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.

6 files changed, 14 insertions, 3 deletions

diff --git a/src/core/ngx_connection.h b/src/core/ngx_connection.h
index 8cc14755a..6d3348d9c 100644
--- a/src/core/ngx_connection.h
+++ b/src/core/ngx_connection.h
@@ -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 --git a/src/event/ngx_event_connect.c b/src/event/ngx_event_connect.c
index adbbde633..668084a7b 100644
--- a/src/event/ngx_event_connect.c
+++ b/src/event/ngx_event_connect.c
@@ -179,6 +179,8 @@ ngx_event_connect_peer(ngx_peer_connection_t *pc)
         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 --git a/src/event/ngx_event_udp.c b/src/event/ngx_event_udp.c
index 640b37757..1ac82c7f5 100644
--- a/src/event/ngx_event_udp.c
+++ b/src/event/ngx_event_udp.c
@@ -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 --git a/src/http/ngx_http_write_filter_module.c b/src/http/ngx_http_write_filter_module.c
index 932f26dd3..89ab49e12 100644
--- a/src/http/ngx_http_write_filter_module.c
+++ b/src/http/ngx_http_write_filter_module.c
@@ -227,7 +227,8 @@ ngx_http_write_filter(ngx_http_request_t *r, ngx_chain_t *in)
 
     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 --git a/src/http/v2/ngx_http_v2_filter_module.c b/src/http/v2/ngx_http_v2_filter_module.c
index 9ffb155df..62b6a047c 100644
--- a/src/http/v2/ngx_http_v2_filter_module.c
+++ b/src/http/v2/ngx_http_v2_filter_module.c
@@ -665,6 +665,7 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
 
     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_connection_t *h2c,
 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 --git a/src/stream/ngx_stream_write_filter_module.c b/src/stream/ngx_stream_write_filter_module.c
index 156a61c3d..07dc7b52e 100644
--- a/src/stream/ngx_stream_write_filter_module.c
+++ b/src/stream/ngx_stream_write_filter_module.c
@@ -235,7 +235,7 @@ ngx_stream_write_filter(ngx_stream_session_t *s, ngx_chain_t *in,
     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 */) {