title: flask socket io private chat
body: <p>How to send personal message in flask socket io?  I have a hint about request.sid but i don't know how can i get the request.sid of person whom i am sending message?  How can i assign a common room to sender and receiver?</p>
  
  <pre><code>if user_exist:
          @socketio.on('private message', namespace='/message/')
          def join(msg):
              join_room(request.sid)
              room = request.sid
              emit("my response",{ "data" : msg['data'] },room=room)
  </code></pre>
  
  <p>Here the request.sid refers the sid of sender not of receiver, so how can i assign both of them same room?</p>