[net] HostResolverImpl + DnsTransaction + DnsConfigService = Asynchronous DNS ready for experiments.

chrome/browser/io_thread.cc

 // Copyright (c) 2011 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 "chrome/browser/io_thread.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/bind.h"
@@ skipping 118 matching lines @@
     // Parse the switch (it should be a non-negative integer).
     int n;
     if (base::StringToInt(s, &n) && n >= 0) {
       retry_attempts = static_cast<size_t>(n);
     } else {
       LOG(ERROR) << "Invalid switch for host resolver retry attempts: " << s;
     }
   }
 
   net::HostResolver* global_host_resolver = NULL;
   if (command_line.HasSwitch(switches::kDnsServer)) {

[cbentzel, 2012/02/10 19:51:08]

I'd be fine with getting rid of this for now.

     std::string dns_ip_string =
       command_line.GetSwitchValueASCII(switches::kDnsServer);
     net::IPAddressNumber dns_ip_number;
     if (net::ParseIPLiteralToNumber(dns_ip_string, &dns_ip_number)) {
-      global_host_resolver =
-        net::CreateAsyncHostResolver(parallelism, dns_ip_number, net_log);
+      // TODO(szym): Somehow pass |dns_ip_number| to the DnsConfigService.
+      LOG(WARNING) << "Configuration currently ignored --dns-server";
     } else {
       LOG(ERROR) << "Invalid IP address specified for --dns-server: "
                  << dns_ip_string;
     }
   }
 
+  if (command_line.HasSwitch(switches::kEnableAsyncDns)) {
+    global_host_resolver =
+        net::CreateAsyncHostResolver(parallelism, retry_attempts, net_log);
+  }
+
   if (!global_host_resolver) {
     global_host_resolver =
       net::CreateSystemHostResolver(parallelism, retry_attempts, net_log);
   }
 
   // Determine if we should disable IPv6 support.
   if (!command_line.HasSwitch(switches::kEnableIPv6)) {
     if (command_line.HasSwitch(switches::kDisableIPv6)) {
       global_host_resolver->SetDefaultAddressFamily(net::ADDRESS_FAMILY_IPV4);
     } else {
@@ skipping 452 matching lines @@
   system_params.network_delegate = globals_->system_network_delegate.get();
   system_params.net_log = net_log_;
   globals_->system_http_transaction_factory.reset(
       new net::HttpNetworkLayer(
           new net::HttpNetworkSession(system_params)));
   globals_->system_ftp_transaction_factory.reset(
       new net::FtpNetworkLayer(globals_->host_resolver.get()));
   globals_->system_request_context =
       ConstructSystemRequestContext(globals_, net_log_);
 }