[#123] protogen: Treat bytes field as non-nullable

In protobuf 3.12 they have added an support for `optional` keyword,
which has made it into the main branch in 3.15.
https://github.com/protocolbuffers/protobuf/blob/main/docs/implementing_proto3_presence.md
https://github.com/protocolbuffers/protobuf/blob/v3.12.0/docs/field_presence.md#presence-in-proto3-apis

This means that without an explicit `optional` keyword field presence
for scalars is not tracked, thus empty string in JSON should be
unmarshaled to a nil byte slice. Relevant decoding code and tests from
protojson:
fb995f184a/internal/impl/message_reflect_field.go (L327)
fb995f184a/encoding/protojson/decode_test.go (L134)
fb995f184a/encoding/protojson/decode_test.go (L156)

We do not support `optional` keyword and the generator will fail if it sees on.
So only implement the default behaviour.

Refs #122

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

acl/grpc/types_frostfs.pb.go

@@ -691,7 +691,13 @@ func (x *EACLRecord_Target) UnmarshalEasyJSON(in *jlexer.Lexer) {
 				var list [][]byte
 				in.Delim('[')
 				for !in.IsDelim(']') {
-					f = in.Bytes()
+					{
+						tmp := in.Bytes()
+						if len(tmp) == 0 {
+							tmp = nil
+						}
+						f = tmp
+					}
 					list = append(list, f)
 					in.WantComma()
 				}

ape/grpc/types_frostfs.pb.go

@@ -401,7 +401,13 @@ func (x *Chain) UnmarshalEasyJSON(in *jlexer.Lexer) {
 			x.Kind = xx
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				xx.Raw = f
 			}
 		}

apemanager/grpc/service_frostfs.pb.go

@@ -558,7 +558,13 @@ func (x *AddChainResponse_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "chainId":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.ChainId = f
 			}
 		}
@@ -974,7 +980,13 @@ func (x *RemoveChainRequest_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "chainId":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.ChainId = f
 			}
 		}

container/grpc/types_frostfs.pb.go

@@ -500,7 +500,13 @@ func (x *Container) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "nonce":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Nonce = f
 			}
 		case "basicACL":

netmap/grpc/types_frostfs.pb.go

@@ -1855,7 +1855,13 @@ func (x *NodeInfo) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "publicKey":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.PublicKey = f
 			}
 		case "addresses":
@@ -2279,13 +2285,25 @@ func (x *NetworkConfig_Parameter) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "key":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Key = f
 			}
 		case "value":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Value = f
 			}
 		}

object/grpc/service_frostfs.pb.go

@@ -924,7 +924,13 @@ func (x *GetResponse_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 			x.ObjectPart = xx
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				xx.Chunk = f
 			}
 		case "splitInfo":
@@ -1699,7 +1705,13 @@ func (x *PutRequest_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 			x.ObjectPart = xx
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				xx.Chunk = f
 			}
 		}
@@ -6254,7 +6266,13 @@ func (x *GetRangeResponse_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 			x.RangePart = xx
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				xx.Chunk = f
 			}
 		case "splitInfo":
@@ -6802,7 +6820,13 @@ func (x *GetRangeHashRequest_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "salt":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Salt = f
 			}
 		case "type":
@@ -7267,7 +7291,13 @@ func (x *GetRangeHashResponse_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 				var list [][]byte
 				in.Delim('[')
 				for !in.IsDelim(']') {
-					f = in.Bytes()
+					{
+						tmp := in.Bytes()
+						if len(tmp) == 0 {
+							tmp = nil
+						}
+						f = tmp
+					}
 					list = append(list, f)
 					in.WantComma()
 				}
@@ -8455,7 +8485,13 @@ func (x *PatchRequest_Body_Patch) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "chunk":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Chunk = f
 			}
 		}

object/grpc/types_frostfs.pb.go

@@ -1015,7 +1015,13 @@ func (x *Header_Split) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "splitID":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.SplitId = f
 			}
 		}
@@ -1436,13 +1442,25 @@ func (x *Header_EC) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "header":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Header = f
 			}
 		case "parentSplitID":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.ParentSplitId = f
 			}
 		case "parentSplitParentID":
@@ -2347,7 +2365,13 @@ func (x *Object) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "payload":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Payload = f
 			}
 		}
@@ -2552,7 +2576,13 @@ func (x *SplitInfo) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "splitId":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.SplitId = f
 			}
 		case "lastPart":

refs/grpc/types_frostfs.pb.go

@@ -390,7 +390,13 @@ func (x *ObjectID) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "value":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Value = f
 			}
 		}
@@ -529,7 +535,13 @@ func (x *ContainerID) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "value":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Value = f
 			}
 		}
@@ -668,7 +680,13 @@ func (x *OwnerID) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "value":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Value = f
 			}
 		}
@@ -1063,13 +1081,25 @@ func (x *Signature) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "key":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Key = f
 			}
 		case "signature":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Sign = f
 			}
 		case "scheme":
@@ -1264,13 +1294,25 @@ func (x *SignatureRFC6979) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "key":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Key = f
 			}
 		case "signature":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Sign = f
 			}
 		}
@@ -1466,7 +1508,13 @@ func (x *Checksum) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "sum":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Sum = f
 			}
 		}

session/grpc/service_frostfs.pb.go

@@ -598,13 +598,25 @@ func (x *CreateResponse_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "id":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Id = f
 			}
 		case "sessionKey":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.SessionKey = f
 			}
 		}

session/grpc/types_frostfs.pb.go

@@ -1284,7 +1284,13 @@ func (x *SessionToken_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "id":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Id = f
 			}
 		case "ownerID":
@@ -1304,7 +1310,13 @@ func (x *SessionToken_Body) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "sessionKey":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.SessionKey = f
 			}
 		case "object":

status/grpc/types_frostfs.pb.go

@@ -439,7 +439,13 @@ func (x *Status_Detail) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "value":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.Value = f
 			}
 		}

tombstone/grpc/types_frostfs.pb.go

@@ -231,7 +231,13 @@ func (x *Tombstone) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "splitID":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.SplitId = f
 			}
 		case "members":

util/proto/marshal_test.go

@@ -50,9 +50,6 @@ func TestStableMarshalSingle(t *testing.T) {
 
 			var actualFrostfs generated.Primitives
 			require.NoError(t, actualFrostfs.UnmarshalJSON(r))
-			if len(actualFrostfs.FieldA) == 0 {
-				actualFrostfs.FieldA = nil
-			}
 			require.Equal(t, input, &actualFrostfs)
 
 			primitivesEqual(t, input, &actual)
@@ -110,9 +107,6 @@ func TestStableMarshalSingle(t *testing.T) {
 
 				var actualFrostfs generated.Primitives
 				require.NoError(t, actualFrostfs.UnmarshalJSON(r))
-				if len(actualFrostfs.FieldA) == 0 {
-					actualFrostfs.FieldA = nil
-				}
 				require.Equal(t, tc.input, &actualFrostfs)
 
 				primitivesEqual(t, tc.input, &actual)
@@ -124,9 +118,7 @@ func TestStableMarshalSingle(t *testing.T) {
 func primitivesEqual(t *testing.T, a *generated.Primitives, b *test.Primitives) {
 	// Compare each field directly, because proto-generated code has private fields.
 	require.Equal(t, len(a.FieldA), len(b.FieldA))
-	if len(a.FieldA) != 0 {
 	require.Equal(t, a.FieldA, b.FieldA)
-	}
 	require.Equal(t, a.FieldB, b.FieldB)
 	require.Equal(t, a.FieldC, b.FieldC)
 	require.Equal(t, a.FieldD, b.FieldD)

util/proto/test/custom/test_frostfs.pb.go

@@ -771,7 +771,13 @@ func (x *Primitives) UnmarshalEasyJSON(in *jlexer.Lexer) {
 		case "fieldA":
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				x.FieldA = f
 			}
 		case "fieldB":
@@ -903,7 +909,13 @@ func (x *Primitives) UnmarshalEasyJSON(in *jlexer.Lexer) {
 			x.FieldM = xx
 			{
 				var f []byte
-				f = in.Bytes()
+				{
+					tmp := in.Bytes()
+					if len(tmp) == 0 {
+						tmp = nil
+					}
+					f = tmp
+				}
 				xx.FieldMa = f
 			}
 		case "fieldMe":
@@ -1520,7 +1532,13 @@ func (x *RepPrimitives) UnmarshalEasyJSON(in *jlexer.Lexer) {
 				var list [][]byte
 				in.Delim('[')
 				for !in.IsDelim(']') {
-					f = in.Bytes()
+					{
+						tmp := in.Bytes()
+						if len(tmp) == 0 {
+							tmp = nil
+						}
+						f = tmp
+					}
 					list = append(list, f)
 					in.WantComma()
 				}

util/protogen/internalgengo/json.go

@@ -129,7 +129,17 @@ func emitJSONFieldRead(g *protogen.GeneratedFile, f *protogen.Field, name string
 	case protoreflect.StringKind:
 		template = "%s = in.String()"
 	case protoreflect.BytesKind:
-		template = "%s = in.Bytes()"
+		// Since some time ago proto3 support optional keyword, thus the presence is not tracked by default:
+		// https://github.com/protocolbuffers/protobuf-go/blob/fb995f184a1719ec42b247a3771d1036d92adf67/internal/impl/message_reflect_field.go#L327
+		// We do not explicitly support `optional` keyword, protoc will fail on such fileds.
+		// Thus, treat empty string as `[]byte(nil)`.
+		template = `{
+			tmp := in.Bytes()
+			if len(tmp) == 0 {
+				tmp = nil
+			}
+			%s = tmp
+		}`
 	case protoreflect.MessageKind:
 		if f.Desc.IsList() {
 			g.P("f = ", fieldType(g, f)[2:], "{}")