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Start an asynchronous send on a connected socket.
template< typename ConstBufferSequence, typename WriteToken = default_completion_token_t<executor_type>> DEDUCED async_send( const ConstBufferSequence & buffers, WriteToken && token = default_completion_token_t< executor_type >());
This function is used to asynchronously send data on the raw socket. It is an initiating function for an asynchronous operation, and always returns immediately.
One or more data buffers to be sent on the socket. Although the buffers object may be copied as necessary, ownership of the underlying memory blocks is retained by the caller, which must guarantee that they remain valid until the completion handler is called.
                  The completion
                  token that will be used to produce a completion handler,
                  which will be called when the send completes. Potential completion
                  tokens include use_future, use_awaitable, yield_context, or a function
                  object with the correct completion signature. The function signature
                  of the completion handler must be:
                
void handler( const asio::error_code& error, // Result of operation. std::size_t bytes_transferred // Number of bytes sent. );
                  Regardless of whether the asynchronous operation completes immediately
                  or not, the completion handler will not be invoked from within
                  this function. On immediate completion, invocation of the handler
                  will be performed in a manner equivalent to using post.
                
void(asio::error_code, std::size_t)
The async_send operation can only be used with a connected socket. Use the async_send_to function to send data on an unconnected raw socket.
            To send a single data buffer use the buffer function as follows:
          
socket.async_send(asio::buffer(data, size), handler);
            See the buffer
            documentation for information on sending multiple buffers in one go,
            and how to use it with arrays, boost::array or std::vector.
          
            On POSIX or Windows operating systems, this asynchronous operation supports
            cancellation for the following cancellation_type values:
          
cancellation_type::terminal
              cancellation_type::partial
              cancellation_type::total