Package com.lightstreamer.interfaces.metadata

Interface MetadataProvider

All Known Implementing Classes:
LiteralBasedProvider, MetadataProviderAdapter
public interface MetadataProvider
Provides an interface to be implemented by a Metadata Adapter in order to attach a Metadata Provider to Lightstreamer Kernel. The configuration of an Adapter instance requires the following items:
  • a unique identification for the instance;
  • the Adapter class name;
  • optional configuration parameters.
A Metadata Provider is used by Lightstreamer Kernel in combination with one or multiple Data Providers, uniquely associated with it. The configuration is accomplished through the "adapters.xml" configuration files, by which one or more "Adapter Sets" can be installed into the Server, where each Adapter Set is made up of exactly one Metadata Adapter and one or multiple Data Adapters.
A single instance of each configured Metadata Adapter is created by Lightstreamer Kernel at startup, then its init method is called, providing it with the configuration information. For this purpose, any Metadata Adapter must provide a void constructor.
Note: in order to support method extensions, the Server may inspect The Metadata Adapter binaries to look for methods based on old signatures. For this reason, the custom part of the Adapter implementation is only allowed to contain a single public overload for each interface method, otherwise the Adapter can be refused (with the exception of notifyUser, which has two overloaded versions). But see MetadataProviderAdapter and LiteralBasedProvider for special cases related to the use of these classes.

A Metadata Provider is consulted by Lightstreamer Kernel in order to manage the push Requests intended for the associated Data Providers. A Metadata Provider supplies information for several different goals:
  • the resolution of the Group/Schema names used in the Requests;
  • the check of the User accessibility to the requested Items;
  • the check of the resource level granted to the User.
  • the request for specific characteristics of the Items.
Note that each Item may be supplied by one or more of the associated Data Adapters, hence each client Request always references a specific Data Adapter.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    customizeUpdate(String user, String item, String dataAdapter, CustomizableItemEvent event)
    Called by Lightstreamer Kernel in order to customize events pertaining to an ItemEventBuffer, if such customization has been requested through the enableUpdateCustomization method.
    boolean
    enableUpdateCustomization(String user, String item, String dataAdapter)
    Called by Lightstreamer Kernel to know whether the Metadata Adapter must or must not be given a chance to modify the values carried by the updates for a supplied Item in a push Session owned by a supplied User.
    int
    getAllowedBufferSize(String user, String item, String dataAdapter)
    Called by Lightstreamer Kernel to ask for the maximum size allowed for the buffer internally used to enqueue subsequent ItemUpdates for the same Item.
    double
    getAllowedMaxBandwidth(String user)
    Called by Lightstreamer Kernel to ask for the bandwidth level to be allowed to a User for a push Session.
    double
    getAllowedMaxItemFrequency(String user, String item, String dataAdapter)
    Called by Lightstreamer Kernel to ask for the ItemUpdate frequency to be allowed to a User for a specific Item.
    int
    getDistinctSnapshotLength(String item, String dataAdapter)
    Called by Lightstreamer Kernel to ask for the maximum allowed length for a Snapshot of an Item that has been requested with publishing Mode DISTINCT.
    String[]
    getItems(String user, String sessionID, String group, String dataAdapter)
    Called by Lightstreamer Kernel to resolve an Item Group name (or Item List specification) supplied in a Request.
    double
    getMinSourceFrequency(String item, String dataAdapter)
    Called by Lightstreamer Kernel to ask for the minimum ItemEvent frequency that ensures that all subscribers of an Item can be fed with an adequate amount of information.
    String[]
    getSchema(String user, String sessionID, String group, String dataAdapter, String schema)
    Called by Lightstreamer Kernel to resolve a Field Schema name (or Field List specification) supplied in a Request.
    default int
    getSessionTimeToLive(String user, String session)
    Called by Lightstreamer Kernel to ask for an optional time-to-live setting for a session just started.
    void
    init(Map params, File configDir)
    Called by Lightstreamer Kernel to provide initialization information to the Metadata Adapter.
    boolean
    isModeAllowed(String user, String item, String dataAdapter, Mode mode)
    Called by Lightstreamer Kernel to ask for the allowance of a publishing Mode for an Item.
    boolean
    isSelected(String user, String item, String dataAdapter, String selector, ItemEvent event)
    Called by Lightstreamer Kernel in order to filter events pertaining to an ItemEventBuffer, if the related Item was requested within a Table (i.e.: Subscription) with an associated Selector.
    boolean
    isSelectorAllowed(String user, String item, String dataAdapter, String selector)
    Called by Lightstreamer Kernel to ask for the allowance of a Selector for an Item.
    boolean
    modeMayBeAllowed(String item, String dataAdapter, Mode mode)
    Called by Lightstreamer Kernel to ask for the allowance of a publishing Mode for an Item (for at least one User).
    void
    notifyMpnDeviceAccess(String user, String sessionID, MpnDeviceInfo device)
    Called by Lightstreamer Kernel to check that a User is enabled to access the specified MPN device.
    void
    notifyMpnDeviceTokenChange(String user, String sessionID, MpnDeviceInfo device, String newDeviceToken)
    Called by Lightstreamer Kernel to check that a User is enabled to change the token of an MPN device.
    void
    notifyMpnSubscriptionActivation(String user, String sessionID, TableInfo table, MpnSubscriptionInfo mpnSubscription)
    Called by Lightstreamer Kernel to check that a User is enabled to activate a Push Notification subscription.
    void
    notifyNewSession(String user, String sessionID, Map clientContext)
    Called by Lightstreamer Kernel to check that a User is enabled to open a new push Session.
    void
    notifyNewTables(String user, String sessionID, TableInfo[] tables)
    Called by Lightstreamer Kernel to check that a User is enabled to add some Tables (i.e.: Subscriptions) to a push Session.
    void
    notifySessionClose(String sessionID)
    Called by Lightstreamer Kernel to notify the Metadata Adapter that a push Session has been closed.
    void
    notifyTablesClose(String sessionID, TableInfo[] tables)
    Called by Lightstreamer Kernel to notify the Metadata Adapter that some Tables (i.e.: Subscriptions) have been removed from a push Session.
    void
    notifyUser(String user, String password, Map httpHeaders)
    Called by Lightstreamer Kernel as a preliminary check that a user is enabled to make Requests to any of the related Data Providers.
    void
    notifyUser(String user, String password, Map httpHeaders, String clientPrincipal)
    Called by Lightstreamer Kernel, instead of calling the 3-arguments version, in case the Server has been instructed to acquire the client principal from the client TLS/SSL certificate through the <use_client_auth> configuration flag.
    void
    notifyUserMessage(String user, String sessionID, String message)
    Called by Lightstreamer Kernel to forward a message received by a User.
    default void
    setListener(MetadataControlListener listener)
    Called by Lightstreamer Kernel to provide a listener to receive requests about sessions and any asynchronous severe error notification.
    boolean
    wantsTablesNotification(String user)
    Called by Lightstreamer Kernel to know whether the Metadata Adapter must or must not be notified any time a Table (i.e.: Subscription) is added or removed from a push Session owned by a supplied User.

  • Method Details

    • init

      void init(@Nonnull Map params, @Nonnull File configDir) throws MetadataProviderException
      Called by Lightstreamer Kernel to provide initialization information to the Metadata Adapter.

      The call must not be blocking; any polling cycle or similar must be started in a different thread. Any delay in returning from this call will in turn delay the Kernel initialization. If an exception occurs in this method, Lightstreamer Kernel can't complete the startup and must exit.
      Parameters:
      params - A Map-type value object that contains name-value pairs corresponding to the "param" elements supplied in the Metadata Adapter configuration file under the "metadata_provider" element. Both names and values are represented as String objects.
      In addition, the following entries are added by the Server:
      • "adapters_conf.id" - the associated value is a string which reports the name configured for the Adapter Set, i.e. the name specified for the "id" attribute of the <adapters_conf> element.
      configDir - The path of the directory on the local disk where the Metadata Adapter configuration file resides.
      Throws:
      MetadataProviderException - if an error occurs that prevents the correct behavior of the Metadata Adapter. This causes the Server not to complete the startup and to exit.

    • setListener

      default void setListener(@Nonnull MetadataControlListener listener)
      Called by Lightstreamer Kernel to provide a listener to receive requests about sessions and any asynchronous severe error notification. If these features are not needed, the method can be left unimplemented (sticking to its default implementation). The listener is set after init and before any other method is called and it is never changed.
      Parameters:
      listener - a listener.

    • notifyUser

      void notifyUser(@Nullable String user, @Nullable String password, @Nonnull Map httpHeaders) throws AccessException, CreditsException
      Called by Lightstreamer Kernel as a preliminary check that a user is enabled to make Requests to any of the related Data Providers. It is invoked upon each session request and it is called prior to any other session-related request. So, any other method with a User argument can assume that the supplied User argument has already been checked.
      The User authentication should be based on the user and password arguments supplied by the client. The full report of the request HTTP headers is also available; they could be used in order to gather information about the client, but should not be used for authentication, as they may not be under full control by client code. See also the discussion about the <use_protected_js> Server configuration element, if available.

      The method should perform as fast as possible. If the implementation is slow because of complex data gathering operations, it might delay the client session activation. In that case, configuring a dedicated "AUTHENTICATION" thread pool for authentication requests on this Adapter Set is recommended, in order not to block operations for different Adapter Sets or different operations for this Adapter Set. Also consider that a slow implementation may cause a "connection timeout" posed on the client side to expire, with a consequent new attempt; it is advisable that the second invocation can take advantage of the work already performed during the first invocation.
      Parameters:
      user - A User name.
      password - A password optionally required to validate the User.
      httpHeaders - A Map-type value object that contains a name-value pair for each header found in the HTTP request that originated the call. The header names are reported in lower-case form.
      For headers defined multiple times, a unique name-value pair is reported, where the value is a concatenation of all the supplied header values, separated by a ",".
      Throws:
      AccessException - if the User name is not known or the supplied password is not correct.
      If the User credentials cannot be validated because of a temporary lack of resources, then a ResourceUnavailableException can be thrown. This will instruct the client to retry in short time.
      CreditsException - if the User is known but is not enabled to make further Requests at the moment.
      See Also:

    • notifyUser

      void notifyUser(@Nullable String user, @Nullable String password, @Nonnull Map httpHeaders, @Nonnull String clientPrincipal) throws AccessException, CreditsException
      Called by Lightstreamer Kernel, instead of calling the 3-arguments version, in case the Server has been instructed to acquire the client principal from the client TLS/SSL certificate through the <use_client_auth> configuration flag.
      Note that the above flag can be set for each listening port independently (and it can be set for TLS/SSL ports only), hence, both overloads may be invoked, depending on the port used by the client.
      Also note that in case client certificate authentication is not forced on a listening port through <force_client_auth>, a client request issued on that port may not be authenticated, hence it may have no principal associated. In that case, if <use_client_auth> is set, this overload will still be invoked, with null principal.
      See the base 3-arguments version for other notes.
      Edition Note:
      https is an optional feature, available depending on Edition and License Type. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).
      Parameters:
      user - A User name.
      password - A password optionally required to validate the User.
      httpHeaders - A Map-type value object that contains a name-value pair for each header found in the HTTP request that originated the call.
      clientPrincipal - the identification name reported in the client TLS/SSL certificate supplied on the socket connection used to issue the request that originated the call; it can be null if client has not authenticated itself or the authentication has failed.
      Throws:
      AccessException - if the User name is not known or the supplied password is not correct.
      If the User credentials cannot be validated because of a temporary lack of resources, then a ResourceUnavailableException can be thrown. This will instruct the client to retry in short time.
      CreditsException - if the User is known but is not enabled to make further Requests at the moment.

    • getItems

      @Nonnull String[] getItems(@Nullable String user, @Nonnull String sessionID, @Nonnull String group, @Nonnull String dataAdapter) throws ItemsException
      Called by Lightstreamer Kernel to resolve an Item Group name (or Item List specification) supplied in a Request. The names of the Items in the Group must be returned. For instance, the client could be allowed to specify the "NASDAQ100" Group name and, upon that, the list of all items corresponding to the stocks included in that index could be returned.
      Possibly, the content of an Item Group may be dependent on the User who is issuing the Request or on the specific Session instance.

      When an Item List specification is supplied, it is made of a space-separated list of the names of the items in the List. This convention is used by some of the subscription methods provided by the various client libraries. The specifications for these methods require that "A LiteralBasedProvider or equivalent Metadata Adapter is needed on the Server in order to understand the Request".
      When any of these interface methods is used by client code accessing this Metadata Adapter, the supplied "group" argument should be inspected as a space-separated list of Item names and an array with these names in the same order should be returned.

      Another typical case is when the same Item has different contents depending on the User that is issuing the request. On the Data Adapter side, different Items (one for each User) can be used; nevertheless, on the client side, the same name can be specified in the subscription request and the actual user-related name can be determined and returned here. For instance: 
       
 if (group.equals("portfolio")) {
     String itemName = "PF_" + user;
     return new String[] { itemName };
 } else if (group.startsWith("PF_")) {
     // protection from unauthorized use of user-specific items
     throw new ItemsException("Unexpected group name");
 }
      Obviously, the two above techniques can be combined, hence any element of an Item List can be replaced with a decorated or alternative Item name: the related updates will be associated to the original name used in the supplied Item List specification by client library code.

      The method should perform fast. External information needed to execute it should have been previously gathered and cached by notifyUser(String, String, Map). If the implementation is slow, it might delay the subscription request management. In that case, configuring a dedicated "SET" thread pool for requests on this Adapter Set is recommended, in order not to block operations for different Adapter Sets. If the delay affects requests for a specific Data Adapter, then configuring a dedicated "DATA" thread pool for that Data Adapter is a better option.
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User.
      group - An Item Group name (or Item List specification).
      dataAdapter - The name of the Data Adapter to which the subscription is targeted.
      Returns:
      An array with the names of the Items in the Group.
      Throws:
      ItemsException - if the supplied Item Group name (or Item List specification) is not recognized.

    • getSchema

      @Nonnull String[] getSchema(@Nullable String user, @Nonnull String sessionID, @Nonnull String group, @Nonnull String dataAdapter, @Nonnull String schema) throws ItemsException, SchemaException
      Called by Lightstreamer Kernel to resolve a Field Schema name (or Field List specification) supplied in a Request. The names of the Fields in the Schema must be returned.
      Possibly, the content of a Field Schema may be dependent on the User who is issuing the Request, on the specific Session instance or on the Item Group (or Item List) to which the Request is related.

      When a Field List specification is supplied, it is made of a space-separated list of the names of the Fields in the Schema. This convention is used by some of the subscription methods provided by the various client libraries. The specifications for these methods require that "A LiteralBasedProvider or equivalent Metadata Adapter is needed on the Server in order to understand the Request".
      When any of these interface methods is used by client code accessing this Metadata Adapter, the supplied "schema" argument should be inspected as a space-separated list of Field names and an array with these names in the same order should be returned; returning decorated or alternative Field names is also possible: they will be associated to the corresponding names used in the supplied Field List specification by client library code.

      The method should perform fast. See the notes for getItems(String, String, String, String).
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User.
      group - The name of the Item Group (or specification of the Item List) whose Items the Schema is to be applied to.
      dataAdapter - The name of the Data Adapter to which the subscription is targeted.
      schema - A Field Schema name (or Field List specification).
      Returns:
      An array with the names of the Fields in the Schema.
      Throws:
      ItemsException - if the supplied Item Group name (or Item List specification) is not recognized.
      SchemaException - if the supplied Field Schema name (or Field List specification) is not recognized.

    • getAllowedMaxBandwidth

      double getAllowedMaxBandwidth(@Nullable String user)
      Called by Lightstreamer Kernel to ask for the bandwidth level to be allowed to a User for a push Session.

      The method should perform fast. External information needed to execute it should have been previously gathered and cached by notifyUser(String, String, Map). If the implementation is slow, it might delay the client session activation. In that case, configuring a dedicated "SET" thread pool for requests on this Adapter Set is recommended, in order not to block operations for different Adapter Sets.
      Edition Note:
      Bandwidth Control is an optional feature, available depending on Edition and License Type. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).
      Parameters:
      user - A User name.
      Returns:
      The allowed bandwidth, in Kbit/sec. A zero return value means an unlimited bandwidth.

    • getAllowedMaxItemFrequency

      double getAllowedMaxItemFrequency(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter)
      Called by Lightstreamer Kernel to ask for the ItemUpdate frequency to be allowed to a User for a specific Item. An unlimited frequency can also be specified.
      Such filtering applies only to Items requested with publishing Mode MERGE, DISTINCT and COMMAND (in the latter case, the frequency limitation applies to the UPDATE events for each single key). If an Item is requested with publishing Mode MERGE, DISTINCT or COMMAND and unfiltered dispatching has been specified, then returning any limited maximum frequency will cause the refusal of the request by the Kernel.

      The method should perform fast. See the notes for getItems(String, String, String, String).
      Edition Note:
      A further global frequency limit could also be imposed by the Server, depending on Edition and License Type; this specific limit also applies to RAW mode and to unfiltered dispatching. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).
      Parameters:
      user - A User name.
      item - An Item Name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      Returns:
      The allowed Update frequency, in Updates/sec. A zero return value means no frequency restriction.

    • getAllowedBufferSize

      int getAllowedBufferSize(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter)
      Called by Lightstreamer Kernel to ask for the maximum size allowed for the buffer internally used to enqueue subsequent ItemUpdates for the same Item. If this buffer is more than 1 element deep, a short burst of ItemEvents from the Data Adapter can be forwarded to the Client without losses, though with some delay.
      The buffer size is specified in the Request. Its maximum allowed size can be different for different Users.
      Such buffering applies only to Items requested with publishing Mode MERGE or DISTINCT. However, if the Item has been requested with unfiltered dispatching, then the buffer size is always unlimited and buffer size settings are ignored.

      The method should perform fast. See the notes for getItems(String, String, String, String).
      Parameters:
      user - A User name.
      item - An Item Name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      Returns:
      The allowed buffer size. A zero return value means a potentially unlimited buffer.

    • isModeAllowed

      boolean isModeAllowed(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter, @Nonnull Mode mode)
      Called by Lightstreamer Kernel to ask for the allowance of a publishing Mode for an Item. A publishing Mode can or cannot be allowed depending on the User.
      The Metadata Adapter should ensure that conflicting Modes are not both allowed for the same Item (even for different Users), otherwise some Requests will be eventually refused by Lightstreamer Kernel. The conflicting Modes are MERGE, DISTINCT and COMMAND.

      The method should perform fast. See the notes for getItems(String, String, String, String).
      Parameters:
      user - A User name.
      item - An Item name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      mode - A publishing Mode.
      Returns:
      true if the publishing Mode is allowed.

    • modeMayBeAllowed

      boolean modeMayBeAllowed(@Nonnull String item, @Nonnull String dataAdapter, @Nonnull Mode mode)
      Called by Lightstreamer Kernel to ask for the allowance of a publishing Mode for an Item (for at least one User). The Metadata Adapter should ensure that conflicting Modes are not both allowed for the same Item. The conflicting Modes are MERGE, DISTINCT and COMMAND.

      The method should perform fast. If the implementation is slow, it might delay the subscription request management. In that case, configuring a dedicated "SET" thread pool for requests on this Adapter Set is recommended, in order not to block operations for different Adapter Sets. If the delay affects requests for a specific Data Adapter, then configuring a dedicated "DATA" thread pool for that Data Adapter is a better option.
      Parameters:
      item - An Item name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      mode - A publishing Mode.
      Returns:
      true if the publishing Mode is allowed.

    • isSelectorAllowed

      boolean isSelectorAllowed(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter, @Nonnull String selector)
      Called by Lightstreamer Kernel to ask for the allowance of a Selector for an Item. Typically, a Selector is intended for one Item or for a specific set of Items with some characteristics. Moreover, a Selector can or cannot be allowed depending on the User.

      The method should perform fast. See the notes for getItems(String, String, String, String).
      Parameters:
      user - A User name.
      item - An Item name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      selector - A selector name.
      Returns:
      true if the Selector is allowed.

    • isSelected

      boolean isSelected(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter, @Nonnull String selector, @Nonnull ItemEvent event)
      Called by Lightstreamer Kernel in order to filter events pertaining to an ItemEventBuffer, if the related Item was requested within a Table (i.e.: Subscription) with an associated Selector. If the return value is true, the event is dispatched to the ItemEventBuffer; otherwise, it is filtered out.
      If any consistency rule for the update flow is guaranteed by the Server for the Item (e.g. mandatory snapshot in MERGE mode or ADD-UPDATE-DELETE sequencing in COMMAND mode), it is a responsibility of the isSelected method implementation to ensure that these consistency rules keep being honored.
      Upon a ItemEventListener.clearSnapshot(java.lang.String) request issued by the Data Adapter for an item in COMMAND mode, a special event is associated, with "key" field null and "command" field valued with "DELETEALL"; this event is equivalent to a DELETE event for each active key and it is shown to allow for keeping the item state and to help obeying the consistency rules, but it cannot be filtered out.

      The method must perform fast. External information needed to execute it must have been previously gathered and cached by notifyUser(String, String, Map). If the implementation were slow, the whole update delivery process, even for different sessions, would be slowed down.
      Parameters:
      user - A User name.
      item - An Item name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      selector - A selector name.
      event - An update event for the Item.
      Returns:
      true if the event is to be processed by the ItemEventBuffer.

    • enableUpdateCustomization

      boolean enableUpdateCustomization(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter)
      Called by Lightstreamer Kernel to know whether the Metadata Adapter must or must not be given a chance to modify the values carried by the updates for a supplied Item in a push Session owned by a supplied User. If this method returns true, the customizeUpdate method will be called for each update for these Item and User. If it returns false, the customizeUpdate method will never be called for these Item and User, saving some processing time.

      The method should perform fast. See the notes for getItems(String, String, String, String).
      Parameters:
      user - A User name.
      item - An Item name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      Returns:
      true if the Metadata Adapter must be notified any time an update for the Item is received in a Session owned by the User.

    • customizeUpdate

      void customizeUpdate(@Nullable String user, @Nonnull String item, @Nonnull String dataAdapter, @Nonnull CustomizableItemEvent event)
      Called by Lightstreamer Kernel in order to customize events pertaining to an ItemEventBuffer, if such customization has been requested through the enableUpdateCustomization method.
      The supplied event can be changed inside this method before being processed by the ItemEventBuffer. Note that the applied changes only affect one ItemEventBuffer instance. This means that impacts on overall performance may be significant if customization for some items applies to all sessions.
      If any consistency rule for the update is guaranteed by the Server for the Item, it is a responsibility of the customizeUpdate method implementation to ensure that these consistency rules keep being honoured; for example, "key" and "command" fields for an Item to be requested in COMMAND mode should not be altered.
      Upon a ItemEventListener.clearSnapshot(java.lang.String) request issued by the Data Adapter for an item in COMMAND mode, a special event is associated, with "key" field null and "command" field valued with "DELETEALL"; this event is equivalent to a DELETE event for each active key and it is shown to allow for keeping the item state, but it cannot be customized in any way.

      The method must perform fast. External information needed to execute it must have been previously gathered and cached by notifyUser(String, String, Map). If the implementation were slow, the whole update delivery process, even for different sessions, would be slowed down.
      Parameters:
      user - A User name.
      item - An Item name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      event - An update event for the Item, ready to be changed.

    • getMinSourceFrequency

      double getMinSourceFrequency(@Nonnull String item, @Nonnull String dataAdapter)
      Called by Lightstreamer Kernel to ask for the minimum ItemEvent frequency that ensures that all subscribers of an Item can be fed with an adequate amount of information. In practice, in case of an incoming ItemEvent frequency from the Data Adapter that is greater than the specified value, Lightstreamer Kernel may prefilter the events flow, by resampling it down to the specified frequency, before feeding the ItemEventBuffers. Such prefiltering applies only for Items requested with publishing Mode MERGE or DISTINCT.
      The frequency set should be greater than the ItemUpdate frequencies allowed to the different Users for the Item. Moreover, because this filtering is made without buffers, the frequency set should be far greater than the ItemUpdate frequencies allowed for the Item, in case buffering of event bursts is desired. If an Item is requested with publishing Mode MERGE or DISTINCT but with unfiltered dispatching, then specifying any limited source frequency will cause the refusal of the request by the Kernel.
      This feature is just for ItemEventBuffers protection against Items with a very fast flow on the supplier Data Adapter and a very slow flow allowed to the Clients. If this is the case, but just a few Clients need a fast or unfiltered flow for the same MERGE or DISTINCT Item, the use of two differently named Items that receive the same flow from the Data Adapter is suggested.

      The method should perform fast. See the notes for modeMayBeAllowed(String, String, Mode).
      Parameters:
      item - An Item Name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      Returns:
      The minimum ItemEvent frequency that must be processed without loss of information, in ItemEvents/sec. A zero return value indicates that incoming ItemEvents must not be prefiltered. If the ItemEvents frequency for the Item is known to be very low, returning zero allows Lightstreamer Kernel to save any prefiltering effort.

    • getDistinctSnapshotLength

      int getDistinctSnapshotLength(@Nonnull String item, @Nonnull String dataAdapter)
      Called by Lightstreamer Kernel to ask for the maximum allowed length for a Snapshot of an Item that has been requested with publishing Mode DISTINCT. In fact, in DISTINCT publishing Mode, the Snapshot for an Item is made by the last events received for the Item and the Client can specify how many events it would like to receive. Thus, Lightstreamer Kernel must always keep a buffer with some of the last events received for the Item and the lenght of the buffer is limited by the value returned by this method. The maximum Snapshot size cannot be unlimited.

      The method should perform fast. See the notes for modeMayBeAllowed(String, String, Mode).
      Parameters:
      item - An Item Name.
      dataAdapter - The name of the Data Adapter which supplies the specified item.
      Returns:
      The maximum allowed length for the Snapshot; a zero return value means that no Snapshot information should be kept.

    • notifyUserMessage

      void notifyUserMessage(@Nullable String user, @Nonnull String sessionID, @Nonnull String message) throws CreditsException, NotificationException
      Called by Lightstreamer Kernel to forward a message received by a User. The interpretation of the message is up to the Metadata Adapter. A message can also be refused.

      The method should perform fast and the message processing should be done asynchronously. If the implementation is slow, it might propagate the delay to other operations and other sessions. In that case, configuring a dedicated "MSG" thread pool for message management on the related Adapter Set is recommended, in order not to block other types of operations.
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User.
      message - A non-null string.
      Throws:
      CreditsException - if the User is not enabled to send the message or the message cannot be correctly managed.
      NotificationException - if something is wrong in the parameters, such as a nonexistent Session ID.

    • notifyNewSession

      void notifyNewSession(@Nullable String user, @Nonnull String sessionID, @Nonnull Map clientContext) throws CreditsException, NotificationException
      Called by Lightstreamer Kernel to check that a User is enabled to open a new push Session. If the check succeeds, this also notifies the Metadata Adapter that the Session is being assigned to the User.
      Request context information is also available; this allows for differentiating group, schema and message management based on specific Request characteristics.

      The method should perform as fast as possible. External information needed to execute it should have been previously gathered and cached by notifyUser(String, String, Map). If the implementation is slow because of complex data gathering operations, it might delay the client session activation. In that case, configuring a dedicated "SET" thread pool for this Adapter Set is recommended, in order not to block operations for different Adapter Sets.
      Parameters:
      user - A User name.
      sessionID - The ID of a new Session.
      clientContext - A Map-type value object that contains information about the request context. Unless specified, the values are supplied as strings. Information related to a client connection refers to the HTTP request that originated the call. Available keys are:
      • "REMOTE_IP" - string representation of the remote IP related to the current connection; it may be a proxy address
      • "REMOTE_PORT" - string representation of the remote port related to the current connection
      • "USER_AGENT" - the user-agent as declared in the current connection HTTP header
      • "FORWARDING_INFO" - the comma-separated list of addresses forwarded by intermediaries, obtained from the X-Forwarded-For HTTP header, related to the current connection; intermediate proxies usually set this header to supply connection routing information. Note that if the number of forwards to be considered local to the Server environment has been specified through the <skip_local_forwards> configuration element, in order to better determine the remote address, then these forwards will not be included in the list.
      • "LOCAL_SERVER" - the name of the specific server socket that handles the current connection, as configured through the <http_server> or <https_server> element
      • "CLIENT_TYPE" - the type of client API in use. The value may be null for some old client APIs
      • "CLIENT_VERSION" - the signature, including version and build number, of the client API in use. The signature may be only partially complete, or even null, for some old client APIs and for some custom clients
      • "HTTP_HEADERS" - the same Map object that has just been supplied to notifyUser(String, String, Map) for the current client request instance; note that any authorization information that was supplied by the backend through the authentication request could be added to the Map in notifyUser(String, String, Map) and can be got back here. This allows for using local authentication-related details for the authorization task.
      Throws:
      CreditsException - if the User is not enabled to open the new Session.
      If it's possibile that the User would be enabled as soon as another Session were closed, then a ConflictingSessionException can be thrown, in which the ID of the other Session must be specified. In this case, a second invocation of the method with the same "HTTP_HEADERS" Map and a different Session ID will be received.
      NotificationException - if something is wrong in the parameters, such as the ID of a Session already open for this or a different User.

    • getSessionTimeToLive

      default int getSessionTimeToLive(@Nullable String user, @Nonnull String session)
      Called by Lightstreamer Kernel to ask for an optional time-to-live setting for a session just started. If this setting is not needed, the method can be left unimplemented (sticking to its default implementation, which poses no limit).
      If the session is terminated due to this setting, the originating client will receive the notification of the termination according with the API in use, together with a proper cause code.

      The method should perform fast. External information needed to execute it should have been previously gathered and cached by notifyNewSession(String, String, Map). If the implementation is slow, it might delay the client session activation. In that case, configuring a dedicated "SET" thread pool for requests on this Adapter Set is recommended, in order not to block operations for different Adapter Sets.
      Parameters:
      user - A User name.
      session - A session ID.
      Returns:
      The time-to-live setting to be applied to the specified session, as a positive number of seconds. If zero or negative, no time-to-live limit will be applied.

    • notifySessionClose

      void notifySessionClose(@Nonnull String sessionID) throws NotificationException
      Called by Lightstreamer Kernel to notify the Metadata Adapter that a push Session has been closed. After this invocation, no more calls to notifyNewTables(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.TableInfo[]) and notifyTablesClose(java.lang.String, com.lightstreamer.interfaces.metadata.TableInfo[]) for this sessionID are possible. On the other hand, trailing invocations of methods related with the validation of client requests, like getItems(String, String, String, String), are still possible on parallel threads and accepting them would have no effect. However, if the method may have side-effects on the Adapter, like notifyUserMessage(java.lang.String, java.lang.String, java.lang.String), the Adapter is responsible for checking if the session is still valid.

      The method must perform fast. A slow implementation could propagate delays also on different sessions.
      Parameters:
      sessionID - A Session ID.
      Throws:
      NotificationException - if something is wrong in the parameters, such as the ID of a Session that is not currently open.

    • wantsTablesNotification

      boolean wantsTablesNotification(@Nullable String user)
      Called by Lightstreamer Kernel to know whether the Metadata Adapter must or must not be notified any time a Table (i.e.: Subscription) is added or removed from a push Session owned by a supplied User. If this method returns false, the methods notifyNewTables(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.TableInfo[]) and notifyTablesClose(java.lang.String, com.lightstreamer.interfaces.metadata.TableInfo[]) will never be called for this User, saving some processing time. In this case, the User will be allowed to add to his Sessions any Tables (i.e.: Subscriptions) he wants.

      The method should perform fast. See the notes for getAllowedMaxBandwidth(String).
      Parameters:
      user - A User name.
      Returns:
      true if the Metadata Adapter must be notified any time a Table (i.e.: Subscription) is added or removed from a Session owned by the User.

    • notifyNewTables

      void notifyNewTables(@Nullable String user, @Nonnull String sessionID, @Nonnull TableInfo[] tables) throws CreditsException, NotificationException
      Called by Lightstreamer Kernel to check that a User is enabled to add some Tables (i.e.: Subscriptions) to a push Session. If the check succeeds, this also notifies the Metadata Adapter that the Tables are being added to the Session.
      The method is invoked only if enabled for the User through wantsTablesNotification(java.lang.String).

      The method should perform fast. Any complex data gathering operation (like a check on the overall number of subscribed Items) should have been already performed asynchronously. See the notes for getItems(String, String, String, String) for details; but see the <sequentialize_table_notifications> parameter available in adapters.xml as well.
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User.
      tables - An array of TableInfo instances, each of them containing the details of a Table (i.e.: Subscription) to be added to the Session. The elements in the array represent Tables (i.e.: Subscriptions) whose subscription is requested atomically by the client. A single element should be expected in the array, unless clients based on a very old version of a client library or text protocol may be in use.
      Throws:
      CreditsException - if the User is not allowed to add the specified Tables (i.e.: Subscriptions) to the Session.
      NotificationException - if something is wrong in the parameters, such as the ID of a Session that is not currently open or inconsistent information about a Table (i.e.: Subscription).

    • notifyTablesClose

      void notifyTablesClose(@Nonnull String sessionID, @Nonnull TableInfo[] tables) throws NotificationException
      Called by Lightstreamer Kernel to notify the Metadata Adapter that some Tables (i.e.: Subscriptions) have been removed from a push Session.
      The method is invoked only if enabled for the User through wantsTablesNotification(java.lang.String).

      The method must perform fast. A slow implementation could propagate delays also on different sessions.
      Parameters:
      sessionID - A Session ID.
      tables - An array of TableInfo instances, each of them containing the details of a Table (i.e.: Subscription) that has been removed from the Session. The supplied array is in 1:1 correspondance with the array supplied by notifyNewTables(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.TableInfo[]) in a previous call; the correspondance can be recognized by matching TableInfo.getWinIndex() as returned by the included objects (if multiple objects are included, it must be the same for all of them).
      Throws:
      NotificationException - if something is wrong in the parameters, such as the ID of a Session that is not currently open or a Table (i.e.: Subscription) that is not contained in the Session.

    • notifyMpnDeviceAccess

      void notifyMpnDeviceAccess(@Nullable String user, @Nonnull String sessionID, @Nonnull MpnDeviceInfo device) throws CreditsException, NotificationException
      Called by Lightstreamer Kernel to check that a User is enabled to access the specified MPN device. The success of this method call is a prerequisite for all MPN operations, including the activation of a subscription, the deactivation of a subscription, the change of a device token, etc. Some of these operations have a subsequent specific notification, i.e. notifyMpnSubscriptionActivation(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.TableInfo, com.lightstreamer.interfaces.metadata.MpnSubscriptionInfo) and notifyMpnDeviceTokenChange(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.MpnDeviceInfo, java.lang.String).

      Take particular precautions when authorizing device access, if possible ensure the user is entitled to the specific platform, device token and application ID.

      The method should perform fast. External information needed to execute it should have been previously gathered and cached by notifyUser(String, String, Map). If the implementation is slow, it might delay the notification request management. In that case, configuring a dedicated "MPN_REQUESTS" thread pool for MPN-related requests on this Adapter Set is recommended, in order not to block operations for different Adapter Sets or different operations for this Adapter Set.
      Edition Note:
      Push Notifications is an optional feature, available depending on Edition and License Type. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User.
      device - specifies an MPN device.
      Throws:
      CreditsException - if the User is not allowed to access the specified MPN device in the Session.
      NotificationException - if something is wrong in the parameters, such as inconsistent information about the device.

    • notifyMpnSubscriptionActivation

      void notifyMpnSubscriptionActivation(@Nullable String user, @Nonnull String sessionID, @Nonnull TableInfo table, @Nonnull MpnSubscriptionInfo mpnSubscription) throws CreditsException, NotificationException
      Called by Lightstreamer Kernel to check that a User is enabled to activate a Push Notification subscription. If the check succeeds, this also notifies the Metadata Adapter that Push Notifications are being activated.

      Take particular precautions when authorizing subscriptions, if possible check for validity the trigger expression reported by MpnSubscriptionInfo.getTrigger(), as it may contain maliciously crafted code. The MPN notifiers configuration file contains a first-line validation mechanism based on regular expression that may also be used for this purpose.

      The method should perform fast. Any complex data gathering operation (like a check on the overall number of Push Notifications activated) should have been already performed asynchronously. See the notes for notifyMpnDeviceAccess(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.MpnDeviceInfo) for details.
      Edition Note:
      Push Notifications is an optional feature, available depending on Edition and License Type. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User. The session ID is provided for a thorough validation of the Table information, but Push Notification subscriptions are persistent and survive the session. Thus, any association between this Session ID and this Push Notification subscription should be considered temporary.
      table - A TableInfo instance, containing the details of a Table (i.e.: Subscription) for which Push Notification have to be activated.
      mpnSubscription - An MpnSubscriptionInfo instance, containing the details of a Push Notification to be activated.
      Throws:
      CreditsException - if the User is not allowed to activate the specified Push Notification in the Session.
      NotificationException - if something is wrong in the parameters, such as inconsistent information about a Table (i.e.: Subscription) or a Push Notification.

    • notifyMpnDeviceTokenChange

      void notifyMpnDeviceTokenChange(@Nullable String user, @Nonnull String sessionID, @Nonnull MpnDeviceInfo device, @Nonnull String newDeviceToken) throws CreditsException, NotificationException
      Called by Lightstreamer Kernel to check that a User is enabled to change the token of an MPN device. If the check succeeds, this also notifies the Metadata Adapter that future client requests should be issued by specifying the new device token.

      Take particular precautions when authorizing device token changes, if possible ensure the user is entitled to the new device token.

      The method should perform fast. Any complex data gathering operation (like a check on the devices currently served) should have been already performed asynchronously. See the notes for notifyMpnDeviceAccess(java.lang.String, java.lang.String, com.lightstreamer.interfaces.metadata.MpnDeviceInfo) for details.
      Edition Note:
      Push Notifications is an optional feature, available depending on Edition and License Type. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).
      Parameters:
      user - A User name.
      sessionID - The ID of a Session owned by the User.
      device - specifies an MPN device.
      newDeviceToken - The new token being assigned to the device.
      Throws:
      CreditsException - if the User is not allowed to change the specified device token.
      NotificationException - if something is wrong in the parameters, such as inconsistent information about the device.