Cannot define Field refering ProtoField defined in LUA. Bug 3513 (https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3513)

When a new Field is created, does as following: 

* Check whether that field is registered, by using `proto_registrar_get_byname`. This is current behavior.
* (patched) If not registered, check whether that field is defined in LUA and will be registered. This is performed in `wslua_is_field_available` accessing LUA context.
* If not, an error "a field with this name must exist"  occurs.


svn path=/trunk/; revision=52771

epan/wslua/wslua.h

@@ -463,4 +463,6 @@ extern int wslua_set_tap_enums(lua_State* L);
 
 extern int luaopen_bit(lua_State *L);
 
+extern int wslua_is_field_available(lua_State* L, const char* field_abbr);
+
 #endif

epan/wslua/wslua_field.c

@@ -483,7 +483,7 @@ WSLUA_CONSTRUCTOR Field_new(lua_State *L) {
 
     if (!name) return 0;
 
-    if (!proto_registrar_get_byname(name))
+    if (!proto_registrar_get_byname(name) && !wslua_is_field_available(L, name))
         WSLUA_ARG_ERROR(Field_new,FIELDNAME,"a field with this name must exist");
 
     if (!wanted_fields)

epan/wslua/wslua_proto.c

@@ -1595,6 +1595,36 @@ int Proto_register(lua_State* L) {
     return 1;
 }
 
+/**
+ * Query field abbr that is defined and bound to a Proto in lua.
+ * They are not registered untill the end of the initialization.
+ */
+int wslua_is_field_available(lua_State* L, const char* field_abbr) {
+    lua_rawgeti(L, LUA_REGISTRYINDEX, protocols_table_ref);
+    lua_pushnil(L);
+    while (lua_next(L, -2)) {
+        Proto proto;
+        proto = checkProto(L, -1);
+        
+        lua_rawgeti(L, LUA_REGISTRYINDEX, proto->fields);
+        
+        lua_pushnil(L);
+        while (lua_next(L, -2)) {
+            ProtoField f = checkProtoField(L, -1);
+            if (strcmp(field_abbr, f->abbr) == 0) {
+                /* found! */
+                lua_pop(L, 6);
+                return 1;
+            }
+            lua_pop(L, 1); /* table value */
+        }
+        lua_pop(L, 2); /* proto->fields and table value */
+    }
+    lua_pop(L, 1); /* protocols_table_ref */
+    
+    return 0;
+}
+
 int Proto_commit(lua_State* L) {
     lua_settop(L,0);
     lua_rawgeti(L, LUA_REGISTRYINDEX, protocols_table_ref);