make parseRemoteObject handle other kinds that can be nil correctly (#…

…1260)

Besides `reflect.Pointer`, the value of the following kinds can be nil too:

- reflect.Chan
- reflect.Func
- reflect.Interface
- reflect.Map
- reflect.Slice

---------

Co-authored-by: luster <xxt@nosugartech.com>

eval.go

@@ -29,8 +29,9 @@ type EvaluateAction Action
 // For all other cases, the result of the script will be returned "by value" (i.e.,
 // JSON-encoded), and subsequently an attempt will be made to json.Unmarshal
 // the script result to res. When the script result is "undefined" or "null",
-// and the value that res points to is not a pointer, it returns [ErrJSUndefined]
-// of [ErrJSNull] respectively.
+// and the value that res points to can not be nil (only the value of a chan,
+// func, interface, map, pointer, or slice can be nil), it returns [ErrJSUndefined]
+// or [ErrJSNull] respectively.
 func Evaluate(expression string, res interface{}, opts ...EvaluateOption) EvaluateAction {
 	return ActionFunc(func(ctx context.Context) error {
 		// set up parameters
@@ -55,8 +56,7 @@ func Evaluate(expression string, res interface{}, opts ...EvaluateOption) Evalua
 			return exp
 		}
 
-		err = parseRemoteObject(v, res)
-		return err
+		return parseRemoteObject(v, res)
 	})
 }
 
@@ -75,23 +75,30 @@ func parseRemoteObject(v *runtime.RemoteObject, res interface{}) (err error) {
 		return
 	}
 
-	if v.Type == "undefined" || v.Value == nil {
+	value := v.Value
+	if value == nil {
 		rv := reflect.ValueOf(res)
-		// `res` should be a pointer. When the value that `res` points to is
-		// not a pointer, it can not be nil. In this case,
-		// return [ErrJSUndefined] or [ErrJSNull] respectively.
-		if rv.Kind() == reflect.Pointer && rv.Elem().Kind() != reflect.Pointer {
-			if v.Type == "undefined" {
-				return ErrJSUndefined
+		if rv.Kind() == reflect.Pointer {
+			switch rv.Elem().Kind() {
+			// Common kinds that can be nil.
+			case reflect.Pointer, reflect.Map, reflect.Slice:
+			// It's weird that res is a pointer to the following kinds,
+			// but they can be nil too.
+			case reflect.Chan, reflect.Func, reflect.Interface:
+			default:
+				// When the value that `res` points to can not be set to nil,
+				// return [ErrJSUndefined] or [ErrJSNull] respectively.
+				if v.Type == "undefined" {
+					return ErrJSUndefined
+				}
+				return ErrJSNull
 			}
-			return ErrJSNull
 		}
-		// Otherwise, change the value to the json literal null.
-		v.Value = []byte("null")
+		// Change the value to the json literal null to make json.Unmarshal happy.
+		value = []byte("null")
 	}
 
-	err = json.Unmarshal(v.Value, res)
-	return
+	return json.Unmarshal(value, res)
 }
 
 // EvaluateAsDevTools is an action that evaluates a JavaScript expression as

example_test.go

@@ -638,7 +638,7 @@ func ExampleEvaluate() {
 		}
 	}
 
-	// Accept undefined/nil result:
+	// Accept undefined/null result:
 	{
 		var val *int
 		if err := chromedp.Run(ctx,
@@ -649,6 +649,28 @@ func ExampleEvaluate() {
 		fmt.Println(val)
 	}
 
+	// Receive an array value:
+	{
+		var val []int
+		if err := chromedp.Run(ctx,
+			chromedp.Evaluate(`[1,2]`, &val),
+		); err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println(val)
+	}
+
+	// Map and Slice accept undefined/null:
+	{
+		var val []int
+		if err := chromedp.Run(ctx,
+			chromedp.Evaluate(`null`, &val),
+		); err != nil {
+			log.Fatal(err)
+		}
+		fmt.Println("slice is nil:", val == nil)
+	}
+
 	// Receive the raw bytes:
 	{
 		var buf []byte
@@ -678,6 +700,8 @@ func ExampleEvaluate() {
 	// encountered an undefined value
 	// encountered a null value
 	// <nil>
+	// [1 2]
+	// slice is nil: true
 	// {}
 	// objectId is present
 }