protojson: add UseHexForBytes option

encoding/protojson/decode.go

@@ -6,6 +6,7 @@ package protojson
 
 import (
 	"encoding/base64"
+	"encoding/hex"
 	"fmt"
 	"math"
 	"strconv"
@@ -41,6 +42,10 @@ type UnmarshalOptions struct {
 	// If DiscardUnknown is set, unknown fields and enum name values are ignored.
 	DiscardUnknown bool
 
+	// If UseHexForBytes is set, bytes fields are un-marshaled as hex
+	// strings instead of base64.
+	UseHexForBytes bool
+
 	// Resolver is used for looking up types when unmarshaling
 	// google.protobuf.Any messages or extension fields.
 	// If nil, this defaults to using protoregistry.GlobalTypes.
@@ -338,8 +343,14 @@ func (d decoder) unmarshalScalar(fd protoreflect.FieldDescriptor) (protoreflect.
 		}
 
 	case protoreflect.BytesKind:
-		if v, ok := unmarshalBytes(tok); ok {
-			return v, nil
+		if d.opts.UseHexForBytes {
+			if v, ok := unmarshalBytesFromHex(tok); ok {
+				return v, nil
+			}
+		} else {
+			if v, ok := unmarshalBytes(tok); ok {
+				return v, nil
+			}
 		}
 
 	case protoreflect.EnumKind:
@@ -488,6 +499,19 @@ func unmarshalBytes(tok json.Token) (protoreflect.Value, bool) {
 	return protoreflect.ValueOfBytes(b), true
 }
 
+func unmarshalBytesFromHex(tok json.Token) (protoreflect.Value, bool) {
+	if tok.Kind() != json.String {
+		return protoreflect.Value{}, false
+	}
+
+	s := tok.ParsedString()
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		return protoreflect.Value{}, false
+	}
+	return protoreflect.ValueOfBytes(b), true
+}
+
 func unmarshalEnum(tok json.Token, fd protoreflect.FieldDescriptor, discardUnknown bool) (protoreflect.Value, bool) {
 	switch tok.Kind() {
 	case json.String:

encoding/protojson/encode.go

@@ -6,6 +6,7 @@ package protojson
 
 import (
 	"encoding/base64"
+	"encoding/hex"
 	"fmt"
 
 	"google.golang.org/protobuf/internal/encoding/json"
@@ -102,6 +103,10 @@ type MarshalOptions struct {
 	// a strict superset of the latter.
 	EmitDefaultValues bool
 
+	// If UseHexForBytes is set, bytes fields are marshaled as hex strings
+	// instead of base64.
+	UseHexForBytes bool
+
 	// Resolver is used for looking up types when expanding google.protobuf.Any
 	// messages. If nil, this defaults to using protoregistry.GlobalTypes.
 	Resolver interface {
@@ -324,7 +329,13 @@ func (e encoder) marshalSingular(val protoreflect.Value, fd protoreflect.FieldDe
 		e.WriteFloat(val.Float(), 64)
 
 	case protoreflect.BytesKind:
-		e.WriteString(base64.StdEncoding.EncodeToString(val.Bytes()))
+		var encoded string
+		if e.opts.UseHexForBytes {
+			encoded = hex.EncodeToString(val.Bytes())
+		} else {
+			encoded = base64.StdEncoding.EncodeToString(val.Bytes())
+		}
+		e.WriteString(encoded)
 
 	case protoreflect.EnumKind:
 		if fd.Enum().FullName() == genid.NullValue_enum_fullname {