protoutil: add OverwriteMasked method

Add a method to copy selected fields from one proto message to another
(of the same type), using a FieldMask. This is intended for use in a new
databroker Patch method.

pkg/protoutil/fieldmask.go

@@ -0,0 +1,95 @@
+package protoutil
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+
+	"golang.org/x/exp/maps"
+	"google.golang.org/protobuf/proto"
+	"google.golang.org/protobuf/reflect/protoreflect"
+	"google.golang.org/protobuf/types/known/fieldmaskpb"
+)
+
+// OverwriteMasked copies values from src to dst subject to a field mask. It
+// will will return an error if dst and src are not the same type of message,
+// or if some path in the field mask is not valid for that message type.
+func OverwriteMasked(dst, src proto.Message, m *fieldmaskpb.FieldMask) error {
+	return newFieldMaskTree(m).overwrite(dst.ProtoReflect(), src.ProtoReflect())
+}
+
+// fieldMaskTree represents a FieldMask as a tree, making it simpler to operate
+// on messages recursively.
+type fieldMaskTree map[string]fieldMaskTree
+
+func newFieldMaskTree(m *fieldmaskpb.FieldMask) fieldMaskTree {
+	var t fieldMaskTree
+	for _, p := range m.GetPaths() {
+		t.addFieldPath(p)
+	}
+	return t
+}
+
+// This is inspired by FieldMaskTree.java from the Java protobuf library:
+// https://github.com/protocolbuffers/protobuf/blob/3667102d9/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java#L76
+func (t *fieldMaskTree) addFieldPath(path string) {
+	if *t == nil {
+		*t = make(map[string]fieldMaskTree)
+	}
+
+	parts := strings.Split(path, ".")
+
+	node := *t
+	for _, p := range parts {
+		m := node[p]
+		if m == nil {
+			m = make(fieldMaskTree)
+			node[p] = m
+		} else if len(m) == 0 {
+			return
+		}
+		node = m
+	}
+	maps.Clear(node)
+}
+
+// ErrDescriptorMismatch indicates an operation could not be performed because
+// two proto messages did not have identical descriptors.
+var ErrDescriptorMismatch = errors.New("descriptor mismatch")
+
+func (t fieldMaskTree) overwrite(dst, src protoreflect.Message) error {
+	dd, sd := dst.Descriptor(), src.Descriptor()
+	if dd != sd {
+		return fmt.Errorf("%w: %v, %v", ErrDescriptorMismatch, dd.FullName(), sd.FullName())
+	}
+
+	fields := dd.Fields()
+
+	for p, subTree := range t {
+		f := fields.ByName(protoreflect.Name(p))
+		if f == nil {
+			return fmt.Errorf("cannot overwrite unknown field %q in message %v", p, dd.FullName())
+		}
+
+		if len(subTree) > 0 {
+			if f.Cardinality() == protoreflect.Repeated || f.Kind() != protoreflect.MessageKind {
+				return fmt.Errorf("cannot overwrite sub-fields of field %q in message %v",
+					f.TextName(), dd.FullName())
+			}
+			if !src.Has(f) && !src.Has(f) {
+				// no need to copy fields that don't exist
+				continue
+			}
+			subTree.overwrite(dst.Mutable(f).Message(), src.Get(f).Message())
+			continue
+		}
+
+		if src.Has(f) {
+			dst.Set(f, src.Get(f))
+		} else {
+			dst.Clear(f)
+		}
+	}
+
+	return nil
+}

pkg/protoutil/fieldmask_test.go

@@ -0,0 +1,66 @@
+package protoutil_test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/types/known/fieldmaskpb"
+	"google.golang.org/protobuf/types/known/timestamppb"
+
+	"github.com/pomerium/pomerium/internal/testutil"
+	"github.com/pomerium/pomerium/pkg/grpc/session"
+	"github.com/pomerium/pomerium/pkg/protoutil"
+)
+
+func TestOverwriteMasked(t *testing.T) {
+	t.Parallel()
+
+	s1 := &session.Session{
+		Id:       "session-id",
+		IssuedAt: timestamppb.New(time.Date(2023, 10, 25, 10, 0, 0, 0, time.UTC)),
+	}
+	s2 := &session.Session{
+		Id:         "new-session-id",
+		AccessedAt: timestamppb.New(time.Date(2023, 10, 25, 12, 0, 0, 0, time.UTC)),
+		OauthToken: &session.OAuthToken{
+			AccessToken: "new-access-token",
+			TokenType:   "bearer",
+		},
+	}
+
+	m, err := fieldmaskpb.New(s2,
+		"issued_at", "accessed_at", "oauth_token.access_token", "id_token.raw")
+	require.NoError(t, err)
+
+	err = protoutil.OverwriteMasked(s1, s2, m)
+	require.NoError(t, err)
+
+	testutil.AssertProtoJSONEqual(t, `{
+		"id": "session-id",
+		"accessedAt": "2023-10-25T12:00:00Z",
+		"oauthToken": {
+			"accessToken": "new-access-token"
+		}
+	}`, s1)
+}
+
+func TestOverwriteMaskedErrors(t *testing.T) {
+	t.Parallel()
+
+	var s1, s2 session.Session
+	var o session.OAuthToken
+
+	err := protoutil.OverwriteMasked(&s1, &s2, &fieldmaskpb.FieldMask{Paths: []string{"foo"}})
+	assert.Equal(t, `cannot overwrite unknown field "foo" in message session.Session`, err.Error())
+
+	err = protoutil.OverwriteMasked(&s1, &s2,
+		&fieldmaskpb.FieldMask{Paths: []string{"device_credentials.type_id"}})
+	assert.Equal(t, `cannot overwrite sub-fields of field "device_credentials" in message `+
+		"session.Session", err.Error())
+
+	m, _ := fieldmaskpb.New(&s1, "expires_at")
+	err = protoutil.OverwriteMasked(&s1, &o, m)
+	assert.Equal(t, "descriptor mismatch: session.Session, session.OAuthToken", err.Error())
+}

pkg/protoutil/fieldmasktree_test.go

@@ -0,0 +1,55 @@
+package protoutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/protobuf/types/known/fieldmaskpb"
+)
+
+func TestFieldMaskTree(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		tr := newFieldMaskTree(&fieldmaskpb.FieldMask{})
+		assert.Equal(t, fieldMaskTree(nil), tr)
+	})
+	t.Run("basic", func(t *testing.T) {
+		tr := newFieldMaskTree(&fieldmaskpb.FieldMask{
+			Paths: []string{"foo", "bar", "baz"},
+		})
+		assert.Equal(t, fieldMaskTree{
+			"foo": {},
+			"bar": {},
+			"baz": {},
+		}, tr)
+	})
+	t.Run("nested", func(t *testing.T) {
+		tr := newFieldMaskTree(&fieldmaskpb.FieldMask{
+			Paths: []string{"foo.bar.baz", "foo.bar.xyz", "foo.quux"},
+		})
+		assert.Equal(t, fieldMaskTree{
+			"foo": {
+				"bar": {
+					"baz": {},
+					"xyz": {},
+				},
+				"quux": {},
+			},
+		}, tr)
+	})
+	t.Run("overlapping fields 1", func(t *testing.T) {
+		tr := newFieldMaskTree(&fieldmaskpb.FieldMask{
+			Paths: []string{"foo", "foo.bar"},
+		})
+		assert.Equal(t, fieldMaskTree{
+			"foo": {},
+		}, tr)
+	})
+	t.Run("overlapping fields 2", func(t *testing.T) {
+		tr := newFieldMaskTree(&fieldmaskpb.FieldMask{
+			Paths: []string{"foo.bar", "foo"},
+		})
+		assert.Equal(t, fieldMaskTree{
+			"foo": {},
+		}, tr)
+	})
+}