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  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="idm45873516462464"></a>
  31 Read some data asynchronously.
  32         </p>
  33 <h6>
  34 <a name="beast.ref.boost__beast__basic_stream.async_read_some.h0"></a>
  35           <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>
  36         </h6>
  37 <pre class="programlisting"><span class="keyword">template</span><span class="special">&lt;</span>
  38     <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>
  39     <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">&lt;</span><span class="identifier">executor_type</span><span class="special">&gt;&gt;</span>
  40 <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>
  41 <span class="identifier">async_read_some</span><span class="special">(</span>
  42     <span class="identifier">MutableBufferSequence</span> <span class="keyword">const</span><span class="special">&amp;</span> <span class="identifier">buffers</span><span class="special">,</span>
  43     <span class="identifier">ReadHandler</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>
  44 </pre>
  45 <h6>
  46 <a name="beast.ref.boost__beast__basic_stream.async_read_some.h1"></a>
  47           <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>
  48         </h6>
  49 <p>
  50           This function is used to asynchronously read data from the stream. This
  51           call always returns immediately. The asynchronous operation will continue
  52           until one of the following conditions is true:
  53         </p>
  54 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
  55 <li class="listitem">
  56               One or more bytes are read from the stream.
  57             </li>
  58 <li class="listitem">
  59               An error occurs.
  60             </li>
  61 </ul></div>
  62 <p>
  63           The algorithm, known as a <span class="emphasis"><em>composed asynchronous operation</em></span>,
  64           is implemented in terms of calls to the next layer's <code class="computeroutput"><span class="identifier">async_read_some</span></code>
  65           function. The program must ensure that no other calls to <a class="link" href="read_some.html" title="basic_stream::read_some"><code class="computeroutput"><span class="identifier">basic_stream</span><span class="special">::</span><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">basic_stream</span><span class="special">::</span><span class="identifier">async_read_some</span></code></a> are performed
  66           until this operation completes. If the timeout timer expires while the
  67           operation is outstanding, the operation will be canceled and the completion
  68           handler will be invoked with the error <a class="link" href="../boost__beast__error.html" title="error"><code class="computeroutput"><span class="identifier">timeout</span></code></a>.
  69         </p>
  70 <h6>
  71 <a name="beast.ref.boost__beast__basic_stream.async_read_some.h2"></a>
  72           <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>
  73         </h6>
  74 <div class="informaltable"><table class="table">
  75 <colgroup>
  76 <col>
  77 <col>
  78 </colgroup>
  79 <thead><tr>
  80 <th>
  81                   <p>
  82                     Name
  83                   </p>
  84                 </th>
  85 <th>
  86                   <p>
  87                     Description
  88                   </p>
  89                 </th>
  90 </tr></thead>
  91 <tbody>
  92 <tr>
  93 <td>
  94                   <p>
  95                     <code class="computeroutput"><span class="identifier">buffers</span></code>
  96                   </p>
  97                 </td>
  98 <td>
  99                   <p>
 100                     The buffers into which the data will be read. If the size of
 101                     the buffers is zero bytes, the operation always completes immediately
 102                     with no error. Although the buffers object may be copied as necessary,
 103                     ownership of the underlying memory blocks is retained by the
 104                     caller, which must guarantee that they remain valid until the
 105                     handler is called.
 106                   </p>
 107                 </td>
 108 </tr>
 109 <tr>
 110 <td>
 111                   <p>
 112                     <code class="computeroutput"><span class="identifier">handler</span></code>
 113                   </p>
 114                 </td>
 115 <td>
 116                   <p>
 117                     The completion handler to invoke when the operation completes.
 118                     The implementation takes ownership of the handler by performing
 119                     a decay-copy. The equivalent function signature of the handler
 120                     must be:
 121                   </p>
 122 <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>
 123     <span class="identifier">error_code</span> <span class="identifier">error</span><span class="special">,</span>               <span class="comment">// Result of operation.</span>
 124     <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>
 125 <span class="special">);</span>
 126 </pre>
 127                   <p>
 128                     Regardless of whether the asynchronous operation completes immediately
 129                     or not, the handler will not be invoked from within this function.
 130                     Invocation of the handler will be performed in a manner equivalent
 131                     to using <code class="computeroutput"><span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span></code>.
 132                   </p>
 133                 </td>
 134 </tr>
 135 </tbody>
 136 </table></div>
 137 <h6>
 138 <a name="beast.ref.boost__beast__basic_stream.async_read_some.h3"></a>
 139           <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>
 140         </h6>
 141 <p>
 142           The <code class="computeroutput"><span class="identifier">async_read_some</span></code> operation
 143           may not receive all of the requested number of bytes. Consider using the
 144           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
 145           the requested amount of data is read before the asynchronous operation
 146           completes.
 147         </p>
 148 </div>
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