fix: Union Decoder uses readInt (#387)

Co-authored-by: Brian Shih <brianshih@Brians-MacBook-Pro.local>

codec_generic_internal_test.go

@@ -173,6 +173,14 @@ func TestGenericDecode(t *testing.T) {
  want: map[string]any{"string": "foo"},
  wantErr: require.NoError,
  },
+ {
+ name: "Union Zero Index",
+ // 0x80 represents 128. So the bytes below will result in 0
+ // as a result of zig-zag encoding.
+ data: []byte{0x80, 0x80, 0x80, 0x80, 0x30},
+ schema: `["null"]`,
+ wantErr: require.NoError,
+ },
  {
  name: "Union Nil",
  data: []byte{0x00},

codec_union.go

@@ -152,7 +152,7 @@ func (e *mapUnionEncoder) Encode(ptr unsafe.Pointer, w *Writer) {
  return
  }
 
- w.WriteLong(int64(pos))
+ w.WriteInt(int32(pos))
 
  if schema.Type() == Null && val == nil {
  return
@@ -259,26 +259,26 @@ func encoderOfNullableUnion(cfg *frozenConfig, schema Schema, typ reflect2.Type)
  schema: union,
  encoder: encoder,
  isPtr: isPtr,
- nullIdx: int64(nullIdx),
- typeIdx: int64(typeIdx),
+ nullIdx: int32(nullIdx),
+ typeIdx: int32(typeIdx),
  }
 }
 
 type unionNullableEncoder struct {
  schema *UnionSchema
  encoder ValEncoder
  isPtr bool
- nullIdx int64
- typeIdx int64
+ nullIdx int32
+ typeIdx int32
 }
 
 func (e *unionNullableEncoder) Encode(ptr unsafe.Pointer, w *Writer) {
  if *((*unsafe.Pointer)(ptr)) == nil {
- w.WriteLong(e.nullIdx)
+ w.WriteInt(e.nullIdx)
  return
  }
 
- w.WriteLong(e.typeIdx)
+ w.WriteInt(e.typeIdx)
  newPtr := ptr
  if e.isPtr {
  newPtr = *((*unsafe.Pointer)(ptr))
@@ -445,15 +445,15 @@ type unionResolverEncoder struct {
 }
 
 func (e *unionResolverEncoder) Encode(ptr unsafe.Pointer, w *Writer) {
- w.WriteLong(int64(e.pos))
+ w.WriteInt(int32(e.pos))
 
  e.encoder.Encode(ptr, w)
 }
 
 func getUnionSchema(schema *UnionSchema, r *Reader) (int, Schema) {
  types := schema.Types()
 
- idx := int(r.ReadLong())
+ idx := int(r.ReadInt())
  if idx < 0 || idx > len(types)-1 {
  r.ReportError("decode union type", "unknown union type")
  return 0, nil