Adding an Event Endpoint

Workflow

Copy this checklist and track your progress:

Creating or modifying an event endpoint:
- [ ] Step 1: Read local AGENTS.md file
- [ ] Step 2: Define in service.yaml
- [ ] Step 3: Generate Boilerplate Code
- [ ] Step 4: Define Custom Types
- [ ] Step 5: Triggering an Outbound Event
- [ ] Step 6: Test the Trigger
- [ ] Step 7: Document the Microservice
- [ ] Step 8: Versioning

Step 1: Read local AGENTS.md file

Check for and read a local AGENTS.md file in that microservice's directory. The local AGENTS.md file contains microservice-specific instructions that should take precedence over global instructions.

Step 2: Define in service.yaml

Define the outbound event in the events array in the service.yaml of the microservice.

• The signature of the outbound event must follow Go function syntax exactly. Do not include a context.Context input argument nor an error output argument. The name of the event must start with On.
• The description should explain what circumstances trigger the event. It should start with the name of the event.

events:
  - signature: OnMyNewEvent(primitiveParam string, customParam CustomType) (result string)
    description: OnMyNewEvent does X, Y and Z.

Step 3: Generate Boilerplate Code

If you've made changes to service.yaml, run go generate to generate the boilerplate code.

Step 4: Define Custom Types

If the new event is using non-primitive custom types such as structs, look for their definition in the API directory.

• Define the properties of any custom types as needed. Property names should be in PascalCase.
• Define JSON tags for all properties. JSON tag names should be in camelCase. Include ,omitzero in all JSON tags.

// CustomType is X, Y, Z
type CustomType struct {
	PropertyName string `json:"propertyName,omitzero"`
}

Step 5: Triggering an Outbound Event

Use the MulticastTrigger in the API package to trigger an outbound event and publish it to all subscribers.

func (svc *Service) DeleteUser(ctx context.Context, id int) (err error) {
    user, err := svc.LoadUser(ctx, id)
    if err != nil {
        return errors.Trace(err)
    }
    // Trigger an event: iterate over the responses
    for resp := range myserviceapi.NewMulticastTrigger(svc).OnBeforeDeleteUser(ctx, user) {
        allow, err := resp.Get()
        if err != nil {
            return errors.Trace(err)
        }
        if !allow {
            return errors.New("deletion disallowed")
        }
    }

    _, err = db.sql.ExecuteContext(ctx, "DELETE FROM users WHERE id=?", id)
    if err != nil {
        return errors.Trace(err)
    }

    // Trigger an event: fire and forget, don't wait for responses
	svc.Go(ctx, func(ctx context.Context) (err error) {
        myserviceapi.NewMulticastTrigger(svc).OnUserDeleted(ctx, id)
        return nil
    })
    
    return nil
}

Step 6: Test the Trigger

Look for the integration test created in service_test.go for the outbound event and implement or adjust it appropriately.

• Follow the pattern recommendation in the code
• Add downstream microservices or their mocks to the testing app

func TestMyservice_OnMyNewEvent(t *testing.T) {
	// Implement testing here
}

Step 7: Document the Microservice

Generate documentation for this microservice that captures its purpose, context, and design rationale. Focus on the reasons behind decisions rather than describing what the code does. Explain design choices, tradeoffs, and the context needed for someone to safely evolve this microservice in the future. Store the result in the microservice's local AGENTS.md file.

Step 8: Versioning

Run go generate to version the code.