MEDIUM: connection: inform si_alloc_conn() whether existing conn is OK or not

When allocating a new connection, only the caller knows whether it's
acceptable to reuse the previous one or not. Let's pass this information
to si_alloc_conn() which will do the cleanup if the connection is not
acceptable.

include/proto/connection.h

@@ -126,7 +126,8 @@ static inline void conn_full_close(struct connection *conn)
 }
 
 /* Force to close the connection whatever the tracking state. This is mainly
- * used on the error path where the tracking does not make sense.
+ * used on the error path where the tracking does not make sense, or to kill
+ * an idle connection we want to abort immediately.
  */
 static inline void conn_force_close(struct connection *conn)
 {

include/proto/stream_interface.h

@@ -212,11 +212,15 @@ static inline void si_applet_release(struct stream_interface *si)
 		applet->release(si);
 }
 
+/* Try to allocate a new connection and assign it to the interface. If
+ * a connection was previously allocated and the <reuse> flag is set,
+ * it is returned unmodified. Otherwise it is reset.
+ */
 /* Returns the stream interface's existing connection if one such already
  * exists, or tries to allocate and initialize a new one which is then
  * assigned to the stream interface.
  */
-static inline struct connection *si_alloc_conn(struct stream_interface *si)
+static inline struct connection *si_alloc_conn(struct stream_interface *si, int reuse)
 {
 	struct connection *conn;
 
@@ -225,8 +229,13 @@ static inline struct connection *si_alloc_conn(struct stream_interface *si)
 	 */
 	if (si->end) {
 		conn = objt_conn(si->end);
-		if (conn)
+		if (conn) {
+			if (!reuse) {
+				conn_force_close(conn);
+				conn_init(conn);
+			}
 			return conn;
+		}
 		/* it was an applet then */
 		si_release_endpoint(si);
 	}

src/backend.c

@@ -982,7 +982,7 @@ static void assign_tproxy_address(struct session *s)
 int connect_server(struct session *s)
 {
 	struct connection *cli_conn;
-	struct connection *srv_conn = si_alloc_conn(s->req->cons);
+	struct connection *srv_conn = si_alloc_conn(s->req->cons, 0);
 	struct server *srv;
 	int err;
 

src/proto_http.c

@@ -3742,7 +3742,8 @@ int http_process_request(struct session *s, struct channel *req, int an_bit)
 	if ((s->be->options & PR_O_HTTP_PROXY) && !(s->flags & SN_ADDR_SET)) {
 		struct connection *conn;
 
-		if (unlikely((conn = si_alloc_conn(req->cons)) == NULL)) {
+		/* Note that for now we don't reuse existing proxy connections */
+		if (unlikely((conn = si_alloc_conn(req->cons, 0)) == NULL)) {
 			txn->req.msg_state = HTTP_MSG_ERROR;
 			txn->status = 500;
 			req->analysers = 0;