06-broadcast-msgs.md

Lesson 6 - Broadcasting Messages (15-20 minutes)

Goals

Finally, to the heart of the matter! Chatting!

To chat with each other, we need to be able to read messages from each individual ChatUser's socket, then broadcast them back to all of the other user sockets.

Here's how it will work:

• We have a channel ChatRoom.incoming where we will put all of the messages that come in from all of the user sockets.
• Each ChatUser object will be modified to have a loop that looks for any new lines read in from the client, and sends it to ChatRoom.incoming channel.
• In our ChatRoom.ListenForMessages, we will look for any new messages on ChatRoom.incoming and call Broadcast to broadcast it out to all of the other connected sockets.

Got it?? Not sure? No worries, Let's go through the steps.

Steps

1. Look for the empty ChatUser.ReadIncomingMessages function. Let's implement it so it constantly reads incoming messages from the socket buffer.

  func (cu *ChatUser) ReadIncomingMessages(chatroom *ChatRoom) {
  	// TODO: read incoming messages in a loop
  }

1. In ChatUser.ReadIncomingMessages, implement the following:

1. :star2: Create a `for` loop, and ensure this loop runs in a goroutine.
1. :star2: In the loop, call `cu.ReadLine` to read an incoming msg.
1. :star2: Prepend the incoming msg with the username surrounded by brackets, e.g.: `msg = "[" + cu.username "]" + msg`
1. :star2: Place this modified message on the `chatroom.incoming` queue.

[Stuck on any of the steps above? Ask your TA, or see the solution!](code/06-broadcast-msgs/chat.go#L100-L109)

1. Now, you need to make sure that the ReadIncomingMessages goroutine is started in ChatUser.Login.

1. :star2: Modify the `Login` function to start the goroutine for `ReadIncomingMessages` after `WriteOutgoingMessages`.

[Stuck on any of the steps above? Ask your TA, or see the solution!](code/06-broadcast-msgs/chat.go#L138)

1. Cool. Remember ChatRoom.ListenForMessages()? Let's modify it so it sees the new messages on the chatroom.incoming channel.

2. 🌟 Add a 'case' within the for/select loop that reads a msg string from the incoming channel.

3. 🌟 Call ChatRoom.Broadcast on the read msg.

Stuck on any of the steps above? Ask your TA, or see the solution!

At the end it will look like:

func (cr *ChatRoom) ListenForMessages() {
    go func() {
    	for {
    		select {
    		case msg := <-cr.incoming:
    			cr.Broadcast(msg)
    		case user := <-cr.joins:
    			cr.users[user.username] = user
    			cr.Broadcast("*** " + user.username + " just joined the chatroom")
    		}
    	}
    }()
}

1. Verify everything works as designed. Connect to port 6677, then type a message and hit enter to send a chat msg to everyone. You can try connecting with multiple simultaneous clients to test how messages look to other users.

 $ nc localhost 6677
 Welcome to Jen's chat server!
 Please enter your username: funcuddles
 Welcome, funcuddles
 *** funcuddles just joined the chatroom
 hello this is dog
 [funcuddles] hello this is dog

Next lesson - Handle user disconnects