micro/go-micro · error

subscriber error

Error message

subscriber error: %s

What it means

When a message is delivered, the gRPC subscriber runs each registered handler in parallel and collects handler errors. If one or more handlers returned errors, Subscribe's message-handling function aggregates them into a single error formatted as `subscriber error: <joined messages>`. It tells you the message was received but at least one subscriber handler failed.

Solutions

1. Read the joined error strings to identify which handler(s) failed and fix the root cause in those handlers
2. Add error handling/logging inside each subscriber handler so expected failures do not propagate as errors
3. If handlers legitimately disagree about success, isolate them (separate topics/subscribers) so one failure does not fail the whole delivery

Example fix

// before
func (h *handler) Handle(ctx context.Context, e *Event) error { return process(e) }
// after
func (h *handler) Handle(ctx context.Context, e *Event) error {
    if err := process(e); err != nil {
        log.Errorf("handle event: %v", err)
        return nil // or return err if delivery should fail
    }
    return nil
}

if err := server.Publish(ctx, msg); err != nil {
	var subErr error
	if strings.HasPrefix(err.Error(), "subscriber error: ") {
		detail := strings.TrimPrefix(err.Error(), "subscriber error: ")
		for _, line := range strings.Split(detail, "\n") {
			log.Errorf("subscriber failed: %s", line)
		}
	} else {
		// transport-level failure: safe to retry
		err = retry(err)
	}
	_ = subErr
}

When it happens

Trigger: Publishing to a topic where one or more registered subscriber handler methods return a non-nil error; the error strings of all failing handlers are joined with newlines.

Common situations: A handler's business logic fails (DB down, validation error); a decode error in a handler; one bad subscriber causing publishers to see errors even though other handlers succeeded.

Related errors

• invalid subscriber: expected *subscriber
• subscriber argument type not exported
• subscriber has wrong number of outs: require signature
• subscriber returns not error
• subscriber takes wrong number of args: required signature

AI-assisted analysis of micro/go-micro@24529f1404 (2026-09-01). Data as JSON: /api/errors/850e3febb04ab9f2. Report an issue: GitHub.

Appendix: source

Thrown at server/grpc/subscriber.go:270

				}
				err := fn(ctx, &rpcMessage{
					topic:       sb.topic,
					contentType: ct,
					payload:     req.Interface(),
					header:      msg.Header,
					body:        msg.Body,
				})
				results <- err
			}()
		}
		var errors []string
		for i := 0; i < len(sb.handlers); i++ {
			if rerr := <-results; rerr != nil {
				errors = append(errors, rerr.Error())
			}
		}
		if len(errors) > 0 {
			err = fmt.Errorf("subscriber error: %s", strings.Join(errors, "\n"))
		}

		return err
	}
}

func (s *subscriber) Topic() string {
	return s.topic
}

func (s *subscriber) Subscriber() interface{} {
	return s.subscriber
}

func (s *subscriber) Endpoints() []*registry.Endpoint {
	return s.endpoints
}

View on GitHub (pinned to 24529f1404)