Interface SessionTrees
- All Superinterfaces:
Feature
- All Known Subinterfaces:
Topics
A session tree is a virtual view of the topic tree presented to a session by fetch and subscription operations. Custom session trees for different sessions can be configured using declarative rules maintained by the server to meet data security, data optimisation, or personalisation and localisation requirements. Each session can be presented with a unique session tree based on its session properties.
A session tree is produced by applying branch mappings to the topic tree. Branch mappings are organised into branch mapping tables. Each branch mapping table is assigned to a unique path – the session tree branch.
A session tree is composed of session paths. Each session path is mapped via the branch mapping tables to a unique topic path.
A branch mapping table is an ordered list of (session filter, topic tree
branch) pairs. For example, the branch mapping table for the session tree
branch market/prices
might be:
Session filter Topic tree branch ============== ================= USER_TIER is '1' or $Country is 'DE' backend/discounted_prices USER_TIER is '2' backend/standard_prices $Principal is '' backend/delayed_prices
With this configuration, if an unauthenticated session (one that matches the
$Principal is ''
session filter) subscribes to the session path
market/prices/X
, and there is a topic bound to the topic path
backend/delayed_prices/X
, the subscription will complete. The session
will receive a subscription notification under the session path
market/prices/X
, together with the topic properties and the value of
the topic. The session is unaware that the data originates from a topic bound
to a different topic path. If no topic is bound to
backend/delayed_prices/X
, the subscription will not resolve and the
session will receive no data, even if there is a topic bound to
market/prices/X
.
Session trees complement the data transformation capabilities of
topic views
. In our example, the time delayed time feed at
backend/delayed_prices
could be maintained by a topic view using the
delay by clause.
Branch mappings are persisted by the server and shared across a cluster, in a similar manner to topic views, security stores, and metric collectors. Branch mappings are editable using this feature, and via the management console.
For a given session and session path, at most one branch mapping applies. The applicable branch mapping is chosen as follows:
- Each branch mapping table with session tree branch that is a prefix of the session path is considered. For a given table, the first branch mapping with a session filter that matches the session's properties is the one that applies. A branch mapping table may have no applicable branch mappings for a session.
- If there are several such branch mapping tables with a branch mapping that for the session, the one with the longest prefix of the session path applies.
- If no branch mapping table has a branch mapping for the session, the session path is translated to the identical topic path.
Access control
To subscribe to or fetch from a session path, a session must be granted the
appropriate path permission to the session path for the operation
(SELECT_TOPIC
, or
READ_TOPIC
). The session doesn't require
any permissions to the topic path of the topic providing the data.
To create or replace branch mappings, a session needs the
MODIFY_TOPIC
path permission for the
session tree branch of the branch mapping table,
EXPOSE_BRANCH
path permission for the
topic tree branch of each branch mapping, and (if an existing table with the
same session tree branch is being replaced)
EXPOSE_BRANCH
permission for each branch
mapping of existing table.
To retrieve a branch mapping table, a session needs the
READ_TOPIC
path permission for its session
tree branch.
Accessing the feature
This feature may be obtained from a session
as follows:
SessionTrees sessionTrees = session.feature(SessionTrees.class);
This feature is also extended by the Topics
feature. This
means is it possible to use the methods described here through the
Topics
feature.
- Since:
- 6.7
- Author:
- DiffusionData Limited
-
Nested Class Summary
Nested ClassesModifier and TypeInterfaceDescriptionstatic interface
A session tree branch mapping.static interface
A session tree branch mapping table.static class
Exception indicating an invalidSessionTrees.BranchMapping
orSessionTrees.BranchMappingTable
. -
Method Summary
Modifier and TypeMethodDescriptiongetBranchMappingTable
(String sessionTreeBranch) Retrieve a branch mapping table from the server.Retrieve the session tree branches of the server's branch mapping tables.putBranchMappingTable
(SessionTrees.BranchMappingTable branchMappingTable) Create or replace a branch mapping table.Methods inherited from interface com.pushtechnology.diffusion.client.session.Feature
getSession
-
Method Details
-
putBranchMappingTable
Create or replace a branch mapping table.The server ensures that there is at most one branch mapping table for a session tree branch. Putting a new branch mapping table will replace any previous branch mapping table with the same session tree branch. To remove all branch mappings for a session tree branch, put an empty branch mapping table.
- Parameters:
branchMappingTable
- the new table- Returns:
- a CompletableFuture that completes when a response is received
from the server.
If the task completes successfully, the CompletableFuture result will be null. The result type is any rather than Void to provide forward compatibility with future iterations of this API that may provide a non-null result with a more specific result type.
Otherwise, the CompletableFuture will complete exceptionally with a
CompletionException
. Common reasons for failure, listed by the exception reported as thecause
, include:SessionTrees.InvalidBranchMappingException
– if branchMappingTable or one of its branch mappings is invalid;PermissionsException
– if the calling session does not have theMODIFY_TOPIC
permission for the session tree branch of the branch mapping table,EXPOSE_BRANCH
permission for each branch mapping of branchMappingTable, and (if there is an existing table for the session tree branch)EXPOSE_BRANCH
permission for each branch mapping of existing table;ClusterRoutingException
– if the operation failed due to a transient cluster error;SessionClosedException
– if the session is closed.
-
listSessionTreeBranchesWithMappings
CompletableFuture<List<String>> listSessionTreeBranchesWithMappings()Retrieve the session tree branches of the server's branch mapping tables. The results will only include the session tree branches of branch mapping tables that have at least one branch mapping and for which the calling session hasREAD_TOPIC
path permission for the session tree branch.Individual branch mapping tables can be retrieved using
getBranchMappingTable(String)
.- Returns:
- a CompletableFuture that completes when a response is received
from the server, returning a list of session tree branches in
path order.
If the task fails, the CompletableFuture will complete exceptionally with a
CompletionException
. Common reasons for failure, listed by the exception reported as thecause
, include:SessionClosedException
– if the session is closed.
-
getBranchMappingTable
Retrieve a branch mapping table from the server.If there is no branch mapping table at the given session tree branch, this method will return an empty branch mapping table.
- Parameters:
sessionTreeBranch
- the session tree branch that identifies the branch mapping table- Returns:
- a CompletableFuture that completes when a response is received
from the server, returning the branch mapping table for
sessionTreeBranch.
If the task fails, the CompletableFuture will complete exceptionally with a
CompletionException
. Common reasons for failure, listed by the exception reported as thecause
, include:PermissionsException
– if the calling session does not have theREAD_TOPIC
permission for sessionTreeBranch;SessionClosedException
– if the session is closed.
-