Pull request 2319: websvc-patch

Merge in DNS/adguard-home from websvc-patch to master

Squashed commit of the following:

commit b2a10faf12b16f13f617b3ed3ef3e81cb0479ff8
Merge: 38f749106 8f53f6505
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Wed Dec 11 17:33:15 2024 +0300

    Merge branch 'master' into websvc-patch

commit 38f7491069d90d4080e7ad98b09bf9ce19138195
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Tue Dec 10 19:57:54 2024 +0300

    next: add json merge patch utils

internal/next/jsonpatch/jsonpatch.go

@@ -0,0 +1,43 @@
+// Package jsonpatch contains utilities for JSON Merge Patch APIs.
+//
+// See https://www.rfc-editor.org/rfc/rfc7396.
+package jsonpatch
+
+import (
+	"bytes"
+	"encoding/json"
+
+	"github.com/AdguardTeam/golibs/errors"
+)
+
+// NonRemovable is a type that prevents JSON null from being used to try and
+// remove a value.
+type NonRemovable[T any] struct {
+	Value T
+	IsSet bool
+}
+
+// type check
+var _ json.Unmarshaler = (*NonRemovable[struct{}])(nil)
+
+// UnmarshalJSON implements the [json.Unmarshaler] interface for *NonRemovable.
+func (v *NonRemovable[T]) UnmarshalJSON(b []byte) (err error) {
+	if v == nil {
+		return errors.Error("jsonpatch.NonRemovable is nil")
+	}
+
+	if bytes.Equal(b, []byte("null")) {
+		return errors.Error("property cannot be removed")
+	}
+
+	v.IsSet = true
+
+	return json.Unmarshal(b, &v.Value)
+}
+
+// Set sets ptr if the value has been provided.
+func (v NonRemovable[T]) Set(ptr *T) {
+	if v.IsSet {
+		*ptr = v.Value
+	}
+}

internal/next/jsonpatch/jsonpatch_test.go

@@ -0,0 +1,29 @@
+package jsonpatch_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/next/jsonpatch"
+	"github.com/AdguardTeam/golibs/testutil"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNonRemovable(t *testing.T) {
+	type T struct {
+		Value jsonpatch.NonRemovable[int] `json:"value"`
+	}
+
+	var v T
+
+	err := json.Unmarshal([]byte(`{"value":null}`), &v)
+	testutil.AssertErrorMsg(t, "property cannot be removed", err)
+
+	err = json.Unmarshal([]byte(`{"value":42}`), &v)
+	assert.NoError(t, err)
+
+	var got int
+	v.Value.Set(&got)
+
+	assert.Equal(t, 42, got)
+}