From f341b31ea593c5b69c6694299d4bf8a096d5e19a Mon Sep 17 00:00:00 2001
From: Masaaki Goshima <goccy54@gmail.com>
Date: Sun, 2 May 2021 16:02:14 +0900
Subject: [PATCH] Fix decoding of backslash char at the end of string

---
 decode_context.go | 38 ++++++++++-----------
 decode_stream.go  | 42 ++++++++++++++++++-----
 decode_test.go    | 85 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 135 insertions(+), 30 deletions(-)

diff --git a/decode_context.go b/decode_context.go
index 305f0d6..eac8163 100644
--- a/decode_context.go
+++ b/decode_context.go
@@ -55,10 +55,12 @@ func skipObject(buf []byte, cursor, depth int64) (int64, error) {
 			for {
 				cursor++
 				switch buf[cursor] {
-				case '"':
-					if buf[cursor-1] == '\\' {
-						continue
+				case '\\':
+					cursor++
+					if buf[cursor] == nul {
+						return 0, errUnexpectedEndOfJSON("string of object", cursor)
 					}
+				case '"':
 					goto SWITCH_OUT
 				case nul:
 					return 0, errUnexpectedEndOfJSON("string of object", cursor)
@@ -99,10 +101,12 @@ func skipArray(buf []byte, cursor, depth int64) (int64, error) {
 			for {
 				cursor++
 				switch buf[cursor] {
-				case '"':
-					if buf[cursor-1] == '\\' {
-						continue
+				case '\\':
+					cursor++
+					if buf[cursor] == nul {
+						return 0, errUnexpectedEndOfJSON("string of object", cursor)
 					}
+				case '"':
 					goto SWITCH_OUT
 				case nul:
 					return 0, errUnexpectedEndOfJSON("string of object", cursor)
@@ -130,10 +134,12 @@ func skipValue(buf []byte, cursor, depth int64) (int64, error) {
 			for {
 				cursor++
 				switch buf[cursor] {
-				case '"':
-					if buf[cursor-1] == '\\' {
-						continue
+				case '\\':
+					cursor++
+					if buf[cursor] == nul {
+						return 0, errUnexpectedEndOfJSON("string of object", cursor)
 					}
+				case '"':
 					return cursor + 1, nil
 				case nul:
 					return 0, errUnexpectedEndOfJSON("string of object", cursor)
@@ -184,18 +190,8 @@ func skipValue(buf []byte, cursor, depth int64) (int64, error) {
 			cursor += 5
 			return cursor, nil
 		case 'n':
-			buflen := int64(len(buf))
-			if cursor+3 >= buflen {
-				return 0, errUnexpectedEndOfJSON("null", cursor)
-			}
-			if buf[cursor+1] != 'u' {
-				return 0, errUnexpectedEndOfJSON("null", cursor)
-			}
-			if buf[cursor+2] != 'l' {
-				return 0, errUnexpectedEndOfJSON("null", cursor)
-			}
-			if buf[cursor+3] != 'l' {
-				return 0, errUnexpectedEndOfJSON("null", cursor)
+			if err := validateNull(buf, cursor); err != nil {
+				return 0, err
 			}
 			cursor += 4
 			return cursor, nil
diff --git a/decode_stream.go b/decode_stream.go
index 6019aaa..257b8fc 100644
--- a/decode_stream.go
+++ b/decode_stream.go
@@ -126,10 +126,18 @@ func (s *stream) skipObject(depth int64) error {
 			for {
 				cursor++
 				switch char(p, cursor) {
-				case '"':
-					if char(p, cursor-1) == '\\' {
-						continue
+				case '\\':
+					cursor++
+					if char(p, cursor) == nul {
+						s.cursor = cursor
+						if s.read() {
+							s.cursor-- // for retry current character
+							_, cursor, p = s.stat()
+							continue
+						}
+						return errUnexpectedEndOfJSON("string of object", cursor)
 					}
+				case '"':
 					goto SWITCH_OUT
 				case nul:
 					s.cursor = cursor
@@ -183,10 +191,18 @@ func (s *stream) skipArray(depth int64) error {
 			for {
 				cursor++
 				switch char(p, cursor) {
-				case '"':
-					if char(p, cursor-1) == '\\' {
-						continue
+				case '\\':
+					cursor++
+					if char(p, cursor) == nul {
+						s.cursor = cursor
+						if s.read() {
+							s.cursor-- // for retry current character
+							_, cursor, p = s.stat()
+							continue
+						}
+						return errUnexpectedEndOfJSON("string of object", cursor)
 					}
+				case '"':
 					goto SWITCH_OUT
 				case nul:
 					s.cursor = cursor
@@ -235,10 +251,18 @@ func (s *stream) skipValue(depth int64) error {
 			for {
 				cursor++
 				switch char(p, cursor) {
-				case '"':
-					if char(p, cursor-1) == '\\' {
-						continue
+				case '\\':
+					cursor++
+					if char(p, cursor) == nul {
+						s.cursor = cursor
+						if s.read() {
+							s.cursor-- // for retry current character
+							_, cursor, p = s.stat()
+							continue
+						}
+						return errUnexpectedEndOfJSON("value of string", s.totalOffset())
 					}
+				case '"':
 					s.cursor = cursor + 1
 					return nil
 				case nul:
diff --git a/decode_test.go b/decode_test.go
index cfc6df3..fb4ea65 100644
--- a/decode_test.go
+++ b/decode_test.go
@@ -3417,3 +3417,88 @@ func TestDecodeByteSliceNull(t *testing.T) {
 		}
 	})
 }
+
+func TestDecodeBackSlash(t *testing.T) {
+	t.Run("unmarshal", func(t *testing.T) {
+		t.Run("string", func(t *testing.T) {
+			var v1 map[string]stdjson.RawMessage
+			if err := stdjson.Unmarshal([]byte(`{"c":"\\"}`), &v1); err != nil {
+				t.Fatal(err)
+			}
+			var v2 map[string]json.RawMessage
+			if err := json.Unmarshal([]byte(`{"c":"\\"}`), &v2); err != nil {
+				t.Fatal(err)
+			}
+			if len(v1) != len(v2) || !bytes.Equal(v1["c"], v2["c"]) {
+				t.Fatalf("failed to decode backslash: expected %#v but got %#v", v1, v2)
+			}
+		})
+		t.Run("array", func(t *testing.T) {
+			var v1 map[string]stdjson.RawMessage
+			if err := stdjson.Unmarshal([]byte(`{"c":["\\"]}`), &v1); err != nil {
+				t.Fatal(err)
+			}
+			var v2 map[string]json.RawMessage
+			if err := json.Unmarshal([]byte(`{"c":["\\"]}`), &v2); err != nil {
+				t.Fatal(err)
+			}
+			if len(v1) != len(v2) || !bytes.Equal(v1["c"], v2["c"]) {
+				t.Fatalf("failed to decode backslash: expected %#v but got %#v", v1, v2)
+			}
+		})
+		t.Run("object", func(t *testing.T) {
+			var v1 map[string]stdjson.RawMessage
+			if err := stdjson.Unmarshal([]byte(`{"c":{"\\":"\\"}}`), &v1); err != nil {
+				t.Fatal(err)
+			}
+			var v2 map[string]json.RawMessage
+			if err := json.Unmarshal([]byte(`{"c":{"\\":"\\"}}`), &v2); err != nil {
+				t.Fatal(err)
+			}
+			if len(v1) != len(v2) || !bytes.Equal(v1["c"], v2["c"]) {
+				t.Fatalf("failed to decode backslash: expected %#v but got %#v", v1, v2)
+			}
+		})
+	})
+	t.Run("stream", func(t *testing.T) {
+		t.Run("string", func(t *testing.T) {
+			var v1 map[string]stdjson.RawMessage
+			if err := stdjson.NewDecoder(strings.NewReader(`{"c":"\\"}`)).Decode(&v1); err != nil {
+				t.Fatal(err)
+			}
+			var v2 map[string]json.RawMessage
+			if err := json.NewDecoder(strings.NewReader(`{"c":"\\"}`)).Decode(&v2); err != nil {
+				t.Fatal(err)
+			}
+			if len(v1) != len(v2) || !bytes.Equal(v1["c"], v2["c"]) {
+				t.Fatalf("failed to decode backslash: expected %#v but got %#v", v1, v2)
+			}
+		})
+		t.Run("array", func(t *testing.T) {
+			var v1 map[string]stdjson.RawMessage
+			if err := stdjson.NewDecoder(strings.NewReader(`{"c":["\\"]}`)).Decode(&v1); err != nil {
+				t.Fatal(err)
+			}
+			var v2 map[string]json.RawMessage
+			if err := json.NewDecoder(strings.NewReader(`{"c":["\\"]}`)).Decode(&v2); err != nil {
+				t.Fatal(err)
+			}
+			if len(v1) != len(v2) || !bytes.Equal(v1["c"], v2["c"]) {
+				t.Fatalf("failed to decode backslash: expected %#v but got %#v", v1, v2)
+			}
+		})
+		t.Run("object", func(t *testing.T) {
+			var v1 map[string]stdjson.RawMessage
+			if err := stdjson.NewDecoder(strings.NewReader(`{"c":{"\\":"\\"}}`)).Decode(&v1); err != nil {
+				t.Fatal(err)
+			}
+			var v2 map[string]json.RawMessage
+			if err := json.NewDecoder(strings.NewReader(`{"c":{"\\":"\\"}}`)).Decode(&v2); err != nil {
+				t.Fatal(err)
+			}
+			if len(v1) != len(v2) || !bytes.Equal(v1["c"], v2["c"]) {
+				t.Fatalf("failed to decode backslash: expected %#v but got %#v", v1, v2)
+			}
+		})
+	})
+}