Assignment Requirements

Your task is to write an application which acts as a pub/sub message broker server and communicates via QUIC.

Server specifications:

• Accepts QUIC connections on 2 ports (Publisher port, Subscriber port)
• The server notifies publishers if a subscriber has connected
• If no subscribers are connected, the server must inform the publishers
• The server sends any messages received from publishers to all connected subscribers

How to Run

Server

Run the command with go and specify path to configuration file, and certificate files in the command line arguments:

go run server/cmd/main.go server/config/base.yaml secrets/server.crt secrets/server.key

or alternatively run with make:

make run-server

Publisher Client

Run the command with go and specify the publisher port as a cmd argument:

go run client/publisher/cmd/main.go 8081

or alternatively run with make:

make run-publisher

Once the publisher client is running, use the console input to publish messages.

Subscriber Client

Run the command with go and specify the subscriber port as a cmd argument:

go run client/subscriber/cmd/main.go 8080

or alternatively run with make:

make run-subscriber

Tests

Execute the command to run unit tests:

go test ./...

or alternatively run with make:

make test

Mocks were generated using the mockgen tool.

Implementation Details

This project contains three different applications: server, publisher client, and subscriber client. Their corresponding code can be found in server, client/publisher, and client/subscriber directories accordingly. Common code can be found in lib directory.

Server

Server can be configured via a configuration yaml file (server/config/base.yaml) that is loaded up on start up based on given configuration path.

On start up the Server creates two Listeners, one for subscribers and the other for publishers. Listeners start accepting incoming connections on separate goroutines. When a Listener accepts a new incoming connection then it executes the callback function provided by the Server and passes the connection along. Then the Server opens either a bi-directional stream (ReadWriteStream) for publishers, or a uni-directional write stream (WriteStream) for subscribers. When the stream is successfully opened, the Server passes it to the communication controller (CommsController).

CommsController is responsible for orchestrating the communication between subscribers and publishers. When CommsController receives a new publisher or subscriber stream, it then wraps the stream with a notifier. notifier runs in a separate goroutine, has a separate message queue, and is responsible for sending messages only to the given subscriber or publisher stream.

When CommsController receives a new message from a publisher it then puts the message to its' own message queue. CommsController processes the message queue in a separate goroutine. When processing a new message from a publisher, the CommsController will pass that message to all subscribers' notifiers to send the message independently of one another.

CommsController informs newly connected publishers of the current subscriber count (and if there aren't any). CommsController informs publishers when a new subscriber connects. CommsController sends the messages it receives from publishers to all subscribers.

CommsController maintains active subscribers and publishers, and removes them when they disconnect.

Publisher Client

On start up the publisher Client connects to the server and accepts a bi-directional stream (ReadWriteStream). The Client will print out any messages it receives to the console output. Alternatively, a custom message receiver can be set by calling Client.SetMessageReceiver. New messages can be published to the server via Client.Publish.

The publisher client application will read console input and send the entered text to publishers on return (enter).

Publisher client will automatically shut down when the server shuts down.

Subscriber Client

On start up the subscriber Client connects to the server and accepts a uni-directional read stream (ReadStream). The Client will print out any messages it receives to the console output. Alternatively, a custom message receiver can be set by calling Client.SetMessageReceiver.

Subscriber client will automatically shut down when the server shuts down.