node-msgr

node-msgr

node-msgr is a node amqp client built on top of libamqp and meant to be a companion to the ruby msgr gem. It supports standard publishing and consuming as well as the RPC pattern. By convention all queues are bound to the msgr exchange and the client deals exclusively with routing keys on this exchange instead of individual queue names.

Connecting to a rabbit server

To begin using the client create a new instance with the url for the server you want to connect to as an argument to the constructor.

const msgr = new Msgr('amqp://myserverurl');

This will immediately return a usable client instance.

Publishing a message

Publishing a message to the exchange is done with the publish() method. The first argument is the routing key and the second is the data you want to send and can be anything serializable by JSON.stringify(). There is an optional third parameter to set options when publishing that is passed through to libamqp. Available options are documented here.

const data = {
    some: "thing",
    to: "send"
};
msgr.publish('my_topic', data);

Consuming messages

Consuming messages requires a routing key and a callback. Consuming can also take an optional third param to configure the consumer/queue. Those options are documented here.

msgr.consume('my_topic', (message) => {
    // do a thing with the message
});

A message will be an object with:

• A content property containing the deserialized body of the message
• properties and fields properties containing some additional informationa about the message mostly used internally by libamqp. See the libamqp docs for more info.
• An ack method for use if the queue requires messages to be acknowledged. This method is available on every message, even if the originating queue was created with noAck: true. Calling this method on a message that cannot be acknowledged will cause an error.

RPC

The rpcExec() method takes the same set of parameters as publish() including options. It returns a promise that will be resolved with the content of the reply message (not the message itself) or be rejected with either a timeout error or an error provided by the rpc server. The default timeout is 15 seconds and can be adjusted by setting the timeout option with the desired value in milliseconds. The response from the rpc server is expected to be an object with three properties, data, trace, and error.

const data = {
    some: "thing",
    to: "send"
};
msgr.rpcExec('my_topic', data).then((response) => {
    // do a thing with the response
});

Client Errors

If the value of error is true and trace is falsy then data is presumed to be an array of error messages for the client. The promise will be rejected with an InputError containing a generic message and the value of data will be appended to the error object as clientMessages.

{
    message: 'Client error',
    clientMessages: ['Error messages from the consumer'],
    ...
}

Consumer Errors

If the consumer encounters and unhandled error processing the message the trace property will be set to a truthy value, usually the stack trace from the consumer's error. In this case the promise will be rejected with a generic error and no additional feedback is provided.

{
    message: 'Fatal consumer error',
    ...
}

Caveats

• Only JSON payloads are supported
• There is no method for creating an RPC server/listener (yet)