[PATCH] Upstream: flush low-level buffers on write retry

[Piotr Sikora]

# HG changeset patch
# User Patryk Lesiewicz <patryk at google.com>
# Date 1512172754 28800
#      Fri Dec 01 15:59:14 2017 -0800
# Node ID 0e2e2da798261fe5105017d9678566267b07e2b9
# Parent  fc0d06224edac2c7cfbfd9a4def478f285d9957b
Upstream: flush low-level buffers on write retry.

If the data to write is bigger than what the socket can send, and the
reminder is smaller than NGX_SSL_BUFSIZE, then SSL_write() fails with
SSL_ERROR_WANT_WRITE. The reminder of payload however is successfully
copied to the low-level buffer and all the output chain buffers are
flushed. This means that retry logic doesn't work because
ngx_http_upstream_process_non_buffered_request() checks only if there's
anything in the output chain buffers and ignores the fact that something
may be buffered in low-level parts of the stack.

Signed-off-by: Patryk Lesiewicz <patryk at google.com>

diff -r fc0d06224eda -r 0e2e2da79826 src/http/ngx_http_upstream.c
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -3533,7 +3533,7 @@ ngx_http_upstream_process_non_buffered_r
 
         if (do_write) {
 
-            if (u->out_bufs || u->busy_bufs) {
+            if (u->out_bufs || u->busy_bufs || downstream->buffered) {
                 rc = ngx_http_output_filter(r, u->out_bufs);
 
                 if (rc == NGX_ERROR) {