Websocket send to specific client instead broadcast

Question

I'm trying to modify the gorilla chat example to to send a message to a specific client instead of broadcast. First I'm storing the specific client in the hub against it's Id.

Hub.go

type Hub struct {
        Clients    map[int]*Client // Changed this piece to store id (int)
        Broadcast  chan []byte   
        Register   chan *Client   
        Unregister chan *Client   
}

func (h *Hub) Run() {
        for {
                    select {
                    case client := <-h.Register:
                                fmt.Println("hub client register")
                                h.Clients[client.Id] = client
                    case client := <-h.Unregister:
                                fmt.Println("hub client Unregister")
                                fmt.Println(h.Clients[client.Id])
                                if h.Clients[client.Id] != nil {
                                            delete(h.Clients, client.Id)
                                            close(client.Send)
                                }
                    case message := <-h.Broadcast:
                                fmt.Println("to send to a specific client", string(message))
                    }
        }
}

Client

I've added a field Id int to Client to know which client has sent a message

type Client struct {
        Hub  *Hub
        Conn *websocket.Conn
        Send chan []byte    
        Id   int // Id of the client,
}

func (c *Client) readPump() {
        defer func() {
                    c.Hub.Unregister <- c
                    c.Conn.Close()
        }()
        c.Conn.SetReadLimit(maxMessageSize)
        c.Conn.SetReadDeadline(time.Now().Add(pongWait))
        c.Conn.SetPongHandler(func(string) error { c.Conn.SetReadDeadline(time.Now().Add(pongWait)); return nil })
        for {
                    _, message, err := c.Conn.ReadMessage()
                    if err != nil {
                                if websocket.IsUnexpectedCloseError(err, websocket.CloseGoingAway) {
                                            log.Printf("error: %v", err)
                                }
                                break
                    }
                    message = bytes.TrimSpace(bytes.Replace(message, newline, space, -1))

                    fmt.Println("client read message", string(message), "from", c.Id)
        // {"to":512,"message":"Hi there."}
                    c.Hub.Broadcast <- message
        }
}

What are the next steps to take to be able to send the message to a specific client instead of broadcasting.

the message itself is coming as JSON from the client specifying 'to' indicating who to send and what message to send.

{"to":512,"message":"Hi there."}

user5728991 · Accepted Answer · 2017-04-12 20:44:03Z

3

Define a type representing a message:

type Message struct {
    id int
    data []byte
}

Add a field to Hub:

Send chan Message

and initialize the channel along with the hub's other channels.

Add the following case to the hub's select:

case m := <-h.Send:
    c, ok := clients[m.id]
    if ok {
        select {
        case c.send <- m.data:
        default:
           delete(h.Clients, c.Id)
           close(c.Send)
        }
    }

In the client's receive loop, parse the JSON to get the id and message data and send it to the hub:

    c.Hub.Send <- Message{id: id, data: data}

answered Apr 12, 2017 at 20:44

user5728991

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5 Comments

Developer Over a year ago

Thanks. Do we need default clause? I've unregistered handler in the hub doing the same thing. Please enlighten.

zero_cool Over a year ago

I'm also using gorilla, and something very similar to the above implementation. I'm looking to prevent a broadcast to the client who created the message. How would you accomplish that?

zero_cool Over a year ago

when I log "client" I get: &{0xc421084d50 0xc4210be280 0xc421066240 0} - how do you make this human readable?

zero_cool Over a year ago

By "receive loop" (in the answer above) do you mean the readPump func?

zero_cool Over a year ago

Looks like all my browser tabs have the same id - the chat works as expected. How do you get each client to have a unique id?

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