[nginx] Resolver: added missing event handling after reading.

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/eb54227110f0
branches:  
changeset: 7808:eb54227110f0
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Sun Mar 28 17:45:31 2021 +0300
description:
Resolver: added missing event handling after reading.

If we need to be notified about further events, ngx_handle_read_event()
needs to be called after a read event is processed.  Without this,
an event can be removed from the kernel and won't be reported again,
notably when using oneshot event methods, such as eventport on Solaris.

While here, error handling is also added, similar to one present in
ngx_resolver_tcp_read().  This is not expected to make a difference
and mostly added for consistency.

diffstat:

 src/core/ngx_resolver.c |  19 +++++++++++++++++--
 1 files changed, 17 insertions(+), 2 deletions(-)

diffs (34 lines):

diff -r e0844646099b -r eb54227110f0 src/core/ngx_resolver.c
--- a/src/core/ngx_resolver.c	Sun Mar 28 17:45:29 2021 +0300
+++ b/src/core/ngx_resolver.c	Sun Mar 28 17:45:31 2021 +0300
@@ -1563,13 +1563,28 @@ ngx_resolver_udp_read(ngx_event_t *rev)
     do {
         n = ngx_udp_recv(c, buf, NGX_RESOLVER_UDP_SIZE);
 
-        if (n < 0) {
-            return;
+        if (n == NGX_AGAIN) {
+            break;
+        }
+
+        if (n == NGX_ERROR) {
+            goto failed;
         }
 
         ngx_resolver_process_response(rec->resolver, buf, n, 0);
 
     } while (rev->ready);
+
+    if (ngx_handle_read_event(rev, 0) != NGX_OK) {
+        goto failed;
+    }
+
+    return;
+
+failed:
+
+    ngx_close_connection(rec->udp);
+    rec->udp = NULL;
 }