Determining when Websocket is closed by client

[mge...@pivotallabs.com]

Greetings all,

We are writing a websockets server that needs to detect when the client disconnects so we can stop running a loop.

Here is the code we have so far:

func myHandler(ws *websocket.Conn) {

    for {    // Until the client is disconnected! ... this is where I need help!

        // Do things while the client is connected...

    }

}

func main() {

    http.Handle("/tail", websocket.Handler(myHandler))

    err := http.ListenAndServe(":8080", nil)

    if err != nil {

        panic(err)

    }

}

While poking around the http docs we found the idea of a CloseNotifier but can not figure out how to get a hold of that for a websocket Connection like we have above.

Does anyone have any ideas?

Thanks in advance.

[Jesse McNelis]

On Tue, Jul 2, 2013 at 6:04 AM, <mge...@pivotallabs.com> wrote:

Greetings all,

We are writing a websockets server that needs to detect when the client disconnects so we can stop running a loop.

When you try to write to the client you'll get an error informing you that they have disconnected if they have disconnected.

This is how the CloseNotifier in net/http does it.

 

Here is the code we have so far:

func myHandler(ws *websocket.Conn) {

    for {    // Until the client is disconnected! ... this is where I need help!

        // Do things while the client is connected...

    }

}

func main() {

    http.Handle("/tail", websocket.Handler(myHandler))

    err := http.ListenAndServe(":8080", nil)

    if err != nil {

        panic(err)

    }

}

While poking around the http docs we found the idea of a CloseNotifier but can not figure out how to get a hold of that for a websocket Connection like we have above.

Does anyone have any ideas?

Thanks in advance.

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[Chris Hines]

In my experience attempts to read from or write to the websocket will return an error if the client has disconnected. If your loop spends most of it's time blocking on websocket I/O then it should be pretty responsive to client disconnects. 

[Sean Murphy]

Thought I'd chime in:

reading detects the closed connection much quicker than writing. I decided to spin up a go-routine to do my writing, and then my reading was done on the server managed go-routine. I noticed that my read would stop much quicker, and the write would go on for quite awhile before it's err clause triggered. So I used a boolean available to both that if either one errored would break the read/write loops. This helped my server close out more nicely.

Example:

func WSServer(ws *websocket.Conn) {

        //TODO Set this connection up as a listener for system events

        isOpen := true

        //Start a go routine to listen

        go func() {

                for isOpen {

                        var data Message

                        err := websocket.JSON.Receive(ws, &data)

                        if err != nil {

                                isOpen = false

                                fmt.Println("Receiver Closing", err)

                                break

                        }

                        fmt.Println("Recieved", data.Msg, data.Count)

                }

        }()

        //Block this routine to send

        var count int

        for isOpen {

                time.Sleep(time.Second)

                err := websocket.JSON.Send(ws, Message{"Hello", count})

                if err != nil {

                        isOpen = false

                        fmt.Println("Sender Closing", err)

                        break

                }

                fmt.Println("Sent", count)

                count++

        }

        //TODO Cleanup

        //Remove the connection from all channels it is subscribed to