J7mbo/sse

Server-sent events server in Go. Messages = RabbitMQ -> SSE -> Browser.

SSE

An example Server-Sent events server.

Reads from RabbitMQ and sends messages to the corresponding /topic/userid/nonce combination.

Uses a middleware to check the user + nonce combination exists in a postgres db.

Subscribe with EventSource in JS to /subscribe/topic/userid/nonce, where all three params are v4 uuids. Then place a payload of type FoundContract (this is my implementation) in RabbitMQ, and it will be published. Check internal /rabitmq/message for the required message payload.

You will need to set up RabbitMQ and Postgres yourself as they are not a part of this service.

Of interest

• Go, implicit interfaces, channels, some "idiomatic go" in case that's your thing
• TLS everywhere, make, ansible, docker, docker-compose
• Logfiles are output in a format that can be parsed by Logstash / Filebeat etc (for Kibana)
• Mockery, testify etc

Prerequisites

• Docker, docker-compose.
• Ansible, and ansible-playbook on your host machine.
• RabbitMQ running somewhere that you can connect to (configure in #Configuration), with TLS.
• Mockery if you want to generate mocks with make mock
• Patience. Ensure RabbitMQ is on the same docker network ;)

Usage

Run: make to see your options.

You'll need to place the user in the users db table first, which is just a list of users that are allowed to connect. Schema needs to have uuid and sse_token strings. Save a new user into your users table with these values to allow a connection. Alternatively, just remove the call to postgres in the middleware wont need a database.

CREATE DATABASE app;
CREATE TABLE users (uuid varchar(36), sse_token varchar(36));
INSERT INTO users (uuid, sse_token) VALUES('bb6819a5-c346-4924-ab09-d48b47fdf087', 'bb6819a5-c346-4924-ab09-d48b47fdf087');

Add the following JavaScript to connect:

let topic = "some-topic";
let uuid = "bb6819a5-c346-4924-ab09-d48b47fdf087";
let token = "bb6819a5-c346-4924-ab09-d48b47fdf087"

let url = `https://localhost:8001/subscribe/${topic}/${uuid}/${token}`;

let es1 = new EventSource(url);
es1.onmessage = function (event) {
    console.log(event.data);
};

Place the following message in rabbitmq, and it will appear in the front-end console:

{
    "userid":  "bb6819a5-c346-4924-ab09-d48b47fdf087", 
    "filename":  "some data here", 
    "filepath":  "some data here",
    "finished": false, 
    "type": "foundcontract"
}

The general flow I'm using is a custom one. In my implementation, the service which provides the nonce to the front-end also shares its database with the SSE server. This makes SSE less of a microservice. However, the SoC is still there and the service can still be scaled, albeit around the Postgres dependency which can also be scaled.

Configuration

See infrastructure/dev.env. If you don't pass these environment variables then they default to those in internal/config.go, allowing two local environments: locally and in a docker container.

TLS

Configure the certificates directory under SSE_CERTS_DIR in dev.env. Ensure the following files exist and are readable:

For the SSE server:

• ${SSE_CERTS_DIR}/cert.pem
• ${SSE_CERTS_DIR}/key.pem
• ${SSE_CERTS_DIR}/ca.pem

For the connection to Rabbitmq:

• ${SSE_CERTS_DIR}/server_certificate.pem
• ${SSE_CERTS_DIR}/server_key.pem
• ${SSE_CERTS_DIR}/ca_certificate.pem

For the connection to Postgres:

• ${SSE_CERTS_DIR}/postgresca.crt

Ansible takes care of the SSE certs for you, but you need to retrieve the postgres and rabbitmq certs yourself. If you're using mkcert to generate the RabbitMQ certs, you need the -client parameter.