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  26 <div class="titlepage"><div><div><h6 class="title">
  27 <a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2"></a><a class="link" href="overload2.html" title="websocket::stream::async_handshake (2 of 2 overloads)">websocket::stream::async_handshake
  28           (2 of 2 overloads)</a>
  29 </h6></div></div></div>
  30 <p>
  31             Perform the WebSocket handshake asynchronously in the client role.
  32           </p>
  33 <h7><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.h0"></a>
  34             <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.synopsis"></a></span><a class="link" href="overload2.html#beast.ref.boost__beast__websocket__stream.async_handshake.overload2.synopsis">Synopsis</a>
  35           </h7><pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  36     <span class="keyword">class</span> <span class="identifier">HandshakeHandler</span> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special">&lt;</span><span class="identifier">executor_type</span><span class="special">&gt;&gt;</span>
  37 <a href="../../../../../../../../doc/html/boost_asio/reference/asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type" target="_top"><span class="emphasis"><em>DEDUCED</em></span></a>
  38 <span class="identifier">async_handshake</span><span class="special">(</span>
  39     <span class="identifier">response_type</span><span class="special">&amp;</span> <span class="identifier">res</span><span class="special">,</span>
  40     <span class="identifier">string_view</span> <span class="identifier">host</span><span class="special">,</span>
  41     <span class="identifier">string_view</span> <span class="identifier">target</span><span class="special">,</span>
  42     <span class="identifier">HandshakeHandler</span><span class="special">&amp;&amp;</span> <span class="identifier">handler</span> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special">&lt;</span> <span class="identifier">executor_type</span> <span class="special">&gt;{});</span>
  43 </pre>
  44 <h7><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.h1"></a>
  45             <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.description"></a></span><a class="link" href="overload2.html#beast.ref.boost__beast__websocket__stream.async_handshake.overload2.description">Description</a>
  46           </h7><p>
  47             This initiating function is used to asynchronously begin performing the
  48             <a href="https://en.wikipedia.org/wiki/WebSocket#Protocol_handshake" target="_top">WebSocket
  49             handshake</a>, required before messages can be sent and received.
  50             During the handshake, the client sends the Websocket Upgrade HTTP request,
  51             and the server replies with an HTTP response indicating the result of
  52             the handshake. This call always returns immediately. The asynchronous
  53             operation will continue until one of the following conditions is true:
  54           </p>
  55 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  56 <li class="listitem">
  57                 The request is sent and the response is received.
  58               </li>
  59 <li class="listitem">
  60                 An error occurs.
  61               </li>
  62 </ul></div>
  63 <p>
  64             The algorithm, known as a <span class="emphasis"><em>composed asynchronous operation</em></span>,
  65             is implemented in terms of calls to the next layer's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
  66             and <code class="computeroutput"><span class="identifier">async_write_some</span></code>
  67             functions. No other operation may be performed on the stream until this
  68             operation completes. The handshake is successful if the received HTTP
  69             response indicates the upgrade was accepted by the server, represented
  70             by a <a href="https://tools.ietf.org/html/rfc7230#section-3.1.2" target="_top">status-code</a>
  71             of <a class="link" href="../../boost__beast__http__status.html" title="http::status"><code class="computeroutput"><span class="identifier">http</span><span class="special">::</span><span class="identifier">switching_protocols</span></code></a>.
  72           </p>
  73 <h7><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.h2"></a>
  74             <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.parameters"></a></span><a class="link" href="overload2.html#beast.ref.boost__beast__websocket__stream.async_handshake.overload2.parameters">Parameters</a>
  75           </h7><div class="informaltable"><table class="table">
  76 <colgroup>
  77 <col>
  78 <col>
  79 </colgroup>
  80 <thead><tr>
  81 <th>
  82                     <p>
  83                       Name
  84                     </p>
  85                   </th>
  86 <th>
  87                     <p>
  88                       Description
  89                     </p>
  90                   </th>
  91 </tr></thead>
  92 <tbody>
  93 <tr>
  94 <td>
  95                     <p>
  96                       <code class="computeroutput"><span class="identifier">res</span></code>
  97                     </p>
  98                   </td>
  99 <td>
 100                     <p>
 101                       The HTTP Upgrade response returned by the remote endpoint.
 102                       The caller may use the response to access any additional information
 103                       sent by the server. This object will be assigned before the
 104                       completion handler is invoked.
 105                     </p>
 106                   </td>
 107 </tr>
 108 <tr>
 109 <td>
 110                     <p>
 111                       <code class="computeroutput"><span class="identifier">host</span></code>
 112                     </p>
 113                   </td>
 114 <td>
 115                     <p>
 116                       The name of the remote host. This is required by the HTTP protocol
 117                       to set the "Host" header field. The implementation
 118                       will not access the string data after the initiating function
 119                       returns.
 120                     </p>
 121                   </td>
 122 </tr>
 123 <tr>
 124 <td>
 125                     <p>
 126                       <code class="computeroutput"><span class="identifier">target</span></code>
 127                     </p>
 128                   </td>
 129 <td>
 130                     <p>
 131                       The request-target, in origin-form. The server may use the
 132                       target to distinguish different services on the same listening
 133                       port. The implementation will not access the string data after
 134                       the initiating function returns.
 135                     </p>
 136                   </td>
 137 </tr>
 138 <tr>
 139 <td>
 140                     <p>
 141                       <code class="computeroutput"><span class="identifier">handler</span></code>
 142                     </p>
 143                   </td>
 144 <td>
 145                     <p>
 146                       The completion handler to invoke when the operation completes.
 147                       The implementation takes ownership of the handler by performing
 148                       a decay-copy. The equivalent function signature of the handler
 149                       must be:
 150                     </p>
 151 <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span>
 152     <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">ec</span>    <span class="comment">// Result of operation</span>
 153 <span class="special">);</span>
 154 </pre>
 155                     <p>
 156                       Regardless of whether the asynchronous operation completes
 157                       immediately or not, the handler will not be invoked from within
 158                       this function. Invocation of the handler will be performed
 159                       in a manner equivalent to using <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code>.
 160                     </p>
 161                   </td>
 162 </tr>
 163 </tbody>
 164 </table></div>
 165 <h7><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.h3"></a>
 166             <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.example"></a></span><a class="link" href="overload2.html#beast.ref.boost__beast__websocket__stream.async_handshake.overload2.example">Example</a>
 167           </h7><pre class="programlisting"><span class="identifier">response_type</span> <span class="identifier">res</span><span class="special">;</span>
 168 <span class="identifier">ws</span><span class="special">.</span><span class="identifier">async_handshake</span><span class="special">(</span><span class="identifier">res</span><span class="special">,</span> <span class="string">"localhost"</span><span class="special">,</span> <span class="string">"/"</span><span class="special">,</span>
 169     <span class="special">[&amp;</span><span class="identifier">res</span><span class="special">](</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">)</span>
 170     <span class="special">{</span>
 171         <span class="keyword">if</span><span class="special">(</span><span class="identifier">ec</span><span class="special">)</span>
 172             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special">&lt;&lt;</span> <span class="string">"Error: "</span> <span class="special">&lt;&lt;</span> <span class="identifier">ec</span><span class="special">.</span><span class="identifier">message</span><span class="special">()</span> <span class="special">&lt;&lt;</span> <span class="string">"\n"</span><span class="special">;</span>
 173         <span class="keyword">else</span>
 174             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">res</span><span class="special">;</span>
 175
 176     <span class="special">});</span>
 177 </pre>
 178 <h7><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.h4"></a>
 179             <span class="phrase"><a name="beast.ref.boost__beast__websocket__stream.async_handshake.overload2.see_also"></a></span><a class="link" href="overload2.html#beast.ref.boost__beast__websocket__stream.async_handshake.overload2.see_also">See
 180             Also</a>
 181           </h7><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
 182 <li class="listitem">
 183                 <a href="https://tools.ietf.org/html/rfc6455#section-4.1" target="_top">Websocket
 184                 Opening Handshake Client Requirements (RFC6455)</a>
 185               </li>
 186 <li class="listitem">
 187                 <a href="https://tools.ietf.org/html/rfc7230#section-5.4" target="_top">Host
 188                 field (RFC7230)</a>
 189               </li>
 190 <li class="listitem">
 191                 <a href="https://tools.ietf.org/html/rfc7230#section-3.1.1" target="_top">request-target
 192                 (RFC7230)</a>
 193               </li>
 194 <li class="listitem">
 195                 <a href="https://tools.ietf.org/html/rfc7230#section-5.3.1" target="_top">origin-form
 196                 (RFC7230)</a>
 197               </li>
 198 </ul></div>
 199 </div>
 200 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 201 <td align="left"></td>
 202 <td align="right"><div class="copyright-footer">Copyright &#169; 2016-2019 Vinnie
 203       Falco<p>
 204         Distributed under the Boost Software License, Version 1.0. (See accompanying
 205         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
 206       </p>
 207 </div></td>
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