chatr

Chatr - Azure Web PubSub Sample App

This is a demonstration & sample application designed to be a simple multi-user web based chat system.
It provides persistent group chats, user to user private chats, a user list, idle (away from keyboard) detection and several other features.

It is built on several Azure technologies, including: Web PubSub, Static Web Apps and Table Storage

👁‍🗨 Note. This was created as a personal project, created to aid learning while building something interesting. The code comes with all the caveats you might expect from such a project.

Goals:

Use cases & key features:

Screenshot

Architecture

Client / Frontend

This is the main web frontend as used by end users via the browser.

The source for this is found in client/ and consists of a static standalone pure ES6 JS application, no bundling or Node.js is required. It is written using Vue.js as a supporting framework, and Bulma as a CSS framework.

Some notes:

Server

This is the backend, handling websocket events to and from Azure Web PubSub, and providing REST API for some operations.

The source for this is found in api/ and consists of a Node.js Azure Function App. It connects to Azure Table Storage to persist group chat and user data (Table Storage was picked as it’s simple & cheap). This is not hosted in a standalone Azure Function App but instead deployed into the Static Web App as part of it’s serverless API support

There are four HTTP functions all served from the default /api/ path

State is handled with state.js which is an ES6 module exporting functions supporting state CRUD for users and chats. This module carries out all the interaction with Azure Tables, and provides a relatively transparent interface, so a different storage backend could be swapped in.

WebSocket & API Message Flows

There is two way message flow between clients and the server via Azure Web PubSub and event handlers

The json.webpubsub.azure.v1 subprotocol is used rather than basic WebSockets, this provides a number of features: users can be added to groups, clients can send custom events (using type: event), and also send messages direct to other clients without going via the server (using type: sendToGroup)

Notes:

Client Messaging

Events & chat are sent using the json.webpubsub.azure.v1 subprotocol

Chat messages sent from the client use sendToGroup and a custom JSON payload with three fields message, fromUserId & fromUserName, these messages are relayed client to client by Azure Web PubSub, the server is never notified of them:

{
  type: 'sendToGroup',
  group: <chatId>,
  dataType: 'json',
  data: {
    message: <message text>,
    fromUserId: <userId>,
    fromUserName: <userName>,
  },
}

Events destined for the backend server are sent as WebSocket messages from the client via the same subprotocol with the event type, and an application specific sub-type, e.g.

{
  type: 'event',
  event: 'joinChat',
  dataType: 'text',
  data: <chatId>,
}

The types of events are:

The backend API eventHandler function has cases for each of these user events, along with handlers for connection & disconnection system events.

Server Messaging

Messages sent from the server have a custom Chatr app specific payload as follows:

{
  chatEvent: <eventType>,
  data: <JSON object type dependant>
}

Where eventType is one of:

The client code in client/js/app.js handles these messages as they are received by the client, and reacts accordingly.

Some Notes on Design and Service Choice

The plan of this project was to use Azure Web PubSub and Azure Static Web Apps, and to host the server side component as a set of serverless functions in the Static Web Apps API support (which is in fact Azure Functions under the hood). Azure Static Web Apps was selected because it has amazing support for codeless and config-less user sign-in and auth, which I wanted to leverage.

Some comments on this approach:

State & Entity Design

State in Azure Tables consists of two tables (collections) named chats and users

Chats Table

As each chat contains nested objects inside the members field, each chat is stored as a JSON string in a field called data. The PartitionKey is not used and hardcoded to a string “chatr”. The RowKey and the id field inside the data object are the same.

Example of a chat data entity

{
  "id": "eab4b030-1a3d-499a-bd89-191578395910",
  "name": "This is a group chat",
  "members": {
    "0987654321": {
      "userId": "0987654321",
      "userName": "Another Guy"
    },
    "1234567890": {
      "userId": "1234567890",
      "userName": "Ben"
    }
  },
  "owner": "1234567890"
}

Users Table

Users are stored as entities with the fields (columns) described below. As there are no nested fields, there is no need to encode as a JSON string. Again the PartitionKey is not used and hardcoded to a string “chatr”.

Running and Deploying the App

Working Locally

See makefile

$ make
help                 💬 This help message
lint                 🔎 Lint & format, will not fix but sets exit code on error
lint-fix             📜 Lint & format, will try to fix errors and modify code
run                  🏃 Run server locally using Static Web Apps CLI
clean                🧹 Clean up project
deploy               🚀 Deploy everything to Azure using Bicep
tunnel               🚇 Start loophole tunnel to expose localhost

Deploying to Azure

Deployment is slightly complex due to the number of components and the configuration between them. The makefile target deploy should deploy everything for you in a single step using Bicep templates found in the deploy/ folder

See readme in deploy folder for details and instructions

Running Locally

This is possible but requires a little effort as the Azure Web PubSub service needs to be able call the HTTP endpoint on your location machine, so a tunnel has employed.

When running locally the Static Web Apps CLI is used and this provides a fake user authentication endpoint for us.

A summary of the steps is:

Known Issues

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