1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>basic_stream::async_connect (3 of 5 overloads)</title> 5<link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../../../index.html" title="Chapter 1. Boost.Beast"> 8<link rel="up" href="../async_connect.html" title="basic_stream::async_connect"> 9<link rel="prev" href="overload2.html" title="basic_stream::async_connect (2 of 5 overloads)"> 10<link rel="next" href="overload4.html" title="basic_stream::async_connect (4 of 5 overloads)"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> 15<td align="center"><a href="../../../../../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="overload2.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_connect.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload4.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h6 class="title"> 27<a name="beast.ref.boost__beast__basic_stream.async_connect.overload3"></a><a class="link" href="overload3.html" title="basic_stream::async_connect (3 of 5 overloads)">basic_stream::async_connect 28 (3 of 5 overloads)</a> 29</h6></div></div></div> 30<p> 31 Establishes a connection by trying each endpoint in a sequence asynchronously. 32 </p> 33<h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h0"></a> 34 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.synopsis"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.synopsis">Synopsis</a> 35 </h7><pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> 36 <span class="keyword">class</span> <a href="../../../../../../../../doc/html/boost_asio/reference/EndpointSequence.html" target="_top"><span class="emphasis"><em>EndpointSequence</em></span></a><span class="special">,</span> 37 <span class="keyword">class</span> <a href="../../../../../../../../doc/html/boost_asio/reference/ConnectCondition.html" target="_top"><span class="emphasis"><em>ConnectCondition</em></span></a><span class="special">,</span> 38 <span class="keyword">class</span> <a href="../../../../../../../../doc/html/boost_asio/reference/RangeConnectHandler.html" target="_top"><span class="emphasis"><em>RangeConnectHandler</em></span></a> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">default_completion_token_t</span><span class="special"><</span><a class="link" href="../executor_type.html" title="basic_stream::executor_type">executor_type</a><span class="special">>></span> 39<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> 40<span class="identifier">async_connect</span><span class="special">(</span> 41 <span class="identifier">EndpointSequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">endpoints</span><span class="special">,</span> 42 <span class="identifier">ConnectCondition</span> <span class="identifier">connect_condition</span><span class="special">,</span> 43 <span class="identifier">RangeConnectHandler</span><span class="special">&&</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"><</span> <a class="link" href="../executor_type.html" title="basic_stream::executor_type">executor_type</a> <span class="special">>{});</span> 44</pre> 45<h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h1"></a> 46 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.description"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.description">Description</a> 47 </h7><p> 48 This function attempts to connect the stream to one of a sequence of 49 endpoints by trying each endpoint until a connection is successfully 50 established. The underlying socket is automatically opened if needed. 51 An automatically opened socket is not returned to the closed state upon 52 failure. The algorithm, known as a <span class="emphasis"><em>composed asynchronous operation</em></span>, 53 is implemented in terms of calls to the underlying socket's <code class="computeroutput"><span class="identifier">async_connect</span></code> function. If the timeout 54 timer expires while the operation is outstanding, the current connection 55 attempt will be canceled and the completion handler will be invoked with 56 the error <a class="link" href="../../boost__beast__error.html" title="error"><code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">timeout</span></code></a>. 57 </p> 58<h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h2"></a> 59 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.parameters"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.parameters">Parameters</a> 60 </h7><div class="informaltable"><table class="table"> 61<colgroup> 62<col> 63<col> 64</colgroup> 65<thead><tr> 66<th> 67 <p> 68 Name 69 </p> 70 </th> 71<th> 72 <p> 73 Description 74 </p> 75 </th> 76</tr></thead> 77<tbody> 78<tr> 79<td> 80 <p> 81 <code class="computeroutput"><span class="identifier">endpoints</span></code> 82 </p> 83 </td> 84<td> 85 <p> 86 A sequence of endpoints. This this object must meet the requirements 87 of <span class="emphasis"><em>EndpointSequence</em></span>. 88 </p> 89 </td> 90</tr> 91<tr> 92<td> 93 <p> 94 <code class="computeroutput"><span class="identifier">connect_condition</span></code> 95 </p> 96 </td> 97<td> 98 <p> 99 A function object that is called prior to each connection attempt. 100 The signature of the function object must be: 101 </p> 102<pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="keyword">bool</span> <span class="identifier">connect_condition</span><span class="special">(</span> 103 <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span> 104 <span class="keyword">typename</span> <span class="identifier">Protocol</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">next</span><span class="special">);</span> 105</pre> 106 <p> 107 The <code class="computeroutput"><span class="identifier">ec</span></code> parameter 108 contains the result from the most recent connect operation. 109 Before the first connection attempt, <code class="computeroutput"><span class="identifier">ec</span></code> 110 is always set to indicate success. The <code class="computeroutput"><span class="identifier">next</span></code> 111 parameter is the next endpoint to be tried. The function object 112 should return true if the next endpoint should be tried, and 113 false if it should be skipped. 114 </p> 115 </td> 116</tr> 117<tr> 118<td> 119 <p> 120 <code class="computeroutput"><span class="identifier">handler</span></code> 121 </p> 122 </td> 123<td> 124 <p> 125 The completion handler to invoke when the operation completes. 126 The implementation takes ownership of the handler by performing 127 a decay-copy. The equivalent function signature of the handler 128 must be: 129 </p> 130<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> 131 <span class="comment">// Result of operation. if the sequence is empty, set to</span> 132 <span class="comment">// net::error::not_found. Otherwise, contains the</span> 133 <span class="comment">// error from the last connection attempt.</span> 134 <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span> 135 136 <span class="comment">// On success, the successfully connected endpoint.</span> 137 <span class="comment">// Otherwise, a default-constructed endpoint.</span> 138 <span class="keyword">typename</span> <span class="identifier">Protocol</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">endpoint</span> 139<span class="special">);</span> 140</pre> 141 <p> 142 Regardless of whether the asynchronous operation completes 143 immediately or not, the handler will not be invoked from within 144 this function. Invocation of the handler will be performed 145 in a manner equivalent to using <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code>. 146 </p> 147 </td> 148</tr> 149</tbody> 150</table></div> 151<h7><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.h3"></a> 152 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_connect.overload3.example"></a></span><a class="link" href="overload3.html#beast.ref.boost__beast__basic_stream.async_connect.overload3.example">Example</a> 153 </h7><p> 154 The following connect condition function object can be used to output 155 information about the individual connection attempts: 156 </p> 157<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_connect_condition</span> 158<span class="special">{</span> 159 <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">()(</span> 160 <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">ec</span><span class="special">,</span> 161 <span class="identifier">net</span><span class="special">::</span><span class="identifier">ip</span><span class="special">::</span><span class="identifier">tcp</span><span class="special">::</span><span class="identifier">endpoint</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">next</span><span class="special">)</span> 162 <span class="special">{</span> 163 <span class="keyword">if</span> <span class="special">(</span><span class="identifier">ec</span><span class="special">)</span> 164 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Error: "</span> <span class="special"><<</span> <span class="identifier">ec</span><span class="special">.</span><span class="identifier">message</span><span class="special">()</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 165 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Trying: "</span> <span class="special"><<</span> <span class="identifier">next</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 166 <span class="keyword">return</span> <span class="keyword">true</span><span class="special">;</span> 167 <span class="special">}</span> 168<span class="special">};</span> 169</pre> 170</div> 171<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 172<td align="left"></td> 173<td align="right"><div class="copyright-footer">Copyright © 2016-2019 Vinnie 174 Falco<p> 175 Distributed under the Boost Software License, Version 1.0. (See accompanying 176 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>) 177 </p> 178</div></td> 179</tr></table> 180<hr> 181<div class="spirit-nav"> 182<a accesskey="p" href="overload2.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../async_connect.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="overload4.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> 183</div> 184</body> 185</html> 186
