Boost receive data from the tcp socket

问题

I am trying to read specific number of bytes from the socket. My server is sending:

1) byte[0] - length of the message 2) byte[1:N] - the actual message

How do I read the first byte and then read the remaining bytes using boost::asio::ip::tcp::socket::read ? Here is the code snippet:

 // receive data through the socket
    void TCPTestClient::ReceiveData( )
    {
        try
        {
            boost::system::error_code error;

            boost::asio::streambuf receivedStreamBuffer;

            // reserve 512 bytes in output sequence
            boost::asio::streambuf::mutable_buffers_type bufs =receivedStreamBuffer.prepare( 512 );
            boost::asio::read( m_socket,
                                   bufs,
                                   error );

            // transfer the buffer contents to string
            std::istream is( &receivedStreamBuffer );
            is >> m_receivedMessageStr;


            // throw exception if error occurred
            if ( error )
            {
                throw NetworkTestFailedException( error.message() );
            }
        }
        catch(...)
        {

        }
    }

回答1:

You'll want to prepare a buffer for the one byte header, then prepare another buffer for the message. A simplified example might be

boost::asio::read(                                                                                                                       
        m_socket,                                                                                                                        
        receivedStreamBuffer.prepare(1),                                                                                                 
        error                                                                                                                            
        );                                                                                                                               

if ( error ) {                                                                                                                           
    std::cerr << "Read header failed: " << boost::system::system_error(error).what() << std::endl;                                       
    return;                                                                                                                              
}                                                                                                                                        
receivedStreamBuffer.commit(1);                                                                                                          
std::istream header( &receivedStreamBuffer );                                                                                            
uint8_t size;                                                                                                                            
header >> size;                                                                                                                          

// reserve message size in output sequence                                                                                               
boost::asio::read(                                                                                                                       
        m_socket,                                                                                                                        
        receivedStreamBuffer.prepare( size ),                                                                                                 
        bufs,                                                                                                                            
        error                                                                                                                            
        );                                                                                                                               
if ( error ) {                                                                                                                           
    std::cerr << "Read message failed: " << boost::system::system_error(error).what() << std::endl;                                      
    return;                                                                                                                              
}                                                                                                                                        
receivedStreamBuffer.commit( size );                                                                                                     

// transfer the buffer contents to string                                                                                                
std::istream is( &receivedStreamBuffer );                                                                                                
is >> m_receivedMessageStr;    

来源：https://stackoverflow.com/questions/14324060/boost-receive-data-from-the-tcp-socket