1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>http::async_read_header</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. 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23<a accesskey="p" href="boost__beast__http__read_header/overload2.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../ref.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="boost__beast__http__read.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="beast.ref.boost__beast__http__async_read_header"></a><a class="link" href="boost__beast__http__async_read_header.html" title="http::async_read_header">http::async_read_header</a> 28</h4></div></div></div> 29<p> 30 <a class="indexterm" name="idm46057506171168"></a> 31 </p> 32<p> 33 Read a complete message header asynchronously from a stream using a parser. 34 </p> 35<h5> 36<a name="beast.ref.boost__beast__http__async_read_header.h0"></a> 37 <span class="phrase"><a name="beast.ref.boost__beast__http__async_read_header.synopsis"></a></span><a class="link" href="boost__beast__http__async_read_header.html#beast.ref.boost__beast__http__async_read_header.synopsis">Synopsis</a> 38 </h5> 39<p> 40 Defined in header <code class="literal"><<a href="../../../../../../boost/beast/http/read.hpp" target="_top">boost/beast/http/read.hpp</a>></code> 41 </p> 42<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> 43 <span class="keyword">class</span> <a href="../../../../../../doc/html/boost_asio/reference/AsyncReadStream.html" target="_top"><span class="emphasis"><em>AsyncReadStream</em></span></a><span class="special">,</span> 44 <span class="keyword">class</span> <a class="link" href="../concepts/DynamicBuffer.html" title="DynamicBuffer"><span class="emphasis"><em>DynamicBuffer</em></span></a><span class="special">,</span> 45 <span class="keyword">bool</span> <span class="identifier">isRequest</span><span class="special">,</span> 46 <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> <span class="identifier">executor_type</span><span class="special"><</span><span class="identifier">AsyncReadStream</span><span class="special">>>></span> 47<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> 48<span class="identifier">async_read_header</span><span class="special">(</span> 49 <span class="identifier">AsyncReadStream</span><span class="special">&</span> <span class="identifier">stream</span><span class="special">,</span> 50 <span class="identifier">DynamicBuffer</span><span class="special">&</span> <span class="identifier">buffer</span><span class="special">,</span> 51 <span class="identifier">basic_parser</span><span class="special"><</span> <span class="identifier">isRequest</span> <span class="special">>&</span> <span class="identifier">parser</span><span class="special">,</span> 52 <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="boost__beast__executor_type.html" title="executor_type">executor_type</a><span class="special"><</span> <span class="identifier">AsyncReadStream</span> <span class="special">>>{});</span> 53</pre> 54<h5> 55<a name="beast.ref.boost__beast__http__async_read_header.h1"></a> 56 <span class="phrase"><a name="beast.ref.boost__beast__http__async_read_header.description"></a></span><a class="link" href="boost__beast__http__async_read_header.html#beast.ref.boost__beast__http__async_read_header.description">Description</a> 57 </h5> 58<p> 59 This function is used to asynchronously read a complete message header from 60 a stream into an instance of <a class="link" href="boost__beast__http__basic_parser.html" title="http::basic_parser"><code class="computeroutput"><span class="identifier">basic_parser</span></code></a>. The function call 61 always returns immediately. The asynchronous operation will continue until 62 one of the following conditions is true: 63 </p> 64<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 65<li class="listitem"> 66 <a class="link" href="boost__beast__http__basic_parser/is_header_done.html" title="http::basic_parser::is_header_done"><code class="computeroutput"><span class="identifier">basic_parser</span><span class="special">::</span><span class="identifier">is_header_done</span></code></a> returns <code class="computeroutput"><span class="keyword">true</span></code> 67 </li> 68<li class="listitem"> 69 An error occurs. 70 </li> 71</ul></div> 72<p> 73 This operation is implemented in terms of zero or more calls to the next 74 layer's <code class="computeroutput"><span class="identifier">async_read_some</span></code> function, 75 and is known as a <span class="emphasis"><em>composed operation</em></span>. The program must 76 ensure that the stream performs no other reads until this operation completes. 77 The implementation may read additional bytes from the stream that lie past 78 the end of the message being read. These additional bytes are stored in the 79 dynamic buffer, which must be preserved for subsequent reads. If the end 80 of file error is received while reading from the stream, then the error returned 81 from this function will be: 82 </p> 83<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 84<li class="listitem"> 85 <a class="link" href="boost__beast__http__error.html" title="http::error"><code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">end_of_stream</span></code></a> 86 if no bytes were parsed, or 87 </li> 88<li class="listitem"> 89 <a class="link" href="boost__beast__http__error.html" title="http::error"><code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">partial_message</span></code></a> 90 if any bytes were parsed but the message was incomplete, otherwise: 91 </li> 92<li class="listitem"> 93 A successful result. The next attempt to read will return <a class="link" href="boost__beast__http__error.html" title="http::error"><code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">end_of_stream</span></code></a> 94 </li> 95</ul></div> 96<h5> 97<a name="beast.ref.boost__beast__http__async_read_header.h2"></a> 98 <span class="phrase"><a name="beast.ref.boost__beast__http__async_read_header.parameters"></a></span><a class="link" href="boost__beast__http__async_read_header.html#beast.ref.boost__beast__http__async_read_header.parameters">Parameters</a> 99 </h5> 100<div class="informaltable"><table class="table"> 101<colgroup> 102<col> 103<col> 104</colgroup> 105<thead><tr> 106<th> 107 <p> 108 Name 109 </p> 110 </th> 111<th> 112 <p> 113 Description 114 </p> 115 </th> 116</tr></thead> 117<tbody> 118<tr> 119<td> 120 <p> 121 <code class="computeroutput"><span class="identifier">stream</span></code> 122 </p> 123 </td> 124<td> 125 <p> 126 The stream from which the data is to be read. The type must meet 127 the <span class="emphasis"><em>AsyncReadStream</em></span> requirements. 128 </p> 129 </td> 130</tr> 131<tr> 132<td> 133 <p> 134 <code class="computeroutput"><span class="identifier">buffer</span></code> 135 </p> 136 </td> 137<td> 138 <p> 139 Storage for additional bytes read by the implementation from the 140 stream. This is both an input and an output parameter; on entry, 141 the parser will be presented with any remaining data in the dynamic 142 buffer's readable bytes sequence first. The type must meet the 143 <span class="emphasis"><em>DynamicBuffer</em></span> requirements. The object must 144 remain valid at least until the handler is called; ownership is 145 not transferred. 146 </p> 147 </td> 148</tr> 149<tr> 150<td> 151 <p> 152 <code class="computeroutput"><span class="identifier">parser</span></code> 153 </p> 154 </td> 155<td> 156 <p> 157 The parser to use. The object must remain valid at least until 158 the handler is called; ownership is not transferred. 159 </p> 160 </td> 161</tr> 162<tr> 163<td> 164 <p> 165 <code class="computeroutput"><span class="identifier">handler</span></code> 166 </p> 167 </td> 168<td> 169 <p> 170 The completion handler to invoke when the operation completes. 171 The implementation takes ownership of the handler by performing 172 a decay-copy. The equivalent function signature of the handler 173 must be: 174 </p> 175<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> 176 <span class="identifier">error_code</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">error</span><span class="special">,</span> <span class="comment">// result of operation</span> 177 <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">bytes_transferred</span> <span class="comment">// the total number of bytes transferred from the stream</span> 178<span class="special">);</span> 179</pre> 180 <p> 181 Regardless of whether the asynchronous operation completes immediately 182 or not, the handler will not be invoked from within this function. 183 Invocation of the handler will be performed in a manner equivalent 184 to using <a class="link" href="boost__beast__http__verb.html" title="http::verb"><code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code></a>. 185 </p> 186 </td> 187</tr> 188</tbody> 189</table></div> 190<h5> 191<a name="beast.ref.boost__beast__http__async_read_header.h3"></a> 192 <span class="phrase"><a name="beast.ref.boost__beast__http__async_read_header.remarks"></a></span><a class="link" href="boost__beast__http__async_read_header.html#beast.ref.boost__beast__http__async_read_header.remarks">Remarks</a> 193 </h5> 194<p> 195 The completion handler will receive as a parameter the total number of bytes 196 transferred from the stream. This may be zero for the case where there is 197 sufficient pre-existing message data in the dynamic buffer. The implementation 198 will call <a class="link" href="boost__beast__http__basic_parser/eager/overload1.html" title="http::basic_parser::eager (1 of 2 overloads)"><code class="computeroutput"><span class="identifier">basic_parser</span><span class="special">::</span><span class="identifier">eager</span></code></a> with the value <code class="computeroutput"><span class="keyword">false</span></code> on the parser passed in. 199 </p> 200</div> 201<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 202<td align="left"></td> 203<td align="right"><div class="copyright-footer">Copyright © 2016-2019 Vinnie 204 Falco<p> 205 Distributed under the Boost Software License, Version 1.0. (See accompanying 206 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>) 207 </p> 208</div></td> 209</tr></table> 210<hr> 211<div class="spirit-nav"> 212<a accesskey="p" href="boost__beast__http__read_header/overload2.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../ref.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="boost__beast__http__read.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 213</div> 214</body> 215</html> 216
