Fix null value for struct field

decode_array.go

@@ -20,6 +20,11 @@ func (d *arrayDecoder) decodeStream(s *stream, p uintptr) error {
 	for {
 		switch s.char() {
 		case ' ', '\n', '\t', '\r':
+		case 'n':
+			if err := nullBytes(s); err != nil {
+				return err
+			}
+			return nil
 		case '[':
 			idx := 0
 			for {
@@ -63,6 +68,22 @@ func (d *arrayDecoder) decode(buf []byte, cursor int64, p uintptr) (int64, error
 		switch buf[cursor] {
 		case ' ', '\n', '\t', '\r':
 			continue
+		case 'n':
+			buflen := int64(len(buf))
+			if cursor+3 >= buflen {
+				return 0, errUnexpectedEndOfJSON("null", cursor)
+			}
+			if buf[cursor+1] != 'u' {
+				return 0, errInvalidCharacter(buf[cursor+1], "null", cursor)
+			}
+			if buf[cursor+2] != 'l' {
+				return 0, errInvalidCharacter(buf[cursor+2], "null", cursor)
+			}
+			if buf[cursor+3] != 'l' {
+				return 0, errInvalidCharacter(buf[cursor+3], "null", cursor)
+			}
+			cursor += 4
+			return cursor, nil
 		case '[':
 			idx := 0
 			for {

decode_map.go

@@ -47,7 +47,14 @@ func (d *mapDecoder) setValueStream(s *stream, key interface{}) error {
 
 func (d *mapDecoder) decodeStream(s *stream, p uintptr) error {
 	s.skipWhiteSpace()
-	if s.char() != '{' {
+	switch s.char() {
+	case 'n':
+		if err := nullBytes(s); err != nil {
+			return err
+		}
+		return nil
+	case '{':
+	default:
 		return errExpected("{ character for map value", s.totalOffset())
 	}
 	mapValue := makemap(d.mapType, 0)
@@ -94,7 +101,24 @@ func (d *mapDecoder) decode(buf []byte, cursor int64, p uintptr) (int64, error)
 	if buflen < 2 {
 		return 0, errExpected("{} for map", cursor)
 	}
-	if buf[cursor] != '{' {
+	switch buf[cursor] {
+	case 'n':
+		if cursor+3 >= buflen {
+			return 0, errUnexpectedEndOfJSON("null", cursor)
+		}
+		if buf[cursor+1] != 'u' {
+			return 0, errInvalidCharacter(buf[cursor+1], "null", cursor)
+		}
+		if buf[cursor+2] != 'l' {
+			return 0, errInvalidCharacter(buf[cursor+2], "null", cursor)
+		}
+		if buf[cursor+3] != 'l' {
+			return 0, errInvalidCharacter(buf[cursor+3], "null", cursor)
+		}
+		cursor += 4
+		return cursor, nil
+	case '{':
+	default:
 		return 0, errExpected("{ character for map value", cursor)
 	}
 	cursor++

decode_slice.go

@@ -62,6 +62,11 @@ func (d *sliceDecoder) decodeStream(s *stream, p uintptr) error {
 		case ' ', '\n', '\t', '\r':
 			s.cursor++
 			continue
+		case 'n':
+			if err := nullBytes(s); err != nil {
+				return err
+			}
+			return nil
 		case '[':
 			idx := 0
 			slice := d.newSlice()
@@ -136,6 +141,22 @@ func (d *sliceDecoder) decode(buf []byte, cursor int64, p uintptr) (int64, error
 		switch buf[cursor] {
 		case ' ', '\n', '\t', '\r':
 			continue
+		case 'n':
+			buflen := int64(len(buf))
+			if cursor+3 >= buflen {
+				return 0, errUnexpectedEndOfJSON("null", cursor)
+			}
+			if buf[cursor+1] != 'u' {
+				return 0, errInvalidCharacter(buf[cursor+1], "null", cursor)
+			}
+			if buf[cursor+2] != 'l' {
+				return 0, errInvalidCharacter(buf[cursor+2], "null", cursor)
+			}
+			if buf[cursor+3] != 'l' {
+				return 0, errInvalidCharacter(buf[cursor+3], "null", cursor)
+			}
+			cursor += 4
+			return cursor, nil
 		case '[':
 			idx := 0
 			slice := d.newSlice()

decode_test.go

@@ -135,12 +135,26 @@ func Test_Decoder(t *testing.T) {
 		assertEq(t, "struct.D.AA", 2, v.D.AA)
 		assertEq(t, "struct.D.BB", "world", v.D.BB)
 		assertEq(t, "struct.D.CC", true, v.D.CC)
-		t.Run("struct.null", func(t *testing.T) {
+		t.Run("struct.field null", func(t *testing.T) {
 			var v struct {
 				A string
+				B []string
+				C []int
+				D map[string]interface{}
+				E [2]string
+				F interface{}
 			}
-			assertErr(t, json.Unmarshal([]byte(`{"a":null}`), &v))
+			assertErr(t, json.Unmarshal([]byte(`{"a":null,"b":null,"c":null,"d":null,"e":null,"f":null}`), &v))
-			assertEq(t, "string is null", v.A, "")
+			assertEq(t, "string", v.A, "")
+			assertNeq(t, "[]string", v.B, nil)
+			assertEq(t, "[]string", len(v.B), 0)
+			assertNeq(t, "[]int", v.C, nil)
+			assertEq(t, "[]int", len(v.C), 0)
+			assertNeq(t, "map", v.D, nil)
+			assertEq(t, "map", len(v.D), 0)
+			assertNeq(t, "array", v.E, nil)
+			assertEq(t, "array", len(v.E), 2)
+			assertEq(t, "interface{}", v.F, nil)
 		})
 	})
 	t.Run("interface", func(t *testing.T) {

helper_test.go

@@ -15,3 +15,10 @@ func assertEq(t *testing.T, msg string, exp interface{}, act interface{}) {
 		t.Fatalf("failed to test for %s. exp=[%v] but act=[%v]", msg, exp, act)
 	}
 }
+
+func assertNeq(t *testing.T, msg string, exp interface{}, act interface{}) {
+	t.Helper()
+	if exp == act {
+		t.Fatalf("failed to test for %s. expected value is not [%v] but got same value", msg, act)
+	}
+}