Fix unwrapping of DeadlineExceeded errors into ErrTaskTimeout.

context.Cause() was called on the parent context, not the task context.
This resulted in the error handler being called with a nil err.

nanoq.go

@@ -412,14 +412,9 @@ func (p *Processor) processTask(ctx context.Context, t Task) error {
 			return fmt.Errorf("task %v canceled: %v", t.ID, context.Cause(ctx))
 		}
 
-		if errors.Is(err, context.DeadlineExceeded) {
-			// Extract a more specific timeout error, if any.
-			err = context.Cause(ctx)
-		}
 		if p.errorHandler != nil {
 			p.errorHandler(ctx, t, err)
 		}
-
 		if t.Retries < t.MaxRetries && !errors.Is(err, ErrSkipRetry) {
 			retryIn := p.retryPolicy(t)
 			if err := p.client.RetryTask(ctx, t, retryIn); err != nil {
@@ -455,8 +450,17 @@ func callHandler(ctx context.Context, h Handler, t Task) (err error) {
 			err = fmt.Errorf("panic [%s:%d]: %v: %w", file, line, r, ErrSkipRetry)
 		}
 	}()
-	ctx, cancel := context.WithTimeoutCause(ctx, t.Timeout(), ErrTaskTimeout)
+	taskCtx, cancel := context.WithTimeoutCause(ctx, t.Timeout(), ErrTaskTimeout)
 	defer cancel()
 
-	return h(ctx, t)
+	err = h(taskCtx, t)
+	if err != nil && errors.Is(err, context.DeadlineExceeded) {
+		// Extract a more specific timeout error, if any.
+		// context.Cause returns nil if the canceled context is a child of taskCtx.
+		if cerr := context.Cause(taskCtx); cerr != nil {
+			err = cerr
+		}
+	}
+
+	return err
 }

nanoq_test.go

@@ -561,3 +561,58 @@ func TestProcessor_Run_Cancel(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+func TestProcessor_Run_Timeout(t *testing.T) {
+	db, mock, _ := sqlmock.New()
+	defer db.Close()
+	client := nanoq.NewClient(sqlx.NewDb(db, "sqlmock"))
+	processor := nanoq.NewProcessor(client, zerolog.Nop())
+	processor.Handle("my-type", func(ctx context.Context, task nanoq.Task) error {
+		for {
+			select {
+			case <-ctx.Done():
+				return ctx.Err()
+			default:
+				continue
+			}
+		}
+	})
+	errorHandlerCalled := 0
+	processor.OnError(func(ctx context.Context, task nanoq.Task, err error) {
+		if !errors.Is(err, nanoq.ErrTaskTimeout) {
+			t.Errorf("error handler called with unexpected error: %v", err)
+		}
+		errorHandlerCalled++
+	})
+
+	// Task claim, timeout_seconds=1.
+	mock.ExpectBegin()
+	rows := sqlmock.NewRows([]string{"id", "fingerprint", "type", "payload", "retries", "max_retries", "timeout_seconds", "created_at", "scheduled_at"}).
+		AddRow("01HQJHTZCAT5WDCGVTWJ640VMM", "25c084d0", "my-type", "{}", "0", "0", "1", time.Now(), time.Now())
+	mock.ExpectQuery(`SELECT \* FROM tasks WHERE(.+)`).WillReturnRows(rows)
+
+	mock.ExpectExec("UPDATE tasks SET claimed_at = (.+) WHERE id = (.+)").WithArgs(sqlmock.AnyArg(), "01HQJHTZCAT5WDCGVTWJ640VMM").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectCommit()
+
+	mock.ExpectBegin()
+	mock.ExpectExec("DELETE FROM tasks WHERE id = (.+)").WithArgs("01HQJHTZCAT5WDCGVTWJ640VMM").
+		WillReturnResult(sqlmock.NewResult(0, 1))
+	mock.ExpectCommit()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	go processor.Run(ctx, 1, 1*time.Millisecond)
+	time.Sleep(2 * time.Second)
+	cancel()
+	// Wait for the processor to shut down.
+	time.Sleep(2 * time.Millisecond)
+
+	err := mock.ExpectationsWereMet()
+	if err != nil {
+		t.Error(err)
+	}
+
+	if errorHandlerCalled != 1 {
+		t.Errorf("erorr handler called %v times instead of %v", errorHandlerCalled, 1)
+	}
+}