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Diffstat (limited to 'docs/en/cowboy/2.0/guide/loop_handlers/index.html')
-rw-r--r-- | docs/en/cowboy/2.0/guide/loop_handlers/index.html | 255 |
1 files changed, 129 insertions, 126 deletions
diff --git a/docs/en/cowboy/2.0/guide/loop_handlers/index.html b/docs/en/cowboy/2.0/guide/loop_handlers/index.html index 442bc7e0..0b0b50b5 100644 --- a/docs/en/cowboy/2.0/guide/loop_handlers/index.html +++ b/docs/en/cowboy/2.0/guide/loop_handlers/index.html @@ -7,7 +7,7 @@ <meta name="description" content=""> <meta name="author" content="Loïc Hoguin based on a design from (Soft10) Pol Cámara"> - <meta name="generator" content="Hugo 0.17" /> + <meta name="generator" content="Hugo 0.26" /> <title>Nine Nines: Loop handlers</title> @@ -67,137 +67,140 @@ <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 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">State</span>) <span style="color: #990000">-></span>
- {<span style="color: #FF6600">cowboy_loop</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>}<span style="color: #990000">.</span></tt></pre></div></div>
-<div class="paragraph"><p>This 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">State</span>) <span style="color: #990000">-></span>
- {<span style="color: #FF6600">cowboy_loop</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>
-</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="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">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: #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 an <code>event</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">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:stream_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: #009900">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">event</span>, <span style="color: #009900">Data</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:stream_body</span></span>(<span style="color: #009900">Data</span>, <span style="color: #FF6600">nofin</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>
-</div>
-<div class="sect1">
-<h2 id="_cleaning_up">Cleaning up</h2>
-<div class="sectionbody">
-<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 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 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 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">State</span>) <span style="color: #990000">-></span> + {<span style="color: #FF6600">cowboy_loop</span>, <span style="color: #009900">Req</span>, <span style="color: #009900">State</span>}<span style="color: #990000">.</span></tt></pre></div></div> +<div class="paragraph"><p>This 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">State</span>) <span style="color: #990000">-></span> + {<span style="color: #FF6600">cowboy_loop</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> +</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="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">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: #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 an <code>event</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">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:stream_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: #009900">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">event</span>, <span style="color: #009900">Data</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:stream_body</span></span>(<span style="color: #009900">Data</span>, <span style="color: #FF6600">nofin</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> +</div> +<div class="sect1"> +<h2 id="_cleaning_up">Cleaning up</h2> +<div class="sectionbody"> +<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 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> + + + <nav style="margin:1em 0"> |