Scanner for json-parser's internal state.

Summary:
We have a surprise-check in the JSON parser loop, to catch
heap-ooms from huge json blobs. When a GC triggers here,
we must scan the parser's state-stack.

Reviewed By: ricklavoie

Differential Revision: D2807258

fb-gh-sync-id: b8e704f921a794d84e3b80841c390fe58a53027a

hphp/runtime/ext/json/JSON_parser.cpp

@@ -615,6 +615,7 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
       json->stack[i].key.reset();
       json->stack[i].val.unset();
     }
+    json->mark = -1;
   };
 
   json->mark = json->top = -1;
@@ -970,6 +971,15 @@ bool JSON_parser(Variant &z, const char *p, int length, bool const assoc,
   return false;
 }
 
+void json_parser_scan(IMarker& mark) {
+  if (s_json_parser.isNull()) return;
+  auto json = s_json_parser.get();
+  if (json->mark < 0 || json->stack.empty()) return;
+  for (int i = 0; i <= json->mark; ++i) {
+    mark(json->stack[i].key);
+    mark(json->stack[i].val);
+  }
+}
 }
 
 #endif /* HAVE_JSONC */

hphp/runtime/ext/json/JSON_parser.h

@@ -24,11 +24,13 @@ namespace HPHP {
 
 struct StringBuffer;
 struct Variant;
+struct IMarker;
 
 void utf16_to_utf8(StringBuffer& buf, unsigned short utf16);
 bool JSON_parser(Variant& z, const char *p, int length,
                  bool assoc, int depth, int64_t options);
 void json_parser_init(); // called at request-init
+void json_parser_scan(IMarker&);
 
 enum json_error_codes {
   JSON_ERROR_NONE = 0,

hphp/runtime/ext/json/ext_json.cpp

@@ -258,7 +258,13 @@ class JsonExtension final : public Extension {
     loadSystemlib();
   }
 
-  void requestInit() override { json_parser_init(); }
+  void requestInit() override {
+    json_parser_init();
+  }
+
+  void vscan(IMarker& mark) const override {
+    json_parser_scan(mark);
+  }
 
 } s_json_extension;