Postcard (Js version)

An abstraction layer over message broker clients

This library, created for both languages Javascript(https://www.npmjs.com/package/postcard-js) and Ruby(https://rubygems.org/gems/postcard_rb), is an abstraction layer over RabbitMQ client. It allows the communication among the microservices, providing functionality for publishing and subscribing events.

The microservices interact through topics created with one of three routing types: Wide, Explicit and PatternMatching.

Each topic may have multiple rooms and, according to the routing type, microservices exchange messages on a different way.

Wide topic

(Under construction!)

Explicit topic

For this kind of topic a message is published on an specific room using its exact name.

// Send a message

let topic = postcard.createTopic({ name: "topic1", routing: Routing.Explicit });

topic.publish({
  room: "room1", 
  payload: "Message for topic1/room1"
});

// Receive a message

let topic = postcard.createTopic({ name: "topic1", routing: Routing.Explicit });

try {
  let room = await topic.createRoom({ name: "room1", autoDelete: true });

  room.subscribe(async (msg) => {
    console.log("[x] Received " + msg.content);
  });
} catch (error) {
  return;
}

Pattern matching topic

Using a pattern matching routing, a microservice subscribe to a room based on matching between a message routing key and the pattern that was used to create that room.

// Send a message

let topic = postcard.createTopic({ name: "topic1", routing: Routing.Explicit });

topic.publish({
  room: "room1", 
  payload: "Message for topic1/room1"
});

// Receive a message

let topic = postcard.createTopic({ name: "topic1", routing: Routing.Explicit });

try {
  let room = await topic.createRoom({ name: "room1", autoDelete: true });

room.subscribe(async (msg) => {
    console.log("[x] Received " + msg.content);
  });
} catch (error) {
  return;
}

---

Prerequisites

What things you need to install the software

docker 17+
docker-compose 1.19.0+

---

Development

# Change the directory to the docker development 
cd docker/dev

# Create a .env file with your local application folder
echo "APP_FOLDER=/path-to-your-local/app" > .env 

# Run the services using docker compose
sudo docker-compose up -d

# Try the examples opening new bash(es) with the following command:
# sudo docker exec -it Postcard bash

# The examples folder path into the running container is:
# /usr/src/app/examples

---

Publish to NPM

# Go to the docker dev folder
cd docker/dev

# Compose the docker containers
sudo docker-compose up -d

# Modify the npm package version on build/src/package.json

# Connect to the Postcard container
sudo docker exec -it Postcard bash

# Move to the application folder
cd /usr/src/app

# Build the new npm
npm run build

# Login to the npm repository
npm login

# Move to the dist folder
cd /usr/src/app/build/dist

# Publish the new version to the npm repository
npm publish

---

Authors

• Simone Adelchino - claclacla

---

License

This project is licensed under the MIT License

---

Acknowledgments

• RabbitMQ