1. set TCP_NODELAY = true this can be set after the socket open. So we can't set it in constructor. (async_connect will open the socket)
2. does the order of calling all the when_done matter when error occur? in write path when_done(error triggered) -> close_socket(in destructor) in read path close_socket(directly call) -> when_done(error triggered)
3. keep the old path for all request if stream_mode_ = false

already addressed all the comment.