Added support for trailers in HTTP responses. Example: ngx_table_elt_t *h; h = ngx_list_push(&r->headers_out.trailers); if (h == NULL) { return NGX_ERROR; } ngx_str_set(&h->key, "Fun"); ngx_str_set(&h->value, "with trailers"); h->hash = ngx_hash_key_lc(h->key.data, h->key.len); The code above adds "Fun: with trailers" trailer to the response. Modules that want to emit trailers must set r->expect_trailers = 1 in header filter, otherwise they might not be emitted for HTTP/1.1 responses that aren't already chunked. This change also adds $sent_trailer_* variables. Signed-off-by: Piotr Sikora <piotrsikora@google.com>

--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2485,6 +2485,13 @@ ngx_http_subrequest(ngx_http_request_t *
         return NGX_ERROR;
     }
 
+    if (ngx_list_init(&sr->headers_out.trailers, r->pool, 4,
+                      sizeof(ngx_table_elt_t))
+        != NGX_OK)
+    {
+        return NGX_ERROR;
+    }
+
     cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
     sr->main_conf = cscf->ctx->main_conf;
     sr->srv_conf = cscf->ctx->srv_conf;