MINOR: mux-h1: Simplify handling of 1xx responses

Because of previous changes on http tunneling, the synchronization of the
transaction can be simplified. Only the check on intermediate messages remains
and it only concerns the response path.

This patch must be backported to 1.9. It is not strictly speaking required but
it will ease futur backports.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index 91d94ed..606e174 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -946,6 +946,21 @@
 }
 
 /*
+ * Handle 100-Continue responses or any other informational 1xx responses which
+ * is non-final. In such case, this function reset the response parser. It is
+ * the caller responsibility to call this function when appropriate.
+ */
+static void h1_handle_1xx_response(struct h1s *h1s, struct h1m *h1m)
+{
+	if ((h1m->flags & H1_MF_RESP) && h1m->state == H1_MSG_DONE &&
+	    h1s->status < 200 && (h1s->status == 100 || h1s->status >= 102)) {
+		h1m_init_res(&h1s->res);
+		h1m->flags |= H1_MF_NO_PHDR;
+		h1s->h1c->flags &= ~H1C_F_IN_BUSY;
+	}
+}
+
+/*
  * Parse HTTP/1 headers. It returns the number of bytes parsed if > 0, or 0 if
  * it couldn't proceed. Parsing errors are reported by setting H1S_F_*_ERROR
  * flag and filling h1s->err_pos and h1s->err_state fields. This functions is
@@ -1320,33 +1335,6 @@
 }
 
 /*
- * Synchronize the request and the response before reseting them. Except for 1xx
- * responses, we wait that the request and the response are in DONE state and
- * that all data are forwarded for both. For 1xx responses, only the response is
- * reset, waiting the final one. Many 1xx messages can be sent.
- */
-static void h1_sync_messages(struct h1c *h1c)
-{
-	struct h1s *h1s = h1c->h1s;
-
-	if (!h1s)
-		return;
-
-	if (h1s->res.state == H1_MSG_DONE &&
-	    (h1s->status < 200 && (h1s->status == 100 || h1s->status >= 102)) &&
-	    (conn_is_back(h1c->conn) || !b_data(&h1c->obuf))) {
-		/* For 100-Continue response or any other informational 1xx
-		 * response which is non-final, don't reset the request, the
-		 * transaction is not finished. We take care the response was
-		 * transferred before.
-		 */
-		h1m_init_res(&h1s->res);
-		h1s->res.flags |= H1_MF_NO_PHDR;
-		h1c->flags &= ~H1C_F_IN_BUSY;
-	}
-}
-
-/*
  * Process incoming data. It parses data and transfer them from h1c->ibuf into
  * <buf>. It returns the number of bytes parsed and transferred if > 0, or 0 if
  * it couldn't proceed.
@@ -1379,6 +1367,9 @@
 		goto end;
 	rsv = ((flags & CO_RFL_KEEP_RSV) ? global.tune.maxrewrite : 0);
 
+	if (htx_is_empty(htx))
+		h1_handle_1xx_response(h1s, h1m);
+
 	do {
 		if (h1m->state <= H1_MSG_LAST_LF) {
 			ret = h1_process_headers(h1s, h1m, htx, &h1c->ibuf, &total, count);
@@ -1424,10 +1415,8 @@
 
 	h1s->cs->flags &= ~(CS_FL_RCV_MORE | CS_FL_WANT_ROOM);
 
-	if (!b_data(&h1c->ibuf)) {
+	if (!b_data(&h1c->ibuf))
 		h1_release_buf(h1c, &h1c->ibuf);
-		h1_sync_messages(h1c);
-	}
 	else if (!htx_is_empty(htx))
 		h1s->cs->flags |= CS_FL_RCV_MORE | CS_FL_WANT_ROOM;
 
@@ -1723,6 +1712,9 @@
 		}
 	}
 
+	if (htx_is_empty(chn_htx))
+		h1_handle_1xx_response(h1s, h1m);
+
   copy:
 	/* when the output buffer is empty, tmp shares the same area so that we
 	 * only have to update pointers and lengths.
@@ -1882,7 +1874,6 @@
 	/* We're done, no more to send */
 	if (!b_data(&h1c->obuf)) {
 		h1_release_buf(h1c, &h1c->obuf);
-		h1_sync_messages(h1c);
 		if (h1c->flags & H1C_F_CS_SHUTW_NOW)
 			h1_shutw_conn(conn, CS_SHW_NORMAL);
 	}