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| author | Loïc Hoguin <[email protected]> | 2016-03-28 15:36:42 +0200 |
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| committer | Loïc Hoguin <[email protected]> | 2016-03-28 15:36:42 +0200 |
| commit | fe3492a98de29942477b061cd02c92246f4bf85a (patch) | |
| tree | 2255b796a657e6e4dfb72beec1141258d17f1220 /docs/en/cowboy/2.0/guide/loop_handlers | |
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diff --git a/docs/en/cowboy/2.0/guide/loop_handlers/index.html b/docs/en/cowboy/2.0/guide/loop_handlers/index.html new file mode 100644 index 00000000..d3081aac --- /dev/null +++ b/docs/en/cowboy/2.0/guide/loop_handlers/index.html @@ -0,0 +1,284 @@ +<!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"> + + <meta name="generator" content="Hugo 0.15" /> + + <title>Nine Nines: Loop handlers</title> + + <link href='http://fonts.googleapis.com/css?family=Open+Sans:400,700,400italic' rel='stylesheet' type='text/css'> + + <link href="/css/bootstrap.min.css" rel="stylesheet"> + <link href="/css/99s.css" 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="Keep in touch!" href="http://twitter.com/lhoguin"><img src="/img/ico_microblog.png" data-hover="/img/ico_microblog_alt.png"></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> + +<div class="paragraph"><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></div>
+<div class="paragraph"><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></div>
+<div class="paragraph"><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 known as server-sent events.</p></div>
+<div class="paragraph"><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></div>
+<div class="paragraph"><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></div>
+<div class="sect1">
+<h2 id="_initialization">Initialization</h2>
+<div class="sectionbody">
+<div class="paragraph"><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
+a timeout value and/or the atom <code>hibernate</code> to make the
+process enter hibernation until a message is received.</p></div>
+<div class="paragraph"><p>This snippet enables the loop handler.</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight 3.1.8
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt><span style="font-weight: bold"><span style="color: #000000">init</span></span>(<span style="color: #009900">Req</span>, <span style="color: #009900">_Opts</span>) <span style="color: #990000">-></span>
+ {<span style="color: #FF6600">cowboy_loop</span>, <span style="color: #009900">Req</span>, <span style="color: #008080">#state</span>{}}<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>However it is largely recommended that you set a timeout
+value. The next example sets a timeout value of 30s and
+also makes the process hibernate.</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight 3.1.8
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt><span style="font-weight: bold"><span style="color: #000000">init</span></span>(<span style="color: #009900">Req</span>, <span style="color: #009900">_Opts</span>) <span style="color: #990000">-></span>
+ {<span style="color: #FF6600">cowboy_loop</span>, <span style="color: #009900">Req</span>, <span style="color: #008080">#state</span>{}, <span style="color: #993399">30000</span>, <span style="color: #FF6600">hibernate</span>}<span style="color: #990000">.</span></tt></pre></div></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_receive_loop">Receive loop</h2>
+<div class="sectionbody">
+<div class="paragraph"><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></div>
+<div class="paragraph"><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>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight 3.1.8
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt><span style="font-weight: bold"><span style="color: #000000">info</span></span>({<span style="color: #FF6600">reply</span>, <span style="color: #009900">Body</span>}, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
+ <span style="color: #009900">Req2</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:reply</span></span>(<span style="color: #993399">200</span>, [], <span style="color: #009900">Body</span>, <span style="color: #009900">Req</span>),
+ {<span style="color: #FF6600">stop</span>, <span style="color: #009900">Req2</span>, <span style="color: #009900">State</span>};
+<span style="font-weight: bold"><span style="color: #000000">info</span></span>(<span style="color: #009900">_Msg</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
+ {<span style="color: #FF6600">ok</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>, <span style="color: #FF6600">hibernate</span>}<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>Do note that the <code>reply</code> tuple here may be any message
+and is simply an example.</p></div>
+<div class="paragraph"><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></div>
+<div class="paragraph"><p>The callback may also choose to do nothing at all and just
+skip the message received.</p></div>
+<div class="paragraph"><p>If a reply is sent, then the <code>stop</code> tuple should be returned.
+This will instruct Cowboy to end the request.</p></div>
+<div class="paragraph"><p>Otherwise an <code>ok</code> tuple should be returned.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_streaming_loop">Streaming loop</h2>
+<div class="sectionbody">
+<div class="paragraph"><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></div>
+<div class="paragraph"><p>The following snippet does exactly that. As you can see
+a chunk is sent every time a <code>chunk</code> message is received,
+and the loop is stopped by sending an <code>eof</code> message.</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight 3.1.8
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt><span style="font-weight: bold"><span style="color: #000000">init</span></span>(<span style="color: #009900">Req</span>, <span style="color: #009900">_Opts</span>) <span style="color: #990000">-></span>
+ <span style="color: #009900">Req2</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:chunked_reply</span></span>(<span style="color: #993399">200</span>, [], <span style="color: #009900">Req</span>),
+ {<span style="color: #FF6600">cowboy_loop</span>, <span style="color: #009900">Req2</span>, <span style="color: #008080">#state</span>{}}<span style="color: #990000">.</span>
+
+<span style="font-weight: bold"><span style="color: #000000">info</span></span>(<span style="color: #FF6600">eof</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
+ {<span style="color: #FF6600">stop</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>};
+<span style="font-weight: bold"><span style="color: #000000">info</span></span>({<span style="color: #FF6600">chunk</span>, <span style="color: #009900">Chunk</span>}, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
+ <span style="font-weight: bold"><span style="color: #000000">cowboy_req:chunk</span></span>(<span style="color: #009900">Chunk</span>, <span style="color: #009900">Req</span>),
+ {<span style="color: #FF6600">ok</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>};
+<span style="font-weight: bold"><span style="color: #000000">info</span></span>(<span style="color: #009900">_Msg</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>) <span style="color: #990000">-></span>
+ {<span style="color: #FF6600">ok</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>}<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="sect3">
+<h4 id="_cleaning_up">Cleaning up</h4>
+<div class="paragraph"><p>It is recommended that you set the connection header to
+<code>close</code> when replying, as this process may be reused for
+a subsequent request.</p></div>
+<div class="paragraph"><p>Please refer to the <a href="../handlers">Handlers chapter</a>
+for general instructions about cleaning up.</p></div>
+</div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_timeout">Timeout</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>By default Cowboy will not attempt to close the connection
+if there is no activity from the client. This is not always
+desirable, which is why you can set a timeout. Cowboy will
+close the connection if no data was received from the client
+after the configured time. The timeout only needs to be set
+once and can’t be modified afterwards.</p></div>
+<div class="paragraph"><p>Because the request may have had a body, or may be followed
+by another request, Cowboy is forced to buffer all data it
+receives. This data may grow to become too large though,
+so there is a configurable limit for it. The default buffer
+size is of 5000 bytes, but it may be changed by setting the
+<code>loop_max_buffer</code> middleware environment value.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_hibernate">Hibernate</h2>
+<div class="sectionbody">
+<div class="paragraph"><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></div>
+</div>
+</div>
+ + + +</div> + +<div class="span3 sidecol"> + + +<h3> + Cowboy + 2.0 + + User Guide +</h3> + +<ul> + + <li><a href="/docs/en/cowboy/2.0/guide">User Guide</a></li> + + + <li><a href="/docs/en/cowboy/2.0/manual">Function Reference</a></li> + + +</ul> + +<h4 id="docs-nav">Navigation</h4> + +<h4>Version select</h4> +<ul> + + + + <li><a href="/docs/en/cowboy/1.0/guide">1.0</a></li> + + <li><a href="/docs/en/cowboy/2.0/guide">2.0</a></li> + +</ul> + +</div> +</div> +</div> +</div> + + <footer> + <div class="container"> + <div class="row"> + <div class="span6"> + <p id="scroll-top"><a href="#">↑ Scroll to top</a></p> + <nav> + <ul> + <li><a href="mailto:[email protected]" title="Contact us">Contact us</a></li><li><a href="https://github.com/ninenines/ninenines.github.io" title="Github repository">Contribute to this site</a></li> + </ul> + </nav> + </div> + <div class="span6 credits"> + <p><img src="/img/footer_logo.png"></p> + <p>Copyright © Loïc Hoguin 2012-2016</p> + </div> + </div> + </div> + </footer> + + + <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script> + <script src="/js/bootstrap-carousel.js"></script> + <script src="/js/bootstrap-dropdown.js"></script> + <script src="/js/custom.js"></script> + </body> +</html> + + |