template< class DynamicBuffer, class ReadHandler> async_return_type< ReadHandler, void(error_code)> async_read( opcode& op, DynamicBuffer& buffer, ReadHandler&& handler);
This function is used to asynchronously read a message from the stream. The function call always returns immediately. The asynchronous operation will continue until one of the following is true:
This operation is implemented in terms of one or more calls to the next
and is known as a composed operation. The program
must ensure that the stream performs no other reads until this operation
Upon a success, op is set to either binary or text depending on the message type, and the input area of the stream buffer will hold all the message payload bytes (which may be zero in length).
During reads, the implementation handles control frames as follows:
ping_callbackis invoked when a ping frame or pong frame is received.
Because of the need to handle control frames, read operations can cause
writes to take place. These writes are managed transparently; callers can
still have one active asynchronous read and asynchronous write operation
pending simultaneously (a user initiated call to
async_close counts as a write).
A value to receive the message type. This object must remain valid until the handler is called.
A dynamic buffer to hold the message data after any masking or decompression has been applied. This object must remain valid until the handler is called.
The handler to be called when the read operation completes. Copies will be made of the handler as required. The function signature of the handler must be:
void handler( error_code const& ec // Result of operation );
Regardless of whether the asynchronous operation completes immediately
or not, the handler will not be invoked from within this function.
Invocation of the handler will be performed in a manner equivalent