Cleanly distinguish Supervisor Cmd.Wait errors

The os.Process API is strange in that it returns an error instead of
(ProcessState, error). This makes it difficult to distinguish between
"regular" process errors and failures that occur while actually waiting
on the process.

Nevertheless, try to distinguish between these two cases to produce
more accurate log messages: If the error is nil or unwraps into
an *exec.ExitErr, treat it as a "regular" process error. Consider
everything else an error indicating a problem with waiting.

Signed-off-by: Tom Wieczorek <[email protected]>

Author: twz123

pkg/supervisor/supervisor.go

@@ -86,13 +86,19 @@ func (s *Supervisor) processWaitQuit(ctx context.Context, cmd *exec.Cmd) bool {
 			}
 		}
 	case err := <-waitresult:
-		if err != nil {
-			s.log.WithError(err).Warn("Failed to wait for process")
-		} else {
-			s.log.Warnf("Process exited: %s", cmd.ProcessState)
+		var exitErr *exec.ExitError
+		state := cmd.ProcessState
+		switch {
+		case errors.As(err, &exitErr):
+			state = exitErr.ProcessState
+			fallthrough
+		case err == nil:
+			s.log.Error("Process terminated unexpectedly: ", state)
+		default:
+			s.log.WithError(err).Error("Failed to wait for process: ", state)
 		}
+		return false
 	}
-	return false
 }
 
 // Supervise Starts supervising the given process