pgproto3: hex-decode CopyData.Data in UnmarshalJSON

MarshalJSON encodes Data with hex.EncodeToString but UnmarshalJSON did
[]byte(msg.Data), so round-tripping any CopyData with non-text bytes
through JSON would silently corrupt the payload (e.g. [0x01 0x02 0xff]
came back as the literal bytes for the string "0102ff"). Now mirrors
the marshal side with hex.DecodeString, with the empty-Data shortcut
preserved so the existing TestJSONUnmarshalCopyData fixture still
unmarshals to []byte{}.

Added a round-trip test.

Signed-off-by: Charlie Tonneslan <cst0520@gmail.com>

Author: c-tonneslan

pgproto3/copy_data.go

@@ -54,6 +54,14 @@ func (dst *CopyData) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
-	dst.Data = []byte(msg.Data)
+	if msg.Data == "" {
+		dst.Data = []byte{}
+		return nil
+	}
+	b, err := hex.DecodeString(msg.Data)
+	if err != nil {
+		return err
+	}
+	dst.Data = b
 	return nil
 }

pgproto3/json_test.go

@@ -172,6 +172,25 @@ func TestJSONUnmarshalCopyData(t *testing.T) {
 	}
 }
 
+func TestJSONRoundTripCopyData(t *testing.T) {
+	want := CopyData{
+		Data: []byte{0x00, 0x01, 0x02, 0xff, 'h', 'i'},
+	}
+
+	b, err := json.Marshal(want)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+
+	var got CopyData
+	if err := json.Unmarshal(b, &got); err != nil {
+		t.Fatalf("unmarshal: %v", err)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("round-trip mismatch:\n want: %v\n got:  %v", want.Data, got.Data)
+	}
+}
+
 func TestJSONUnmarshalCopyInResponse(t *testing.T) {
 	data := []byte(`{"Type":"CopyBothResponse", "OverallFormat": "W"}`)
 	want := CopyBothResponse{