Fix simple protocol encoding of json.RawMessage

The underlying type of json.RawMessage is a []byte so to avoid it being
considered binary data we need to handle it specifically. This is done
by registerDefaultPgTypeVariants. In addition, handle json.RawMessage in
the JSONCodec PlanEncode to avoid it being mutated by json.Marshal.

#1763

pgtype/json.go

@@ -25,6 +25,11 @@ func (c JSONCodec) PlanEncode(m *Map, oid uint32, format int16, value any) Encod
 	case []byte:
 		return encodePlanJSONCodecEitherFormatByteSlice{}
 
+	// Handle json.RawMessage specifically because if it is run through json.Marshal it may be mutated.
+	// e.g. `{"foo": "bar"}` -> `{"foo":"bar"}`.
+	case json.RawMessage:
+		return encodePlanJSONCodecEitherFormatJSONRawMessage{}
+
 	// Cannot rely on driver.Valuer being handled later because anything can be marshalled.
 	//
 	// https://github.com/jackc/pgx/issues/1430
@@ -79,6 +84,18 @@ func (encodePlanJSONCodecEitherFormatByteSlice) Encode(value any, buf []byte) (n
 	return buf, nil
 }
 
+type encodePlanJSONCodecEitherFormatJSONRawMessage struct{}
+
+func (encodePlanJSONCodecEitherFormatJSONRawMessage) Encode(value any, buf []byte) (newBuf []byte, err error) {
+	jsonBytes := value.(json.RawMessage)
+	if jsonBytes == nil {
+		return nil, nil
+	}
+
+	buf = append(buf, jsonBytes...)
+	return buf, nil
+}
+
 type encodePlanJSONCodecEitherFormatMarshal struct{}
 
 func (encodePlanJSONCodecEitherFormatMarshal) Encode(value any, buf []byte) (newBuf []byte, err error) {

pgtype/pgtype_default.go

@@ -1,6 +1,7 @@
 package pgtype
 
 import (
+	"encoding/json"
 	"net"
 	"net/netip"
 	"reflect"
@@ -173,6 +174,7 @@ func initDefaultMap() {
 	registerDefaultPgTypeVariants[time.Time](defaultMap, "timestamptz")
 	registerDefaultPgTypeVariants[time.Duration](defaultMap, "interval")
 	registerDefaultPgTypeVariants[string](defaultMap, "text")
+	registerDefaultPgTypeVariants[json.RawMessage](defaultMap, "json")
 	registerDefaultPgTypeVariants[[]byte](defaultMap, "bytea")
 
 	registerDefaultPgTypeVariants[net.IP](defaultMap, "inet")

pgtype/pgtype_test.go

@@ -546,6 +546,14 @@ func TestMapEncodePlanCacheUUIDTypeConfusion(t *testing.T) {
 	require.Error(t, err)
 }
 
+// https://github.com/jackc/pgx/issues/1763
+func TestMapEncodeRawJSONIntoUnknownOID(t *testing.T) {
+	m := pgtype.NewMap()
+	buf, err := m.Encode(0, pgtype.TextFormatCode, json.RawMessage(`{"foo": "bar"}`), nil)
+	require.NoError(t, err)
+	require.Equal(t, []byte(`{"foo": "bar"}`), buf)
+}
+
 func BenchmarkMapScanInt4IntoBinaryDecoder(b *testing.B) {
 	m := pgtype.NewMap()
 	src := []byte{0, 0, 0, 42}