diff options
| author |   José Bollo <jose.bollo@iot.bzh> | 2016-05-27 17:31:30 +0200 |
|---|---|---|
| committer | José Bollo <jose.bollo@iot.bzh> | 2016-05-27 17:31:30 +0200 |
| commit | b81bab801d1a39cce7254b0c056d991412ec4331 (patch) | |
| tree | e691cd4ad9528da09778adef27ad5f495e245d1f /doc/writing-afb-plugins.html | |
| parent | 13a8c36f354376b622cebb3348f2500d87b980a9 (diff) | |
improves documentation
Change-Id: I5abae06cd5b5127fca97ba12aa8f18d037a95d79
Signed-off-by: José Bollo <jose.bollo@iot.bzh>
Diffstat (limited to 'doc/writing-afb-plugins.html')
| -rw-r--r-- | doc/writing-afb-plugins.html | 783 |
1 files changed, 0 insertions, 783 deletions
diff --git a/doc/writing-afb-plugins.html b/doc/writing-afb-plugins.html deleted file mode 100644 index 712d30ee..00000000 --- a/doc/writing-afb-plugins.html +++ /dev/null @@ -1,783 +0,0 @@ -<html> -<head> - <link rel="stylesheet" type="text/css" href="doc.css"> - <meta charset="UTF-8"> -</head> -<body> -<h1 id="HOWTO.WRITE.a.PLUGIN.for.AFB-DAEMON">HOWTO WRITE a PLUGIN for AFB-DAEMON</h1> - -<pre><code>version: 1 -Date: 25 May 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="#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.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="#Sending.messages.to.the.log.system">Sending messages to the log system</a></li> - <li><a href="#How.to.build.a.plugin">How to build a plugin</a></li> - </ul> - </li> -</ul></p> - -<h2 id="Summary">Summary</h2> - -<p>The binder afb-daemon serves files through -the HTTP protocol and offers access to API’s through -HTTP or WebSocket protocol.</p> - -<p>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.</p> - -<p>Before going into details, through a tiny example, -a short overview plugins basis is needed.</p> - -<h3 id="Nature.of.a.plugin">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> - -<h3 id="Kinds.of.plugins">Kinds of plugins</h3> - -<p>There is two kinds of plugins: application plugins and service -plugins.</p> - -<h4 id="Application.plugins">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> - -<h4 id="Service.plugins">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> - -<h3 id="Live.cycle.of.a.plugin.within.afb-daemon">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’s verbs.</p> - -<p>When initialized, the functions implementing the API’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 ‘atexit’ -or ‘on_exit’ during initialisation if they need to -perform specific actions when stopping.</p> - -<h3 id="Content.of.a.plugin">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> - -<h4 id="The.name.of.the.plugin">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> - -<h4 id="Names.of.verbs">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> - -<h4 id="The.initialisation.function">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> - - -<h4 id="Functions.implementing.verbs">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’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> - -<h2 id="The.Tic-Tac-Toe.example">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> - -<h2 id="Choosing.names">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> - -<h3 id="Names.for.API..plugin.">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 { ‘ ’, ‘“’, ‘#’, ‘%’, ‘&’, -‘’‘, ’/‘, ’?‘, ’`‘, ’\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> - -<h3 id="Names.for.verbs">Names for verbs</h3> - -<p>The names of the verbs are not checked.</p> - -<p>However, the validity rules for verb’s names are the -same as for API’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> - -<h3 id="Names.for.arguments">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 “index” and “Index” -are not the same.</p> - -<h3 id="Forging.names.widely.available">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> - -<h2 id="Options.to.set.when.compiling.plugins">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> - -<h2 id="Header.files.to.include">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 <stdio.h> -#include <string.h> -#include <json-c/json.h> -#include <afb/afb-plugin.h> -</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> - -<h2 id="Writing.a.synchronous.verb.implementation">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->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> - - -<h3 id="The.incoming.request">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> - -<h3 id="Associating.a.context.to.the.session">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> - -<h3 id="Sending.the.reply.to.a.request">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 “success” 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). - */ -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. - */ -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 “failure” 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. - */ -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. - */ -void afb_req_fail_f(struct afb_req req, const char *status, const char *info, ...); -</code></pre> - -<h2 id="Getting.argument.of.invocation">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->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> - -<h3 id="Basic.functions.for.querying.arguments">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>“”</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> - -<h3 id="Arguments.for.received.files">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><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> -</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… -But when the reply is sent and the query is terminated, the file at -this path is destroyed if it still exist.</p> - -<h3 id="Arguments.as.a.JSON.object">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 { “file”: “…”, “path”: “…” }</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 -<em>json_object_get_string(json_object_object_get(afb_req_json(req), name))</em></p></blockquote> - -<h2 id="Sending.messages.to.the.log.system">Sending messages to the log system</h2> - -<h2 id="How.to.build.a.plugin">How to build a plugin</h2> - -<p>Afb-daemon provides a <em>pkg-config</em> configuration file.</p> -</body> -</html> |