jsonparse: Fix a bug allowing a trailing comma in objects

5 files changed, 35 insertions, 18 deletions

diff --git a/ReleaseNotes.md b/ReleaseNotes.md
index 71973aa..be5b8ff 100644
--- a/ReleaseNotes.md
+++ b/ReleaseNotes.md
@@ -37,6 +37,9 @@
      now reflect the `InvalidUTF8` setting, rather than simply saying
      "unflushed unicode garbage".
 
+   - Bugfix: No longer allows a comma after the last key:value pair in
+     an object.
+
 # v0.3.7 (2023-02-20)
 
   Theme: Fixes from fuzzing (part 1?)
diff --git a/compat/json/compat_test.go b/compat/json/compat_test.go
index 3de48f7..af92093 100644
--- a/compat/json/compat_test.go
+++ b/compat/json/compat_test.go
@@ -196,6 +196,7 @@ func TestCompatUnmarshal(t *testing.T) {
 		"syntax-01": {In: `{}x`, ExpErr: `invalid character 'x' after top-level value`},
 		"syntax-02": {In: `x`, ExpErr: `invalid character 'x' looking for beginning of value`},
 		"syntax-03": {In: `{x`, ExpErr: `invalid character 'x' looking for beginning of object key string`},
+		"syntax-18": {In: `{"":0,}`, ExpErr: `invalid character '}' looking for beginning of object key string`},
 		"syntax-04": {In: `{""x`, ExpErr: `invalid character 'x' after object key`},
 		"syntax-05": {In: `{"":0x`, ExpErr: `invalid character 'x' after object key:value pair`},
 		"syntax-06": {In: `[0x`, ExpErr: `invalid character 'x' after array element`},
diff --git a/compat/json/testdata/fuzz/FuzzEquiv/f9afef161f73f7cf b/compat/json/testdata/fuzz/FuzzEquiv/f9afef161f73f7cf
new file mode 100644
index 0000000..6618d0f
--- /dev/null
+++ b/compat/json/testdata/fuzz/FuzzEquiv/f9afef161f73f7cf
@@ -0,0 +1,2 @@
+go test fuzz v1
+[]byte("{\"\":{},}")
diff --git a/internal/jsonparse/parse.go b/internal/jsonparse/parse.go
index 5547df4..ce71a65 100644
--- a/internal/jsonparse/parse.go
+++ b/internal/jsonparse/parse.go
@@ -279,7 +279,8 @@ type Parser struct {
 	// rule; they need some special assignments:
 	//
 	//   {   object: waiting for key to start or '}'
-	//   »   object: reading key / waiting for colon
+	//   }   object: waiting for key to start
+	//   :   object: reading key / waiting for colon
 	//   o   object: reading value / waiting for ',' or '}'
 	//
 	//   [   array: waiting for item to start or ']'
@@ -298,17 +299,17 @@ type Parser struct {
 	//   stack   processed
 	//   ?
 	//   {       {
-	//   »"      {"
-	//   »"      {"x
-	//   »       {"x"
+	//   :"      {"
+	//   :"      {"x
+	//   :       {"x"
 	//   o?      {"x":
 	//   o"      {"x":"
 	//   o"      {"x":"y
 	//   o       {"x":"y"
-	//   {       {"x":"y",
-	//   »"      {"x":"y","
-	//   »"      {"x":"y","a
-	//   »       {"x":"y","a"
+	//   }       {"x":"y",
+	//   :"      {"x":"y","
+	//   :"      {"x":"y","a
+	//   :       {"x":"y","a"
 	//   o?      {"x":"y","a":
 	//   o"      {"x":"y","a":"
 	//   o"      {"x":"y","a":"b
@@ -627,7 +628,7 @@ func (par *Parser) HandleRune(c rune, isRune bool) (RuneType, error) {
 		case 0x0020, 0x000A, 0x000D, 0x0009:
 			return RuneTypeSpace, nil
 		case '"':
-			par.replaceState(RuneTypeStringEnd)
+			par.replaceState(RuneTypeObjectColon)
 			return par.pushState(RuneTypeStringBeg), nil
 		case '}':
 			par.popState()
@@ -635,7 +636,17 @@ func (par *Parser) HandleRune(c rune, isRune bool) (RuneType, error) {
 		default:
 			return RuneTypeError, &InvalidCharacterError{c, isRune, "looking for beginning of object key string"}
 		}
-	case RuneTypeStringEnd: // waiting for ':'
+	case RuneTypeObjectEnd: // waiting for key to start
+		switch c {
+		case 0x0020, 0x000A, 0x000D, 0x0009:
+			return RuneTypeSpace, nil
+		case '"':
+			par.replaceState(RuneTypeObjectColon)
+			return par.pushState(RuneTypeStringBeg), nil
+		default:
+			return RuneTypeError, &InvalidCharacterError{c, isRune, "looking for beginning of object key string"}
+		}
+	case RuneTypeObjectColon: // waiting for ':'
 		switch c {
 		case 0x0020, 0x000A, 0x000D, 0x0009:
 			return RuneTypeSpace, nil
@@ -651,7 +662,7 @@ func (par *Parser) HandleRune(c rune, isRune bool) (RuneType, error) {
 		case 0x0020, 0x000A, 0x000D, 0x0009:
 			return RuneTypeSpace, nil
 		case ',':
-			par.replaceState(RuneTypeObjectBeg)
+			par.replaceState(RuneTypeObjectEnd)
 			return RuneTypeObjectComma, nil
 		case '}':
 			par.popState()
diff --git a/internal/jsonparse/parse_test.go b/internal/jsonparse/parse_test.go
index acb43e8..fe94c58 100644
--- a/internal/jsonparse/parse_test.go
+++ b/internal/jsonparse/parse_test.go
@@ -24,17 +24,17 @@ func TestParserHandleRune(t *testing.T) {
 				// st,// processed
 				`?`,
 				`{`,  // {
-				`»"`, // {"
-				`»"`, // {"x
-				`»`,  // {"x"
+				`:"`, // {"
+				`:"`, // {"x
+				`:`,  // {"x"
 				`o?`, // {"x":
 				`o"`, // {"x":"
 				`o"`, // {"x":"y
 				`o`,  // {"x":"y"
-				`{`,  // {"x":"y",
-				`»"`, // {"x":"y","
-				`»"`, // {"x":"y","a
-				`»`,  // {"x":"y","a"
+				`}`,  // {"x":"y",
+				`:"`, // {"x":"y","
+				`:"`, // {"x":"y","a
+				`:`,  // {"x":"y","a"
 				`o?`, // {"x":"y","a":
 				`o"`, // {"x":"y","a":"
 				`o"`, // {"x":"y","a":"b