HostResolver supports optional CNAME lookups.

net/base/host_resolver_proc.cc

 // Copyright (c) 2010 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.
 
 #include "net/base/host_resolver_proc.h"
 
 #include "build/build_config.h"
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
 #include <resolv.h>
@@ skipping 49 matching lines @@
   HostResolverProc* old = default_proc_;
   default_proc_ = proc;
   return old;
 }
 
 // static
 HostResolverProc* HostResolverProc::GetDefault() {
   return default_proc_;
 }
 
-int HostResolverProc::ResolveUsingPrevious(const std::string& host,
-                                           AddressFamily address_family,
-                                           AddressList* addrlist) {
+int HostResolverProc::ResolveUsingPrevious(
+    const std::string& host,
+    AddressFamily address_family,
+    HostResolverFlags host_resolver_flags,
+    AddressList* addrlist) {
   if (previous_proc_)
-    return previous_proc_->Resolve(host, address_family, addrlist);
+    return previous_proc_->Resolve(host, address_family,
+                                   host_resolver_flags, addrlist);
 
   // Final fallback is the system resolver.
-  return SystemHostResolverProc(host, address_family, addrlist);
+  return SystemHostResolverProc(host, address_family,
+                                host_resolver_flags, addrlist);
 }
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
 // On Linux/BSD, changes to /etc/resolv.conf can go unnoticed thus resulting
 // in DNS queries failing either because nameservers are unknown on startup
 // or because nameserver info has changed as a result of e.g. connecting to
 // a new network. Some distributions patch glibc to stat /etc/resolv.conf
 // to try to automatically detect such changes but these patches are not
 // universal and even patched systems such as Jaunty appear to need calls
 // to res_ninit to reload the nameserver information in different threads.
@@ skipping 57 matching lines @@
 };
 
 // A TLS slot to the TimeTicks for the current thread.
 // static
 ThreadLocalStorage::Slot DnsReloadTimer::tls_index_(base::LINKER_INITIALIZED);
 
 #endif  // defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
 
 int SystemHostResolverProc(const std::string& host,
                            AddressFamily address_family,
+                           HostResolverFlags host_resolver_flags,
                            AddressList* addrlist) {
   // The result of |getaddrinfo| for empty hosts is inconsistent across systems.
   // On Windows it gives the default interface's address, whereas on Linux it
   // gives an error. We will make it fail on all platforms for consistency.
   if (host.empty())
     return ERR_NAME_NOT_RESOLVED;
 
   struct addrinfo* ai = NULL;
   struct addrinfo hints = {0};
 
@@ skipping 33 matching lines @@
   //   The IPv4 or IPv6 loopback address is not considered a valid global
   //   address.
   // See http://crbug.com/5234.
   //
   // OpenBSD does not support it, either.
   hints.ai_flags = 0;
 #else
   hints.ai_flags = AI_ADDRCONFIG;
 #endif
 
+  if (host_resolver_flags & HOST_RESOLVER_CANONNAME)
+    hints.ai_flags |= AI_CANONNAME;
+
   // Restrict result set to only this socket type to avoid duplicates.
   hints.ai_socktype = SOCK_STREAM;
 
   int err = getaddrinfo(host.c_str(), NULL, &hints, &ai);
 #if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
   net::DnsReloadTimer* dns_timer = Singleton<net::DnsReloadTimer>::get();
   // If we fail, re-initialise the resolver just in case there have been any
   // changes to /etc/resolv.conf and retry. See http://crbug.com/11380 for info.
   if (err && dns_timer->Expired()) {
     res_nclose(&_res);
     if (!res_ninit(&_res))
       err = getaddrinfo(host.c_str(), NULL, &hints, &ai);
   }
 #endif
 
   if (err)
     return ERR_NAME_NOT_RESOLVED;
 
   addrlist->Adopt(ai);
   return OK;
 }
 
 }  // namespace net