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<title>Stream descriptor service requirements</title>
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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.StreamDescriptorService"></a><a class="link" href="StreamDescriptorService.html" title="Stream descriptor service requirements">Stream
descriptor service requirements</a>
</h3></div></div></div>
<p>
A stream descriptor service must meet the requirements for a <a class="link" href="DescriptorService.html" title="Descriptor service requirements">descriptor
service</a>, as well as the additional requirements listed below.
</p>
<p>
In the table below, <code class="computeroutput"><span class="identifier">X</span></code> denotes
a stream descriptor service class, <code class="computeroutput"><span class="identifier">a</span></code>
denotes a value of type <code class="computeroutput"><span class="identifier">X</span></code>,
<code class="computeroutput"><span class="identifier">b</span></code> denotes a value of type
<code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">implementation_type</span></code>, <code class="computeroutput"><span class="identifier">ec</span></code>
denotes a value of type <code class="computeroutput"><span class="identifier">error_code</span></code>,
<code class="computeroutput"><span class="identifier">mb</span></code> denotes a value satisfying
<a class="link" href="MutableBufferSequence.html" title="Mutable buffer sequence requirements">mutable buffer
sequence</a> requirements, <code class="computeroutput"><span class="identifier">rh</span></code>
denotes a value meeting <a class="link" href="ReadHandler.html" title="Read handler requirements"><code class="computeroutput"><span class="identifier">ReadHandler</span></code></a> requirements, <code class="computeroutput"><span class="identifier">cb</span></code> denotes a value satisfying <a class="link" href="ConstBufferSequence.html" title="Constant buffer sequence requirements">constant
buffer sequence</a> requirements, and <code class="computeroutput"><span class="identifier">wh</span></code>
denotes a value meeting <a class="link" href="WriteHandler.html" title="Write handler requirements"><code class="computeroutput"><span class="identifier">WriteHandler</span></code></a> requirements.
</p>
<div class="table">
<a name="boost_asio.reference.StreamDescriptorService.t0"></a><p class="title"><b>Table 31. StreamDescriptorService requirements</b></p>
<div class="table-contents"><table class="table" summary="StreamDescriptorService requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
expression
</p>
</th>
<th>
<p>
return type
</p>
</th>
<th>
<p>
assertion/note<br> pre/post-condition
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">read_some</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
<span class="identifier">mb</span><span class="special">,</span>
<span class="identifier">ec</span><span class="special">);</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">size_t</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
<br> Reads one or more bytes of data from a descriptor <code class="computeroutput"><span class="identifier">b</span></code>.<br> <br> The mutable buffer
sequence <code class="computeroutput"><span class="identifier">mb</span></code> specifies
memory where the data should be placed. The operation shall always
fill a buffer in the sequence completely before proceeding to the
next.<br> <br> If successful, returns the number of bytes read.
Otherwise returns <code class="computeroutput"><span class="number">0</span></code>.
If the total size of all buffers in the sequence <code class="computeroutput"><span class="identifier">mb</span></code> is <code class="computeroutput"><span class="number">0</span></code>,
the function shall return <code class="computeroutput"><span class="number">0</span></code>
immediately.<br> <br> If the operation completes due to graceful
connection closure by the peer, the operation shall fail with
<code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">eof</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
<span class="identifier">mb</span><span class="special">,</span>
<span class="identifier">rh</span><span class="special">);</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
<br> Initiates an asynchronous operation to read one or more
bytes of data from a descriptor <code class="computeroutput"><span class="identifier">b</span></code>.
The operation is performed via the <code class="computeroutput"><span class="identifier">io_service</span></code>
object <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">get_io_service</span><span class="special">()</span></code>
and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous
operation</a> requirements.<br> <br> The mutable buffer
sequence <code class="computeroutput"><span class="identifier">mb</span></code> specifies
memory where the data should be placed. The operation shall always
fill a buffer in the sequence completely before proceeding to the
next.<br> <br> The implementation shall maintain one or more
copies of <code class="computeroutput"><span class="identifier">mb</span></code> until
such time as the read operation no longer requires access to the
memory specified by the buffers in the sequence. The program must
ensure the memory is valid until:<br> <br> — the last copy of
<code class="computeroutput"><span class="identifier">mb</span></code> is destroyed,
or<br> <br> — the handler for the asynchronous operation is invoked,<br>
<br> whichever comes first. If the total size of all buffers
in the sequence <code class="computeroutput"><span class="identifier">mb</span></code>
is <code class="computeroutput"><span class="number">0</span></code>, the asynchronous
read operation shall complete immediately and pass <code class="computeroutput"><span class="number">0</span></code> as the argument to the handler
that specifies the number of bytes read.<br> <br> If the operation
completes due to graceful connection closure by the peer, the operation
shall fail with <code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">eof</span></code>.<br>
<br> If the operation completes successfully, the <code class="computeroutput"><span class="identifier">ReadHandler</span></code> object <code class="computeroutput"><span class="identifier">rh</span></code> is invoked with the number
of bytes transferred. Otherwise it is invoked with <code class="computeroutput"><span class="number">0</span></code>.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">write_some</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
<span class="identifier">cb</span><span class="special">,</span>
<span class="identifier">ec</span><span class="special">);</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="identifier">size_t</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
<br> Writes one or more bytes of data to a descriptor <code class="computeroutput"><span class="identifier">b</span></code>.<br> <br> The constant
buffer sequence <code class="computeroutput"><span class="identifier">cb</span></code>
specifies memory where the data to be written is located. The operation
shall always write a buffer in the sequence completely before proceeding
to the next.<br> <br> If successful, returns the number of
bytes written. Otherwise returns <code class="computeroutput"><span class="number">0</span></code>.
If the total size of all buffers in the sequence <code class="computeroutput"><span class="identifier">cb</span></code> is <code class="computeroutput"><span class="number">0</span></code>,
the function shall return <code class="computeroutput"><span class="number">0</span></code>
immediately.
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">async_write_some</span><span class="special">(</span><span class="identifier">b</span><span class="special">,</span>
<span class="identifier">cb</span><span class="special">,</span>
<span class="identifier">wh</span><span class="special">);</span></code>
</p>
</td>
<td>
<p>
<code class="computeroutput"><span class="keyword">void</span></code>
</p>
</td>
<td>
<p>
pre: <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">is_open</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>.<br>
<br> Initiates an asynchronous operation to write one or more
bytes of data to a descriptor <code class="computeroutput"><span class="identifier">b</span></code>.
The operation is performed via the <code class="computeroutput"><span class="identifier">io_service</span></code>
object <code class="computeroutput"><span class="identifier">a</span><span class="special">.</span><span class="identifier">get_io_service</span><span class="special">()</span></code>
and behaves according to <a class="link" href="asynchronous_operations.html" title="Requirements on asynchronous operations">asynchronous
operation</a> requirements.<br> <br> The constant buffer
sequence <code class="computeroutput"><span class="identifier">cb</span></code> specifies
memory where the data to be written is located. The operation shall
always write a buffer in the sequence completely before proceeding
to the next.<br> <br> The implementation shall maintain one
or more copies of <code class="computeroutput"><span class="identifier">cb</span></code>
until such time as the write operation no longer requires access
to the memory specified by the buffers in the sequence. The program
must ensure the memory is valid until:<br> <br> — the last copy
of <code class="computeroutput"><span class="identifier">cb</span></code> is destroyed,
or<br> <br> — the handler for the asynchronous operation is invoked,<br>
<br> whichever comes first. If the total size of all buffers
in the sequence <code class="computeroutput"><span class="identifier">cb</span></code>
is <code class="computeroutput"><span class="number">0</span></code>, the asynchronous
operation shall complete immediately and pass <code class="computeroutput"><span class="number">0</span></code>
as the argument to the handler that specifies the number of bytes
read.<br> <br> If the operation completes successfully, the
<code class="computeroutput"><span class="identifier">WriteHandler</span></code> object
<code class="computeroutput"><span class="identifier">wh</span></code> is invoked with
the number of bytes transferred. Otherwise it is invoked with
<code class="computeroutput"><span class="number">0</span></code>.
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break">
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2014 Christopher M. Kohlhoff<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
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>)
</p>
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