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diff --git a/doc/writing-afb-plugins.html b/doc/writing-afb-plugins.html index 5aeca0a5..712d30ee 100644 --- a/doc/writing-afb-plugins.html +++ b/doc/writing-afb-plugins.html @@ -4,11 +4,10 @@ <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> +<h1 id="HOWTO.WRITE.a.PLUGIN.for.AFB-DAEMON">HOWTO WRITE a PLUGIN for AFB-DAEMON</h1> <pre><code>version: 1 -Date: 24 mai 2016 +Date: 25 May 2016 Author: José Bollo </code></pre> @@ -18,6 +17,12 @@ Author: José Bollo <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> @@ -44,18 +49,24 @@ Author: José Bollo <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="#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></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> -<a name="Summary"></a> -<h2>Summary</h2> +<h2 id="Summary">Summary</h2> <p>The binder afb-daemon serves files through the HTTP protocol and offers access to API’s through @@ -69,8 +80,7 @@ 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> +<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 @@ -78,8 +88,33 @@ 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> +<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> @@ -97,8 +132,7 @@ Consequently, developpers of plugins should use ‘atexit’ or ‘on_exit’ 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> +<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> @@ -124,8 +158,7 @@ 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> +<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> @@ -140,8 +173,7 @@ 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> +<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> @@ -154,8 +186,7 @@ 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> +<h4 id="The.initialisation.function">The initialisation function</h4> <p>The initialisation function serves several purposes.</p> @@ -171,8 +202,7 @@ requirements and implmentations of the verbs that it exposes.</p></li> </ol> -<a name="Functions.implementing.verbs"></a> -<h4>Functions implementing verbs</h4> +<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 @@ -198,8 +228,7 @@ returning are named <em>asynchronous implementations</em>.</p> 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> +<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 @@ -208,8 +237,7 @@ 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> +<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 @@ -221,8 +249,7 @@ 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> +<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> @@ -241,8 +268,7 @@ All characters are authorised except:</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> +<h3 id="Names.for.verbs">Names for verbs</h3> <p>The names of the verbs are not checked.</p> @@ -253,8 +279,7 @@ 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> +<h3 id="Names.for.arguments">Names for arguments</h3> <p>The names for arguments are not restricted and can be anything.</p> @@ -263,8 +288,7 @@ anything.</p> string comparison. Thus the names “index” and “Index” are not the same.</p> -<a name="Forging.names.widely.available"></a> -<h3>Forging names widely available</h3> +<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> @@ -287,8 +311,7 @@ valid javascript identifier.</p> 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> +<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> @@ -313,8 +336,7 @@ 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> +<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> @@ -341,8 +363,7 @@ if it needs it:</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> +<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> @@ -352,33 +373,61 @@ Here is its listing:</p> */ static void board(struct afb_req req) { - struct board *board; - struct json_object *description; + 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); + /* 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); + /* describe the board */ + description = describe(board); - /* send the board's description */ - afb_req_success(req, description, NULL); + /* 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> +verb implementation. Let summarize it:</p> -<a name="The.incoming.request"></a> -<h3>The incoming request</h3> +<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 +<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> +<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> -<p>This structure, here named <em>req</em>, is used</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> @@ -394,8 +443,7 @@ 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> +<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> @@ -430,14 +478,14 @@ its context: the board. This function is <em>board_of_req</em>:</p> */ static inline struct board *board_of_req(struct afb_req req) { - return afb_req_context(req, (void*)get_new_board, (void*)release_board); + 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>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> @@ -450,33 +498,286 @@ The casts are required to avoid a warning when compiling.</p> */ 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; + 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 +<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 function <strong>release_board</strong></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> + -<a name="Sending.the.reply.to.a.request"></a> -<h3>Sending the reply to a request</h3> +<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> -<a name="Getting.argument.of.invocation"></a> -<h2>Getting argument of invocation</h2> +<h2 id="Sending.messages.to.the.log.system">Sending messages to the log system</h2> -<a name="How.to.build.a.plugin"></a> -<h2>How to build a plugin</h2> +<h2 id="How.to.build.a.plugin">How to build a plugin</h2> -<p>Afb-daemon provides a The packaging of afb-daemon</p> +<p>Afb-daemon provides a <em>pkg-config</em> configuration file.</p> </body> </html> |