Allow apps to decide if they receive their own broadcast messages

[kriswest]

Enhancement Request

Remove the recommendation that Desktop Agents don't deliver messages back to the sender and let the app implementor decide if they wish to receive them or not.

Use Case

The FDC3 Standard recommends (SHOULD) that DAs don't deliver broadcast messages back to the sender, as it forces some apps to examine context sharing messages before applying them, just to check if they came from themselves. This can / was observed to cause flickering issues in a variety of apps when they changed context, broadcast that context, and immediately received a message back and reapplied the same context.

DesktopAgent implementations SHOULD ensure that context messages broadcast to a channel by an application joined to it are not delivered back to that same application.

See:

• https://fdc3.finos.org/docs/api/ref/DesktopAgent#broadcast
• https://fdc3.finos.org/docs/api/spec#desktop-agent-api-standard-compliance

Since then use cases have popped up for apps, composed of multiple widgets in the same page, to receive their own messages so that they can communicate with each other in the same way that they do other apps. This proposal doesn't solve routing of intents to handlers in the same app, but would make context sharing easier.

Additional Information

Back when this was added to FDC3 (in FDC3 1.2, see #285) the only way to determine if you sent a message, was to do a deep comparison of the context message + assume no one else would send an identical one (there are few small use cases where it makes to resend a message - such as to reset a view).

With the metadata changes proposed for FDC3 3.0 (#1728) that comparison is no longer necessary, as we can simply check if the source of the broadcast was this app instance (compare instanceId). That would allow an argument to getAgent to control whether an app receives its own messages (for FDC3 for web implementation, and potentially preload implementation, either by patching the addContextListener function or passing the argument to the DA somehow).

[kriswest]

@robmoffat theres all the missing context on this one - raised issue based on our discussion - I mostly want to ensure that app devs can rely on consistent behaviour from Desktop Agents, which a SHOULD recommendation doesn't quite achieve.

My preference would be to default to not delivering messages back to the sender and to allow them to set a parameter that enables that.

Note the slight additional complexity with preload desktop agents.

[GaneshPatil7517]

hey @kriswest assign me this also ill work on this....

[kriswest]

Hi @GaneshPatil7517 we'll talk about this one at the next standards working group meeting before we do it. We should then be able to add a lot more detail to this issue before it is implemented (particular relating to the differences between browser-based and preload-based Desktop Agents, as the approaches will be wildly different).

[Roaders]

It makes sense to me. By default don't deliver back to sender but allow an individual app to opt in to receiving it's own messages back again.
It should perhaps be mentioned that this could be done at moment depending on the DA implementation. Messages do have a source property but it is optional so can't be relied on. The propsed changes for 3.0 make this metadata required so it's guaranteed than app will be able to accurately filter out it's own messages.