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

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1678533841 -10800
#      Sat Mar 11 14:24:01 2023 +0300
# Node ID b97f2b983d1564d29280d03828503edca21a79ee
# Parent  8771d35d55d0a2b1cefaab04401d6f837f5a05a2
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.

diff --git a/src/mail/ngx_mail_proxy_module.c b/src/mail/ngx_mail_proxy_module.c
--- a/src/mail/ngx_mail_proxy_module.c
+++ b/src/mail/ngx_mail_proxy_module.c
@@ -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);
         }