appcd-dispatcher

appcd-dispatcher

Provides an HTTP-like API for registering and invoking service endpoints.

Visit https://github.com/appcelerator/appc-daemon for more information.

Installation

npm i appcd-dispatcher

Usage

Dispatcher Instance

import Dispatcher from 'appcd-dispatcher';

const dispatcher = new Dispatcher();

dispatcher.register('/foo/:id?', ctx => {
	if (ctx.request.params.id) {
		return {
			message: `hello ${ctx.request.params.id}!`
		};
	}

	return {
		message: 'hello guest!'
	};
});

try {
	// 200
	let ctx = await dispatcher.call('/foo');
	console.log('Response:', ctx.response);

	// 200 with parameter
	ctx = await dispatcher.call('/foo/123');
	console.log('Response:', ctx.response);

	// 404
	await dispatcher.call('/bar');
} catch (err) {
	console.error(err);
}

Global Dispatcher Instance

Dispatcher has a static register(), unregister(), and call() methods.

Dispatcher.register('/foo/:id?', ctx => {
	const { id } = ctx.request.params;
	ctx.response = {
		message: `hello ${id || 'guest'}!`
	};
});

Streaming Handler

Dispatcher.register('/foo', ({ response }) => {
	setInterval(() => {
		response.write(new Date().toString());
	}, 1000);
});

Responses

Response statuses are based on HTTP status codes. Successful calls return a 200 status, bad requests return a 400 status, route not found returns a 404 status, and errors return a 500 status.

Route handlers can throw any Error and the dispatcher will return it as a 500.

appcd-response provides Response and AppcdError classes to assist with return messages with specific text and statuses.

ServiceDispatcher

A ServiceDispatcher is an abstract base class for implementing services that support calls and subscriptions. You must not directly instantiate a ServiceDispatcher, but rather define your own class that extends it.

If your service just needs to serve a simple object or array dataset, such as a gawked object, then you should use the DataServiceDispatcher. ServiceDispatcher is intended for intances where you need strict control.

Examples of a ServiceDispatcher being used are the ConfigService and FSWatchManager.

import { ServiceDispatcher } from 'appcd-dispatcher';

export default class MyService extends ServiceDispatcher {
	onCall(ctx) {
		return 'Hello from my service';
	}
}

The following are all of the methods that your ServiceDispatcher derived class can implement:

onCall(ctx)

Handles a request with a single response. Note that the response can be a stream, but not efficient if there are multiple incoming requests.

Param	Type	Description
ctx	DispatcherContext (docs)	A dispatcher context containing the original request and a response.

Returns anything. When result is a DispatcherContext, it is returned to the Dispatcher. When result is not undefined, then it is stored in the response of the DispatcherContext (ctx.response) and returned to the dispatcher. onCall() may also return a Promise which resolves a response as previously described.

This method is optional.

getTopic(ctx)

Returns a topic based on the request context.

Param	Type	Description
ctx	DispatcherContext (docs)	A dispatcher context containing the original request and a response.

Returns a String.

This method is optional. By default, the ServiceDispatcher will use the ctx.realPath.

initSubscription({ ctx, publish(), sid, topic })

Called before the first subscription for the given topic is requested. If all subscriptions have been unsubscribed, then the next subscription event would invoke this callback.

Param	Type	Description
ctx	DispatcherContext (docs)	A dispatcher context containing the original request and a response.
publish()	Function	A function that should be called when your service wants to publish an event to all topic subscribers.
sid	String	The subscription id. Useful for unsubscribing.
topic	String	The subscription topic derived from getTopic() or ctx.realPath.

This method returns undefined and is optional unless you are using onSubscribe().

onSubscribe({ ctx, publish(), sid, topic })

Called when a new subscription is requested. Requires the initSubscription() method to be defined.

Param	Type	Description
ctx	DispatcherContext (docs)	A dispatcher context containing the original request and a response.
publish()	Function	A function that should be called when your service wants to publish an event to all topic subscribers.
sid	String	The subscription id. Useful for unsubscribing.
topic	String	The subscription topic derived from getTopic() or ctx.realPath.

This method returns undefined and is optional.

onUnsubscribe({ ctx, publish(), sid, topic })

Called when a subscription has been unsubscribed. Requires the destroySubscription() method to be defined.

Param	Type	Description
ctx	DispatcherContext (docs)	A dispatcher context containing the original request and a response.
sid	String	The subscription id. Useful for unsubscribing.
topic	String	The subscription topic derived from getTopic() or ctx.realPath.

This method returns undefined and is optional.

destroySubscription()

Called after the last subscription for the given topic has been unsubscribed.

Param	Type	Description
ctx	DispatcherContext (docs)	A dispatcher context containing the original request and a response.
publish()	Function	A function that should be called when your service wants to publish an event to all topic subscribers.
sid	String	The subscription id. Useful for unsubscribing.
topic	String	The subscription topic derived from getTopic() or ctx.realPath.

Note that publish() is not intended to be invoked, but rather used to remove any event listeners.

This method returns undefined and is optional unless you are using onUnsubscribe().

DataServiceDispatcher

A DataServiceDispatcher is a ServiceDispatcher implementation for wiring up a object or array dataset to a data-only service. It gives you automatic data responses with filtering and subscriptions.

DataServiceDispatcher has an property called data. It must be a gawked object. You can either pass an object into the constructor or override this.data with your own gawked object.

If you pass in an object, the DataServiceDispatcher will gawk it for you, then directly update properties of data.

import { DataServiceDispatcher } from 'appcd-dispatcher';

export default class MyDataService extends DataServiceDispatcher {
	constructor() {
		super({
			ts: Date.now()
		});

		setInterval(() => {
			this.data.ts = Date.now();
		}, 1000);
	}
}

Examples of a DataServiceDispatcher being used are the StatusMonitor and PluginManagerStatus.

Legal

This project is open source under the Apache Public License v2 and is developed by Axway, Inc and the community. Please read the LICENSE file included in this distribution for more information.