Node.js Client 9.1.0

SubscriptionListener

SubscriptionListener

Interface to be implemented to listen to Subscription events comprehending notifications of subscription/unsubscription, updates, errors and others.
Events for this listeners are executed asynchronously with respect to the code that generates them.
Note that it is not necessary to implement all of the interface methods for the listener to be successfully passed to the Subscription#addListener method.

Constructor

new SubscriptionListener()

This is a dummy constructor not to be used in any case.

Methods

onClearSnapshot(itemName, itemPos)

Event handler that is called by Lightstreamer each time a request to clear the snapshot pertaining to an item in the Subscription has been received from the Server. More precisely, this kind of request can occur in two cases:

  • For an item delivered in COMMAND mode, to notify that the state of the item becomes empty; this is equivalent to receiving an update carrying a DELETE command once for each key that is currently active.
  • For an item delivered in DISTINCT mode, to notify that all the previous updates received for the item should be considered as obsolete; hence, if the listener were showing a list of recent updates for the item, it should clear the list in order to keep a coherent view.

Note that, if the involved Subscription has a two-level behavior enabled, the notification refers to the first-level item (which is in COMMAND mode). This kind of notification is not possible for second-level items (which are in MERGE mode).
This event can be sent by the Lightstreamer Server since version 6.0
Parameters:
Name Type Description
itemName String

name of the involved item. If the Subscription was initialized using an "Item Group" then a null value is supplied.
itemPos Number

1-based position of the item within the "Item List" or "Item Group".

onCommandSecondLevelItemLostUpdates(lostUpdates, key)

Event handler that is called by Lightstreamer to notify that, due to internal resource limitations, Lightstreamer Server dropped one or more updates for an item that was subscribed to as a second-level subscription. Such notifications are sent only if the Subscription was configured in unfiltered mode (second-level items are always in "MERGE" mode and inherit the frequency configuration from the first-level Subscription).
By implementing this method it is possible to perform recovery actions.

Parameters:
Name Type Description
lostUpdates Number

The number of consecutive updates dropped for the item.
key String

The value of the key that identifies the second-level item.
See:

onCommandSecondLevelSubscriptionError(code, message, key)

Event handler that is called when the Server notifies an error on a second-level subscription.
By implementing this method it is possible to perform recovery actions.

Parameters:
Name Type Description
code Number

The error code sent by the Server. It can be one of the following:

  • 14 - the key value is not a valid name for the Item to be subscribed; only in this case, the error is detected directly by the library before issuing the actual request to the Server
  • 17 - bad Data Adapter name or default Data Adapter not defined for the current Adapter Set
  • 21 - bad Group name
  • 22 - bad Group name for this Schema
  • 23 - bad Schema name
  • 24 - mode not allowed for an Item
  • 26 - unfiltered dispatching not allowed for an Item, because a frequency limit is associated to the item
  • 27 - unfiltered dispatching not supported for an Item, because a frequency prefiltering is applied for the item
  • 28 - unfiltered dispatching is not allowed by the current license terms (for special licenses only)
  • 66 - an unexpected exception was thrown by the Metadata Adapter while authorizing the connection
  • 68 - the Server could not fulfill the request because of an internal error.
  • <= 0 - the Metadata Adapter has refused the subscription or unsubscription request; the code value is dependent on the specific Metadata Adapter implementation
message String

The description of the error sent by the Server; it can be null.
key String

The value of the key that identifies the second-level item.
See:

onEndOfSnapshot(itemName, itemPos)

Event handler that is called by Lightstreamer to notify that all snapshot events for an item in the Subscription have been received, so that real time events are now going to be received. The received snapshot could be empty. Such notifications are sent only if the items are delivered in DISTINCT or COMMAND subscription mode and snapshot information was indeed requested for the items. By implementing this method it is possible to perform actions which require that all the initial values have been received.
Note that, if the involved Subscription has a two-level behavior enabled, the notification refers to the first-level item (which is in COMMAND mode). Snapshot-related updates for the second-level items (which are in MERGE mode) can be received both before and after this notification.

Parameters:
Name Type Description
itemName String

name of the involved item. If the Subscription was initialized using an "Item Group" then a null value is supplied.
itemPos Number

1-based position of the item within the "Item List" or "Item Group".
See:

onItemLostUpdates(itemName, itemPos, lostUpdates)

Event handler that is called by Lightstreamer to notify that, due to internal resource limitations, Lightstreamer Server dropped one or more updates for an item in the Subscription. Such notifications are sent only if the items are delivered in an unfiltered mode; this occurs if the subscription mode is:

  • RAW
  • MERGE or DISTINCT, with unfiltered dispatching specified
  • COMMAND, with unfiltered dispatching specified
  • COMMAND, without unfiltered dispatching specified (in this case, notifications apply to ADD and DELETE events only)
By implementing this method it is possible to perform recovery actions.
Parameters:
Name Type Description
itemName String

name of the involved item. If the Subscription was initialized using an "Item Group" then a null value is supplied.
itemPos Number

1-based position of the item within the "Item List" or "Item Group".
lostUpdates Number

The number of consecutive updates dropped for the item.
See:

onItemUpdate(updateInfo)

Event handler that is called by Lightstreamer each time an update pertaining to an item in the Subscription has been received from the Server.

Parameters:
Name Type Description
updateInfo ItemUpdate

a value object containing the updated values for all the fields, together with meta-information about the update itself and some helper methods that can be used to iterate through all or new values.

onListenEnd()

Event handler that receives a notification when the SubscriptionListener instance is removed from a Subscription through Subscription#removeListener. This is the last event to be fired on the listener.

onListenStart()

Event handler that receives a notification when the SubscriptionListener instance is added to a Subscription through Subscription#addListener. This is the first event to be fired on the listener.

onRealMaxFrequency(frequency)

Event handler that is called by Lightstreamer to notify the client with the real maximum update frequency of the Subscription. It is called immediately after the Subscription is established and in response to a requested change (see Subscription#setRequestedMaxFrequency). Since the frequency limit is applied on an item basis and a Subscription can involve multiple items, this is actually the maximum frequency among all items. For Subscriptions with two-level behavior (see Subscription#setCommandSecondLevelFields and Subscription#setCommandSecondLevelFieldSchema) , the reported frequency limit applies to both first-level and second-level items.
The value may differ from the requested one because of restrictions operated on the server side, but also because of number rounding.
Note that a maximum update frequency (that is, a non-unlimited one) may be applied by the Server even when the subscription mode is RAW or the Subscription was done with unfiltered dispatching.

Parameters:
Name Type Description
frequency String

A decimal number, representing the maximum frequency applied by the Server (expressed in updates per second), or the string "unlimited". A null value is possible in rare cases, when the frequency can no longer be determined.

onSubscription()

Event handler that is called by Lightstreamer to notify that a Subscription has been successfully subscribed to through the Server. This can happen multiple times in the life of a Subscription instance, in case the Subscription is performed multiple times through LightstreamerClient#unsubscribe and LightstreamerClient#subscribe. This can also happen multiple times in case of automatic recovery after a connection restart.
This notification is always issued before the other ones related to the same subscription. It invalidates all data that has been received previously.
Note that two consecutive calls to this method are not possible, as before a second onSubscription event is fired an onUnsubscription event is eventually fired.
If the involved Subscription has a two-level behavior enabled, second-level subscriptions are not notified.

onSubscriptionError(code, message)

Event handler that is called when the Server notifies an error on a Subscription. By implementing this method it is possible to perform recovery actions.
Note that, in order to perform a new subscription attempt, LightstreamerClient#unsubscribe and LightstreamerClient#subscribe should be issued again, even if no change to the Subscription attributes has been applied.

Parameters:
Name Type Description
code Number

The error code sent by the Server. It can be one of the following:

  • 15 - "key" field not specified in the schema for a COMMAND mode subscription
  • 16 - "command" field not specified in the schema for a COMMAND mode subscription
  • 17 - bad Data Adapter name or default Data Adapter not defined for the current Adapter Set
  • 21 - bad Group name
  • 22 - bad Group name for this Schema
  • 23 - bad Schema name
  • 24 - mode not allowed for an Item
  • 25 - bad Selector name
  • 26 - unfiltered dispatching not allowed for an Item, because a frequency limit is associated to the item
  • 27 - unfiltered dispatching not supported for an Item, because a frequency prefiltering is applied for the item
  • 28 - unfiltered dispatching is not allowed by the current license terms (for special licenses only)
  • 29 - RAW mode is not allowed by the current license terms (for special licenses only)
  • 30 - subscriptions are not allowed by the current license terms (for special licenses only)
  • 66 - an unexpected exception was thrown by the Metadata Adapter while authorizing the connection
  • 68 - the Server could not fulfill the request because of an internal error.
  • <= 0 - the Metadata Adapter has refused the subscription or unsubscription request; the code value is dependent on the specific Metadata Adapter implementation
message String

The description of the error sent by the Server; it can be null.
See:

onUnsubscription()

Event handler that is called by Lightstreamer to notify that a Subscription has been successfully unsubscribed from. This can happen multiple times in the life of a Subscription instance, in case the Subscription is performed multiple times through LightstreamerClient#unsubscribe and LightstreamerClient#subscribe. This can also happen multiple times in case of automatic recovery after a connection restart.


After this notification no more events can be recieved until a new SubscriptionListener#onSubscription event.
Note that two consecutive calls to this method are not possible, as before a second onUnsubscription event is fired an onSubscription event is eventually fired.
If the involved Subscription has a two-level behavior enabled, second-level unsubscriptions are not notified.