hen the send operation completes. Copies
                  will be made of the handler as required. The function signature
                  of the handler must be:
</p>
<pre class="programlisting">void handler(
  const boost::system::error_code&amp; error, // Result of operation.
  std::size_t bytes_transferred           // Number of bytes sent.
);
</pre>
<p>
                  Regardless of whether the asynchronous operation completes immediately
                  or not, the handler will not be invoked fr