MEDIUM: sample: pass an empty list instead of a null for fetch args

ACL and sample fetches use args list and it is really not convenient to
check for null args everywhere. Now for empty args we pass a constant
list of end of lists. It will allow us to remove many useless checks.

include/proto/arg.h

@@ -54,6 +54,11 @@
 #define ARG7(m, t1, t2, t3, t4, t5, t6, t7) \
 	(ARG6(m, t1, t2, t3, t4, t5, t6) + (ARGT_##t7 << 28))
 
+/* This dummy arg list may be used by default when no arg is found, it helps
+ * parsers by removing pointer checks.
+ */
+extern struct arg empty_arg_list[8];
+
 int make_arg_list(const char *in, int len, unsigned int mask, struct arg **argp,
 		  char **err_msg, const char **err_ptr, int *err_arg);
 

src/acl.c

@@ -1224,7 +1224,8 @@ static struct acl_expr *prune_acl_expr(struct acl_expr *expr)
 		arg++;
 	}
 
-	free(expr->args);
+	if (expr->args != empty_arg_list)
+		free(expr->args);
 	expr->kw->use_cnt--;
 	return expr;
 }
@@ -1352,6 +1353,7 @@ struct acl_expr *parse_acl_expr(const char **args, char **err)
 	aclkw->use_cnt++;
 	LIST_INIT(&expr->patterns);
 	expr->pattern_tree = EB_ROOT_UNIQUE;
+	expr->args = empty_arg_list;
 
 	arg = strchr(args[0], '(');
 	if (aclkw->arg_mask) {
@@ -1380,6 +1382,9 @@ struct acl_expr *parse_acl_expr(const char **args, char **err)
 				goto out_free_expr;
 			}
 
+			if (!expr->args)
+				expr->args = empty_arg_list;
+
 			if (aclkw->val_args && !aclkw->val_args(expr->args, err)) {
 				/* invalid keyword argument, error must have been
 				 * set by val_args().
@@ -2030,10 +2035,8 @@ acl_find_targets(struct proxy *p)
 
 	list_for_each_entry(acl, &p->acl, list) {
 		list_for_each_entry(expr, &acl->expr, list) {
-			for (arg = expr->args; arg; arg++) {
-				if (arg->type == ARGT_STOP)
-					break;
-				else if (!arg->unresolved)
+			for (arg = expr->args; arg && arg->type != ARGT_STOP; arg++) {
+				if (!arg->unresolved)
 					continue;
 				else if (arg->type == ARGT_SRV) {
 					struct proxy *px;

src/arg.c

@@ -36,6 +36,11 @@ static const char *arg_type_names[ARGT_NBTYPES] = {
 	/* Unassigned types must never happen. Better crash during parsing if they do. */
 };
 
+/* This dummy arg list may be used by default when no arg is found, it helps
+ * parsers by removing pointer checks.
+ */
+struct arg empty_arg_list[8] = { };
+
 /* This function builds an argument list from a config line. It returns the
  * number of arguments found, or <0 in case of any error. Everything needed
  * it automatically allocated. A pointer to an error message might be returned

src/haproxy.c

@@ -73,6 +73,7 @@
 
 #include <proto/auth.h>
 #include <proto/acl.h>
+#include <proto/arg.h>
 #include <proto/backend.h>
 #include <proto/channel.h>
 #include <proto/checks.h>
@@ -818,7 +819,8 @@ static void deinit_sample_arg(struct arg *p)
 		p++;
 	}
 
-	free(p_back);
+	if (p_back != empty_arg_list)
+		free(p_back);
 }
 
 static void deinit_stick_rules(struct list *rules)

src/sample.c

@@ -320,6 +320,7 @@ struct sample_expr *sample_parse_expr(char **str, int *idx, char *err, int err_s
 
 	LIST_INIT(&(expr->conv_exprs));
 	expr->fetch = fetch;
+	expr->arg_p = empty_arg_list;
 
 	if (end != endw) {
 		char *err_msg = NULL;
@@ -344,6 +345,9 @@ struct sample_expr *sample_parse_expr(char **str, int *idx, char *err, int err_s
 			goto out_error;
 		}
 
+		if (!expr->arg_p)
+			expr->arg_p = empty_arg_list;
+
 		if (fetch->val_args && !fetch->val_args(expr->arg_p, &err_msg)) {
 			p = my_strndup(str[*idx], endw - str[*idx]);
 			if (p) {
@@ -436,6 +440,9 @@ struct sample_expr *sample_parse_expr(char **str, int *idx, char *err, int err_s
 				goto out_error;
 			}
 
+			if (!conv_expr->arg_p)
+				conv_expr->arg_p = empty_arg_list;
+
 			if (conv->val_args && !conv->val_args(conv_expr->arg_p, &err_msg)) {
 				p = my_strndup(str[*idx], endw - str[*idx]);
 				if (p) {