Boost Asio异步：服务器向客户端发送消息

Question

I am working on a Server/Client application. Client send a message (header+body) to the Server. The server receives the message, make some modifications and sent it back.

So the client sends the message.

async_write (m_socket,boost::asio::buffer(msg -> HeaderData() , msg -> SendLength ()),
    boost::bind ( &Client::HandleSentMessage , this ,
    boost::asio::placeholders::error , boost::asio::placeholders::bytes_transferred));

The server receives the message.

m_socket.async_read_some ( boost::asio::buffer ( *receiveBuffer ) , boost::bind( 
     &ASyncConnectionMT::HandleReceived , shared_from_this() , receiveBuffer , 
     boost::asio::placeholders::error , boost::asio::placeholders::bytes_transferred));

It goes to my function:

void HandleReceived ( BufferPtr receiveBuffer , const boost::system::error_code& ec , size_t size)

And there it changes the message received.

for ( size_t i=0 ; i!=size ; i++ )
    {
         ((*sendBuffer)[i]) = toupper((*receiveBuffer)[i]); 
    }

And sends it back.

async_write ( m_socket,  boost::asio::buffer ( *sendBuffer , size ) , m_strand.wrap( 
       boost::bind ( &ASyncConnectionMT::HandleSent ,shared_from_this() , sendBuffer, 
       boost::asio::placeholders::error,boost::asio::placeholders::bytes_transferred));

So far all good. The code is running flawlessly. But what is my problem. I receive the send message and modify it but, lets say for example I want to send back something else. For example a string.

The problem is that I have to pass buffer as shared_ptr so my object won't be destroyed after leaving this function.

typedef boost::array < char , 65536 > Buffer;
typedef boost::shared_ptr < Buffer > BufferPtr;
BufferPtr receiveBuffer ( new Buffer ) ;
BufferPtr sendBuffer ( new Buffer ) ;

I want the client to send me a message like "I am ready" and the server to send back some information. After the client receives the information, to send a new message to the client that he is ready. So the server can send the next piece of informations. Tried all day, I just can't figure out how to send a string or a char array to client.

Can you show me how to send a string or a char array or to convert them to a shared_ptr ?

Answer 1

You can copy a string to shared pointer like this if you have c++11:

auto shared_string = std::make_shared<std::string>(string_to_send);

Or with boost:

boost::shared_ptr<std::string> ptr = boost::make_shared<std::string>(string_to_send);

And than send it to socket:

async_write(m_socket, boost::asio::buffer(*shared_string), m_strand.wrap(boost::bind(&ASyncConnectionMT::HandleSent, shared_from_this() , shared_string, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));

Note that usualy it is required to send some kind of header, so the client can find out the length of the string. So you can copy string length to boost::array and send it to client first, and than send the string itself, for example.