Detect redefined rules

If a rule is defined more than once, an error is logged and the parsing
fails.

server/modules/filter/dbfwfilter/dbfwfilter.c

@@ -966,6 +966,27 @@ void dbfw_yyerror(void* scanner, const char* error)
               error, dbfw_yyget_text(scanner));
 }
 
+/**
+ * @brief Find a rule by name
+ *
+ * @param rules List of all rules
+ * @param name Name of the rule
+ * @return Pointer to the rule or NULL if rule was not found
+ */
+static RULE* find_rule_by_name(RULE* rules, const char* name)
+{
+    while (rules)
+    {
+        if (strcmp(rules->name, name) == 0)
+        {
+            return rules;
+        }
+        rules = rules->next;
+    }
+
+    return NULL;
+}
+
 /**
  * Create a new rule
  *
@@ -976,25 +997,33 @@ void dbfw_yyerror(void* scanner, const char* error)
  */
 bool create_rule(void* scanner, const char* name)
 {
-    bool rval = true;
+    bool rval = false;
+    struct parser_stack* rstack = dbfw_yyget_extra((yyscan_t)scanner);
+    ss_dassert(rstack);
+
+    if (find_rule_by_name(rstack->rule, name) == NULL)
+    {
         RULE *ruledef = MXS_MALLOC(sizeof(RULE));
 
         if (ruledef && (ruledef->name = MXS_STRDUP(name)))
         {
             ruledef->type = RT_UNDEFINED;
             ruledef->on_queries = QUERY_OP_UNDEFINED;
-        struct parser_stack* rstack = dbfw_yyget_extra((yyscan_t) scanner);
-        ss_dassert(rstack);
             ruledef->next = rstack->rule;
             ruledef->active = NULL;
             ruledef->times_matched = 0;
             ruledef->data = NULL;
             rstack->rule = ruledef;
+            rval = true;
         }
         else
         {
             MXS_FREE(ruledef);
-        rval = false;
+        }
+    }
+    else
+    {
+        MXS_ERROR("Redefinition of rule '%s' on line %d.", name, dbfw_yyget_lineno(scanner));
     }
 
     return rval;
@@ -1310,27 +1339,6 @@ bool define_regex_rule(void* scanner, char* pattern)
     return re != NULL;
 }
 
-/**
- * @brief Find a rule by name
- *
- * @param rules List of all rules
- * @param name Name of the rule
- * @return Pointer to the rule or NULL if rule was not found
- */
-static RULE* find_rule_by_name(RULE* rules, const char* name)
-{
-    while (rules)
-    {
-        if (strcmp(rules->name, name) == 0)
-        {
-            return rules;
-        }
-        rules = rules->next;
-    }
-
-    return NULL;
-}
-
 /**
  * @brief Process the user templates into actual user definitions
  *