[nginx] Upstream: fixed ngx_http_upstream_test_next() conditions.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/4db4fe3bdeda
branches:  
changeset: 7255:4db4fe3bdeda
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Tue Apr 03 02:43:18 2018 +0300
description:
Upstream: fixed ngx_http_upstream_test_next() conditions.

Previously, ngx_http_upstream_test_next() used an outdated condition on
whether it will be possible to switch to a different server or not.  It
did not take into account restrictions on non-idempotent requests, requests
with non-buffered request body, and the next upstream timeout.

For such requests, switching to the next upstream server was rejected
later in ngx_http_upstream_next(), resulting in nginx own error page
being returned instead of the original upstream response.

diffstat:

 src/http/ngx_http_upstream.c |  20 ++++++++++++++++++--
 1 files changed, 18 insertions(+), 2 deletions(-)

diffs (37 lines):

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2389,7 +2389,8 @@ ngx_http_upstream_process_header(ngx_htt
 static ngx_int_t
 ngx_http_upstream_test_next(ngx_http_request_t *r, ngx_http_upstream_t *u)
 {
-    ngx_uint_t                 status;
+    ngx_msec_t                 timeout;
+    ngx_uint_t                 status, mask;
     ngx_http_upstream_next_t  *un;
 
     status = u->headers_in.status_n;
@@ -2400,7 +2401,22 @@ ngx_http_upstream_test_next(ngx_http_req
             continue;
         }
 
-        if (u->peer.tries > 1 && (u->conf->next_upstream & un->mask)) {
+        timeout = u->conf->next_upstream_timeout;
+
+        if (u->request_sent
+            && (r->method & (NGX_HTTP_POST|NGX_HTTP_LOCK|NGX_HTTP_PATCH)))
+        {
+            mask = un->mask | NGX_HTTP_UPSTREAM_FT_NON_IDEMPOTENT;
+
+        } else {
+            mask = un->mask;
+        }
+
+        if (u->peer.tries > 1
+            && ((u->conf->next_upstream & mask) == mask)
+            && !(u->request_sent && r->request_body_no_buffering)
+            && !(timeout && ngx_current_msec - u->peer.start_time >= timeout))
+        {
             ngx_http_upstream_next(r, u, un->mask);
             return NGX_OK;
         }