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

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1643225036 -10800
#      Wed Jan 26 22:23:56 2022 +0300
# Node ID f76e0cf8e525996563e5f0092fa48a4fee873e93
# Parent  56ead48cfe885e8b89b30017459bf621b21d95f5
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 c->need_last_buf is set,
similarly to the existing last buffer handling.

diff --git a/src/http/ngx_http_write_filter_module.c b/src/http/ngx_http_write_filter_module.c
--- a/src/http/ngx_http_write_filter_module.c
+++ b/src/http/ngx_http_write_filter_module.c
@@ -227,7 +227,7 @@ ngx_http_write_filter(ngx_http_request_t
 
     if (size == 0
         && !(c->buffered & NGX_LOWLEVEL_BUFFERED)
-        && !(last && c->need_last_buf))
+        && !((last || flush) && c->need_last_buf))
     {
         if (last || flush || sync) {
             for (cl = r->out; cl; /* void */) {
diff --git a/src/http/v2/ngx_http_v2_filter_module.c b/src/http/v2/ngx_http_v2_filter_module.c
--- a/src/http/v2/ngx_http_v2_filter_module.c
+++ b/src/http/v2/ngx_http_v2_filter_module.c
@@ -1815,7 +1815,11 @@ 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;
     }