This feature allows a client session to configure session trees.
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
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
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:
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.
This feature may be obtained from a session as follows:
const sessionTrees = session.sessionTrees;
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.
the session tree branch that identifies the branch mapping table
a Result that resolves when a response is received from the server, returning the branch mapping table for sessionTreeBranch.
If the task fails, the Result will be rejected with an error. Common reasons for failure include:
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 last one branch mapping and for which the calling session has READ_TOPIC path permission for the session tree branch.
Individual branch mapping tables can be retrieved using getBranchMappingTable.
a Result that resolves when a response is received from the server, returning a list of session tree branches in path order.
If the task fails, the the Result will be rejected with an error. Common reasons for failure include:
Create or replace a branch mapping table.
The server ensures that a session tree branch has at most one branch mapping table. 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.
the new table
a Result that resolves 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 Result will be rejected with an error. Common reasons for failure include: