Invert host/domain checks in SameDomainOrHost

net/base/registry_controlled_domains/registry_controlled_domain.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // NB: Modelled after Mozilla's code (originally written by Pamela Greene,
 // later modified by others), but almost entirely rewritten for Chrome.
 //   (netwerk/dns/src/nsEffectiveTLDService.cpp)
 /* ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1
  *
@@ skipping 311 matching lines @@
   const std::string canon_host(CanonicalizeHost(host, &host_info));
   if (canon_host.empty() || host_info.IsIPAddress())
     return std::string();
   return GetDomainAndRegistryImpl(canon_host, filter).as_string();
 }
 
 bool SameDomainOrHost(
     const GURL& gurl1,
     const GURL& gurl2,
     PrivateRegistryFilter filter) {
+  // First, check if the hosts are identical.
+  const url::Component host1 = gurl1.parsed_for_possibly_invalid_spec().host;
+  const url::Component host2 = gurl2.parsed_for_possibly_invalid_spec().host;
+  if ((host1.len > 0) && (host1.len == host2.len) &&
+      !strncmp(gurl1.possibly_invalid_spec().data() + host1.begin,
+               gurl2.possibly_invalid_spec().data() + host2.begin, host1.len)) {
+    return true;
+  }
+
   // See if both URLs have a known domain + registry, and those values are the
   // same.
   const base::StringPiece domain1 =
       GetDomainAndRegistryAsStringPiece(gurl1, filter);
   const base::StringPiece domain2 =
       GetDomainAndRegistryAsStringPiece(gurl2, filter);
   if (!domain1.empty() || !domain2.empty())
     return domain1 == domain2;
-
-  // No domains.  See if the hosts are identical.
-  const url::Component host1 = gurl1.parsed_for_possibly_invalid_spec().host;
-  const url::Component host2 = gurl2.parsed_for_possibly_invalid_spec().host;
-  if ((host1.len <= 0) || (host1.len != host2.len))
-    return false;
-  return !strncmp(gurl1.possibly_invalid_spec().data() + host1.begin,
-                  gurl2.possibly_invalid_spec().data() + host2.begin,
-                  host1.len);
+  return false;

[Peter Kasting, 2016/11/14 23:00:25]

I think a slightly faster, and hopefully more readable, implementation of this
function would be:

  // Quickly reject cases where either host is empty.
  if (!gurl1.has_host() || !gurl2.has_host())
    return false;

  // Check for exact host matches, which is faster than looking up the domain
  // and registry.
  if (gurl1.host_piece() == gurl2.host_piece())
    return true;

  // Check for a domain and registry match.
  const auto domain1 = GetDomainAndRegistryAsStringPiece(gurl1, filter);
  return !domain1.empty() &&
         (domain1 == GetDomainAndRegistryAsStringPiece(gurl2, filter));

 }
 
 bool SameDomainOrHost(const url::Origin& origin1,
                       const url::Origin& origin2,
                       PrivateRegistryFilter filter) {
   return SameDomainOrHost(origin1.GetURL(), origin2.GetURL(), filter);
 }
 
 bool SameDomainOrHost(const url::Origin& origin1,
                       const base::Optional<url::Origin>& origin2,
@@ skipping 73 matching lines @@
 
 void SetFindDomainGraph(const unsigned char* domains, size_t length) {
   CHECK(domains);
   CHECK_NE(length, 0u);
   g_graph = domains;
   g_graph_length = length;
 }
 
 }  // namespace registry_controlled_domains
 }  // namespace net