use real file cache length, this fixes cache size counting for responses
without "Content-Length" header and 304 responses.

src/http/ngx_http_file_cache.c

diff --git a/src/http/ngx_http_file_cache.c b/src/http/ngx_http_file_cache.c
index 4caca91..0a9b761 100644
--- a/src/http/ngx_http_file_cache.c
+++ b/src/http/ngx_http_file_cache.c
@@ -692,7 +692,7 @@
 void
 ngx_http_file_cache_update(ngx_http_request_t *r, ngx_temp_file_t *tf)
 {
-    off_t                   size;
+    off_t                   size, length;
     ngx_int_t               rc;
     ngx_file_uniq_t         uniq;
     ngx_file_info_t         fi;
@@ -714,6 +714,7 @@
     cache = c->file_cache;
 
     uniq = 0;
+    length = 0;
 
     ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                    "http file cache rename: \"%s\" to \"%s\"",
@@ -738,10 +739,11 @@
 
         } else {
             uniq = ngx_file_uniq(&fi);
+            length = ngx_file_size(&fi);
         }
     }
 
-    size = (c->length + cache->bsize - 1) / cache->bsize;
+    size = (length + cache->bsize - 1) / cache->bsize;
 
     ngx_shmtx_lock(&cache->shpool->mutex);
 
@@ -751,7 +753,7 @@
 
     size = size - (c->node->length + cache->bsize - 1) / cache->bsize;
 
-    c->node->length = c->length;
+    c->node->length = length;
 
     cache->sh->size += size;
 

src/http/ngx_http_upstream.c

diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c
index 1e79a4f..86c5af8 100644
--- a/src/http/ngx_http_upstream.c
+++ b/src/http/ngx_http_upstream.c
@@ -2098,11 +2098,6 @@
             r->cache->date = now;
             r->cache->body_start = (u_short) (u->buffer.pos - u->buffer.start);
 
-            if (r->headers_out.content_length_n != -1) {
-                r->cache->length = r->cache->body_start
-                                   + r->headers_out.content_length_n;
-            }
-
             ngx_http_file_cache_set_header(r, u->buffer.start);
 
         } else {