Cowboy 2.3.0

author: Loïc Hoguin <[email protected]> 2018-04-04 13:13:37 +0200
committer: Loïc Hoguin <[email protected]> 2018-04-04 13:13:37 +0200
commit: d2a3f2cedd7c00d0933222aed9c06b3149aa4db4 (patch)
tree: 4f1499bac639c782b250af0fbf0dec2064315813 /docs/en/cowboy/2.3/guide/flow_diagram/index.html
parent: 1d654719f5fa6be67d2c95145872068665702cb7 (diff)
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+
+<h1 class="lined-header"><span>Flow diagram</span></h1>
+
+<div class="paragraph"><p>Cowboy is a lightweight HTTP server with support for HTTP/1.1,
+HTTP/2 and Websocket.</p></div>
+<div class="paragraph"><p>It is built on top of Ranch. Please see the Ranch guide for more
+information about how the network connections are handled.</p></div>
+<div class="sect1">
+<h2 id="_overview">Overview</h2>
+<div class="sectionbody">
+<div class="imageblock">
+<div class="content">
+<img src="../http_req_resp.png" alt="HTTP request/response flowchart" />
+</div>
+</div>
+<div class="paragraph"><p>As you can see on the diagram, the client
+begins by connecting to the server. This step is handled
+by a Ranch acceptor, which is a process dedicated to
+accepting new connections.</p></div>
+<div class="paragraph"><p>After Ranch accepts a new connection, whether it is an
+HTTP/1.1 or HTTP/2 connection, Cowboy starts receiving
+requests and handling them.</p></div>
+<div class="paragraph"><p>In HTTP/1.1 all requests come sequentially. In HTTP/2
+the requests may arrive and be processed concurrently.</p></div>
+<div class="paragraph"><p>When a request comes in, Cowboy creates a stream, which
+is a set of request/response and all the events associated
+with them. The protocol code in Cowboy defers the handling
+of these streams to stream handler modules. When you
+configure Cowboy you may define one or more module that
+will receive all events associated with a stream, including
+the request, response, bodies, Erlang messages and more.</p></div>
+<div class="paragraph"><p>By default Cowboy comes configured with a stream handler
+called <code>cowboy_stream_h</code>. This stream handler will create
+a new process for every request coming in, and then
+communicate with this process to read the body or send
+a response back. The request process executes middlewares
+which, by default, including the router and then the
+execution of handlers. Like stream handlers, middlewares
+may also be customized.</p></div>
+<div class="paragraph"><p>A response may be sent at almost any point in this
+diagram. If the response must be sent before the stream
+is initialized (because an error occurred early, for
+example) then stream handlers receive a special event
+indicating this error.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_protocol_specific_headers">Protocol-specific headers</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Cowboy takes care of protocol-specific headers and prevents
+you from sending them manually. For HTTP/1.1 this includes
+the <code>transfer-encoding</code> and <code>connection</code> headers. For HTTP/2
+this includes the colon headers like <code>:status</code>.</p></div>
+<div class="paragraph"><p>Cowboy will also remove protocol-specific headers from
+requests before passing them to stream handlers. Cowboy
+tries to hide the implementation details of all protocols
+as well as possible.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_number_of_processes_per_connection">Number of processes per connection</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>By default, Cowboy will use one process per connection,
+plus one process per set of request/response (called a
+stream, internally).</p></div>
+<div class="paragraph"><p>The reason it creates a new process for every request is due
+to the requirements of HTTP/2 where requests are executed
+concurrently and independently from the connection. The
+frames from the different requests end up interleaved on
+the single TCP connection.</p></div>
+<div class="paragraph"><p>The request processes are never reused. There is therefore
+no need to perform any cleanup after the response has been
+sent. The process will terminate and Erlang/OTP will reclaim
+all memory at once.</p></div>
+<div class="paragraph"><p>Cowboy ultimately does not require more than one process
+per connection. It is possible to interact with the connection
+directly from a stream handler, a low level interface to Cowboy.
+They are executed from within the connection process, and can
+handle the incoming requests and send responses. This is however
+not recommended in normal circumstances, as a stream handler
+taking too long to execute could have a negative impact on
+concurrent requests or the state of the connection itself.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_date_header">Date header</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Because querying for the current date and time can be expensive,
+Cowboy generates one <em>Date</em> header value every second, shares it
+to all other processes, which then simply copy it in the response.
+This allows compliance with HTTP/1.1 with no actual performance loss.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_binaries">Binaries</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Cowboy makes extensive use of binaries.</p></div>
+<div class="paragraph"><p>Binaries are more efficient than lists for representing
+strings because they take less memory space. Processing
+performance can vary depending on the operation. Binaries
+are known for generally getting a great boost if the code
+is compiled natively. Please see the HiPE documentation
+for more details.</p></div>
+<div class="paragraph"><p>Binaries may end up being shared between processes. This
+can lead to some large memory usage when one process keeps
+the binary data around forever without freeing it. If you
+see some weird memory usage in your application, this might
+be the cause.</p></div>
+</div>
+</div>
+
+
+
+	
+		
+		
+		
+		
+		
+
+		<nav style="margin:1em 0">
+			
+				<a style="float:left" href="https://ninenines.eu/docs/en/cowboy/2.3/guide/getting_started/">
+					Getting started
+				</a>
+			
+
+			
+				<a style="float:right" href="https://ninenines.eu/docs/en/cowboy/2.3/guide/listeners/">
+					Listeners
+				</a>
+			
+		</nav>
+	
+
+
+
+</div>
+
+<div class="span3 sidecol">
+
+
+<h3>
+	Cowboy
+	2.3
+	
+	User Guide
+</h3>
+
+<ul>
+	
+		<li><a href="/docs/en/cowboy/2.3/guide">User Guide</a></li>
+	
+	
+		<li><a href="/docs/en/cowboy/2.3/manual">Function Reference</a></li>
+	
+	
+</ul>
+
+<h4 id="docs-nav">Navigation</h4>
+
+<h4>Version select</h4>
+<ul>
+	
+	
+	
+		<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>
+</div>
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author	Loïc Hoguin <[email protected]>	2018-04-04 13:13:37 +0200
committer	Loïc Hoguin <[email protected]>	2018-04-04 13:13:37 +0200
commit	d2a3f2cedd7c00d0933222aed9c06b3149aa4db4 (patch)
tree	4f1499bac639c782b250af0fbf0dec2064315813 /docs/en/cowboy/2.3/guide/flow_diagram/index.html
parent	1d654719f5fa6be67d2c95145872068665702cb7 (diff)
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