anchor.diff:  
   ### Get userId from Server [/chat/register/{sessionId}]
   
  -**Server** will send the `userId` to **User** through this API. After **User** send `username` to **Server**
  -
   + Parameters
       + sessionId: 1441428112793 (required, string) - The current sessionId of the user
   
  
positive.code: 
  ### Send message to users [/chat/public]
  
  The **Server** will send message to the users through this api.
  
  ### Receive message from server [GET]
  
  + Attributes
  
negative.code: 
  ### Mechanism
  
  `. When a **User** connects to **Server**. He will input his `username` and pushes his `sessionId` and `username` to the **Server**.
  2. After that, the **Server** save the **User** information and response `userId` to **User**.
  3. When he pushes a message. The **Server** will receive it and broadcasts to the others.
  4. When a user *joins* or *leave* the room. Other people will be *notified* by **Server**.
  
  ### Register a new user [/chat/register]
  
  