MEDIUM: log: add a new cookie flag 'U' to report situations where cookie is not used

This happens when a "use-server" rule sets the server instead.

doc/configuration.txt

@@ -9184,6 +9184,10 @@ each of which has a special meaning :
             the cookie is consider too OLD and is ignored. The request will be
             redispatched just as if there was no cookie.
 
+        U : a cookie was present but was not used to select the server because
+            some other server selection mechanism was used instead (typically a
+            "use-server" rule).
+
         - : does not apply (no cookie set in configuration).
 
   - the last character reports what operations were performed on the persistence

include/types/proto_http.h

@@ -43,6 +43,7 @@
 #define TX_CK_VALID	0x00000060	/* this session had cookie matching a valid server */
 #define TX_CK_EXPIRED	0x00000080	/* this session had an expired cookie (idle for too long) */
 #define TX_CK_OLD	0x000000A0	/* this session had too old a cookie (offered too long ago) */
+#define TX_CK_UNUSED	0x000000C0	/* this session had a cookie but it was not used (eg: use-server was preferred) */
 #define TX_CK_MASK	0x000000E0	/* mask to get this session's cookie flags */
 #define TX_CK_SHIFT	5		/* bit shift */
 

src/log.c

@@ -688,7 +688,7 @@ extern fd_set hdr_encode_map[];
 extern fd_set url_encode_map[];
 
 
-const char sess_cookie[8]     = "NIDVEO67";	/* No cookie, Invalid cookie, cookie for a Down server, Valid cookie, Expired cookie, Old cookie, unknown */
+const char sess_cookie[8]     = "NIDVEOU7";	/* No cookie, Invalid cookie, cookie for a Down server, Valid cookie, Expired cookie, Old cookie, Unused, unknown */
 const char sess_set_cookie[8] = "NPDIRU67";	/* No set-cookie, Set-cookie found and left unchanged (passive),
 						   Set-cookie Deleted, Set-Cookie Inserted, Set-cookie Rewritten,
 						   Set-cookie Updated, unknown, unknown */

src/proto_http.c

@@ -6249,9 +6249,12 @@ void manage_client_side_cookies(struct session *t, struct buffer *req)
 				}
 
 				if (!srv && !(txn->flags & (TX_CK_DOWN|TX_CK_EXPIRED|TX_CK_OLD))) {
-					/* no server matched this cookie */
+					/* no server matched this cookie or we deliberately skipped it */
 					txn->flags &= ~TX_CK_MASK;
-					txn->flags |= TX_CK_INVALID;
+					if ((t->flags & (SN_IGNORE_PRST | SN_ASSIGNED)))
+						txn->flags |= TX_CK_UNUSED;
+					else
+						txn->flags |= TX_CK_INVALID;
 				}
 
 				/* depending on the cookie mode, we may have to either :