vdv-453-client

A JavaScript client for realtime public transport data systems following the VDV-453 v2.3.2b/VDV-454 v1.2.2 specs (from 2013). Such systems are widespread in Germany, being the realtime data backends (Datendrehscheiben) of many regional transit authorities/associations.

vdv-453-client is a library only, intended to be embedded into other tools (e.g. vdv-453-nats-adapter). It subscribes to services (see below), fetches the XML data, converts it to JSON, and emits it via an event.

[!NOTE] This client supports neither the latest 2.x spec versions (VDV-453 v2.6.1/VDV-454 v2.2.1) nor the latest 3.x spec versions (VDV-453 v3.0/VDV-454 v3.0). Refer to the tracking Issue #2.

The VDV-453 spec defines the basic protocol that client (usually the data consumer) and server (usually the provider) use to communicate; It uses HTTP POST requests with XML bodies. VDV-453 also defines some (domain-specific) services on top, e.g. DFI for fetching departures at stops/stations. A client subscribes to such services, optionally with service-specific parameters, e.g. filters to reduce the number of subscribed items.

On top of VDV-453, VDV-454 defines two additional services: REF-AUS for the exchange of daily schedule data, and AUS for realtime data like prognosed delays & cancellations.

vdv-453-client has been written specifically for VBB's Datendrehscheibe. However, we're open to changes that make vdv-453-client compatible with other VDV-453/-454 systems.

Installation

npm install vdv-453-client

Getting Started

[!IMPORTANT] While vdv-453-client is used in a production system at VBB, it hasn't been tested with other VDV-453/-454 systems. Also, there's tracking issue #1 regarding automated tests.

Leitstellenkennung

With the organisation providing the VDV 453 API, you will have to agree upon your client's Leitstellenkennung, which – a bit like an HTTP User-Agent – allows the server to identify your client:

6.1.3 Leitstellenkennung

Um Botschaften verschiedener Kommunikationspartner innerhalb eines Dienstes unterscheiden zu können, enthält jede Nachricht eine eindeutige Leitstellenkennung (Attribut Sender) des nachfragenden Systems. […]

const LEITSTELLE = 'MY_VDV_CLIENT'

You will also have to configure their Leitstellenkennung, which they use for calls to your client.

const THEIR_LEITSTELLE = 'SOME_VDV_API'

server address

We configure the server's address. It needs to be the HTTP(S) base URL without your Leitstellenkennung.

const ENDPOINT = 'http://vdv-api.example.org/'

local HTTP server

[!NOTE] The VDV-453 spec expects the client (consumer) to listen for HTTP requests from the server (provider), in order to allow the server to notify the client when new data is available, sort of like a webhook. This means that your client's machine will have to have an open TCP port! Once you have chosen your client's port, it needs to be configured on the server side.

5.1.3.1 Datenbereitstellung signalisieren (DatenBereitAnfrage)

Ist das Abonnement eingerichtet und sind die Daten bereitgestellt, wird der Datenkonsument durch eine DatenBereitAnfrage über das Vorhandensein aktualisierter Daten informiert.

5.1.8 Alive-Handling

Die Statusabfrage dient dem Feststellen der Verfügbarkeit von Diensten. Dazu werden zwei spezielle Informationskanäle verwendet (Ziel-URL status.xml, clientstatus.xml), die jeder Dienst bereitstellen muss.

configuring the client

import {createClient as createVdv453Client} from 'vdv-453-client'

const {
	httpServer,
	data,
	dfiSubscribe,
	dfiUnsubscribe,
	ausSubscribe,
	ausUnsubscribe,
} = createVdv453Client({
	leitstelle: LEITSTELLE,
	theirLeitstelle: THEIR_LEITSTELLE,
	endpoint: ENDPOINT,
})

// createClient() returns an HTTP server, which you still need to call listen() on.
await new Promise((resolve, reject) => {
	httpServer.listen(3000, (err) => {
		if (err) reject(err)
		else resolve()
	})
})

const unsubscribeTasks = []
process.once('SIGINT', {
	Promise.all(unsubscribeTasks.map(task => task()))
	.then(() => {
		httpServer.close()
	})
	.catch((err) => {
		console.error(err)
		process.exit(1)
	})
})

subscribing to services

By design, every VDV-453/-454 subscription must have a TTL – in other words: a pre-set point in time at which it expires.

5.1.1 Abonnement-Verfahren – Überblick

[…]

Abonnements besitzen eine vom Client definierte Lebensspanne und werden nach Ablauf automatisch vom Server gelöscht. […]

5.1.2.1 Abonnementsanfrage (AboAnfrage)

[…]

Allen Abonnements aller Dienste wird beim Einrichten ein Verfallszeitstempel (VerfallZst) durch den Client mitgegeben. […]

Therefore, when subscribing to a service, the client must provide an expiration date+time. Use opt.expiresAt to provide a different TTL than vdv-453-client's default of 1 hour.

// subscribe to VDV-453 DFI service
// the ID of the stop/station (a.k.a. "Anzeigerbereich") depends on your region's data
const SOME_ANZEIGERBEREICH_ID = 'my stop ID'
const {aboId: dfiAboId} = await dfiSubscribe(SOME_ANZEIGERBEREICH_ID)
unsubscribeTasks.push(() => dfiUnsubscribe(dfiAboId))
data.on('dfi:AZBNachricht', (azbNachricht) => {
	console.log(azbNachricht)
})

// subscribe to VDV-454 AUS service
const {aboId: ausAboId} = await ausSubscribe({
	expiresAt: Date.now() + 10 * 60 * 1000, // 10 minutes from now
})
unsubscribeTasks.push(() => ausUnsubscribe(ausAboId))
data.on('aus:IstFahrt', (istFahrt) => {
	console.log(istFahrt)
})

[!WARNING] Currently, vdv-453-client has some shortcomings in the handling of subscriptions; For example, it does not persist the information about its subscriptions, and it does not respond to the server with its active subscriptions (AktiveAbos) when asked. Refer to the tracking Issue #3 for more details.

API

[!TIP] The REF-AUS & AUS services are defined in VDV-454. All other services are defined in VDV-453.

A client instance can be created by calling createClient(), which returns an object with the following fields.

client.httpServer

The client HTTP server (see section above), an http.Server that you still need to call listen() on.

client.data

An EventEmitter that will emit ${service}:${rootSubTag}, where service & rootSubTag depend on the service that you subscribe on.

[!NOTE] The arguments of the events below, unless otherwise noted, are JSON equivalents of the XML trees sent by the server (see the XML to JSON mapping section).

event aus:IstFahrt

Arguments:

1. istFahrt – The AUS IstFahrt.

event raw:dfi:AZBNachricht

Arguments:

1. azbNachricht – The whole DFI AZBNachricht, usually containing many AZBFahrplanlages, AZBFahrtLoeschens, etc.

event raw:aus:AUSNachricht

Arguments:

1. ausNachricht – The whole AUS AUSNachricht, usually containing many IstFahrts.

client.dfiSubscribe()

dfiSubscribe(azbId, opt = {}) is an async function that takes the following arguments:

1. azbId: The ID of a DFI Anzeigerbereich, a.k.a. a stop or station.
2. opt (optional): An object whose fields override the following defaults:
   • expiresAt: Date.now() + DFI_DEFAULT_SUBSCRIPTION_TTL,
   • linienId: null,
   • richtungsId: null,
   • vorschauzeit: 10 (in minutes)
   • hysterese: 1 (in seconds)
   • fetchInterval: 30_000 (in milliseconds)

After subscribing successfully, it will return an object with the following fields:

• aboId: The ID that represents the subscription. It can be used to unsubscribe.

client.dfiFetchData()

dfiFetchData(opt = {}) is an async function that takes the following arguments:

1. opt (optional): An object whose fields override the following defaults:
   • abortController: inactive AbortController – Pass in your own to be able to .abort() the fetching.

client.dfiUnsubscribe()

dfiUnsubscribe(...aboIds) is an async function that takes the following arguments:

1. aboIds: >0 subscription IDs.

client.dfiUnsubscribeAll()

dfiUnsubscribeAll() is an async function that 0 arguments. It unsubscribes from all active DFI subscriptions the server knows about.

client.ausSubscribe()

ausSubscribe(opt = {}) is an async function that takes the following arguments:

1. opt (optional): An object whose fields override the following defaults:
   • expiresAt: Date.now() + AUS_DEFAULT_SUBSCRIPTION_TTL,
   • vorschauzeit: 10 (in minutes)
   • hysterese: 60 (in seconds)
   • fetchInterval: 30_000 (in milliseconds)

After subscribing successfully, it will return an object with the following fields:

• aboId: The ID that represents the subscription. It can be used to unsubscribe.

client.ausFetchData()

Works like client.dfiFetchData(), except for AUS.

client.ausUnsubscribe()

Works like client.dfiUnsubscribe(), except for AUS.

client.ausUnsubscribeAll()

Works like client.dfiUnsubscribeAll(), except for AUS.

client.unsubscribeAllOwned()

An async function that will unsubscribe from all (unexpired) subscriptions created using client.

error handling

The functions in client may reject with the following errors:

• Vdv453HttpError – The server has rejected the client's HTTP request, e.g. because it is malformed, or because the server is overloaded.
• Vdv453ApiError – The server has accepted the client's HTTP request but signaled that it couldn't process it, e.g. because a subscription filter is not valid.
• Error – A generic error thrown in some cases.

XML to JSON mapping

vdv-453-client uses xml-stream-saxes to parse XML into JavaScript/JSON trees.

For example, the following (simplified) XML IstFahrt:

<IstFahrt Zst="2024-04-11T09:10:11Z">
	<LinienID>M8</LinienID>
	<Komplettfahrt>false</Komplettfahrt>
	<IstHalt>
		<HaltID>ODEG_900170006</HaltID>
		<Abfahrtszeit>2024-04-11T11:52:00Z</Abfahrtszeit>
	</IstHalt>
	<IstHalt>
		<HaltID>ODEG_900171517</HaltID>
		<Abfahrtszeit>2024-04-11T12:07:00Z</Abfahrtszeit>
	</IstHalt>
</IstFahrt>

into the following JSON tree.

{
	'$name': 'IstFahrt',
	'$': {
		Zst: '2024-04-11T09:10:11Z',
	},
	'$children': [
		{
			'$name': 'LinienID',
			'$text': 'M8',
			'$children': ['M8'],
		},
		{
			'$name': 'Komplettfahrt',
			'$text': 'false',
			'$children': ['false'],
		},
		{
			'$name': 'IstHalt',
			'$children': [
				{
					'$name': 'HaltID',
					'$text': 'ODEG_900170006',
					'$children': ['ODEG_900170006'],
				},
				{
					'$name': 'Abfahrtszeit',
					'$text': '2024-04-11T11:52:00Z',
					'$children': ['2024-04-11T11:52:00Z'],
				}
			],
			HaltID: {
				'$name': 'HaltID',
				'$text': 'ODEG_900170006',
				'$children': ['ODEG_900170006'],
			},
			Abfahrtszeit: {
				'$name': 'Abfahrtszeit',
				'$text': '2024-04-11T11:52:00Z',
				'$children': ['2024-04-11T11:52:00Z'],
			},
		},
		{
			'$name': 'IstHalt',
			'$children': [
				{
					'$name': 'HaltID',
					'$text': 'ODEG_900171517',
					'$children': ['ODEG_900171517'],
				},
				{
					'$name': 'Abfahrtszeit',
					'$text': '2024-04-11T12:07:00Z',
					'$children': ['2024-04-11T12:07:00Z'],
				}
			],
			HaltID: {
				'$name': 'HaltID',
				'$text': 'ODEG_900171517',
				'$children': ['ODEG_900171517'],
			},
			Abfahrtszeit: {
				'$name': 'Abfahrtszeit',
				'$text': '2024-04-11T12:07:00Z',
				'$children': ['2024-04-11T12:07:00Z'],
			},
		}
	],
	LinienID: {
		'$name': 'LinienID',
		'$text': 'M8',
		'$children': ['M8'],
	},
	Komplettfahrt: {
		'$name': 'Komplettfahrt',
		'$text': 'false',
		'$children': ['false'],
	},
	IstHalt: {
		'$name': 'IstHalt',,
		'$children': [
			{
				'$name': 'HaltID',
				'$text': 'ODEG_900171517',
				'$children': ['ODEG_900171517'],
			},
			{
				'$name': 'Abfahrtszeit',
				'$text': '2024-04-11T12:07:00Z',
				'$children': ['2024-04-11T12:07:00Z'],
			}
		],
		HaltID: {
			'$name': 'HaltID',
			'$text': 'ODEG_900171517',
			'$children': ['ODEG_900171517'],
		},
		Abfahrtszeit: {
			'$name': 'Abfahrtszeit',
			'$text': '2024-04-11T12:07:00Z',
			'$children': ['2024-04-11T12:07:00Z'],
		},
	},
}

[!WARNING] Among all children of a node, the last of each kind ($name) will also be exposed on the node as node[child.$name] (e.g. LinienID above). Because you usually can't predict the number of children in a node for sure (nor the order), we recommend to always iterate over $children and only use the "direct" named properties if you know what you're doing.

Related

• vdv-453-nats-adapter – Send events from a VDV-453/VDV-454 endpoint to NATS (JetStream).

Contributing

If you have a question or need support using vdv-453-client, please double-check your code and setup first. If you think you have found a bug or want to propose a feature, use the issues page.