Messaging (pubsub)

Messaging (or Pubsub) is an important part of any distributed architecture. If you're not familiar with the other types of resources like functions and websites, I recommend you start there. With that said, let's create a messaging channel.

Creation

Navigate to Messaging in the side menu and click the + button.

Name it ws_chan. Set the topic matcher to /ws/chan. And toggle Websocket. Then validate.

Once done, you should see your new it in the list.

To apply these changes to your project, click the green push button in the bottom right corner. You'll be able to review the changes, write a commit message, and push them to the repository.

Messaging in action

Go to Functions and click on the + button. Then click on the Template Select button. Select Go and get_websocket_url.

Make sure domain is set to GeneratedDomain and add /api/ws to the path.

You can use the template code and just replace the topic. However we're going to use a query variable to create a unique channel for each room. Switch to the code view and replace the code with:

package lib

import (
    "crypto/md5"
    "encoding/hex"

    "github.com/taubyte/go-sdk/event"
    http "github.com/taubyte/go-sdk/http/event"
    pubsub "github.com/taubyte/go-sdk/pubsub/node"
)

func fail(h http.Event, err error, code int) uint32 {
    h.Write([]byte(err.Error()))
    h.Return(code)
    return 1
}

//export getsocketurl
func getsocketurl(e event.Event) uint32 {
    h, err := e.HTTP()
    if err != nil {
        return 1
    }

    // get room from query
    room, err := h.Query().Get("room")
    if err != nil {
        return fail(h, err, 500)
    }

    // hash the room to create a channel name
    hash := md5.New()
    hash.Write([]byte(room))
    roomHash := hex.EncodeToString(hash.Sum(nil))

    // create/open a channel with the hash
    channel, err := pubsub.Channel("chat-" + roomHash)
    if err != nil {
        return fail(h, err, 500)
    }

    // get the websocket url
    url, err := channel.WebSocket().Url()
    if err != nil {
        return fail(h, err, 500)
    }

    // write the url to the response
    h.Write([]byte(url.Path))

    return 0
}

Validate the new function then push the changes.

Head back to your terminal and trigger build:

dream inject push-all

Let's test the websocket relay. First, let make sure you have wscat installed:

npm install -g wscat

Next, get the url for room="tau":

curl http://evy8manx0.blackhole.localtau:11005/api/ws?room=tau

💡 Note: Replace evy8manx0.blackhole.localtau with your own domain and 11005 with your own port.

Output:

ws-QmbaJ2gJCmjNLoGNSRk2F5WbpW1b45bxLCQWVcn8Butfa3/chat-4580c2740ab6d9222ef06d7c6865583e

💡 Note: The url will be different for you.

Then on two separate terminals, run:

wscat -c ws://evy8manx0.blackhole.localtau:11005/ws-QmbaJ2gJCmjNLoGNSRk2F5WbpW1b45bxLCQWVcn8Butfa3/chat-4580c2740ab6d9222ef06d7c6865583e

This is what you should see: