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diff --git a/docs/en/cowboy/2.8/guide/loop_handlers/index.html b/docs/en/cowboy/2.8/guide/loop_handlers/index.html new file mode 100644 index 00000000..0cc3c388 --- /dev/null +++ b/docs/en/cowboy/2.8/guide/loop_handlers/index.html @@ -0,0 +1,245 @@ +<!DOCTYPE html> +<html lang="en"> + +<head> + <meta charset="utf-8"> + <meta name="viewport" content="width=device-width, initial-scale=1.0"> + <meta name="description" content=""> + <meta name="author" content="Loïc Hoguin based on a design from (Soft10) Pol Cámara"> + + <title>Nine Nines: Loop handlers</title> + + <link href='https://fonts.googleapis.com/css?family=Open+Sans:400,700,400italic' rel='stylesheet' type='text/css'> + <link href="/css/99s.css?r=7" rel="stylesheet"> + + <link rel="shortcut icon" href="/img/ico/favicon.ico"> + <link rel="apple-touch-icon-precomposed" sizes="114x114" href="/img/ico/apple-touch-icon-114.png"> + <link rel="apple-touch-icon-precomposed" sizes="72x72" href="/img/ico/apple-touch-icon-72.png"> + <link rel="apple-touch-icon-precomposed" href="/img/ico/apple-touch-icon-57.png"> + + +</head> + + +<body class=""> + <header id="page-head"> + <div id="topbar" class="container"> + <div class="row"> + <div class="span2"> + <h1 id="logo"><a href="/" title="99s">99s</a></h1> + </div> + <div class="span10"> + + <div id="side-header"> + <nav> + <ul> + <li><a title="Hear my thoughts" href="/articles">Articles</a></li> + <li><a title="Watch my talks" href="/talks">Talks</a></li> + <li class="active"><a title="Read the docs" href="/docs">Documentation</a></li> + <li><a title="Request my services" href="/services">Consulting & Training</a></li> + </ul> + </nav> + <ul id="social"> + <li> + <a href="https://github.com/ninenines" title="Check my Github repositories"><img src="/img/ico_github.png" data-hover="/img/ico_github_alt.png" alt="Github"></a> + </li> + <li> + <a title="Contact me" href="mailto:[email protected]"><img src="/img/ico_mail.png" data-hover="/img/ico_mail_alt.png"></a> + </li> + </ul> + </div> + </div> + </div> + </div> + + +</header> + +<div id="contents" class="two_col"> +<div class="container"> +<div class="row"> +<div id="docs" class="span9 maincol"> + +<h1 class="lined-header"><span>Loop handlers</span></h1> + +<p>Loop handlers are a special kind of HTTP handlers used when the response can not be sent right away. The handler enters instead a receive loop waiting for the right message before it can send a response.</p> +<p>Loop handlers are used for requests where a response might not be immediately available, but where you would like to keep the connection open for a while in case the response arrives. The most known example of such practice is known as long polling.</p> +<p>Loop handlers can also be used for requests where a response is partially available and you need to stream the response body while the connection is open. The most known example of such practice is server-sent events, but it also applies to any response that takes a long time to send.</p> +<p>While the same can be accomplished using plain HTTP handlers, it is recommended to use loop handlers because they are well-tested and allow using built-in features like hibernation and timeouts.</p> +<p>Loop handlers essentially wait for one or more Erlang messages and feed these messages to the <code>info/3</code> callback. It also features the <code>init/2</code> and <code>terminate/3</code> callbacks which work the same as for plain HTTP handlers.</p> +<h2 id="_initialization">Initialization</h2> +<p>The <code>init/2</code> function must return a <code>cowboy_loop</code> tuple to enable loop handler behavior. This tuple may optionally contain the atom <code>hibernate</code> to make the process enter hibernation until a message is received.</p> +<p>This snippet enables the loop handler:</p> +<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.9 +by Lorenzo Bettini +http://www.lorenzobettini.it +http://www.gnu.org/software/src-highlite --> +<pre><tt><b><font color="#000000">init</font></b>(<font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + {<font color="#FF6600">cowboy_loop</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}<font color="#990000">.</font></tt></pre> +</div></div> +<p>This also makes the process hibernate:</p> +<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.9 +by Lorenzo Bettini +http://www.lorenzobettini.it +http://www.gnu.org/software/src-highlite --> +<pre><tt><b><font color="#000000">init</font></b>(<font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + {<font color="#FF6600">cowboy_loop</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>, <font color="#FF6600">hibernate</font>}<font color="#990000">.</font></tt></pre> +</div></div> +<h2 id="_receive_loop">Receive loop</h2> +<p>Once initialized, Cowboy will wait for messages to arrive in the process' mailbox. When a message arrives, Cowboy calls the <code>info/3</code> function with the message, the Req object and the handler's state.</p> +<p>The following snippet sends a reply when it receives a <code>reply</code> message from another process, or waits for another message otherwise.</p> +<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.9 +by Lorenzo Bettini +http://www.lorenzobettini.it +http://www.gnu.org/software/src-highlite --> +<pre><tt><b><font color="#000000">info</font></b>({<font color="#FF6600">reply</font>, <font color="#009900">Body</font>}, <font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + <b><font color="#000000">cowboy_req:reply</font></b>(<font color="#993399">200</font>, #{}, <font color="#009900">Body</font>, <font color="#009900">Req</font>), + {<font color="#FF6600">stop</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}; +<b><font color="#000000">info</font></b>(<font color="#009900">_Msg</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + {<font color="#FF6600">ok</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>, <font color="#FF6600">hibernate</font>}<font color="#990000">.</font></tt></pre> +</div></div> +<p>Do note that the <code>reply</code> tuple here may be any message and is simply an example.</p> +<p>This callback may perform any necessary operation including sending all or parts of a reply, and will subsequently return a tuple indicating if more messages are to be expected.</p> +<p>The callback may also choose to do nothing at all and just skip the message received.</p> +<p>If a reply is sent, then the <code>stop</code> tuple should be returned. This will instruct Cowboy to end the request.</p> +<p>Otherwise an <code>ok</code> tuple should be returned.</p> +<h2 id="_streaming_loop">Streaming loop</h2> +<p>Another common case well suited for loop handlers is streaming data received in the form of Erlang messages. This can be done by initiating a chunked reply in the <code>init/2</code> callback and then using <code>cowboy_req:chunk/2</code> every time a message is received.</p> +<p>The following snippet does exactly that. As you can see a chunk is sent every time an <code>event</code> message is received, and the loop is stopped by sending an <code>eof</code> message.</p> +<div class="listingblock"><div class="content"><!-- Generator: GNU source-highlight 3.1.9 +by Lorenzo Bettini +http://www.lorenzobettini.it +http://www.gnu.org/software/src-highlite --> +<pre><tt><b><font color="#000000">init</font></b>(<font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + <font color="#009900">Req2</font> <font color="#990000">=</font> <b><font color="#000000">cowboy_req:stream_reply</font></b>(<font color="#993399">200</font>, <font color="#009900">Req</font>), + {<font color="#FF6600">cowboy_loop</font>, <font color="#009900">Req2</font>, <font color="#009900">State</font>}<font color="#990000">.</font> + +<b><font color="#000000">info</font></b>(<font color="#FF6600">eof</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + {<font color="#FF6600">stop</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}; +<b><font color="#000000">info</font></b>({<font color="#FF6600">event</font>, <font color="#009900">Data</font>}, <font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + <b><font color="#000000">cowboy_req:stream_body</font></b>(<font color="#009900">Data</font>, <font color="#FF6600">nofin</font>, <font color="#009900">Req</font>), + {<font color="#FF6600">ok</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}; +<b><font color="#000000">info</font></b>(<font color="#009900">_Msg</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>) <font color="#990000">-></font> + {<font color="#FF6600">ok</font>, <font color="#009900">Req</font>, <font color="#009900">State</font>}<font color="#990000">.</font></tt></pre> +</div></div> +<h2 id="_cleaning_up">Cleaning up</h2> +<p>Please refer to the <a href="../handlers">Handlers chapter</a> for general instructions about cleaning up.</p> +<h2 id="_hibernate">Hibernate</h2> +<p>To save memory, you may hibernate the process in between messages received. This is done by returning the atom <code>hibernate</code> as part of the <code>loop</code> tuple callbacks normally return. Just add the atom at the end and Cowboy will hibernate accordingly.</p> + + + + + + + + + + + + <nav style="margin:1em 0"> + + <a style="float:left" href="https://ninenines.eu/docs/en/cowboy/2.8/guide/handlers/"> + Handlers + </a> + + + + <a style="float:right" href="https://ninenines.eu/docs/en/cowboy/2.8/guide/static_files/"> + Static files + </a> + + </nav> + + + + +</div> + +<div class="span3 sidecol"> + + +<h3> + Cowboy + 2.8 + + User Guide +</h3> + +<ul> + + <li><a href="/docs/en/cowboy/2.8/guide">User Guide</a></li> + + + <li><a href="/docs/en/cowboy/2.8/manual">Function Reference</a></li> + + +</ul> + +<h4 id="docs-nav">Navigation</h4> + +<h4>Version select</h4> +<ul> + + + + <li><a href="/docs/en/cowboy/2.8/guide">2.8</a></li> + + <li><a href="/docs/en/cowboy/2.7/guide">2.7</a></li> + + <li><a href="/docs/en/cowboy/2.6/guide">2.6</a></li> + + <li><a href="/docs/en/cowboy/2.5/guide">2.5</a></li> + + <li><a href="/docs/en/cowboy/2.4/guide">2.4</a></li> + + <li><a href="/docs/en/cowboy/2.3/guide">2.3</a></li> + +</ul> + +<h3 id="_like_my_work__donate">Like my work? 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