[nginx] Mail: fixed handling of blocked client read events in proxy.

[Sergey Kandaurov]

details:   https://hg.nginx.org/nginx/rev/a5e6e8510634
branches:  
changeset: 8151:a5e6e8510634
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Fri Mar 24 02:53:21 2023 +0300
description:
Mail: fixed handling of blocked client read events in proxy.

When establishing a connection to the backend, nginx blocks reading
from the client with ngx_mail_proxy_block_read().  Previously, such
events were lost, and in some cases this resulted in connection hangs.

Notably, this affected mail_imap_ssl.t on Windows, since the test
closes connections after requesting authentication, but without
waiting for any responses (so the connection close events might be
lost).

Fix is to post an event to read from the client after connecting to
the backend if there were blocked events.

diffstat:

 src/mail/ngx_mail_proxy_module.c |  12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diffs (36 lines):

diff -r 8771d35d55d0 -r a5e6e8510634 src/mail/ngx_mail_proxy_module.c
--- a/src/mail/ngx_mail_proxy_module.c	Fri Mar 10 07:43:50 2023 +0300
+++ b/src/mail/ngx_mail_proxy_module.c	Fri Mar 24 02:53:21 2023 +0300
@@ -327,7 +327,9 @@ ngx_mail_proxy_pop3_handler(ngx_event_t 
         c->log->action = NULL;
         ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");
 
-        if (s->buffer->pos < s->buffer->last) {
+        if (s->buffer->pos < s->buffer->last
+            || s->connection->read->ready)
+        {
             ngx_post_event(c->write, &ngx_posted_events);
         }
 
@@ -486,7 +488,9 @@ ngx_mail_proxy_imap_handler(ngx_event_t 
         c->log->action = NULL;
         ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");
 
-        if (s->buffer->pos < s->buffer->last) {
+        if (s->buffer->pos < s->buffer->last
+            || s->connection->read->ready)
+        {
             ngx_post_event(c->write, &ngx_posted_events);
         }
 
@@ -821,7 +825,9 @@ ngx_mail_proxy_smtp_handler(ngx_event_t 
         c->log->action = NULL;
         ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");
 
-        if (s->buffer->pos < s->buffer->last) {
+        if (s->buffer->pos < s->buffer->last
+            || s->connection->read->ready)
+        {
             ngx_post_event(c->write, &ngx_posted_events);
         }