Abstract
Creates an instance of a Client
subclass.
if options are invalid
configuration options for the client
Readonly
clientGets the client's unique client ID to be used for logging purposes, etc.
Readonly
debugGets a debugger function associated with this client instance.
Used to log informational, debug, and error messages. The first argument
is a formatter string with printf-style formatting supporting the
following directives: %O
(object multi-line), %o
(object
single-line), %s
(string), %d
(number), %j
(JSON), %%
(escape).
To turn on debug output for this library, set the DEBUG
environment
variable to vda-5050:*
. To enable low-level MQTT debugging, use
vda-5050:*,mqttjs*
. Use *
to debug all debug-enabled modules in your
application.
Gets the client configuration options as a readonly object.
Protected
isDetermines whether the client has been started.
true if client has been started; false otherwise
Gets the semantic version of the VDA 5050 protocol this implementation conforms to.
a string in the format
"<major-version-number>.<minor-version-number>.<patch-version-number>"
Protected
getGets the VDA 5050 communication topic with an associated object to be registered as a last will message.
Returns undefined
if no last will should be registered (default). To be
overridden by subclasses.
a last will object with a topic, a headerless object, and a
retain indicator, or undefined
Protected
getGets the semantic version of the VDA 5050 protocol this implementation conforms to.
To be overridden by subclasses that provide VDA 5050 extensions. The
default version returned by the base method is the standard VDA 5050
protocol version this Client
class implements.
a string in the format
"<major-version-number>.<minor-version-number>.<patch-version-number>"
Protected
onProtected
onInvoked before the client disconnects actively.
To be overridden by subclasses that need to perform additional synchronous or asynchronous actions, such as publishing a message before the client disconnects actively.
The base method does nothing.
Protected
publishPublishes the given VDA 5050 core or extension object on the given VDA 5050 communication topic related to the given AGV subject.
The AgvId
subject is used to automatically fill in header properties of
the object to be published. Each of its properties must specify a
non-empty string and must be valid as an MQTT topic level.
On successful publication, this async function resolves a promise
containing a copy of the given headerless object including all header
properties as it has been published. If the publication is dropped
according to the dropIfOffline
publish option, the promise resolves
with an undefined
value.
a promise that resolves the published object if publication
succeeds or undefined
if message should be dropped while offline
synchronously if client is not started, if topic or subject is not valid, if object validation fails
the VDA 5050 communication topic to publish on
identity of the AGV which is related to this publication
a VDA 5050 core or extension object without header properties
Optional
options: ClientPublishOptionsclient publish options (optional)
Register a callback function invoked whenever the client's connection state changes.
Upon registration, the given callback is invoked immediately with the current connection state.
You can only register one callback per client; any previously registered callback is discarded.
a callback function
Registers a custom VDA 5050 communication topic with a validator function to check structure and constraints of corresponding extension objects at runtime.
The asInbound
and asOutbound
parameters indicate whether the
registered extension topic should be allowed for inbound communication
and/or outbound communication. If inbound communication is not allowed,
subscribing to the topic will fail. Likewise, if outbound communication
is not allowed, publishing on the topic will fail.
The validator function is invoked on inbound and/or outbound messages
with a registered extension topic according to the client option
topicObjectValidation
.
The validator function should throw a TypeError
synchronously if the
passed extension object structure does not conform to the passed
extension topic and the direction of the message (inbound, outbound).
If the given topic is already registered, its registration will be overridden with the new parameters.
Use the function createValidators
in the create-validators
script
provided by this package to generate JS validation functions for your
custom JSON schemas. Use these functions in this method override.
a custom VDA 5050 communication topic
whether topic should be allowed on inbound communication
whether topic should be allowed on outbound communication
a function that validates message objects against the given extension topic
Protected
resetStarts client interaction by connecting to the configured MQTT broker.
If client is already started, this operation is a noop.
Always await this operation before invoking other operations on this client instance.
a promise resolved when client is initially connected, and rejected when connection fails
Stops client interaction by disconnecting from the MQTT broker and cleaning up all active subscriptions and registered extension topics.
If client is not started, this operation is a noop.
Always await this operation before invoking other operations on this
client instance, such as start
.
After the client is stopped any publish, subscribe, and unsubscribe operations will throw an error until the client is restarted.
a promise resolved when client is disconnected from the underlying MQTT transport.
Protected
subscribeSubscribes to the given VDA 5050 communication topic for the given AGV subject and registers a handler function to be invoked when matching inbound publication messages are received by this client.
In the given partial AgvId
subject, any property must either specify a
non-empty string which is valid as an MQTT topic level or be undefined
or excluded, to support wildcard subscriptions by control clients.
Otherwise, an error is thrown.
If multiple subscription handlers are registered for a given subscription, they are invoked synchronously in series, one after the other, but in arbitrary order.
A subscription handler should never perform long-lasting synchronous operations as it blocks processing of other handlers and incoming messages.
A subscription handler may also perform asynchronous operations but these are are not awaited and not synchronized with the invocation of other handlers.
A subscription handler is responsible for catching any errors. Uncaught errors result in "Uncaught Error" or "Unhandled Promise Rejection" reported by the runtime.
Take care to invoke Client.unsubscribe
method on any subscription ID
that is no longer needed by the application to clean up the
subscription's handler function and to reduce network traffic.
Unsubscribing in a handler function is also possible; use the
corresponding subscription id passed as argument. If you want to keep a
subscription for the lifetime of the client, there is no need to
explicitely unsubscribe it before stopping the client.
a promise that resolves a unique subscription ID when subscription is set up successfully
synchronously if client is not started, if topic or subject is not valid
the VDA 5050 communication topic to subscribe to
identity of the AGV(s) which are related to this subscription
a function invoked on any inbound message matching the subscription
Unsubscribes the subscription issued for the given subscription ID.
The subscription's handler function will be cleaned up and no longer invoked. If there are no other active subscriptions on the associated VDA 5050 topic, the corresponding MQTT topic will also be unsubscribed to prevent unnecessary network traffic.
If the given subscription ID is already unsubscribed, it is silently ignored.
a promise that resolves on successful unsubscription
synchronously if client is not started
the subscription ID related to an issued subscription
Protected
validatePerforms a runtime validation check of the given AGV identity to be used as subject of a subscription or publication.
For publications, all AgvId
properties must be specified and valid. For
subscriptions, any property may be omitted, but existing properties must
have valid values.
a TypeError
if validation check fails
(partial) identity of AGV
whether to validate as a subscription or publication subject
Protected
validatePerforms a runtime validation check of a standard VDA 5050 communication topic with respect to the direction of information exchange.
The base method does nothing. Validation checks need to be defined by subclasses depending on the role of the client (AGV, master control, visualization/monitoring/logging systems, etc.). Such clients are restricted to publish only on certain topics and to only subscribe to certain topics.
if the topic is not valid in the given context
a standard VDA 5050 communication topic
whether to validate the topic for subscription or publication
Protected
validatePerforms a runtime validation check of a VDA 5050 core or extension object with respect to a given VDA 5050 topic.
a TypeError
if validation check fails
a VDA 5050 communication topic
a VDA 5050 core or extension object with header properties
Generated using TypeDoc
Provides basic client functionality for publishing, subscribing, and unsubscribing communication messages over an MQTT transport according to the VDA 5050 communication interface definition.
This class can be used to implement both the coordination plane (control system like master control) as well as the vehicle plane (AGV) of a driverless transport system (DTS). In addition, it can be used to implement visualization, monitoring, or logging clients that passively observe VDA 5050 communication flows within the DTS.
Remarks
This class also lays the basis for proprietary extensions, i.e. non-standard operations between control system and AGVs.
This class abstracts VDA 5050 messaging over MQTT, providing the following features:
By default, publications are buffered while the client is offline due to a broken connection. They are published as soon as the client goes online again upon automatic reconnection. You can also vote to disable offline buffering for individual publications. For example, regular high frequency state messages on the VDA 5050 "visualization" topic should be dropped while offline.
By default, all subscriptions issued while the client has been started are remembered in case the client goes offline due to a broken connection. As soon as the client goes online again upon automatic reconnection these subscriptions are resubscribed.
Note that the asynchronous publish/subscribe/unsubscribe methods throw synchronously on programming errors, i.e. non-operational errors like passing invalid arguments or or invoking the function while the client is not started. In contrast, operational errors are always signaled by rejecting the returned promise.