qjson: Have qobject_from_json() & friends reject empty and blank

The last case where qobject_from_json() & friends return null without
setting an error is empty or blank input.  Callers:

* block.c's parse_json_protocol() reports "Could not parse the JSON
  options".  It's marked as a work-around, because it also covered
  actual bugs, but they got fixed in the previous few commits.

* qobject_input_visitor_new_str() reports "JSON parse error".  Also
  marked as work-around.  The recent fixes have made this unreachable,
  because it currently gets called only for input starting with '{'.

* check-qjson.c's empty_input() and blank_input() demonstrate the
  behavior.

* The other callers are not affected since they only pass input with
  exactly one JSON value or, in the case of negative tests, one error.

Fail with "Expecting a JSON value" instead of returning null, and
simplify callers.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20180823164025.12553-48-armbru@redhat.com>

1 files changed, 0 insertions, 5 deletions

diff --git a/qapi/qobject-input-visitor.c b/qapi/qobject-input-visitor.c
index da57f4c..3e88b27 100644
--- a/qapi/qobject-input-visitor.c
+++ b/qapi/qobject-input-visitor.c
@@ -725,11 +725,6 @@ Visitor *qobject_input_visitor_new_str(const char *str,
     if (is_json) {
         obj = qobject_from_json(str, errp);
         if (!obj) {
-            /* Work around qobject_from_json() lossage TODO fix that */
-            if (errp && !*errp) {
-                error_setg(errp, "JSON parse error");
-                return NULL;
-            }
             return NULL;
         }
         args = qobject_to(QDict, obj);