MINOR: diag: diag if servers use the same cookie value

Add a diagnostic to check that two servers of the same backend does not
use the same cookie value. Ignore backup servers as it is quite common
for them to share a cookie value with a primary one.

src/cfgdiag.c

@@ -1,8 +1,12 @@
 #include <stdarg.h>
 #include <stdlib.h>
 
+#include <import/ebistree.h>
+
 #include <haproxy/cfgdiag.h>
 #include <haproxy/log.h>
+#include <haproxy/proxy.h>
+#include <haproxy/server.h>
 
 /* Use this fonction to emit diagnostic.
  * This can be used as a shortcut to set value pointed by <ret> to 1 at the
@@ -33,6 +37,51 @@ static inline void *diag_alloc(size_t size)
 	return out;
 }
 
+/* Checks that two servers from the same backend does not share the same cookie
+ * value. Backup servers are not taken into account as it can be quite common to
+ * share cookie values in this case.
+ */
+static void check_server_cookies(int *ret)
+{
+	struct cookie_entry {
+		struct ebpt_node node;
+	};
+
+	struct proxy  *px;
+	struct server *srv;
+
+	struct eb_root cookies_tree = EB_ROOT_UNIQUE;
+	struct ebpt_node *cookie_node;
+	struct cookie_entry *cookie_entry;
+	struct ebpt_node *node;
+
+	for (px = proxies_list; px; px = px->next) {
+		for (srv = px->srv; srv; srv = srv->next) {
+			/* do not take into account backup servers */
+			if (!srv->cookie || (srv->flags & SRV_F_BACKUP))
+				continue;
+
+			cookie_node = ebis_lookup(&cookies_tree, srv->cookie);
+			if (cookie_node) {
+				diag_warning(ret, "parsing [%s:%d] : 'server %s' : same cookie value is set for a previous non-backup server in the same backend, it may break connection persistence\n",
+				             srv->conf.file, srv->conf.line, srv->id);
+				continue;
+			}
+
+			cookie_entry = diag_alloc(sizeof(*cookie_entry));
+			cookie_entry->node.key = srv->cookie;
+			ebis_insert(&cookies_tree, &cookie_entry->node);
+		}
+
+		/* clear the tree and free its entries */
+		while ((node = ebpt_first(&cookies_tree))) {
+			cookie_entry = ebpt_entry(node, struct cookie_entry, node);
+			eb_delete(&node->node);
+			free(cookie_entry);
+		}
+	}
+}
+
 /* Placeholder to execute various diagnostic checks after the configuration file
  * has been fully parsed. It will output a warning for each diagnostic found.
  *
@@ -41,5 +90,8 @@ static inline void *diag_alloc(size_t size)
 int cfg_run_diagnostics()
 {
 	int ret = 0;
+
+	check_server_cookies(&ret);
+
 	return ret;
 }