Utility to resolve an hostname using Chromium's code in net/dns

net/tools/gdig/gdig.cc

+#include <stdio.h>
+#include <iostream>
+
+#include "base/at_exit.h"
+#include "base/command_line.h"
+#if defined(OS_MACOSX)
+#include "base/mac/scoped_nsautorelease_pool.h"
+#endif
+#include "base/memory/scoped_ptr.h"
+#include "base/message_loop.h"
+#include "base/string_number_conversions.h"
+
+#include "net/base/host_resolver_impl.h"
+#include "net/base/net_errors.h"
+#include "net/base/net_util.h"
+#include "net/base/sys_addrinfo.h"
+
+#include "net/dns/dns_client.h"
+
+namespace net {
+
+namespace {
+
+class GDig {
+ public:
+  GDig();
+
+  enum Result {
+    RESULT_NO_RESOLVE = -3,
+    RESULT_NO_CONFIG = -2,
+    RESULT_WRONG_USAGE = -1,
+    RESULT_OK = 0,
+  };
+
+  Result Main(int argc, const char* argv[]);
+
+ private:
+  bool ParseCommandLine(int argc, const char* argv[]);
+
+  void Start();
+
+  void OnDnsConfig(const DnsConfig& dns_config);
+  void OnResolveComplete(int val);
+  void OnTimeout();
+
+  Result result_;
+
+  AddressList addrlist_;
+
+  base::CancelableClosure timeout_closure_;
+
+  scoped_ptr<DnsConfigService> dns_config_service_;
+
+  base::TimeDelta timeout_;
+  std::string domain_name_;
+
+  scoped_ptr<HostResolver> resolver_;
+};
+
+GDig::GDig()
+    : result_(GDig::RESULT_OK),
+      timeout_(base::TimeDelta::FromSeconds(5)) {
+}
+
+GDig::Result GDig::Main(int argc, const char* argv[]) {
+  if (!ParseCommandLine(argc, argv)) {
+      std::cout << "usage: " << argv[0] <<
+          " [--config_timeout=<seconds>] domain_name" <<
+          std::endl;
+      return RESULT_WRONG_USAGE;
+  }
+
+#if defined(OS_MACOSX)
+  // Without this there will be a mem leak on osx
+  base::mac::ScopedNSAutoreleasePool scoped_pool;
+#endif
+
+  base::AtExitManager exit_manager;
+  MessageLoop loop(MessageLoop::TYPE_IO);
+
+  Start();
+
+  MessageLoop::current()->Run();
+  dns_config_service_.reset();

[szym, 2012/06/01 22:10:23]

Maybe add a comment: "Destroy it while MessageLoop is alive."

[Daniele, 2012/06/01 22:29:27]

Done.

+  return result_;
+}
+
+void GDig::OnResolveComplete(int val) {
+  MessageLoop::current()->Quit();
+  if (val != OK) {
+    std::cout << "Error trying to resolve hostname " << domain_name_ <<
+        ":" << ErrorToString(val) << std::endl;
+    result_ = RESULT_NO_RESOLVE;
+  } else {
+    for (AddressList::iterator i=addrlist_.begin(); i!=addrlist_.end(); ++i) {
+        std::cout << i->ToStringWithoutPort() << std::endl;
+    }
+  }
+}
+
+void GDig::OnTimeout() {
+  MessageLoop::current()->Quit();
+  std::cout << "Timed out waiting to load the dns config" << std::endl;
+  result_ = RESULT_NO_CONFIG;
+}
+
+void GDig::Start() {
+  dns_config_service_ = DnsConfigService::CreateSystemService();
+  dns_config_service_->Read(base::Bind(&GDig::OnDnsConfig,
+                                       base::Unretained(this)));
+
+  timeout_closure_.Reset(base::Bind(&GDig::OnTimeout, base::Unretained(this)));
+
+  MessageLoop::current()->PostDelayedTask(
+      FROM_HERE,
+      timeout_closure_.callback(),
+      timeout_);
+}
+
+void GDig::OnDnsConfig(const DnsConfig& dns_config) {
+  timeout_closure_.Cancel();
+  DCHECK(dns_config.IsValid());
+
+  scoped_ptr<DnsClient> dns_client(DnsClient::CreateClient(NULL));
+  dns_client->SetConfig(dns_config);
+  resolver_.reset(
+      new HostResolverImpl(
+          HostCache::CreateDefaultCache(),
+          PrioritizedDispatcher::Limits(NUM_PRIORITIES, 1),
+          HostResolverImpl::ProcTaskParams(NULL, 1),
+          scoped_ptr<DnsConfigService>(NULL),
+          dns_client.Pass(),
+          NULL));
+
+  HostResolver::RequestInfo info(HostPortPair(domain_name_.c_str(), 80));
+
+  CompletionCallback callback = base::Bind(&GDig::OnResolveComplete,
+                                           base::Unretained(this));
+  int ret = resolver_->Resolve(info, &addrlist_, callback, NULL, BoundNetLog());
+  DCHECK(ret == ERR_IO_PENDING);
+
+}
+
+bool GDig::ParseCommandLine(int argc, const char* argv[]) {
+  CommandLine::Init(argc, argv);
+  const CommandLine& parsed_command_line = *CommandLine::ForCurrentProcess();
+
+  if (parsed_command_line.GetArgs().size() != 1) {
+      return false;
+  }
+  domain_name_ = parsed_command_line.GetArgs().at(0);
+
+  if (parsed_command_line.HasSwitch("config_timeout")) {
+      int timeout_seconds = 0;
+      base::StringToInt(
+          parsed_command_line.GetSwitchValueASCII("config_timeout"),
+          &timeout_seconds);
+      timeout_ = base::TimeDelta::FromSeconds(timeout_seconds);
+  }
+
+  return true;
+}
+
+}  // empty namespace
+
+}  // namespace net
+
+int main(int argc, const char* argv[]) {
+  net::GDig dig;
+  return dig.Main(argc, argv);
+}