Issue #15: add a way to set a JSON_TOKENER_STRICT flag to forbid commas at the end of arrays and objects.

json_tokener.c

@@ -624,8 +624,15 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
       }
       break;
 
+    case json_tokener_state_array_after_sep:
     case json_tokener_state_array:
       if(c == ']') {
+		if (state == json_tokener_state_array_after_sep &&
+			(tok->flags & JSON_TOKENER_STRICT))
+		{
+			tok->err = json_tokener_error_parse_unexpected;
+			goto out;
+		}
 	saved_state = json_tokener_state_finish;
 	state = json_tokener_state_eatws;
       } else {
@@ -651,7 +658,7 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
 	saved_state = json_tokener_state_finish;
 	state = json_tokener_state_eatws;
       } else if(c == ',') {
-	saved_state = json_tokener_state_array;
+	saved_state = json_tokener_state_array_after_sep;
 	state = json_tokener_state_eatws;
       } else {
 	tok->err = json_tokener_error_parse_array;
@@ -660,7 +667,14 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
       break;
 
     case json_tokener_state_object_field_start:
+    case json_tokener_state_object_field_start_after_sep:
       if(c == '}') {
+		if (state == json_tokener_state_object_field_start_after_sep &&
+		    (tok->flags & JSON_TOKENER_STRICT))
+		{
+			tok->err = json_tokener_error_parse_unexpected;
+			goto out;
+		}
 	saved_state = json_tokener_state_finish;
 	state = json_tokener_state_eatws;
       } else if (c == '"' || c == '\'') {
@@ -731,7 +745,7 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
 	saved_state = json_tokener_state_finish;
 	state = json_tokener_state_eatws;
       } else if(c == ',') {
-	saved_state = json_tokener_state_object_field_start;
+	saved_state = json_tokener_state_object_field_start_after_sep;
 	state = json_tokener_state_eatws;
       } else {
 	tok->err = json_tokener_error_parse_object_value_sep;
@@ -771,3 +785,8 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
 	   json_tokener_errors[tok->err], tok->char_offset);
   return NULL;
 }
+
+void json_tokener_set_flags(struct json_tokener *tok, int flags)
+{
+	tok->flags = flags;
+}

json_tokener.h

@@ -58,7 +58,9 @@ enum json_tokener_state {
   json_tokener_state_object_field_end,
   json_tokener_state_object_value,
   json_tokener_state_object_value_add,
-  json_tokener_state_object_sep
+  json_tokener_state_object_sep,
+  json_tokener_state_array_after_sep,
+  json_tokener_state_object_field_start_after_sep
 };
 
 struct json_tokener_srec
@@ -80,8 +82,21 @@ struct json_tokener
   unsigned int ucs_char;
   char quote_char;
   struct json_tokener_srec *stack;
+  int flags;
 };
 
+/**
+ * Be strict when parsing JSON input.  Use caution with
+ * this flag as what is considered valid may become more
+ * restrictive from one release to the next, causing your
+ * code to fail on previously working input.
+ *
+ * This flag is not set by default.
+ *
+ * @see json_tokener_set_flags()
+ */
+#define JSON_TOKENER_STRICT  0x01
+
 /**
  * Given an error previously returned by json_tokener_get_error(),
  * return a human readable description of the error.
@@ -116,6 +131,11 @@ extern void json_tokener_reset(struct json_tokener *tok);
 extern struct json_object* json_tokener_parse(const char *str);
 extern struct json_object* json_tokener_parse_verbose(const char *str, enum json_tokener_error *error);
 
+/**
+ * Set flags that control how parsing will be done.
+ */
+extern void json_tokener_set_flags(struct json_tokener *tok, int flags);
+
 /** 
  * Parse a string and return a non-NULL json_object if a valid JSON value
  * is found.  The string does not need to be a JSON object or array;

tests/test_parse.c

@@ -183,6 +183,9 @@ struct incremental_step {
 	{ "[1,2,3,]",         -1, -1, json_tokener_success, 0 },
 	{ "[1,2,,3,]",        -1, 5, json_tokener_error_parse_unexpected, 0 },
 
+	{ "[1,2,3,]",         -1, 7, json_tokener_error_parse_unexpected, 3 },
+	{ "{\"a\":1,}",         -1, 7, json_tokener_error_parse_unexpected, 3 },
+
 	{ NULL, -1, -1, json_tokener_success, 0 },
 };
 
@@ -215,6 +218,12 @@ static void test_incremental_parse()
 		struct incremental_step *step = &incremental_steps[ii];
 		int length = step->length;
 		int expected_char_offset = step->char_offset;
+
+		if (step->reset_tokener & 2)
+			json_tokener_set_flags(tok, JSON_TOKENER_STRICT);
+		else
+			json_tokener_set_flags(tok, 0);
+
 		if (length == -1)
 			length = strlen(step->string_to_parse);
 		if (expected_char_offset == -1)
@@ -264,7 +273,7 @@ static void test_incremental_parse()
 		if (new_obj)
 			json_object_put(new_obj);
 
-		if (step->reset_tokener)
+		if (step->reset_tokener & 1)
 			json_tokener_reset(tok);
 
 		if (this_step_ok)

tests/test_parse.expected

@@ -51,5 +51,7 @@ json_tokener_parse_ex(tok, "\t"        ,   4) ... OK: got object of type [string
 json_tokener_parse_ex(tok, [1,2,3]     ,   7) ... OK: got object of type [array]: [ 1, 2, 3 ]
 json_tokener_parse_ex(tok, [1,2,3,]    ,   8) ... OK: got object of type [array]: [ 1, 2, 3 ]
 json_tokener_parse_ex(tok, [1,2,,3,]   ,   9) ... OK: got correct error: unexpected character
-End Incremental Tests OK=27 ERROR=0
+json_tokener_parse_ex(tok, [1,2,3,]    ,   8) ... OK: got correct error: unexpected character
+json_tokener_parse_ex(tok, {"a":1,}    ,   8) ... OK: got correct error: unexpected character
+End Incremental Tests OK=29 ERROR=0
 ==================================