# HG changeset patch
# User Roman Arutyunyan <arut@nginx.com>
# Date 1505133151 -10800
# Node ID 7bfbf73db920cf7494ae9ac392b5247e93765093
# Parent  a0e472a2c4f1a9280404cbc45fc8138e59d8d36e
Stream: relaxed next upstream condition (ticket #1317).

When switching to a next upstream, some buffers could be stuck in the middle
of the filter chain.  A condition existed that raised an error when this
happened.  As it turned out, this condition prevented switching to a next
upstream if ssl preread was used with the TCP protocol (see the ticket).

In fact, the condition does not make sense for TCP, since after successful
connection to an upstream switching to another upstream never happens.  As for
UDP, the issue with stuck buffers is unlikely to happen, but is still possible.
Specifically, if a filter delays sending data to upstream.

The condition can be relaxed to only check the "buffered" bitmask of the
upstream connection.  The new condition is simpler and fixes the ticket issue
as well.  Additionally, the upstream_out chain is now reset for UDP prior to
connecting to a new upstream to prevent repeating the client data twice.

diff --git a/src/stream/ngx_stream_proxy_module.c b/src/stream/ngx_stream_proxy_module.c
--- a/src/stream/ngx_stream_proxy_module.c
+++ b/src/stream/ngx_stream_proxy_module.c
@@ -1665,13 +1665,17 @@ ngx_stream_proxy_next_upstream(ngx_strea
     u = s->upstream;
     pc = u->peer.connection;
 
-    if (u->upstream_out || u->upstream_busy || (pc && pc->buffered)) {
+    if (pc && pc->buffered) {
         ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
-                      "pending buffers on next upstream");
+                      "buffered data on next upstream");
         ngx_stream_proxy_finalize(s, NGX_STREAM_INTERNAL_SERVER_ERROR);
         return;
     }
 
+    if (s->connection->type == SOCK_DGRAM) {
+        u->upstream_out = NULL;
+    }
+
     if (u->peer.sockaddr) {
         u->peer.free(&u->peer, u->peer.data, NGX_PEER_FAILED);
         u->peer.sockaddr = NULL;