1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>basic_stream::async_read_some</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="../boost__beast__basic_stream.html" title="basic_stream"> 9<link rel="prev" href="read_some/overload2.html" title="basic_stream::read_some (2 of 2 overloads)"> 10<link rel="next" href="write_some.html" title="basic_stream::write_some"> 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="read_some/overload2.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost__beast__basic_stream.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="write_some.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h5 class="title"> 27<a name="beast.ref.boost__beast__basic_stream.async_read_some"></a><a class="link" href="async_read_some.html" title="basic_stream::async_read_some">basic_stream::async_read_some</a> 28</h5></div></div></div> 29<p> 30 <a class="indexterm" name="idm46057544460048"></a> 31 </p> 32<p> 33 Read some data asynchronously. 34 </p> 35<h6> 36<a name="beast.ref.boost__beast__basic_stream.async_read_some.h0"></a> 37 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.synopsis"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.synopsis">Synopsis</a> 38 </h6> 39<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> 40 <span class="keyword">class</span> <a href="../../../../../../../doc/html/boost_asio/reference/MutableBufferSequence.html" target="_top"><span class="emphasis"><em>MutableBufferSequence</em></span></a><span class="special">,</span> 41 <span class="keyword">class</span> <a href="../../../../../../../doc/html/boost_asio/reference/ReadHandler.html" target="_top"><span class="emphasis"><em>ReadHandler</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> 42<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> 43<span class="identifier">async_read_some</span><span class="special">(</span> 44 <span class="identifier">MutableBufferSequence</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">buffers</span><span class="special">,</span> 45 <span class="identifier">ReadHandler</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> 46</pre> 47<h6> 48<a name="beast.ref.boost__beast__basic_stream.async_read_some.h1"></a> 49 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.description"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.description">Description</a> 50 </h6> 51<p> 52 This function is used to asynchronously read data from the stream. This 53 call always returns immediately. The asynchronous operation will continue 54 until one of the following conditions is true: 55 </p> 56<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 57<li class="listitem"> 58 One or more bytes are read from the stream. 59 </li> 60<li class="listitem"> 61 An error occurs. 62 </li> 63</ul></div> 64<p> 65 The algorithm, known as a <span class="emphasis"><em>composed asynchronous operation</em></span>, 66 is implemented in terms of calls to the next layer's <code class="computeroutput"><span class="identifier">async_read_some</span></code> 67 function. The program must ensure that no other calls to <a class="link" href="read_some/overload1.html" title="basic_stream::read_some (1 of 2 overloads)"><code class="computeroutput"><span class="identifier">read_some</span></code></a> or <a class="link" href="async_read_some.html" title="basic_stream::async_read_some"><code class="computeroutput"><span class="identifier">async_read_some</span></code></a> are performed 68 until this operation completes. If the timeout timer expires while the 69 operation is outstanding, the operation will be canceled and the completion 70 handler will be invoked with 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>. 71 </p> 72<h6> 73<a name="beast.ref.boost__beast__basic_stream.async_read_some.h2"></a> 74 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.parameters"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.parameters">Parameters</a> 75 </h6> 76<div class="informaltable"><table class="table"> 77<colgroup> 78<col> 79<col> 80</colgroup> 81<thead><tr> 82<th> 83 <p> 84 Name 85 </p> 86 </th> 87<th> 88 <p> 89 Description 90 </p> 91 </th> 92</tr></thead> 93<tbody> 94<tr> 95<td> 96 <p> 97 <code class="computeroutput"><span class="identifier">buffers</span></code> 98 </p> 99 </td> 100<td> 101 <p> 102 The buffers into which the data will be read. If the size of 103 the buffers is zero bytes, the operation always completes immediately 104 with no error. Although the buffers object may be copied as necessary, 105 ownership of the underlying memory blocks is retained by the 106 caller, which must guarantee that they remain valid until the 107 handler is called. 108 </p> 109 </td> 110</tr> 111<tr> 112<td> 113 <p> 114 <code class="computeroutput"><span class="identifier">handler</span></code> 115 </p> 116 </td> 117<td> 118 <p> 119 The completion handler to invoke when the operation completes. 120 The implementation takes ownership of the handler by performing 121 a decay-copy. The equivalent function signature of the handler 122 must be: 123 </p> 124<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> 125 <span class="identifier">error_code</span> <span class="identifier">error</span><span class="special">,</span> <span class="comment">// Result of operation.</span> 126 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span> <span class="comment">// Number of bytes read.</span> 127<span class="special">);</span> 128</pre> 129 <p> 130 Regardless of whether the asynchronous operation completes immediately 131 or not, the handler will not be invoked from within this function. 132 Invocation of the handler will be performed in a manner equivalent 133 to using <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code>. 134 </p> 135 </td> 136</tr> 137</tbody> 138</table></div> 139<h6> 140<a name="beast.ref.boost__beast__basic_stream.async_read_some.h3"></a> 141 <span class="phrase"><a name="beast.ref.boost__beast__basic_stream.async_read_some.remarks"></a></span><a class="link" href="async_read_some.html#beast.ref.boost__beast__basic_stream.async_read_some.remarks">Remarks</a> 142 </h6> 143<p> 144 The <code class="computeroutput"><span class="identifier">async_read_some</span></code> operation 145 may not receive all of the requested number of bytes. Consider using the 146 function <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">async_read</span></code> if you need to ensure that 147 the requested amount of data is read before the asynchronous operation 148 completes. 149 </p> 150</div> 151<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 152<td align="left"></td> 153<td align="right"><div class="copyright-footer">Copyright © 2016-2019 Vinnie 154 Falco<p> 155 Distributed under the Boost Software License, Version 1.0. (See accompanying 156 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>) 157 </p> 158</div></td> 159</tr></table> 160<hr> 161<div class="spirit-nav"> 162<a accesskey="p" href="read_some/overload2.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost__beast__basic_stream.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="write_some.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> 163</div> 164</body> 165</html> 166
