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.
Use cases & key features:
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.
client/js/app.js shows how to create a Vue.js app with child components using this approach. The majority of client logic is here.
client/js/components/chat.js is a Vue.js component used to host each chat tab in the application
.auth/ endpoint provided by Static Web Apps is used to sign users in and fetch their user details, such as userId.
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
eventHandler - Webhook receiver for “upstream” events sent from Azure Web PubSub service, contains the majority of application logic. Not called directly by the client, only Azure WebPub Sub.
getToken - Called by the client to get an access token and URL to connect via WebSockets to the Azure Web PubSub service. Must be called with userId in the URL query, e.g. GET
getUsers - Returns a list of signed in users, note the route for this function is
getChats - Returns a list of active group chats, note the route for this function is
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.
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
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
fromUserName, these messages are relayed client to client by Azure Web PubSub, the server is never notified of them:
message: <message text>,
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.
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.
Messages sent from the server have a custom Chatr app specific payload as follows:
data: <JSON object type dependant>
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.
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:
webPubSubConnection binding. For sending messages back to Web PubSub, the server SDK can simply be used within the function code rather than using the
webPubSub output binding.
State in Azure Tables consists of two tables (collections) named
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
"name": "This is a group chat",
"userName": "Another Guy"
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”.
userId field returned from Static Web Apps auth endpoint
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
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
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:
api/local.settings.json and edit the required settings values.
loophole http 7071 --hostname chatr