fix(form): fix infinite recursion when decoding self-referenced structs

form/decode.go

@@ -22,7 +22,7 @@ func Decode(r *http.Request, dst any) error {
 	t := reflect.TypeOf(dst)
 	v := reflect.ValueOf(dst)
 
-	if t.Kind() != reflect.Ptr || v.Elem().Kind() != reflect.Struct {
+	if t.Kind() != reflect.Pointer || v.Elem().Kind() != reflect.Struct {
 		return errors.New("dst must be pointer to struct")
 	}
 
@@ -56,7 +56,7 @@ func decodeForm(dst reflect.Value, form map[string][]string, prefix string) erro
 		fName := cmp.Or(tagName, field.Name)
 		fType := field.Type
 		fKind := fType.Kind()
-		isPtr := fKind == reflect.Ptr
+		isPtr := fKind == reflect.Pointer
 
 		if prefix != "" && !field.Anonymous {
 			fName = prefix + "." + fName
@@ -70,6 +70,28 @@ func decodeForm(dst reflect.Value, form map[string][]string, prefix string) erro
 				continue
 			}
 
+			if fKind == reflect.Struct {
+				var found bool
+
+				searchPrefix := fName
+				if field.Anonymous {
+					searchPrefix = prefix
+				}
+				if searchPrefix != "" {
+					searchPrefix += "."
+				}
+
+				for k := range form {
+					if searchPrefix == "" || strings.HasPrefix(k, searchPrefix) {
+						found = true
+						break
+					}
+				}
+				if !found {
+					continue
+				}
+			}
+
 			if fieldVal.IsNil() {
 				fieldVal.Set(reflect.New(fType))
 			}
@@ -105,7 +127,7 @@ func decodeForm(dst reflect.Value, form map[string][]string, prefix string) erro
 			}
 		case reflect.Slice:
 			elemType := fType.Elem()
-			isPtr := elemType.Kind() == reflect.Ptr
+			isPtr := elemType.Kind() == reflect.Pointer
 			baseType := elemType
 			if isPtr {
 				baseType = elemType.Elem()

form/decode_benchmarks_test.go

@@ -28,6 +28,8 @@ func BenchmarkSimpleDecodeStruct(b *testing.B) {
 	req, _ := http.NewRequest(http.MethodPost, "/", strings.NewReader(values.Encode()))
 
 	b.ReportAllocs()
+	b.ResetTimer()
+
 	for n := 0; n < b.N; n++ {
 		var s Simple
 
@@ -80,10 +82,45 @@ func BenchmarkComplexDecodeStruct(b *testing.B) {
 	req, _ := http.NewRequest(http.MethodPost, "/", strings.NewReader(values.Encode()))
 
 	b.ReportAllocs()
+	b.ResetTimer()
+
 	for n := 0; n < b.N; n++ {
 		var c Complex
 		if err := form.Decode(req, &c); err != nil {
 			b.Error(err)
 		}
 	}
 }
+
+func BenchmarkSelfReferencingStruct(b *testing.B) {
+	type Node struct {
+		ID       string
+		Name     string
+		Parent   *Node
+		Sibling  *Node
+		Metadata map[string]string
+	}
+
+	values := url.Values{
+		"ID":                 []string{"node-1"},
+		"Name":               []string{"Root Node"},
+		"Parent.ID":          []string{"parent-1"},
+		"Parent.Name":        []string{"Parent Node"},
+		"Sibling.ID":         []string{"sibling-1"},
+		"Sibling.Name":       []string{"Sibling Node"},
+		"Metadata[category]": []string{"test"},
+		"Metadata[version]":  []string{"1.0"},
+	}
+
+	req, _ := http.NewRequest(http.MethodPost, "/", strings.NewReader(values.Encode()))
+
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	for n := 0; n < b.N; n++ {
+		var node Node
+		if err := form.Decode(req, &node); err != nil {
+			b.Error(err)
+		}
+	}
+}