Diffusion Apple API  6.6.2
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PTDiffusionTopicsFeature Class Reference

Introduction

The Topics feature provides a client session with the capability to receive streamed topic updates and/or fetch the state of topics.

This feature allows a client session to subscribe to topics to receive streamed topic updates, fetch the state of topics and/or update topics with new values.

Specifically, the feature provides the ability to:

Subscription and unsubscription

A session can issue requests to subscribe to topics at any time, even if the topics do not exist at the server. Each subscription request provides a topic selector that is evaluated by the server to select matching topics. The session will be subscribed to any topics that match the selector unless they are already subscribed, or the session has insufficient permission. The subscription request is also retained at the server and the session will be automatically subscribed to newly created topics that match the selector (unless a subsequent unsubscription cancels the request).

Sessions receive notifications from topics that they are subscribed to via subscription streams (see below). When a session is subscribed to a topic, all matching streams will first receive a subscription notification that provides details about the topic. If the server has a value for the topic, the value will be delivered to the streams before any other notifications.

A session can unsubscribe from topics at any time. This is also specified using a topic selector. On unsubscription, matching streams are notified via the PTDiffusionTopicUnsubscriptionReason notification. This notification will give the reason for unsubscription (for example, by request of the session, request of the server, or topic removal).

Subscriptions and unsubscriptions can occur for reasons other than requests from the session. A session can be subscribed to or unsubscribed from a topic by another session using the PTDiffusionSubscriptionControlFeature. The removal of a topic also automatically causes unsubscription for subscribed sessions.

Subscription requests are subject to authorization checks. The session must have selectTopic (PTDiffusionPathPermission) permission for the topic selector used to subscribe. Matching topics will be further filtered to those for which the session has readTopic (PTDiffusionPathPermission) permission.

Subscription streams

A session can listen to subscription events and updates for a selection of topics by adding one or more streams. A stream is registered using a topic selector which specifies the topics that the stream applies to. When an update is received for a topic then it will be routed to every stream that matches both the topic selector and the stream's value type. If more than one stream matches, all will receive the update; the order in which they are notified is not defined.

A stream can be added several times for different selectors. If the same stream is registered for several selectors that match an event, the stream will only be notified of the event once. The mapping of topic selectors to streams is maintained locally in the client process.

It is also possible to add one or more fallback streams which will receive updates that do not match any stream registered with a selector. This is useful for default processing or simply to catch unprocessed updates. A fallback stream can be added using addFallbackStream:error: (PTDiffusionTopicsFeature). Zero, one, or more fallback streams may be assigned. If no fallback stream is specified, any updates that are not routed to any other stream will simply be discarded.

If the session is already subscribed to a topic when a matching stream is added, the stream will immediately receive a subscription notification. For most topic types, the latest value is locally cached and will be provided to the stream following the subscription notification.

A stream will receive a diffusionDidCloseStream: (PTDiffusionStreamDelegate-p) callback when unregistered and a diffusionStream:didFailWithError: (PTDiffusionStreamDelegate-p) callback if the session is closed.

Value streams

A PTDiffusionValueStream receives values for matching topics as and when updates are received from the server. Delta updates received from the server are automatically applied to locally cached values so that the stream always receives full values for each update.

Value streams are typed to a specified value class and only updates for compatible topics will be routed to the stream. The following table shows how the value class maps to compatible topic types that will be routed to the stream:

Value Class Compatible Topic Types
JSON JSON STRING INT64 DOUBLE
String STRING
Long INT64
Double DOUBLE
Binary BINARY
Bytes JSON STRING INT64 DOUBLE BINARY RECORD_V2
RecordV2 RECORD_V2

Value stream implementations can be added using addStream:withSelector: (PTDiffusionTopicsFeature)error.

A value stream can be added to received updates from time series topics. The following table shows how the value class specified when adding the stream maps to the event value class of time series topics that will be routed to the stream:

Event Value Class Time Series Event Value Class
JSON JSON STRING INT64 DOUBLE
String STRING
Long INT64
Double DOUBLE
Binary BINARY
Bytes JSON STRING INT64 DOUBLE BINARY RECORD_V2
RecordV2 RECORD_V2

Fetch

A session can issue a request to fetch details of a topic or topics (subject to authorization) at any time. The topics required are specified using a topic selector.

The results of a fetch will return the topic path and type of each selected topic. The results may also optionally return the topic values and/or properties.

A new request can be created using fetchRequest (PTDiffusionTopicsFeature) and modified to specify additional requirements of the fetch operation. The request is issued to the server using the fetchWithTopicSelectorExpression:completionHandler: (PTDiffusionFetchRequest)] method on the request. This will return the results via a completionHandler.

Access control

A session must have selectTopic (PTDiffusionPathPermission) permission for the path prefix of the topic selector used to subscribe or fetch. The topics that result from a subscription or fetch request are further filtered using the readTopic (PTDiffusionPathPermission) permission.

No access control restrictions are applied to unsubscription.

Accessing the feature

This feature can be obtained from a PTDiffusionSession as follows:

   PTDiffusionTopicsFeature *topics = session.topics;
See Also
PTDiffusionSession
Since
5.6
Inheritance diagram for PTDiffusionTopicsFeature:
PTDiffusionTopicUpdateFeature PTDiffusionFeature

Instance Methods

(void) - subscribeWithTopicSelectorExpression:completionHandler:
 
(void) - unsubscribeFromTopicSelectorExpression:completionHandler:
 
(void) - addFallbackStream:
 
(BOOL) - addFallbackStream:error:
 
(void) - addStream:withSelector:
 
(BOOL) - addStream:withSelector:error:
 
(void) - addStream:withSelectorExpression:
 
(BOOL) - addStream:withSelectorExpression:error:
 
(BOOL) - removeStream:
 
(PTDiffusionFetchRequest *) - fetchRequest
 
- Instance Methods inherited from PTDiffusionTopicUpdateFeature
(void) - applyJsonPatch:toPath:completionHandler:
 
(void) - applyJsonPatch:toPath:withConstraint:completionHandler:
 
(void) - setWithPath:toBinaryValue:completionHandler:
 
(void) - setWithPath:toBinaryValue:constraint:completionHandler:
 
(void) - addWithPath:specification:andSetToBinaryValue:completionHandler:
 
(void) - addWithPath:specification:andSetToBinaryValue:constraint:completionHandler:
 
(PTDiffusionBinaryUpdateStream *) - binaryUpdateStreamWithPath:
 
(PTDiffusionBinaryUpdateStream *) - binaryUpdateStreamWithPath:constraint:
 
(PTDiffusionBinaryUpdateStream *) - binaryUpdateStreamWithPath:specification:
 
(PTDiffusionBinaryUpdateStream *) - binaryUpdateStreamWithPath:specification:constraint:
 
(void) - setWithPath:toJSONValue:completionHandler:
 
(void) - setWithPath:toJSONValue:constraint:completionHandler:
 
(void) - addWithPath:specification:andSetToJSONValue:completionHandler:
 
(void) - addWithPath:specification:andSetToJSONValue:constraint:completionHandler:
 
(PTDiffusionJSONUpdateStream *) - jsonUpdateStreamWithPath:
 
(PTDiffusionJSONUpdateStream *) - jsonUpdateStreamWithPath:constraint:
 
(PTDiffusionJSONUpdateStream *) - jsonUpdateStreamWithPath:specification:
 
(PTDiffusionJSONUpdateStream *) - jsonUpdateStreamWithPath:specification:constraint:
 
(BOOL) - setWithPath:toStringValue:completionHandler:error:
 
(void) - setWithPath:toDoubleValue:completionHandler:
 
(BOOL) - setWithPath:toDoubleFloatNumberValue:completionHandler:error:
 
(void) - setWithPath:toLongLongValue:completionHandler:
 
(BOOL) - setWithPath:toInt64NumberValue:completionHandler:error:
 
(BOOL) - setWithPath:toStringValue:constraint:completionHandler:error:
 
(void) - setWithPath:toDoubleValue:constraint:completionHandler:
 
(BOOL) - setWithPath:toDoubleFloatNumberValue:constraint:completionHandler:error:
 
(void) - setWithPath:toLongLongValue:constraint:completionHandler:
 
(BOOL) - setWithPath:toInt64NumberValue:constraint:completionHandler:error:
 
(BOOL) - addWithPath:specification:andSetToStringValue:completionHandler:error:
 
(void) - addWithPath:specification:andSetToDoubleValue:completionHandler:
 
(BOOL) - addWithPath:specification:andSetToDoubleFloatNumberValue:completionHandler:error:
 
(void) - addWithPath:specification:andSetToLongLongValue:completionHandler:
 
(BOOL) - addWithPath:specification:andSetToInt64NumberValue:completionHandler:error:
 
(BOOL) - addWithPath:specification:andSetToStringValue:constraint:completionHandler:error:
 
(void) - addWithPath:specification:andSetToDoubleValue:constraint:completionHandler:
 
(BOOL) - addWithPath:specification:andSetToDoubleFloatNumberValue:constraint:completionHandler:error:
 
(void) - addWithPath:specification:andSetToLongLongValue:constraint:completionHandler:
 
(BOOL) - addWithPath:specification:andSetToInt64NumberValue:constraint:completionHandler:error:
 
(PTDiffusionStringUpdateStream *) - stringUpdateStreamWithPath:
 
(PTDiffusionNumberUpdateStream *) - doubleFloatNumberUpdateStreamWithPath:
 
(PTDiffusionNumberUpdateStream *) - int64NumberUpdateStreamWithPath:
 
(PTDiffusionStringUpdateStream *) - stringUpdateStreamWithPath:constraint:
 
(PTDiffusionNumberUpdateStream *) - doubleFloatNumberUpdateStreamWithPath:constraint:
 
(PTDiffusionNumberUpdateStream *) - int64NumberUpdateStreamWithPath:constraint:
 
(PTDiffusionStringUpdateStream *) - stringUpdateStreamWithPath:specification:
 
(PTDiffusionNumberUpdateStream *) - doubleFloatNumberUpdateStreamWithPath:specification:
 
(PTDiffusionNumberUpdateStream *) - int64NumberUpdateStreamWithPath:specification:
 
(PTDiffusionStringUpdateStream *) - stringUpdateStreamWithPath:specification:constraint:
 
(PTDiffusionNumberUpdateStream *) - doubleFloatNumberUpdateStreamWithPath:specification:constraint:
 
(PTDiffusionNumberUpdateStream *) - int64NumberUpdateStreamWithPath:specification:constraint:
 
(void) - setWithPath:toRecordValue:completionHandler:
 
(void) - setWithPath:toRecordValue:constraint:completionHandler:
 
(void) - addWithPath:specification:andSetToRecordValue:completionHandler:
 
(void) - addWithPath:specification:andSetToRecordValue:constraint:completionHandler:
 
(PTDiffusionRecordV2UpdateStream *) - recordUpdateStreamWithPath:
 
(PTDiffusionRecordV2UpdateStream *) - recordUpdateStreamWithPath:constraint:
 
(PTDiffusionRecordV2UpdateStream *) - recordUpdateStreamWithPath:specification:
 
(PTDiffusionRecordV2UpdateStream *) - recordUpdateStreamWithPath:specification:constraint:
 

Additional Inherited Members

- Properties inherited from PTDiffusionFeature
PTDiffusionSessionsession
 

Method Documentation

- (void) addFallbackStream: (PTDiffusionValueStream *)  stream

When a matching update is received from the server for a topic, it will be passed on to all value streams that have been added with matching selectors. If no value stream is registered with a matching selector, the fallback value streams that have been registered using this method will be called instead.

Zero, one, or many fallback value streams can be set. If there is no fallback value stream, updates that match no other will be discarded.

Parameters
streamHandler of value stream events not handled by an explicitly registered topic selector. The delegate associated with this stream will be sent messages asynchronously on the main dispatch queue.
Exceptions
NSInvalidArgumentExceptionRaised if the supplied stream argument is nil.
Since
5.9
Deprecated:
since 6.5 Use addFallBackStream:error:
- (BOOL) addFallbackStream: (PTDiffusionValueStream *)  stream
error: (NSError **)  error 

When a matching update is received from the server for a topic, it will be passed on to all value streams that have been added with matching selectors. If no value stream is registered with a matching selector, the fallback value streams that have been registered using this method will be called instead.

Zero, one, or many fallback value streams can be set. If there is no fallback value stream, updates that match no other will be discarded.

Parameters
streamHandler of value stream events not handled by an explicitly registered topic selector. The delegate associated with this stream will be sent messages asynchronously on the main dispatch queue.
errorMay be 'nil'. Is supplied then will contain reason on failure.
Returns
YES if stream was successfully added
Exceptions
NSInvalidArgumentExceptionRaised if the supplied stream argument is nil.
Since
6.5
- (void) addStream: (PTDiffusionValueStream *)  stream
withSelector: (PTDiffusionTopicSelector *)  selector 

Add a value stream to receive topic updates for topics that match the given topic selector.

When a value update is received from the server, it will be passed to all streams that have been added with matching selectors. If there is more than one match, the order in which the streams are called is not defined. If there is no matching stream, the fallback stream(s) will be called instead.

Parameters
streamHandler of value stream events against this selector. The delegate associated with this stream will be sent messages asynchronously on the main dispatch queue.
selectorThe topic selector to be evaluated locally.
Exceptions
NSInvalidArgumentExceptionRaised if any supplied arguments are nil.
Since
5.9
Deprecated:
since 6.5 Use addStream:withSelector:error:
- (BOOL) addStream: (PTDiffusionValueStream *)  stream
withSelector: (PTDiffusionTopicSelector *)  selector
error: (NSError **)  error 

Add a value stream to receive topic updates for topics that match the given topic selector.

When a value update is received from the server, it will be passed to all streams that have been added with matching selectors. If there is more than one match, the order in which the streams are called is not defined. If there is no matching stream, the fallback stream(s) will be called instead.

Parameters
streamHandler of value stream events against this selector. The delegate associated with this stream will be sent messages asynchronously on the main dispatch queue.
selectorThe topic selector to be evaluated locally.
errorMay be 'nil'. Is supplied then will contain reason on failure.
Returns
YES if stream was successfully added
Exceptions
NSInvalidArgumentExceptionRaised if any supplied arguments are nil.
Since
6.5
- (void) addStream: (PTDiffusionValueStream *)  stream
withSelectorExpression: (NSString *)  expression 

Add a value stream to receive topic updates for topics that match the given topic selector expression.

This convenience method calls addStream:withSelector: having constructed a PTDiffusionTopicSelector instance using the given expression.

Parameters
streamHandler of value stream events against this selector. The delegate associated with this stream will be sent messages asynchronously on the main dispatch queue.
expressionThe topic selector expression to be evaluated locally.
Exceptions
NSInvalidArgumentExceptionRaised if any supplied arguments are nil.
Since
6.0
Deprecated:
since 6.5 Use addStream:withSelectorExpression:error:
- (BOOL) addStream: (PTDiffusionValueStream *)  stream
withSelectorExpression: (NSString *)  expression
error: (NSError **)  error 

Add a value stream to receive topic updates for topics that match the given topic selector expression.

This convenience method calls addStream:withSelector: having constructed a PTDiffusionTopicSelector instance using the given expression.

Parameters
streamHandler of value stream events against this selector. The delegate associated with this stream will be sent messages asynchronously on the main dispatch queue.
expressionThe topic selector expression to be evaluated locally.
errorMay be 'nil'. Is supplied then will contain reason on failure.
Returns
YES if stream was successfully added
Exceptions
NSInvalidArgumentExceptionRaised if any supplied arguments are nil.
Since
6.5
- (PTDiffusionFetchRequest *) fetchRequest

Creates an unconfigured fetch request.

If the request is invoked by calling fetchWithTopicSelectorExpression:completionHandler: (PTDiffusionFetchRequest) the fetch result will provide the paths and types of all of the topics which the session has permission to read.

You will usually want to restrict the query to a subset of the topic tree, and to retrieve the topic values and/or properties. This is achieved by applying one or more of the builder methods to produce more refined requests.

For example (Swift):

topics.fetchRequest()
    .fetchStringValues(withTopicSelectorExpression: "*A/B//")
    {
        (result: PTDiffusionStringFetchResult?, error: Error?) in
        / / TODO Handle result, if not `nil`, otherwise handle error.
    }
Returns
a new unconfigured fetch request
Since
6.2
- (BOOL) removeStream: (nullable PTDiffusionStream *)  stream

Remove a topic or value stream that was previously added using a topic selector or as a fallback.

Parameters
streamThe stream to remove.
Returns
YES if the stream was removed.
Note
If the supplied stream argument is nil or the stream has already been removed from the feature then calls to this method do nothing and return NO.
Since
5.9
- (void) subscribeWithTopicSelectorExpression: (NSString *)  expression
completionHandler: (NSError *_Nullable error)  completionHandler 

Request subscription to topics.

The session will become subscribed to each existing topic matching the selector unless the session is already subscribed to the topic, or the session does not have READ_TOPIC permission for the topic path. For each topic to which the session becomes subscribed, a subscription notification and initial value (if any) will be delivered to registered value streams before the completion handler is called.

The subscription request is also retained at the server and the session will be automatically subscribed to newly created topics that match the selector (unless a subsequent unsubscription cancels the request).

Parameters
expressionThe topic selector expression to be evaluated by the server.
completionHandlerBlock to be called asynchronously on success or failure. If the operation was successful, the error argument passed to the block will be nil. The completion handler will be called asynchronously on the main dispatch queue.
Exceptions
NSInvalidArgumentExceptionRaised if any supplied arguments are nil.
Since
5.6
- (void) unsubscribeFromTopicSelectorExpression: (NSString *)  expression
completionHandler: (NSError *_Nullable error)  completionHandler 

Request unsubscription from topics.

Parameters
expressionThe topic selector expression to be evaluated by the server.
completionHandlerBlock to be called asynchronously on success or failure. If the operation was successful, the error argument passed to the block will be nil. The completion handler will be called asynchronously on the main dispatch queue.
Exceptions
NSInvalidArgumentExceptionRaised if any supplied arguments are nil.
Since
5.6