conntrackd: add cthelper infrastructure (+ example FTP helper)

This patch adds the user-space helper infrastructure. It also
contains the implementation of the FTP helper in user-space.

There's one example file that you can use to configure conntrackd
as user-space connection tracking helper under:

 doc/helper/conntrackd.conf

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/stack.c b/src/stack.c
new file mode 100644
index 0000000..104b7ba
--- /dev/null
+++ b/src/stack.c
@@ -0,0 +1,56 @@
+/*
+ * (C) 2005-2012 by Pablo Neira Ayuso <pablo@netfilter.org>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include "stack.h"
+
+struct stack_item *
+stack_item_alloc(int type, size_t data_len)
+{
+	struct stack_item *e;
+
+	e = calloc(1, sizeof(struct stack_item) + data_len);
+	if (e == NULL)
+		return NULL;
+
+	e->data_len = data_len;
+	e->type = type;
+
+	return e;
+}
+
+void stack_item_free(struct stack_item *e)
+{
+	free(e);
+}
+
+void stack_item_push(struct stack *s, struct stack_item *e)
+{
+	list_add(&e->head, &s->list);
+}
+
+struct stack_item *stack_item_pop(struct stack *s, int type)
+{
+	struct stack_item *cur, *tmp, *found = NULL;
+
+	list_for_each_entry_safe(cur, tmp, &s->list, head) {
+		if (cur->type != type && type != -1)
+			continue;
+
+		list_del(&cur->head);
+		found = cur;
+		break;
+	}
+
+	return found;
+}