[PATCH] Not Modified: prefer entity tags over date validators

[Piotr Sikora]

# HG changeset patch
# User Piotr Sikora <piotr at cloudflare.com>
# Date 1416359232 28800
#      Tue Nov 18 17:07:12 2014 -0800
# Node ID 3efade6bb02f7962a5120e1a1f95a1dc8f0b6a4c
# Parent  2f7e557eab5b501ba71418febd3de9ef1c0ab4f1
Not Modified: prefer entity tags over date validators.

RFC7232 says:

   A recipient MUST ignore If-Modified-Since if the request contains an
   If-None-Match header field; the condition in If-None-Match is
   considered to be a more accurate replacement for the condition in
   If-Modified-Since, and the two are only combined for the sake of
   interoperating with older intermediaries that might not implement
   If-None-Match.

and:

   A recipient MUST ignore If-Unmodified-Since if the request contains
   an If-Match header field; the condition in If-Match is considered to
   be a more accurate replacement for the condition in
   If-Unmodified-Since, and the two are only combined for the sake of
   interoperating with older intermediaries that might not implement
   If-Match.

Signed-off-by: Piotr Sikora <piotr at cloudflare.com>

diff -r 2f7e557eab5b -r 3efade6bb02f src/http/modules/ngx_http_not_modified_filter_module.c
--- a/src/http/modules/ngx_http_not_modified_filter_module.c	Tue Nov 18 20:41:12 2014 +0300
+++ b/src/http/modules/ngx_http_not_modified_filter_module.c	Tue Nov 18 17:07:12 2014 -0800
@@ -61,48 +61,47 @@ ngx_http_not_modified_header_filter(ngx_
         return ngx_http_next_header_filter(r);
     }
 
-    if (r->headers_in.if_unmodified_since
-        && !ngx_http_test_if_unmodified(r))
-    {
-        return ngx_http_filter_finalize_request(r, NULL,
-                                                NGX_HTTP_PRECONDITION_FAILED);
+    if (r->headers_in.if_match) {
+
+        if (!ngx_http_test_if_match(r, r->headers_in.if_match, 0)) {
+            return ngx_http_filter_finalize_request(r, NULL,
+                                                 NGX_HTTP_PRECONDITION_FAILED);
+        }
+
+    } else if (r->headers_in.if_unmodified_since) {
+
+        if (!ngx_http_test_if_unmodified(r)) {
+            return ngx_http_filter_finalize_request(r, NULL,
+                                                 NGX_HTTP_PRECONDITION_FAILED);
+        }
     }
 
-    if (r->headers_in.if_match
-        && !ngx_http_test_if_match(r, r->headers_in.if_match, 0))
-    {
-        return ngx_http_filter_finalize_request(r, NULL,
-                                                NGX_HTTP_PRECONDITION_FAILED);
+    if (r->headers_in.if_none_match) {
+
+        if (ngx_http_test_if_match(r, r->headers_in.if_none_match, 1)) {
+            goto not_modified;
+        }
+
+    } else if (r->headers_in.if_modified_since) {
+
+        if (!ngx_http_test_if_modified(r)) {
+            goto not_modified;
+        }
     }
 
-    if (r->headers_in.if_modified_since || r->headers_in.if_none_match) {
+    return ngx_http_next_header_filter(r);
 
-        if (r->headers_in.if_modified_since
-            && ngx_http_test_if_modified(r))
-        {
-            return ngx_http_next_header_filter(r);
-        }
+not_modified:
 
-        if (r->headers_in.if_none_match
-            && !ngx_http_test_if_match(r, r->headers_in.if_none_match, 1))
-        {
-            return ngx_http_next_header_filter(r);
-        }
+    r->headers_out.status = NGX_HTTP_NOT_MODIFIED;
+    r->headers_out.status_line.len = 0;
+    r->headers_out.content_type.len = 0;
+    ngx_http_clear_content_length(r);
+    ngx_http_clear_accept_ranges(r);
 
-        /* not modified */
-
-        r->headers_out.status = NGX_HTTP_NOT_MODIFIED;
-        r->headers_out.status_line.len = 0;
-        r->headers_out.content_type.len = 0;
-        ngx_http_clear_content_length(r);
-        ngx_http_clear_accept_ranges(r);
-
-        if (r->headers_out.content_encoding) {
-            r->headers_out.content_encoding->hash = 0;
-            r->headers_out.content_encoding = NULL;
-        }
-
-        return ngx_http_next_header_filter(r);
+    if (r->headers_out.content_encoding) {
+        r->headers_out.content_encoding->hash = 0;
+        r->headers_out.content_encoding = NULL;
     }
 
     return ngx_http_next_header_filter(r);