#Live.cycle.of.a.plugin.within.afb-daemon">Live cycle of a plugin within afb-daemon</a></li>
-   <li><a href="#Content.of.a.plugin">Content of a plugin</a>
-   <ul>
-    <li><a href="#The.name.of.the.plugin">The name of the plugin</a></li>
-    <li><a href="#Names.of.verbs">Names of verbs</a></li>
-    <li><a href="#The.initialisation.function">The initialisation function</a></li>
-    <li><a href="#Functions.implementing.verbs">Functions implementing verbs</a>
-</li>
-   </ul>
-   </li>
-  </ul>
-  </li>
-  <li><a href="#The.Tic-Tac-Toe.example">The Tic-Tac-Toe example</a></li>
-  <li><a href="#Choosing.names">Choosing names</a>
-  <ul>
-   <li><a href="#Names.for.API..plugin.">Names for API (plugin)</a></li>
-   <li><a href="#Names.for.verbs">Names for verbs</a></li>
-   <li><a href="#Names.for.arguments">Names for arguments</a></li>
-   <li><a href="#Forging.names.widely.available">Forging names widely available</a></li>
-  </ul>
-  </li>
-  <li><a href="#Options.to.set.when.compiling.plugins">Options to set when compiling plugins</a></li>
-  <li><a href="#Header.files.to.include">Header files to include</a></li>
-  <li><a href="#Writing.a.synchronous.verb.implementation">Writing a synchronous verb implementation</a>
-  <ul>
-   <li><a href="#The.incoming.request">The incoming request</a></li>
-   <li><a href="#Associating.an.object.to.the.session.for.the.plugin">Associating an object to the session for the plugin</a></li>
-   <li><a href="#Sending.the.reply.to.a.request">Sending the reply to a request</a></li>
-  </ul>
-  </li>
-  <li><a href="#Getting.argument.of.invocation">Getting argument of invocation</a></li>
-  <li><a href="#How.to.build.a.plugin">How to build a plugin</a></li>
- </ul>
- </li>
-</ul></p>
-
-<a name="Summary"></a>
-<h2>Summary</h2>
-
-<p>The binder afb-daemon serves files through
-the HTTP protocol and offers access to API&rsquo;s through
-HTTP or WebSocket protocol.</p>
-
-<p>The plugins are used to add API&rsquo;s to afb-daemon.
-This part describes how to write a plugin for afb-daemon.
-Excepting this summary, this part is intended to be read
-by developpers.</p>
-
-<p>Before going into details, through a tiny example,
-a short overview plugins basis is needed.</p>
-
-<a name="Nature.of.a.plugin"></a>
-<h3>Nature of a plugin</h3>
-
-<p>A plugin is a separate piece of code made of a shared library.
-The plugin is loaded and activated by afb-daemon when afb-daemon
-starts.</p>
-
-<p>Technically, a plugin is not linked to any library of afb-daemon.</p>
-
-<a name="Live.cycle.of.a.plugin.within.afb-daemon"></a>
-<h3>Live cycle of a plugin within afb-daemon</h3>
-
-<p>The plugins are loaded and activated when afb-daemon starts.</p>
-
-<p>At start, the plugin initialise itself.
-If it fails to initialise then afb-daemon stops.</p>
-
-<p>Conversely, if it success to initialize, it must declare
-a name, that must be unique, and a list of API&rsquo;s verbs.</p>
-
-<p>When initialized, the functions implementing the API&rsquo;s verbs
-of the plugin are activated on call.</p>
-
-<p>At the end, nothing special is done by afb-daemon.
-Consequently, developpers of plugins should use &lsquo;atexit&rsquo;
-or &lsquo;on_exit&rsquo; during initialisation if they need to
-perform specific actions when stopping.</p>
-
-<a name="Content.of.a.plugin"></a>
-<h3>Content of a plugin</h3>
-
-<p>For afb-daemon, a plugin contains 2 different
-things: names and functions.</p>
-
-<p>There is two kind of names:
- - the name of the plugin,
- - the names of the verbs.</p>
-
-<p>There is two kind of functions:
- - the initialisation function
- - functions implementing verbs</p>
-
-<p>Afb-daemon translates the name of the method that is
-invoked to a pair of API and verb names. For example,
-the method named <strong>foo/bar</strong> translated to the API
-name <strong>foo</strong> and the verb name <strong>bar</strong>.
-To serve it, afb-daemon search the plugin that record
-the name <strong>foo</strong> and if it also recorded the verb <strong>bar</strong>,
-it calls the implementation function declared for this verb.</p>
-
-<p>Afb-daemon make no distinction between lower case
-and upper case when searching for a method.
-Thus, The names <strong>TicTacToe/Board</strong> and <strong>tictactoe/borad</strong>
-are equals.</p>
-
-<a name="The.name.of.the.plugin"></a>
-<h4>The name of the plugin</h4>
-
-<p>The name of the plugin is also known as the name
-of the API that defines the plugin.</p>
-
-<p>This name is also known as the prefix.</p>
-
-<p>The name of a plugin MUST be unique within afb-daemon.</p>
-
-<p>For example, when a client of afb-daemon
-calls a method named <strong>foo/bar</strong>. Afb-daemon
-extracts the prefix <strong>foo</strong> and the suffix <strong>bar</strong>.
-<strong>foo</strong> is the API name and must match a plugin name,
-the plugin that implements the verb <strong>bar</strong>.</p>
-
-<a name="Names.of.verbs"></a>
-<h4>Names of verbs</h4>
-
-<p>Each plugin exposes a set of verbs that can be called
-by client of afb-daemon.</p>
-
-<p>The name of a verb MUST be unique within a plugin.</p>
-
-<p>Plugins link verbs to functions that are called
-when clients emit requests for that verb.</p>
-
-<p>For example, when a client of afb-daemon
-calls a method named <strong>foo/bar</strong>.</p>
-
-<a name="The.initialisation.function"></a>
-<h4>The initialisation function</h4>
-
-<p>The initialisation function serves several purposes.</p>
-
-<ol>
-<li><p>It allows afb-daemon to check the version
-of the plugin using the name of the initialisation
-functions that it found. Currently, the initialisation
-function is named <strong>pluginAfbV1Register</strong>. It identifies
-the first version of plugins.</p></li>
-<li><p>It allows the plugin to initialise itself.</p></li>
-<li><p>It serves to the plugin to declare names, descriptions,
-requirements and implmentations of the verbs that it exposes.</p></li>
-</ol>
-
-
-<a name="Functions.implementing.verbs"></a>
-<h4>Functions implementing verbs</h4>
-
-<p>When a method is called, afb-daemon constructs a request
-object and pass it to the implementation function for verb
-within the plugin of the API.</p>
-
-<p>An implementation function receives a request object that
-is used to get arguments of the request, to send
-answer, to store session data.</p>
-
-<p>A plugin MUST send an answer to the request.</p>
-
-<p>But it is not mandatory to send the answer
-before to return from the implementing function.
-This behaviour is important for implementing
-asynchronous actions.</p>
-
-<p>Implementation functions that always reply to the request
-before returning are named <em>synchronous implementations</em>.
-Those that don&rsquo;t always reply to the request before
-returning are named <em>asynchronous implementations</em>.</p>
-
-<p>Asynchronous implementations typically initiate an
-asynchronous action and record to send the reply
-on completion of this action.</p>
-
-<a name="The.Tic-Tac-Toe.example"></a>
-<h2>The Tic-Tac-Toe example</h2>
-
-<p>This part explains how to write an afb-plugin.
-For the sake of being practical we will use many
-examples from the tic-tac-toe example.
-This plugin example is in <em>plugins/samples/tic-tac-toe.c</em>.</p>
-
-<p>This plugin is named <strong><em>tictactoe</em></strong>.</p>
-
-<a name="Choosing.names"></a>
-<h2>Choosing names</h2>
-
-<p>The designer of a plugin must defines names for its plugin
-(or its API) and for the verbs of its API. He also
-must defines names for arguments given by name.</p>
-
-<p>While forging names, the designer should take into account
-the rules for making valid names and some rules that make
-the names easy to use across plaforms.</p>
-
-<p>The names and strings used ALL are UTF-8 encoded.</p>
-
-<a name="Names.for.API..plugin."></a>
-<h3>Names for API (plugin)</h3>
-
-<p>The names of the API are checked.
-All characters are authorised except:</p>
-
-<ul>
-<li>the control characters (\u0000 .. \u001f)</li>
-<li>the characters of the set { &lsquo; &rsquo;, &lsquo;&ldquo;&rsquo;, &lsquo;#&rsquo;, &lsquo;%&rsquo;, &lsquo;&amp;&rsquo;,
-&lsquo;&rsquo;&lsquo;, &rsquo;/&lsquo;, &rsquo;?&lsquo;, &rsquo;`&lsquo;, &rsquo;\x7f' }</li>
-</ul>
-
-
-<p>In other words the set of forbidden characters is
-{ \u0000..\u0020, \u0022, \u0023, \u0025..\u0027,
-  \u002f, \u003f, \u0060, \u007f }.</p>
-
-<p>Afb-daemon make no distinction between lower case
-and upper case when searching for an API by its name.</p>
-
-<a name="Names.for.verbs"></a>
-<h3>Names for verbs</h3>
-
-<p>The names of the verbs are not checked.</p>
-
-<p>However, the validity rules for verb&rsquo;s names are the
-same as for API&rsquo;s names except that the dot (.) character
-is forbidden.</p>
-
-<p>Afb-daemon make no distinction between lower case
-and upper case when searching for an API by its name.</p>
-
-<a name="Names.for.arguments"></a>
-<h3>Names for arguments</h3>
-
-<p>The names for arguments are not restricted and can be
-anything.</p>
-
-<p>The arguments are searched with the case sensitive
-string comparison. Thus the names &ldquo;index&rdquo; and &ldquo;Index&rdquo;
-are not the same.</p>
-
-<a name="Forging.names.widely.available"></a>
-<h3>Forging names widely available</h3>
-
-<p>The key names of javascript object can be almost
-anything using the arrayed notation:</p>
-
-<pre><code>object[key] = value
-</code></pre>
-
-<p>That is not the case with the dot notation:</p>
-
-<pre><code>object.key = value
-</code></pre>
-
-<p>Using the dot notation, the key must be a valid javascript
-identifier.</p>
-
-<p>For this reason, the chosen names should better be
-valid javascript identifier.</p>
-
-<p>It is also a good practice, even for arguments, to not
-rely on the case sensitivity and to avoid the use of
-names different only by the case.</p>
-
-<a name="Options.to.set.when.compiling.plugins"></a>
-<h2>Options to set when compiling plugins</h2>
-
-<p>Afb-daemon provides a configuration file for <em>pkg-config</em>.
-Typing the command</p>
-
-<pre><code>pkg-config --cflags afb-daemon
-</code></pre>
-
-<p>will print the flags to use for compiling, like this:</p>
-
-<pre><code>$ pkg-config --cflags afb-daemon
--I/opt/local/include -I/usr/include/json-c 
-</code></pre>
-
-<p>For linking, you should use</p>
-
-<pre><code>$ pkg-config --libs afb-daemon
--ljson-c
-</code></pre>
-
-<p>As you see, afb-daemon automatically includes dependency to json-c.
-This is done through the <strong>Requires</strong> keyword of pkg-config.</p>
-
-<p>If this behaviour is a problem, let us know.</p>
-
-<a name="Header.files.to.include"></a>
-<h2>Header files to include</h2>
-
-<p>The plugin <em>tictactoe</em> has the following lines for its includes:</p>
-
-<pre><code>#define _GNU_SOURCE
-#include &lt;stdio.h&gt;
-#include &lt;string.h&gt;
-#include &lt;json-c/json.h&gt;
-#include &lt;afb/afb-plugin.h&gt;
-</code></pre>
-
-<p>The header <em>afb/afb-plugin.h</em> includes all the features that a plugin
-needs except two foreign header that must be included by the plugin
-if it needs it:</p>
-
-<ul>
-<li><em>json-c/json.h</em>: this header must be include to handle json objects;</li>
-<li><em>systemd/sd-event.h</em>: this must be include to access the main loop;</li>
-<li><em>systemd/sd-bus.h</em>: this may be include to use dbus connections.</li>
-</ul>
-
-
-<p>The <em>tictactoe</em> plugin does not use systemd features so it is not included.</p>
-
-<p>When including <em>afb/afb-plugin.h</em>, the macro <strong>_GNU_SOURCE</strong> must be
-defined.</p>
-
-<a name="Writing.a.synchronous.verb.implementation"></a>
-<h2>Writing a synchronous verb implementation</h2>
-
-<p>The verb <strong>tictactoe/board</strong> is a synchronous implementation.
-Here is its listing:</p>
-
-<pre><code>/*
- * get the board
- */
-static void board(struct afb_req req)
-{
-    struct board *board;
-    struct json_object *description;
-
-    /* retrieves the context for the session */
-    board = board_of_req(req);
-    INFO(afbitf, "method 'board' called for boardid %d", board-&gt;id);
-
-    /* describe the board */
-    description = describe(board);
-
-    /* send the board's description */
-    afb_req_success(req, description, NULL);
-}
-</code></pre>
-
-<p>This examples show many aspects of writing a synchronous
-verb implementation.</p>
-
-<a name="The.incoming.request"></a>
-<h3>The incoming request</h3>
-
-<p>For any implementation,  the request is received by a structure of type
-<strong>struct afb_req</strong>.</p>
-
-<p><strong><em>Important: note that this is a PLAIN structure, not a pointer to a structure.</em></strong></p>
-
-<p>This structure, here named <em>req</em>, is used</p>
-
-<p><em>req</em> is used to get arguments of the request, to send
-answer, to store session data.</p>
-
-<p>This object and its interface is defined and documented
-in the file names <em>afb/afb-req-itf.h</em></p>
-
-<p>The above example uses 2 times the request object <em>req</em>.</p>
-
-<p>The first time, it is used for retrieving the board attached to
-the session of the request.</p>
-
-<p>The second time, it is used to send the reply: an object that
-describes the current board.</p>
-
-<a name="Associating.an.object.to.the.session.for.the.plugin"></a>
-<h3>Associating an object to the session for the plugin</h3>
-
-<p>When the plugin <em>tic-tac-toe</em> receives a request, it musts regain
-the board that describes the game associated to the session.</p>
-
-<p>For a plugin, having data associated to a session is a common case.
-This data is called the context of the plugin for the session.
-For the plugin <em>tic-tac-toe</em>, the context is the board.</p>
-
-<p>The requests <em>afb_req</em> offer four functions for
-storing and retrieving the context associated to the session.</p>
-
-<p>These functions are:</p>
-
-<ul>
-<li><p><strong>afb_req_context_get</strong>:
-retrieves the context data stored for the plugin.</p></li>
-<li><p><strong>afb_req_context_set</strong>:
-store the context data of the plugin.</p></li>
-<li><p><strong>afb_req_context</strong>:
-retrieves the context data of the plugin,
-if needed, creates the context and store it.</p></li>
-<li><p><strong>afb_req_context_clear</strong>:
-reset the stored data.</p></li>
-</ul>
-
-
-<p>The plugin <em>tictactoe</em> use a convenient function to retrieve
-its context: the board. This function is <em>board_of_req</em>:</p>
-
-<pre><code>/*
- * retrieves the board of the request
- */
-static inline struct board *board_of_req(struct afb_req req)
-{
-    return afb_req_context(req, (void*)get_new_board, (void*)release_board);
-}
-</code></pre>
-
-<p>This function is very simple because it merely wraps
-a call to the function <strong>afb_req_context</strong>, providing
-all needed arguments.
-The casts are required to avoid a warning when compiling.</p>
-
-<p>Here is the definition of the function <strong>afb_req_context</strong></p>
-
-<pre><code>/*
- * Gets the pointer stored by the plugin for the session of 'req'.
- * If the stored pointer is NULL, indicating that no pointer was
- * already stored, afb_req_context creates a new context by calling
- * the function 'create_context' and stores it with the freeing function
- * 'free_context'.
- */
-static inline void *afb_req_context(struct afb_req req, void *(*create_context)(), void (*free_context)(void*))
-{
-    void *result = afb_req_context_get(req);
-    if (result == NULL) {
-        result = create_context();
-        afb_req_context_set(req, result, free_context);
-    }
-    return result;
-}
-</code></pre>
-
-<p>This powerful function ensures that the context exists and is
-stored for the session.</p>
-
-<p>The function <strong>get_new_board</strong> creates a new board and set its
-count of use to 1. The boards are counting their count of use
-to free there ressources when no more used.</p>
-
-<p>The function <strong>release_board</strong></p>
-
-<a name="Sending.the.reply.to.a.request"></a>
-<h3>Sending the reply to a request</h3>
-
-<a name="Getting.argument.of.invocation"></a>
-<h2>Getting argument of invocation</h2>
-
-<a name="How.to.build.a.plugin"></a>
-<h2>How to build a plugin</h2>
-
-<p>Afb-daemon provides a The packaging of afb-daemon</p>
-</body>
-</html>
diff --git a/doc/writing-afb-plugins.md b/doc/writing-afb-plugins.md
deleted file mode 100644
index ba2e676a..00000000
--- a/doc/writing-afb-plugins.md
+++ /dev/null
@@ -1,489 +0,0 @@
-HOWTO WRITE a PLUGIN for AFB-DAEMON
-===================================
-    version: 1
-    Date:    25 May 2016
-    Author:  José Bollo
-
-TABLE-OF-CONTENT-HERE
-
-Summary
--------
-
-The binder afb-daemon serves files through
-the HTTP protocol and offers access to API's through
-HTTP or WebSocket protocol.
-
-The plugins are used to add API's to afb-daemon.
-This part describes how to write a plugin for afb-daemon.
-Excepting this summary, this part is intended to be read
-by developpers.
-
-Before going into details, through a tiny example,
-a short overview plugins basis is needed.
-
-### Nature of a plugin
-
-A plugin is a separate piece of code made of a shared library.
-The plugin is loaded and activated by afb-daemon when afb-daemon
-starts.
-
-Technically, a plugin is not linked to any library of afb-daemon.
- 
-### Live cycle of a plugin within afb-daemon
-
-The plugins are loaded and activated when afb-daemon starts.
-
-At start, the plugin initialise itself.
-If it fails to initialise then afb-daemon stops.
-
-Conversely, if it success to initialize, it must declare
-a name, that must be unique, and a list of API's verbs.
-
-When initialized, the functions implementing the API's verbs
-of the plugin are activated on call.
-
-At the end, nothing special is done by afb-daemon.
-Consequently, developpers of plugins should use 'atexit'
-or 'on_exit' during initialisation if they need to
-perform specific actions when stopping.
-
-### Content of a plugin
-
-For afb-daemon, a plugin contains 2 different
-things: names and functions.
-
-There is two kind of names:
- - the name of the plugin,
- - the names of the verbs.
-
-There is two kind of functions:
- - the initialisation function
- - functions implementing verbs
-
-Afb-daemon translates the name of the method that is
-invoked to a pair of API and verb names. For example,
-the method named **foo/bar** translated to the API
-name **foo** and the verb name **bar**.
-To serve it, afb-daemon search the plugin that record
-the name **foo** and if it also recorded the verb **bar**,
-it calls the implementation function declared for this verb.
-
-Afb-daemon make no distinction between lower case
-and upper case when searching for a method.
-Thus, The names **TicTacToe/Board** and **tictactoe/borad**
-are equals.
-
-#### The name of the plugin
-
-The name of the plugin is also known as the name
-of the API that defines the plugin.
-
-This name is also known as the prefix.
-
-The name of a plugin MUST be unique within afb-daemon.
-
-For example, when a client of afb-daemon
-calls a method named **foo/bar**. Afb-daemon
-extracts the prefix **foo** and the suffix **bar**.
-**foo** is the API name and must match a plugin name,
-the plugin that implements the verb **bar**.
-
-#### Names of verbs
-
-Each plugin exposes a set of verbs that can be called
-by client of afb-daemon.
-
-The name of a verb MUST be unique within a plugin.
-
-Plugins link verbs to functions that are called
-when clients emit requests for that verb.
-
-For example, when a client of afb-daemon
-calls a method named **foo/bar**.
-
-#### The initialisation function
-
-The initialisation function serves several purposes.
-
-1. It allows afb-daemon to check the version
-of the plugin using the name of the initialisation
-functions that it found. Currently, the initialisation
-function is named **pluginAfbV1Register**. It identifies
-the first version of plugins.
-
-2. It allows the plugin to initialise itself.
-
-3. It serves to the plugin to declare names, descriptions,
-requirements and implmentations of the verbs that it exposes.
-
-#### Functions implementing verbs
-
-When a method is called, afb-daemon constructs a request
-object and pass it to the implementation function for verb
-within the plugin of the API.
-
-An implementation function receives a request object that
-is used to get arguments of the request, to send
-answer, to store session data.
-
-A plugin MUST send an answer to the request.
-
-But it is not mandatory to send the answer
-before to return from the implementing function.
-This behaviour is important for implementing
-asynchronous actions.
-
-Implementation functions that always reply to the request
-before returning are named *synchronous implementations*.
-Those that don't always reply to the request before
-returning are named *asynchronous implementations*.
-
-Asynchronous implementations typically initiate an
-asynchronous action and record to send the reply
-on completion of this action.
-
-The Tic-Tac-Toe example
------------------------
-
-This part explains how to write an afb-plugin.
-For the sake of being practical we will use many
-examples from the tic-tac-toe example.
-This plugin example is in *plugins/samples/tic-tac-toe.c*.
-
-This plugin is named ***tictactoe***.
-
-Choosing names
---------------
-
-The designer of a plugin must defines names for its plugin
-(or its API) and for the verbs of its API. He also
-must defines names for arguments given by name.
-
-While forging names, the designer should take into account
-the rules for making valid names and some rules that make
-the names easy to use across plaforms.
-
-The names and strings used ALL are UTF-8 encoded.
-
-### Names for API (plugin)
-
-The names of the API are checked.
-All characters are authorised except:
-
-- the control characters (\u0000 .. \u001f)
-- the characters of the set { ' ', '"', '#', '%', '&',
-  '\'', '/', '?', '`', '\x7f' }
-
-In other words the set of forbidden characters is
-{ \u0000..\u0020, \u0022, \u0023, \u0025..\u0027,
-  \u002f, \u003f, \u0060, \u007f }.
-
-Afb-daemon make no distinction between lower case
-and upper case when searching for an API by its name.
-
-### Names for verbs
-
-The names of the verbs are not checked.
-
-However, the validity rules for verb's names are the
-same as for API's names except that the dot (.) character
-is forbidden.
-
-Afb-daemon make no distinction between lower case
-and upper case when searching for an API by its name.
-
-### Names for arguments
-
-The names for arguments are not restricted and can be
-anything.
-
-The arguments are searched with the case sensitive
-string comparison. Thus the names "index" and "Index"
-are not the same.
-
-### Forging names widely available
-
-The key names of javascript object can be almost
-anything using the arrayed notation:
-
-	object[key] = value
-
-That is not the case with the dot notation:
-
-	object.key = value
-
-Using the dot notation, the key must be a valid javascript
-identifier.
-
-For this reason, the chosen names should better be
-valid javascript identifier.
-
-It is also a good practice, even for arguments, to not
-rely on the case sensitivity and to avoid the use of
-names different only by the case.
-
-Options to set when compiling plugins
--------------------------------------
-
-Afb-daemon provides a configuration file for *pkg-config*.
-Typing the command
-
-	pkg-config --cflags afb-daemon
-
-will print the flags to use for compiling, like this:
-
-	$ pkg-config --cflags afb-daemon
-	-I/opt/local/include -I/usr/include/json-c 
-
-For linking, you should use
-
-	$ pkg-config --libs afb-daemon
-	-ljson-c
-
-As you see, afb-daemon automatically includes dependency to json-c.
-This is done through the **Requires** keyword of pkg-config.
-
-If this behaviour is a problem, let us know.
-
-Header files to include
------------------------
-
-The plugin *tictactoe* has the following lines for its includes:
-
-	#define _GNU_SOURCE
-	#include <stdio.h>
-	#include <string.h>
-	#include <json-c/json.h>
-	#include <afb/afb-plugin.h>
-
-The header *afb/afb-plugin.h* includes all the features that a plugin
-needs except two foreign header that must be included by the plugin
-if it needs it:
-
-- *json-c/json.h*: this header must be include to handle json objects;
-- *systemd/sd-event.h*: this must be include to access the main loop;
-- *systemd/sd-bus.h*: this may be include to use dbus connections.
-
-The *tictactoe* plugin does not use systemd features so it is not included.
-
-When including *afb/afb-plugin.h*, the macro **_GNU_SOURCE** must be
-defined.
-
-Writing a synchronous verb implementation
------------------------------------------
-
-The verb **tictactoe/board** is a synchronous implementation.
-Here is its listing:
-
-	/*
-	 * get the board
-	 */
-	static void board(struct afb_req req)
-	{
-		struct board *board;
-		struct json_object *description;
-
-		/* retrieves the context for the session */
-		board = board_of_req(req);
-		INFO(afbitf, "method 'board' called for boardid %d", board->id);
-
-		/* describe the board */
-		description = describe(board);
-
-		/* send the board's description */
-		afb_req_success(req, description, NULL);
-	}
-
-This examples show many aspects of writing a synchronous
-verb implementation. Let summarize it:
-
-1. The function **board_of_req** retrieves the context stored
-for the plugin: the board.
-
-2. The macro **INFO** sends a message of kind *INFO*
-to the logging system. The global variable named **afbitf**
-used represents the interface to afb-daemon.
-
-3. The function **describe** creates a json_object representing
-the board.
-
-4. The function **afb_req_success** sends the reply, attaching to
-it the object *description*.
-
-### The incoming request
-
-For any implementation,  the request is received by a structure of type
-**struct afb_req**.
-
-***Important: note that this is a PLAIN structure, not a pointer to a structure.***
-
-This structure, here named *req*, is used
-
-*req* is used to get arguments of the request, to send
-answer, to store session data.
-
-This object and its interface is defined and documented
-in the file names *afb/afb-req-itf.h*
-
-The above example uses 2 times the request object *req*.
-
-The first time, it is used for retrieving the board attached to
-the session of the request.
-
-The second time, it is used to send the reply: an object that
-describes the current board.
-
-### Associating an object to the session for the plugin
-
-When the plugin *tic-tac-toe* receives a request, it musts regain
-the board that describes the game associated to the session.
-
-For a plugin, having data associated to a session is a common case.
-This data is called the context of the plugin for the session.
-For the plugin *tic-tac-toe*, the context is the board.
-
-The requests *afb_req* offer four functions for
-storing and retrieving the context associated to the session.
-
-These functions are:
-
-- **afb_req_context_get**:
-  retrieves the context data stored for the plugin.
-
-- **afb_req_context_set**:
-  store the context data of the plugin.
-
-- **afb_req_context**:
-  retrieves the context data of the plugin,
-  if needed, creates the context and store it.
-
-- **afb_req_context_clear**:
-  reset the stored data.
-
-The plugin *tictactoe* use a convenient function to retrieve
-its context: the board. This function is *board_of_req*:
-
-	/*
-	 * retrieves the board of the request
-	 */
-	static inline struct board *board_of_req(struct afb_req req)
-	{
-		return afb_req_context(req, (void*)get_new_board, (void*)release_board);
-	}
-
-The function **afb_req_context** ensure an existing context
-for the session of the request.
-Its two last arguments are functions. Here, the casts are required
-to avoid a warning when compiling.
-
-Here is the definition of the function **afb_req_context**
-
-	/*
-	 * Gets the pointer stored by the plugin for the session of 'req'.
-	 * If the stored pointer is NULL, indicating that no pointer was
-	 * already stored, afb_req_context creates a new context by calling
-	 * the function 'create_context' and stores it with the freeing function
-	 * 'free_context'.
-	 */
-	static inline void *afb_req_context(struct afb_req req, void *(*create_context)(), void (*free_context)(void*))
-	{
-		void *result = afb_req_context_get(req);
-		if (result == NULL) {
-			result = create_context();
-			afb_req_context_set(req, result, free_context);
-		}
-		return result;
-	}
-
-The second argument if the function that creates the context.
-For the plugin *tic-tac-toe* it is the function **get_new_board**.
-The function **get_new_board** creates a new board and set its
-count of use to 1. The boards are counting their count of use
-to free there ressources when no more used.
-
-The third argument if the function that frees the context.
-For the plugin *tic-tac-toe* it is the function **release_board**.
-The function **release_board** decrease the the count of use of
-the board given as argument. If the use count decrease to zero,
-the board data are freed.
-
-### Sending the reply to a request
-
-Sending a reply to a request must be done at most one time.
-
-Two kinds of replies can be made: successful replies and
-failure replies.
-
-The functions to send replies are defined as below:
-
-	/*
-	 * Sends a reply of kind success to the request 'req'.
-	 * The status of the reply is automatically set to "success".
-	 * Its send the object 'obj' (can be NULL) with an
-	 * informationnal comment 'info (can also be NULL).
-	 */
-	static inline void afb_req_success(struct afb_req req, struct json_object *obj, const char *info)
-	{
-		req.itf->success(req.closure, obj, info);
-	}
-
-	/*
-	 * Same as 'afb_req_success' but the 'info' is a formatting
-	 * string followed by arguments.
-	 */
-	static inline void afb_req_success_f(struct afb_req req, struct json_object *obj, const char *info, ...)
-	{
-		char *message;
-		va_list args;
-		va_start(args, info);
-		if (info == NULL || vasprintf(&message, info, args) < 0)
-			message = NULL;
-		va_end(args);
-		afb_req_success(req, obj, message);
-		free(message);
-	}
-
-	/*
-	 * Sends a reply of kind failure to the request 'req'.
-	 * The status of the reply is set to 'status' and an
-	 * informationnal comment 'info' (can also be NULL) can be added.
-	 *
-	 * Note that calling afb_req_fail("success", info) is equivalent
-	 * to call afb_req_success(NULL, info). Thus even if possible it
-	 * is strongly recommanded to NEVER use "success" for status.
-	 */
-	static inline void afb_req_fail(struct afb_req req, const char *status, const char *info)
-	{
-		req.itf->fail(req.closure, status, info);
-	}
-
-	/*
-	 * Same as 'afb_req_fail' but the 'info' is a formatting
-	 * string followed by arguments.
-	 */
-	static inline void afb_req_fail_f(struct afb_req req, const char *status, const char *info, ...)
-	{
-		char *message;
-		va_list args;
-		va_start(args, info);
-		if (info == NULL || vasprintf(&message, info, args) < 0)
-			message = NULL;
-		va_end(args);
-		afb_req_fail(req, status, message);
-		free(message);
-	}
-
-
-
-Getting argument of invocation
-------------------------------
-
-Sending messages to the log system
-----------------------------------
-
-How to build a plugin
----------------------
-
-Afb-daemon provides a *pkg-config* configuration file.
-
-