Upstream: implemented $upstream_bytes_sent.

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 3fa86c8..9071055 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -409,6 +409,10 @@
       ngx_http_upstream_response_length_variable, 1,
       NGX_HTTP_VAR_NOCACHEABLE, 0 },
 
+    { ngx_string("upstream_bytes_sent"), NULL,
+      ngx_http_upstream_response_length_variable, 2,
+      NGX_HTTP_VAR_NOCACHEABLE, 0 },
+
 #if (NGX_HTTP_CACHE)
 
     { ngx_string("upstream_cache_status"), NULL,
@@ -4136,6 +4140,10 @@
 
     if (u->peer.sockaddr) {
 
+        if (u->peer.connection) {
+            u->state->bytes_sent = u->peer.connection->sent;
+        }
+
         if (ft_type == NGX_HTTP_UPSTREAM_FT_HTTP_403
             || ft_type == NGX_HTTP_UPSTREAM_FT_HTTP_404)
         {
@@ -4319,6 +4327,10 @@
                                         - u->pipe->preread_size;
             u->state->response_length = u->pipe->read_length;
         }
+
+        if (u->peer.connection) {
+            u->state->bytes_sent = u->peer.connection->sent;
+        }
     }
 
     u->finalize_request(r, rc);
@@ -5502,6 +5514,9 @@
         if (data == 1) {
             p = ngx_sprintf(p, "%O", state[i].bytes_received);
 
+        } else if (data == 2) {
+            p = ngx_sprintf(p, "%O", state[i].bytes_sent);
+
         } else {
             p = ngx_sprintf(p, "%O", state[i].response_length);
         }

src/http/ngx_http_upstream.h

diff --git a/src/http/ngx_http_upstream.h b/src/http/ngx_http_upstream.h
index af84e24..6079d72 100644
--- a/src/http/ngx_http_upstream.h
+++ b/src/http/ngx_http_upstream.h
@@ -64,6 +64,7 @@
     ngx_msec_t                       queue_time;
     off_t                            response_length;
     off_t                            bytes_received;
+    off_t                            bytes_sent;
 
     ngx_str_t                       *peer;
 } ngx_http_upstream_state_t;