Handlers discovery via NServiceBus assembly

skalbe · August 25, 2022, 6:09pm

Is there a way to get all message/command handlers have been scanned/found by NServiceBus ? Some tricky solution (eg via ) will be suitable as well.

Michal_Wojcik · August 26, 2022, 11:38am

Hi,

May I ask what is the use case for the information? Do you have a handler that is not registered correctly, and you try to understand what is happening?

skalbe · August 26, 2022, 5:29pm

Hi, a want to use this so to speak “internal registry” for some validation/logging purposes. I guess i could somehow get this handler list and avoid self-designed assembly scanning.

Michal_Wojcik · September 2, 2022, 9:30am

Hi,

So the information is not easily accessible. Every endpoint scans the available DLLs in search of handlers. Those information is logged inside the diagnostics like in here

github.com

Particular/NServiceBus/blob/master/src/NServiceBus.Core/Receiving/ReceiveComponent.cs#L78-L89


      
          
          var messageHandlerRegistry = configuration.messageHandlerRegistry;
          RegisterMessageHandlers(messageHandlerRegistry, configuration.ExecuteTheseHandlersFirst, hostingConfiguration.Services, hostingConfiguration.AvailableTypes);
          
          foreach (var messageType in messageHandlerRegistry.GetMessageTypes())
          {
              handlerDiagnostics[messageType.FullName] = messageHandlerRegistry.GetHandlersFor(messageType)
                  .Select(handler => handler.HandlerType.FullName)
                  .ToList();
          }
          
          var receiveSettings = new List<ReceiveSettings>

But the major problem is that every endpoint has only a fraction of the information: it knows which endpoint it has, and which it sends/publishes. Which only is a part of the system, so to get all handlers, one would have to analyze that information from every place.

You could have a look at this: GitHub - ParticularLabs/RoutingVisualization: Uses audit data in a ServiceControl database to generate a routing diagram

It is a tool to visualize endpoints and messages based on audits. In readme it describes where does it take the information, it could be something for you to use

Regards
Michael

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