json: Fix streamer not to ignore trailing unterminated structures

json_message_process_token() accumulates tokens until it got the
sequence of tokens that comprise a single JSON value (it counts curly
braces and square brackets to decide).  It feeds those token sequences
to json_parser_parse().  If a non-empty sequence of tokens remains at
the end of the parse, it's silently ignored.  check-qjson.c cases
unterminated_array(), unterminated_array_comma(), unterminated_dict(),
unterminated_dict_comma() demonstrate this bug.

Fix as follows.  Introduce a JSON_END_OF_INPUT token.  When the
streamer receives it, it feeds the accumulated tokens to
json_parser_parse().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180823164025.12553-46-armbru@redhat.com>

include/qapi/qmp/json-lexer.h

@@ -30,6 +30,7 @@ typedef enum json_token_type {
     JSON_INTERP,
     JSON_SKIP,
     JSON_ERROR,
+    JSON_END_OF_INPUT,
 } JSONTokenType;
 
 typedef struct JSONLexer {

qobject/json-lexer.c

@@ -347,6 +347,8 @@ void json_lexer_flush(JSONLexer *lexer)
     if (lexer->state != lexer->start_state) {
         json_lexer_feed_char(lexer, 0, true);
     }
+    json_message_process_token(lexer, lexer->token, JSON_END_OF_INPUT,
+                               lexer->x, lexer->y);
 }
 
 void json_lexer_destroy(JSONLexer *lexer)

qobject/json-streamer.c

@@ -60,6 +60,13 @@ void json_message_process_token(JSONLexer *lexer, GString *input,
     case JSON_ERROR:
         error_setg(&err, "JSON parse error, stray '%s'", input->str);
         goto out_emit;
+    case JSON_END_OF_INPUT:
+        if (g_queue_is_empty(parser->tokens)) {
+            return;
+        }
+        json = json_parser_parse(parser->tokens, parser->ap, &err);
+        parser->tokens = NULL;
+        goto out_emit;
     default:
         break;
     }
@@ -137,6 +144,7 @@ void json_message_parser_feed(JSONMessageParser *parser,
 void json_message_parser_flush(JSONMessageParser *parser)
 {
     json_lexer_flush(&parser->lexer);
+    assert(g_queue_is_empty(parser->tokens));
 }
 
 void json_message_parser_destroy(JSONMessageParser *parser)

tests/check-qjson.c

@@ -1360,7 +1360,7 @@ static void unterminated_array(void)
 {
     Error *err = NULL;
     QObject *obj = qobject_from_json("[32", &err);
-    g_assert(!err);             /* BUG */
+    error_free_or_abort(&err);
     g_assert(obj == NULL);
 }
 
@@ -1368,7 +1368,7 @@ static void unterminated_array_comma(void)
 {
     Error *err = NULL;
     QObject *obj = qobject_from_json("[32,", &err);
-    g_assert(!err);             /* BUG */
+    error_free_or_abort(&err);
     g_assert(obj == NULL);
 }
 
@@ -1384,7 +1384,7 @@ static void unterminated_dict(void)
 {
     Error *err = NULL;
     QObject *obj = qobject_from_json("{'abc':32", &err);
-    g_assert(!err);             /* BUG */
+    error_free_or_abort(&err);
     g_assert(obj == NULL);
 }
 
@@ -1392,7 +1392,7 @@ static void unterminated_dict_comma(void)
 {
     Error *err = NULL;
     QObject *obj = qobject_from_json("{'abc':32,", &err);
-    g_assert(!err);             /* BUG */
+    error_free_or_abort(&err);
     g_assert(obj == NULL);
 }