[nginx] HTTP/2: made it possible to flush response headers (ticket #1743).

[Maxim Dounin]

details:   https://hg.nginx.org/nginx/rev/32b0ba4855a6
branches:  
changeset: 8006:32b0ba4855a6
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Thu Feb 03 01:44:38 2022 +0300
description:
HTTP/2: made it possible to flush response headers (ticket #1743).

Response headers can be buffered in the SSL buffer.  But stream's fake
connection buffered flag did not reflect this, so any attempts to flush
the buffer without sending additional data were stopped by the write filter.

It does not seem to be possible to reflect this in fc->buffered though, as
we never known if main connection's c->buffered corresponds to the particular
stream or not.  As such, fc->buffered might prevent request finalization
due to sending data on some other stream.

Fix is to implement handling of flush buffers when the c->need_flush_buf
flag is set, similarly to the existing last buffer handling.  The same
flag is now used for UDP sockets in the stream module instead of explicit
checking of c->type.

diffstat:

 src/core/ngx_connection.h                   |  1 +
 src/event/ngx_event_connect.c               |  2 ++
 src/event/ngx_event_udp.c                   |  2 ++
 src/http/ngx_http_write_filter_module.c     |  3 ++-
 src/http/v2/ngx_http_v2_filter_module.c     |  7 ++++++-
 src/stream/ngx_stream_write_filter_module.c |  2 +-
 6 files changed, 14 insertions(+), 3 deletions(-)

diffs (84 lines):

diff -r dd718d1cef3c -r 32b0ba4855a6 src/core/ngx_connection.h
--- a/src/core/ngx_connection.h	Tue Feb 01 16:29:28 2022 +0300
+++ b/src/core/ngx_connection.h	Thu Feb 03 01:44:38 2022 +0300
@@ -184,6 +184,7 @@ struct ngx_connection_s {
     unsigned            tcp_nopush:2;    /* ngx_connection_tcp_nopush_e */
 
     unsigned            need_last_buf:1;
+    unsigned            need_flush_buf:1;
 
 #if (NGX_HAVE_SENDFILE_NODISKIO || NGX_COMPAT)
     unsigned            busy_count:2;
diff -r dd718d1cef3c -r 32b0ba4855a6 src/event/ngx_event_connect.c
--- a/src/event/ngx_event_connect.c	Tue Feb 01 16:29:28 2022 +0300
+++ b/src/event/ngx_event_connect.c	Thu Feb 03 01:44:38 2022 +0300
@@ -179,6 +179,8 @@ ngx_event_connect_peer(ngx_peer_connecti
         c->recv = ngx_udp_recv;
         c->send = ngx_send;
         c->send_chain = ngx_udp_send_chain;
+
+        c->need_flush_buf = 1;
     }
 
     c->log_error = pc->log_error;
diff -r dd718d1cef3c -r 32b0ba4855a6 src/event/ngx_event_udp.c
--- a/src/event/ngx_event_udp.c	Tue Feb 01 16:29:28 2022 +0300
+++ b/src/event/ngx_event_udp.c	Thu Feb 03 01:44:38 2022 +0300
@@ -246,6 +246,8 @@ ngx_event_recvmsg(ngx_event_t *ev)
         c->send = ngx_udp_send;
         c->send_chain = ngx_udp_send_chain;
 
+        c->need_flush_buf = 1;
+
         c->log = log;
         c->pool->log = log;
         c->listening = ls;
diff -r dd718d1cef3c -r 32b0ba4855a6 src/http/ngx_http_write_filter_module.c
--- a/src/http/ngx_http_write_filter_module.c	Tue Feb 01 16:29:28 2022 +0300
+++ b/src/http/ngx_http_write_filter_module.c	Thu Feb 03 01:44:38 2022 +0300
@@ -227,7 +227,8 @@ ngx_http_write_filter(ngx_http_request_t
 
     if (size == 0
         && !(c->buffered & NGX_LOWLEVEL_BUFFERED)
-        && !(last && c->need_last_buf))
+        && !(last && c->need_last_buf)
+        && !(flush && c->need_flush_buf))
     {
         if (last || flush || sync) {
             for (cl = r->out; cl; /* void */) {
diff -r dd718d1cef3c -r 32b0ba4855a6 src/http/v2/ngx_http_v2_filter_module.c
--- a/src/http/v2/ngx_http_v2_filter_module.c	Tue Feb 01 16:29:28 2022 +0300
+++ b/src/http/v2/ngx_http_v2_filter_module.c	Thu Feb 03 01:44:38 2022 +0300
@@ -665,6 +665,7 @@ ngx_http_v2_header_filter(ngx_http_reque
 
     fc->send_chain = ngx_http_v2_send_chain;
     fc->need_last_buf = 1;
+    fc->need_flush_buf = 1;
 
     return ngx_http_v2_filter_send(fc, stream);
 }
@@ -1815,7 +1816,11 @@ ngx_http_v2_waiting_queue(ngx_http_v2_co
 static ngx_inline ngx_int_t
 ngx_http_v2_filter_send(ngx_connection_t *fc, ngx_http_v2_stream_t *stream)
 {
-    if (stream->queued == 0) {
+    ngx_connection_t  *c;
+
+    c = stream->connection->connection;
+
+    if (stream->queued == 0 && !c->buffered) {
         fc->buffered &= ~NGX_HTTP_V2_BUFFERED;
         return NGX_OK;
     }
diff -r dd718d1cef3c -r 32b0ba4855a6 src/stream/ngx_stream_write_filter_module.c
--- a/src/stream/ngx_stream_write_filter_module.c	Tue Feb 01 16:29:28 2022 +0300
+++ b/src/stream/ngx_stream_write_filter_module.c	Thu Feb 03 01:44:38 2022 +0300
@@ -235,7 +235,7 @@ ngx_stream_write_filter(ngx_stream_sessi
     if (size == 0
         && !(c->buffered & NGX_LOWLEVEL_BUFFERED)
         && !(last && c->need_last_buf)
-        && !(c->type == SOCK_DGRAM && flush))
+        && !(flush && c->need_flush_buf))
     {
         if (last || flush || sync) {
             for (cl = *out; cl; /* void */) {