rhea-promise

A Promisified layer over rhea AMQP client.

Pre-requisite

Node.js version: 6.x or higher.
We would still encourage you to install the latest available LTS version at any given time from https://nodejs.org. It is a good practice to always install the latest available LTS version of node.js.
Installing node.js on Windows or macOS is very simple with available installers on the node.js website. If you are using a linux based OS, then you can find easy to follow, one step installation instructions over here.

Installation

npm install rhea-promise

Debug logs

You can set the following environment variable to get the debug logs.

Getting debug logs from this library

export DEBUG=rhea-promise*

Getting debug logs from this and the rhea library

export DEBUG=rhea*

If you are not interested in viewing the message transformation (which consumes lot of console/disk space) then you can set the DEBUG environment variable as follows:

export DEBUG=rhea*,-rhea:raw,-rhea:message,-rhea-promise:eventhandler,-rhea-promise:translate

Logging to a file

Set the DEBUG environment variable as shown above and then run your test script as follows:
- Logging statements from you test script go to out.log and logging statement from the sdk go to debug.log.
```
node your-test-script.js > out.log 2>debug.log
```
- Logging statements from your test script and the sdk go to the same file out.log by redirecting stderr to stdout (&1), and then redirect stdout to a file:
```
node your-test-script.js >out.log 2>&1
```
- Logging statements from your test script and the sdk go to the same file out.log.
```
  node your-test-script.js &> out.log
```

Notable differences between rhea and rhea-promise

Error propogation to the parent entity

In AMQP, for two peers to communicate successfully, different entities (Container, Connection, Session, Link) need to be created. There is a relationship between those entities.
- 1 Container can have 1..* Connections.
- 1 Connection can have 1..* Sessions.
- 1 Session can have 1..* Links.
- A Link can have the role of Receiver or Sender.
Each entity (connection, session, link) maintains its own state to let other entities know about what it is doing. Thus,
- if the connection goes down then, everything on the connection - sessions, links are down.
- if a session goes down then, all the the links on that session are down.
When an entity goes down rhea emits *_error and *_close events, where * can be "sender", "receiver", "session", "connection". If event listeners for the aforementioned events are not added at the appropriate level, then rhea propogates those events to its parent entity. If they are not handled at the Container level (uber parent), then they are transformed into an error event. This would cause your application to crash if there is no listener added for the error event.
In rhea-promise, the library creates, equivalent objects Connection, Session, Sender, Receiver and wraps objects from rhea within them. It adds event listeners to all the possible events that can occur at any level and re-emits those events with the same arguments as one would expect from rhea. This makes it easy for consumers of rhea-promise to use the EventEmitter pattern. Users can efficiently use different event emitter methods like .once(), .on(), .prependListeners(), etc. Since rhea-promise add those event listeners on rhea objects, the errors will never be propogated to the parent entity. This can be good as well as bad depending on what you do.
- Good - *_error events and *_close events emitted on an entity will not be propogated to it's parent. Thus ensuring that errors are handled at the right level.
- Bad - If you do not add listeners for *_error and *_close events at the right level, then you will never know why an entity shutdown.

We believe our design enforces good practices to be followed while using the event emitter pattern.

Examples

Please take a look at the sample.env file for examples on how to provide the values for different parameters like host, username, password, port, senderAddress, receiverAddress, etc.

Sending a message.

Running the example from terminal: > ts-node ./examples/send.ts.

NOTE: If you are running the sample with .env config file, then please run the sample from the directory that contains .env config file.

import {
  Connection, Sender, EventContext, Message, ConnectionOptions, Delivery, SenderOptions
} from "rhea-promise";
import * as dotenv from "dotenv"; // Optional for loading environment configuration from a .env (config) file
dotenv.config();

const host = process.env.AMQP_HOST || "host";
const username = process.env.AMQP_USERNAME || "sharedAccessKeyName";
const password = process.env.AMQP_PASSWORD || "sharedAccessKeyValue";
const port = parseInt(process.env.AMQP_PORT || "5671");
const senderAddress = process.env.SENDER_ADDRESS || "address";

async function main(): Promise<void> {
  const connectionOptions: ConnectionOptions = {
    transport: "tls",
    host: host,
    hostname: host,
    username: username,
    password: password,
    port: port,
    reconnect: false
  };
  const connection: Connection = new Connection(connectionOptions);
  const senderName = "sender-1";
  const senderOptions: SenderOptions = {
    name: senderName,
    target: {
      address: senderAddress
    },
    onError: (context: EventContext) => {
      const senderError = context.sender && context.sender.error;
      if (senderError) {
        console.log(">>>>> [%s] An error occurred for sender '%s': %O.",
          connection.id, senderName, senderError);
      }
    },
    onSessionError: (context: EventContext) => {
      const sessionError = context.session && context.session.error;
      if (sessionError) {
        console.log(">>>>> [%s] An error occurred for session of sender '%s': %O.",
          connection.id, senderName, sessionError);
      }
    }
  };

  await connection.open();
  const sender: Sender = await connection.createSender(senderOptions);
  const message: Message = {
    body: "Hello World!!",
    message_id: "12343434343434"
  };

  const delivery: Delivery = await sender.send(message);
  console.log(">>>>>[%s] Delivery id: ", connection.id, delivery.id);

  await sender.close();
  await connection.close();
}

main().catch((err) => console.log(err));

Receiving a message

Running the example from terminal: > ts-node ./examples/receive.ts.