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+
+<h1 class="lined-header"><span>Connection</span></h1>
+
+<div class="paragraph"><p>This chapter describes how to open, monitor and close
+a connection using the Gun client.</p></div>
+<div class="sect1">
+<h2 id="_gun_connections">Gun connections</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Gun is designed with the SPDY and Websocket protocols in mind.
+They are built for long-running connections that allow concurrent
+exchange of data, either in the form of request/responses for
+SPDY or in the form of messages for Websocket.</p></div>
+<div class="paragraph"><p>A Gun connection is an Erlang process that manages a socket to
+a remote endpoint. This Gun connection is owned by a user
+process that is called the <em>owner</em> of the connection, and is
+managed by the supervision tree of the <code>gun</code> application.</p></div>
+<div class="paragraph"><p>The owner process communicates with the Gun connection
+by calling functions from the module <code>gun</code>. All functions
+perform their respective operations asynchronously. The Gun
+connection will send Erlang messages to the owner process
+whenever needed.</p></div>
+<div class="paragraph"><p>When the remote endpoint closes the connection, Gun attempts
+to reconnect automatically.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_opening_a_new_connection">Opening a new connection</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The <code>gun:open/{2,3}</code> function must be used to open a connection.</p></div>
+<div class="listingblock">
+<div class="title">Opening a connection to example.org on port 443</div>
+<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="color: #FF6600">ok</span>, <span style="color: #009900">ConnPid</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">gun:open</span></span>(<span style="color: #FF0000">"example.org"</span>, <span style="color: #993399">443</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>If the port given is 443, Gun will attempt to connect using
+SSL. The protocol will be selected automatically using the
+NPN extension for TLS. By default Gun supports SPDY/3.1,
+SPDY/3 and HTTP/1.1 when connecting using SSL.</p></div>
+<div class="paragraph"><p>For any other port, Gun will attempt to connect using TCP
+and will use the HTTP/1.1 protocol.</p></div>
+<div class="paragraph"><p>The transport and protocol used can be overriden using
+options. The manual documents all available options.</p></div>
+<div class="paragraph"><p>Options can be provided as a third argument, and take the
+form of a map.</p></div>
+<div class="listingblock">
+<div class="title">Opening an SSL connection to example.org on port 8443</div>
+<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="color: #FF6600">ok</span>, <span style="color: #009900">ConnPid</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">gun:open</span></span>(<span style="color: #FF0000">"example.org"</span>, <span style="color: #993399">8443</span>, #{<span style="color: #0000FF">transport</span><span style="color: #990000">=&gt;</span><span style="color: #FF6600">ssl</span>})<span style="color: #990000">.</span></tt></pre></div></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_waiting_for_the_connection_to_be_established">Waiting for the connection to be established</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>When Gun successfully connects to the server, it sends a
+<code>gun_up</code> message with the protocol that has been selected
+for the connection.</p></div>
+<div class="paragraph"><p>Gun provides the functions <code>gun:await_up/{1,2,3}</code> that wait
+for the <code>gun_up</code> message. They can optionally take a monitor
+reference and/or timeout value. If no monitor is provided,
+one will be created for the duration of the function call.</p></div>
+<div class="listingblock">
+<div class="title">Synchronous opening of a connection</div>
+<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="color: #FF6600">ok</span>, <span style="color: #009900">ConnPid</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">gun:open</span></span>(<span style="color: #FF0000">"example.org"</span>, <span style="color: #993399">443</span>),
+{<span style="color: #FF6600">ok</span>, <span style="color: #009900">Protocol</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">gun:await_up</span></span>(<span style="color: #009900">ConnPid</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_handling_connection_loss">Handling connection loss</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>When the connection is lost, Gun will send a <code>gun_down</code>
+message indicating the current protocol, the reason the
+connection was lost and two list of stream references.</p></div>
+<div class="paragraph"><p>The first list indicates open streams that <em>may</em> have been
+processed by the server. The second list indicates open
+streams that the server did not process.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_monitoring_the_connection_process">Monitoring the connection process</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>@todo Gun should detect the owner process being killed</p></div>
+<div class="paragraph"><p>Because software errors are unavoidable, it is important to
+detect when the Gun process crashes. It is also important
+to detect when it exits normally. Erlang provides two ways
+to do that: links and monitors.</p></div>
+<div class="paragraph"><p>Gun leaves you the choice as to which one will be used.
+However, if you use the <code>gun:await/{2,3}</code> or <code>gun:await_body/{2,3}</code>
+functions, a monitor may be used for you to avoid getting
+stuck waiting for a message that will never come.</p></div>
+<div class="paragraph"><p>If you choose to monitor yourself you can do it on a permanent
+basis rather than on every message you will receive, saving
+resources. Indeed, the <code>gun:await/{3,4}</code> and <code>gun:await_body/{3,4}</code>
+functions both accept a monitor argument if you have one already.</p></div>
+<div class="listingblock">
+<div class="title">Monitoring the connection process</div>
+<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="color: #FF6600">ok</span>, <span style="color: #009900">ConnPid</span>} <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">gun:open</span></span>(<span style="color: #FF0000">"example.org"</span>, <span style="color: #993399">443</span>)<span style="color: #990000">.</span>
+<span style="color: #009900">MRef</span> <span style="color: #990000">=</span> <span style="font-weight: bold"><span style="color: #000000">monitor</span></span>(<span style="font-weight: bold"><span style="color: #000080">process</span></span>, <span style="color: #009900">ConnPid</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>This monitor reference can be kept and used until the connection
+process exits.</p></div>
+<div class="listingblock">
+<div class="title">Handling <code>DOWN</code> messages</div>
+<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: #0000FF">receive</span></span>
+ <span style="font-style: italic"><span style="color: #9A1900">%% Receive Gun messages here...</span></span>
+ {<span style="color: #FF6600">'DOWN'</span>, <span style="color: #009900">Mref</span>, <span style="font-weight: bold"><span style="color: #000080">process</span></span>, <span style="color: #009900">ConnPid</span>, <span style="color: #009900">Reason</span>} <span style="color: #990000">-&gt;</span>
+ <span style="font-weight: bold"><span style="color: #000000">error_logger:error_msg</span></span>(<span style="color: #FF0000">"Oops!"</span>),
+ <span style="font-weight: bold"><span style="color: #000080">exit</span></span>(<span style="color: #009900">Reason</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>What to do when you receive a <code>DOWN</code> message is entirely up to you.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_closing_the_connection_abruptly">Closing the connection abruptly</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The connection can be stopped abruptly at any time by calling
+the <code>gun:close/1</code> function.</p></div>
+<div class="listingblock">
+<div class="title">Immediate closing of the connection</div>
+<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">gun:close</span></span>(<span style="color: #009900">ConnPid</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>The process is stopped immediately without having a chance to
+perform the protocol&#8217;s closing handshake, if any.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_closing_the_connection_gracefully">Closing the connection gracefully</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The connection can also be stopped gracefully by calling the
+<code>gun:shutdown/1</code> function.</p></div>
+<div class="listingblock">
+<div class="title">Graceful shutdown of the connection</div>
+<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">gun:shutdown</span></span>(<span style="color: #009900">ConnPid</span>)<span style="color: #990000">.</span></tt></pre></div></div>
+<div class="paragraph"><p>Gun will refuse any new requests or messages after you call
+this function. It will however continue to send you messages
+for existing streams until they are all completed.</p></div>
+<div class="paragraph"><p>For example if you performed a GET request just before calling
+<code>gun:shutdown/1</code>, you will still receive the response before
+Gun closes the connection.</p></div>
+<div class="paragraph"><p>If you set a monitor beforehand, you will receive a message
+when the connection has been closed.</p></div>
+</div>
+</div>
+
+
+
+</div>
+
+<div class="span3 sidecol">
+
+
+<h3>
+ Gun
+ 1.0
+
+ User Guide
+</h3>
+
+<ul>
+
+ <li><a href="/docs/en/gun/1.0/guide">User Guide</a></li>
+
+
+ <li><a href="/docs/en/gun/1.0/manual">Function Reference</a></li>
+
+
+</ul>
+
+<h4 id="docs-nav">Navigation</h4>
+
+<h4>Version select</h4>
+<ul>
+
+
+
+ <li><a href="/docs/en/gun/1.0/guide">1.0</a></li>
+
+</ul>
+
+</div>
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