Avoid unnecessary std::string allocations.

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 130 matching lines @@
     next_dot = host.find('.', curr_start);
   }
 
   // No rule found in the registry.  curr_start now points to the first
   // character of the last subcomponent of the host, so if we allow unknown
   // registries, return the length of this subcomponent.
   return unknown_filter == INCLUDE_UNKNOWN_REGISTRIES ?
       (host.length() - curr_start) : 0;
 }
 
-std::string GetDomainAndRegistryImpl(base::StringPiece host,
-                                     PrivateRegistryFilter private_filter) {
+base::StringPiece GetDomainAndRegistryImpl(
+    base::StringPiece host,
+    PrivateRegistryFilter private_filter) {
   DCHECK(!host.empty());
 
   // Find the length of the registry for this host.
   const size_t registry_length =
       GetRegistryLengthImpl(host, INCLUDE_UNKNOWN_REGISTRIES, private_filter);
   if ((registry_length == std::string::npos) || (registry_length == 0))
-    return std::string();  // No registry.
+    return base::StringPiece();  // No registry.
   // The "2" in this next line is 1 for the dot, plus a 1-char minimum preceding
   // subcomponent length.
   DCHECK(host.length() >= 2);
   if (registry_length > (host.length() - 2)) {
     NOTREACHED() <<
         "Host does not have at least one subcomponent before registry!";
-    return std::string();
+    return base::StringPiece();
   }
 
   // Move past the dot preceding the registry, and search for the next previous
   // dot.  Return the host from after that dot, or the whole host when there is
   // no dot.
   const size_t dot = host.rfind('.', host.length() - registry_length - 2);
   if (dot == std::string::npos)
-    return host.as_string();
-  return host.substr(dot + 1).as_string();
+    return host;
+  return host.substr(dot + 1);
+}
+
+// Same as GetDomainAndRegistry, but returns the domain and registry as a
+// StringPiece that references the underlying string of the passed-in |gurl|.
+// TODO(pkalinnikov): Eliminate this helper by exposing StringPiece as the
+// interface type for all the APIs.
+base::StringPiece GetDomainAndRegistryAsStringPiece(
+    const GURL& gurl,
+    PrivateRegistryFilter filter) {
+  base::StringPiece host = gurl.host_piece();
+  if (host.empty() || gurl.HostIsIPAddress())
+    return base::StringPiece();
+  return GetDomainAndRegistryImpl(host, filter);
 }
 
 }  // namespace
 
-std::string GetDomainAndRegistry(
-    const GURL& gurl,
-    PrivateRegistryFilter filter) {
-  base::StringPiece host = gurl.host_piece();
-  if (host.empty() || gurl.HostIsIPAddress())
-    return std::string();
-  return GetDomainAndRegistryImpl(host, filter);
+std::string GetDomainAndRegistry(const GURL& gurl,
+                                 PrivateRegistryFilter filter) {
+  return GetDomainAndRegistryAsStringPiece(gurl, filter).as_string();
 }
 
 std::string GetDomainAndRegistry(base::StringPiece host,
                                  PrivateRegistryFilter filter) {
   url::CanonHostInfo host_info;
   const std::string canon_host(CanonicalizeHost(host, &host_info));
   if (canon_host.empty() || host_info.IsIPAddress())
     return std::string();
-  return GetDomainAndRegistryImpl(canon_host, filter);
+  return GetDomainAndRegistryImpl(canon_host, filter).as_string();
 }
 
 bool SameDomainOrHost(
     const GURL& gurl1,
     const GURL& gurl2,
     PrivateRegistryFilter filter) {
   // See if both URLs have a known domain + registry, and those values are the
   // same.
-  const std::string domain1(GetDomainAndRegistry(gurl1, filter));
-  const std::string domain2(GetDomainAndRegistry(gurl2, filter));
+  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,
@@ skipping 38 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