hashicorp/nomad · error

unexpected message type: %#v

Error message

unexpected message type: %#v

What it means

Exec streaming loop guard: a message arrived on the exec stream that is none of stdin-close, tty-resize, or heartbeat — an unknown/unset message type, indicating a protocol violation or version mismatch between client and driver.

Source

Thrown at plugins/drivers/execstreaming.go:62

					errCh <- err
					return
				}
			} else if msg.Stdin != nil && msg.Stdin.Close {
				inWriter.Close()
			} else if msg.TtySize != nil {
				select {
				case resize <- TerminalSize{
					Height: int(msg.TtySize.Height),
					Width:  int(msg.TtySize.Width),
				}:
				case <-ctx.Done():
					// process terminated before resize is processed
					return
				}
			} else if isHeartbeat(msg) {
				// do nothing
			} else {
				errCh <- fmt.Errorf("unexpected message type: %#v", msg)
			}
		}
	}()

	var sendLock sync.Mutex
	send := func(v *ExecTaskStreamingResponseMsg) error {
		sendLock.Lock()
		defer sendLock.Unlock()

		return stream.Send(v)
	}

	var outWg sync.WaitGroup
	outWg.Add(2)
	// handle Stdout
	go func() {
		defer outWg.Done()

View on GitHub (pinned to 482b49bf1a)

Solutions

1. Match client and driver plugin versions so the exec protocol messages agree
2. Check the custom driver's streaming implementation sends only known message types

When it happens

Trigger: Thrown at plugins/drivers/execstreaming.go:62 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of hashicorp/nomad@482b49bf1a (2026-09-04). Data as JSON: /api/errors/a596c6c4a2df7bba. Report an issue: GitHub.