Protect handler call against panic

processor.go

@@ -88,7 +88,7 @@ func (p *processor) exec() {
 			}
 			<-p.sema // release token
 		}()
-		err := p.handler(task) // TODO(hibiken): maybe also handle panic?
+		err := perform(p.handler, task)
 		if err != nil {
 			retryTask(p.rdb, msg, err)
 		}
@@ -103,3 +103,15 @@ func (p *processor) restore() {
 		log.Printf("[ERROR] could not move tasks from %q to %q\n", inProgress, defaultQueue)
 	}
 }
+
+// perform calls the handler with the given task.
+// If the call returns without panic, it simply returns the value,
+// otherwise, it recovers from panic and returns an error.
+func perform(handler TaskHandler, task *Task) (err error) {
+	defer func() {
+		if x := recover(); x != nil {
+			err = fmt.Errorf("panic: %v", x)
+		}
+	}()
+	return handler(task)
+}

processor_test.go

@@ -0,0 +1,55 @@
+package asynq
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestPerform(t *testing.T) {
+	tests := []struct {
+		desc    string
+		handler TaskHandler
+		task    *Task
+		wantErr bool
+	}{
+		{
+			desc: "handler returns nil",
+			handler: func(t *Task) error {
+				fmt.Println("processing...")
+				return nil
+			},
+			task:    &Task{Type: "gen_thumbnail", Payload: map[string]interface{}{"src": "some/img/path"}},
+			wantErr: false,
+		},
+		{
+			desc: "handler returns error",
+			handler: func(t *Task) error {
+				fmt.Println("processing...")
+				return fmt.Errorf("something went wrong")
+			},
+			task:    &Task{Type: "gen_thumbnail", Payload: map[string]interface{}{"src": "some/img/path"}},
+			wantErr: true,
+		},
+		{
+			desc: "handler panics",
+			handler: func(t *Task) error {
+				fmt.Println("processing...")
+				panic("something went terribly wrong")
+			},
+			task:    &Task{Type: "gen_thumbnail", Payload: map[string]interface{}{"src": "some/img/path"}},
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		got := perform(tc.handler, tc.task)
+		if !tc.wantErr && got != nil {
+			t.Errorf("%s: perform() = %v, want nil", tc.desc, got)
+			continue
+		}
+		if tc.wantErr && got == nil {
+			t.Errorf("%s: perform() = nil, want non-nil error", tc.desc)
+			continue
+		}
+	}
+}