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POboost::asio::async_read into boost::asio::streambuf blocks when streambuf is populated by previous async_read
 

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  1. POboost::asio::async_read into boost::asio::streambuf blocks when streambuf is populated by previous async_read
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    <p>I have searched other posts, but didn't found anything relevant. Now, I have a protocol consisting of header and body. Protocol is like: Z24,91009802,123456789ABCDEF Where Z24, is the header. Z is message type, 24 is remaining bytes to read. Remaining bytes is variable, so I read until first ',' is found.</p> <pre><code>void handle_handshake(const boost::system::error_code&amp; error) { if (!error) { boost::asio::async_read_until( socket_, inputStreamBuffer_, ',', boost::bind( &amp;session::doReadHeader, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred) ); } else { delete this; } } void doReadHeader( const boost::system::error_code&amp; error, size_t bytes_transferred) { if (!error) { istream is(&amp;inputStreamBuffer_); vector&lt;char&gt; v(bytes_transferred); is.read(&amp;(v[0]),bytes_transferred); request_.append(v.begin(),v.end()); cout &lt;&lt; "request_=#" &lt;&lt; request_ &lt;&lt; "#" &lt;&lt; endl; int nBytes=string_to_llint(request_.substr(1,request_.size()-2)); cout &lt;&lt; "nBytes=" &lt;&lt; nBytes &lt;&lt; endl; cout &lt;&lt; "size=" &lt;&lt; inputStreamBuffer_.size() &lt;&lt; endl; boost::asio::async_read( socket_, inputStreamBuffer_, boost::asio::transfer_at_least(nBytes), boost::bind( &amp;session::doReadBody, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred) ); } else { delete this; } } void doReadBody( const boost::system::error_code&amp; error, size_t bytes_transferred) { if (!error) { istream is(&amp;inputStreamBuffer_); vector&lt;char&gt; v(bytes_transferred); is.read(&amp;(v[0]),bytes_transferred); request_.append(v.begin(),v.end()); string response=cardIssueProcessor_.process(request_); cout &lt;&lt; "request=#" &lt;&lt; request_ &lt;&lt; "#" &lt;&lt; endl; cout &lt;&lt; "response=#" &lt;&lt; response &lt;&lt; "#" &lt;&lt; endl; request_.clear(); boost::asio::async_write( socket_, boost::asio::buffer(response, response.size()), boost::bind( &amp;session::doWriteResponse, this, boost::asio::placeholders::error) ); } else { delete this; } } </code></pre> <p>Now, the header is read. But reading the footer blocks. Apparently the entire message is read in the header call. When I do the second async_read() with boost::asio::transfer_at_least(nBytes), nBytes are already in inputStreamBuffer_, but I think the call doesn't check this?</p> <p>This is dump from the output:</p> <p>request_=#Z24,# nBytes=24 size=24</p> <p>What is the problem, or how can I workaround it. I am a boost newbie, so all help appreciated. Thank you.</p> <p>EDIT: I tried to check the buffer fullness, and don't make async_read() call for the body if it happens to be already read by previous call. It kind of works, but is it the right solution?</p> <pre><code>void doReadHeader( const boost::system::error_code&amp; error, size_t bytes_transferred) { if (!error) { istream is(&amp;inputStreamBuffer_); vector&lt;char&gt; v(bytes_transferred); is.read(&amp;(v[0]),bytes_transferred); request_.assign(v.begin(),v.end()); cout &lt;&lt; "request_=#" &lt;&lt; request_ &lt;&lt; "#" &lt;&lt; endl; int nBytes=string_to_llint(request_.substr(1,request_.size()-2)); cout &lt;&lt; "nBytes=" &lt;&lt; nBytes &lt;&lt; endl; cout &lt;&lt; "size=" &lt;&lt; inputStreamBuffer_.size() &lt;&lt; endl; size_t toReadBytes=nBytes-inputStreamBuffer_.size(); if (toReadBytes&gt;0) { boost::asio::async_read( socket_, inputStreamBuffer_, boost::asio::transfer_at_least(toReadBytes), boost::bind( &amp;session::doReadBody, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred) ); } else { doReadBody(error,nBytes); } } else { delete this; } } </code></pre>
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    1. USildjarn
    1. USDragomir Ivanov
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    1. COI tried to check the buffer fillness, before doing async_read() for the body. I kind of works. Is it the right solution?
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      1. POboost::asio::async_read into boost::asio::streambuf blocks when streambuf is populated by previous async_read
      1. USDragomir Ivanov
    2. COI'm not sure if your requirements allow you to do this, but it's usually easier to use an integer value of a defined byte size to represent the remaining bytes to read instead of a variable length string.
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      1. POboost::asio::async_read into boost::asio::streambuf blocks when streambuf is populated by previous async_read
      1. USdevyndraen
 

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