boost::asio 中async_read與async_receive的區別

boost::asio 中async_read與async_receive的區別

現象：在調用async_read後，即便收到數據包，也沒有調用相應的ReadHandler 回調函數


void handle_connect(const boost::system::error_code & error,
       tcp::resolver::iterator endpoint_iterator)
   {
       if(!error)
       {
           socket_.async_receive(boost::asio::buffer(buf_),            
               boost::bind(&tcp_client::handler_read_response,this,
               boost::asio::placeholders::error,
               boost::asio::placeholders::bytes_transferred));
                       //直到收到的字節數可以填滿buf_(即256個字節)或出錯，才調用handler_read_responsehandler_read_response;不然即便收到包也不進行處理。

           boost::asio::async_read(socket_,boost::asio::buffer(buf_),
               boost::bind(&tcp_client::handler_read_response,this,
               boost::asio::placeholders::error,
               boost::asio::placeholders::bytes_transferred));
                     //一旦收到數據或出錯，就調用handler_read_response
       }
}
tcp::socket socket_;
boost::array buf_;
void handler_read_response(const boost::system::error_code & error, size_t /*bytes_transferred*/) //注意類型，error有引用，而bytes_transferred沒有引用


//聲明：boost/asio/read.hpp
template    
void async_read(AsyncReadStream& s, const MutableBufferSequence& buffers,
    ReadHandler handler);

//定義: boost/asio/impl/read.hpp
* @code void handler(
*   const boost::system::error_code& error, // Result of operation.
*
*   std::size_t bytes_transferred           // Number of bytes copied into the
*                                           // buffers. If an error occurred,
*                                           // this will be the  number of
*                                           // bytes successfully transferred
*                                           // prior to the error.
* );
template
    typename ReadHandler>
inline void async_read(AsyncReadStream& s, const MutableBufferSequence& buffers,
    ReadHandler handler)
{
 async_read(s, buffers, transfer_all(), handler);
}
* @par Example
* To read into a single data buffer use the @ref buffer function as follows:
* @code boost::asio::async_read(s,
*     boost::asio::buffer(data, size),
*     boost::asio::transfer_at_least(32),
*     handler); @endcode
* See the @ref buffer documentation for information on reading into multiple
* buffers in one go, and how to use it with arrays, boost::array or
* std::vector.
*/
template
    typename CompletionCondition, typename ReadHandler>
void async_read(AsyncReadStream& s, const MutableBufferSequence& buffers,
    CompletionCondition completion_condition, ReadHandler handler);

 template
 void async_receive(const MutableBufferSequence& buffers, ReadHandler handler)
 {
    this->service.async_receive(this->implementation, buffers, 0, handler);
 }

結論：

async_receive包含有CompletionCondition， 在調用
void async_read(AsyncReadStream& s, const MutableBufferSequence& buffers,ReadHandler handler)時，必須等到填滿Buffer，不然即便收到數據包，也不會沒有調用ReadHandler句柄；
async_read只要收到數據，就會被調用