47.2 Single-Request, Multiple-Replies

Connext also supports the single-request multiple-reply pattern. This pattern is an extension of the basic request-reply pattern in which multiple reply messages can flow back as a result of a single request.

The single-request multiple-reply pattern is very useful when getting large amounts of data as a reply, such as when querying a system for all data that matches a certain criteria. Another common use-case is invoking a service that goes through multiple stages and provides updates on each: service commencement, progress reports, and final completion.

Figure 47.3: Single Request, Multiple Replies

Request/Reply communication pattern with multiple replies resulting from a single request

For example, a mobile asset management system may need to locate a particular asset (truck, locomotive, etc.). The system sends out the request. The first reply that comes back will read “locating.” The service has not yet determined the position, but it notifies the requester that the search operation has started. The second reply might provide a status update on the search, perhaps including a rough area of location. The third and final reply will have the exact location of the asset.