Cowboy 2.4.0

author: Loïc Hoguin <[email protected]> 2018-05-02 11:35:26 +0200
committer: Loïc Hoguin <[email protected]> 2018-05-02 11:35:26 +0200
commit: fec98300ec9af6c8b5f3120a60f217983c451076 (patch)
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+<!DOCTYPE html>
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+
+<h1 class="lined-header"><span>Reading the request body</span></h1>
+
+<div class="paragraph"><p>The request body can be read using the Req object.</p></div>
+<div class="paragraph"><p>Cowboy will not attempt to read the body until requested.
+You need to call the body reading functions in order to
+retrieve it.</p></div>
+<div class="paragraph"><p>Cowboy will not cache the body, it is therefore only
+possible to read it once.</p></div>
+<div class="paragraph"><p>You are not required to read it, however. If a body is
+present and was not read, Cowboy will either cancel or
+skip its download, depending on the protocol.</p></div>
+<div class="paragraph"><p>Cowboy provides functions for reading the body raw,
+and read and parse form urlencoded or <a href="../multipart">multipart bodies</a>.
+The latter is covered in its own chapter.</p></div>
+<div class="sect1">
+<h2 id="_request_body_presence">Request body presence</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Not all requests come with a body. You can check for
+the presence of a request body with this function:</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+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">cowboy_req:has_body</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>It returns <code>true</code> if there is a body; <code>false</code> otherwise.</p></div>
+<div class="paragraph"><p>In practice, this function is rarely used. When the
+method is <code>POST</code>, <code>PUT</code> or <code>PATCH</code>, the request body
+is often required by the application, which should
+just attempt to read it directly.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_request_body_length">Request body length</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>You can obtain the length of the body:</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt><span style="color: #009900">Length</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:body_length</span></span>(<span style="color: #009900">Req</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>Note that the length may not be known in advance. In
+that case <code>undefined</code> will be returned. This can happen
+with HTTP/1.1&#8217;s chunked transfer-encoding, or HTTP/2
+when no content-length was provided.</p></div>
+<div class="paragraph"><p>Cowboy will update the body length in the Req object
+once the body has been read completely. A length will
+always be returned when attempting to call this function
+after reading the body completely.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_reading_the_body">Reading the body</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>You can read the entire body with one function call:</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt>{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_body</span></span>(<span style="color: #009900">Req0</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>Cowboy returns an <code>ok</code> tuple when the body has been
+read fully.</p></div>
+<div class="paragraph"><p>By default, Cowboy will attempt to read up to 8MB
+of data, for up to 15 seconds. The call will return
+once Cowboy has read at least 8MB of data, or at
+the end of the 15 seconds period.</p></div>
+<div class="paragraph"><p>These values can be customized. For example, to read
+only up to 1MB for up to 5 seconds:</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt>{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_body</span></span>(<span style="color: #009900">Req0</span>,
+    #{<span style="font-weight: bold"><span style="color: #000080">length</span></span> <span style="color: #990000">=&gt;</span> <span style="color: #993399">1000000</span>, <span style="color: #0000FF">period</span> <span style="color: #990000">=&gt;</span> <span style="color: #993399">5000</span>})<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>You may also disable the length limit:</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt>{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_body</span></span>(<span style="color: #009900">Req0</span>, #{<span style="font-weight: bold"><span style="color: #000080">length</span></span> <span style="color: #990000">=&gt;</span> <span style="color: #FF6600">infinity</span>})<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>This makes the function wait 15 seconds and return with
+whatever arrived during that period. This is not
+recommended for public facing applications.</p></div>
+<div class="paragraph"><p>These two options can effectively be used to control
+the rate of transmission of the request body.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_streaming_the_body">Streaming the body</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>When the body is too large, the first call will return
+a <code>more</code> tuple instead of <code>ok</code>. You can call the
+function again to read more of the body, reading
+it one chunk at a time.</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+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">read_body_to_console</span></span>(<span style="color: #009900">Req0</span>) <span style="color: #990000">-&gt;</span>
+    <span style="font-weight: bold"><span style="color: #0000FF">case</span></span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_body</span></span>(<span style="color: #009900">Req0</span>) <span style="font-weight: bold"><span style="color: #0000FF">of</span></span>
+        {<span style="color: #FF6600">ok</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-&gt;</span>
+            <span style="font-weight: bold"><span style="color: #000000">io:format</span></span>(<span style="color: #FF0000">"~s"</span>, [<span style="color: #009900">Data</span>]),
+            <span style="color: #009900">Req</span>;
+        {<span style="color: #FF6600">more</span>, <span style="color: #009900">Data</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">-&gt;</span>
+            <span style="font-weight: bold"><span style="color: #000000">io:format</span></span>(<span style="color: #FF0000">"~s"</span>, [<span style="color: #009900">Data</span>]),
+            <span style="font-weight: bold"><span style="color: #000000">read_body_to_console</span></span>(<span style="color: #009900">Req</span>)
+    <span style="font-weight: bold"><span style="color: #0000FF">end</span></span><span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>The <code>length</code> and <code>period</code> options can also be used.
+They need to be passed for every call.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_reading_a_form_urlencoded_body">Reading a form urlencoded body</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Cowboy provides a convenient function for reading and
+parsing bodies sent as application/x-www-form-urlencoded.</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt>{<span style="color: #FF6600">ok</span>, <span style="color: #009900">KeyValues</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_urlencoded_body</span></span>(<span style="color: #009900">Req0</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>This function returns a list of key/values, exactly like
+the function <code>cowboy_req:parse_qs/1</code>.</p></div>
+<div class="paragraph"><p>The defaults for this function are different. Cowboy will
+read for up to 64KB and up to 5 seconds. They can be modified:</p></div>
+<div class="listingblock">
+<div class="content"><!-- Generator: GNU source-highlight
+by Lorenzo Bettini
+http://www.lorenzobettini.it
+http://www.gnu.org/software/src-highlite -->
+<pre><tt>{<span style="color: #FF6600">ok</span>, <span style="color: #009900">KeyValues</span>, <span style="color: #009900">Req</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">cowboy_req:read_urlencoded_body</span></span>(<span style="color: #009900">Req0</span>,
+    #{<span style="font-weight: bold"><span style="color: #000080">length</span></span> <span style="color: #990000">=&gt;</span> <span style="color: #993399">4096</span>, <span style="color: #0000FF">period</span> <span style="color: #990000">=&gt;</span> <span style="color: #993399">3000</span>})<span style="color: #990000">.</span></tt></pre></div></div>
+</div>
+</div>
+
+
+
+	
+		
+		
+		
+		
+		
+
+		<nav style="margin:1em 0">
+			
+				<a style="float:left" href="https://ninenines.eu/docs/en/cowboy/2.4/guide/req/">
+					The Req object
+				</a>
+			
+
+			
+				<a style="float:right" href="https://ninenines.eu/docs/en/cowboy/2.4/guide/resp/">
+					Sending a response
+				</a>
+			
+		</nav>
+	
+
+
+
+</div>
+
+<div class="span3 sidecol">
+
+
+<h3>
+	Cowboy
+	2.4
+	
+	User Guide
+</h3>
+
+<ul>
+	
+		<li><a href="/docs/en/cowboy/2.4/guide">User Guide</a></li>
+	
+	
+		<li><a href="/docs/en/cowboy/2.4/manual">Function Reference</a></li>
+	
+	
+</ul>
+
+<h4 id="docs-nav">Navigation</h4>
+
+<h4>Version select</h4>
+<ul>
+	
+	
+	
+		<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>
+	
+		<li><a href="/docs/en/cowboy/2.2/guide">2.2</a></li>
+	
+		<li><a href="/docs/en/cowboy/2.1/guide">2.1</a></li>
+	
+		<li><a href="/docs/en/cowboy/2.0/guide">2.0</a></li>
+	
+		<li><a href="/docs/en/cowboy/1.0/guide">1.0</a></li>
+	
+</ul>
+
+</div>
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author	Loïc Hoguin <[email protected]>	2018-05-02 11:35:26 +0200
committer	Loïc Hoguin <[email protected]>	2018-05-02 11:35:26 +0200
commit	fec98300ec9af6c8b5f3120a60f217983c451076 (patch)
tree	9772977293124e8b9b5b253e44d8c2695cddfb44 /docs/en/cowboy/2.4/guide/req_body/index.html
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