dns.cpp

Go to the documentation of this file.

/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
#include "dns.hpp"
#include "../util/scheduler.hpp"

#include <boost/asio/io_service.hpp>
#include <boost/asio/ip/udp.hpp>

namespace ndn {
namespace dns {

class Resolver : noncopyable
{
public:
  typedef boost::asio::ip::udp protocol;
  typedef protocol::resolver::iterator iterator;
  typedef protocol::resolver::query query;

public:
  Resolver(boost::asio::io_service& ioService,
           const AddressSelector& addressSelector)
    : m_resolver(ioService)
    , m_addressSelector(addressSelector)
    , m_scheduler(ioService)
  {
    BOOST_ASSERT(m_addressSelector != nullptr);
  }

  void
  asyncResolve(const query& q,
               const SuccessCallback& onSuccess,
               const ErrorCallback& onError,
               time::nanoseconds timeout,
               const shared_ptr<Resolver>& self)
  {
    m_onSuccess = onSuccess;
    m_onError = onError;

    m_resolver.async_resolve(q, bind(&Resolver::onResolveResult, this, _1, _2, self));

    m_resolveTimeout = m_scheduler.scheduleEvent(timeout, bind(&Resolver::onResolveTimeout, this, self));
  }

  iterator
  syncResolve(const query& q)
  {
    return selectAddress(m_resolver.resolve(q));
  }

private:
  void
  onResolveResult(const boost::system::error_code& error,
                  iterator it, const shared_ptr<Resolver>& self)
  {
    m_scheduler.cancelEvent(m_resolveTimeout);
    // ensure the Resolver isn't destructed while callbacks are still pending, see #2653
    m_resolver.get_io_service().post(bind([] (const shared_ptr<Resolver>&) {}, self));

    if (error) {
      if (error == boost::asio::error::operation_aborted)
        return;

      if (m_onError)
        m_onError("Hostname cannot be resolved: " + error.message());

      return;
    }

    it = selectAddress(it);

    if (it != iterator() && m_onSuccess) {
      m_onSuccess(it->endpoint().address());
    }
    else if (m_onError) {
      m_onError("No endpoints match the specified address selector");
    }
  }

  void
  onResolveTimeout(const shared_ptr<Resolver>& self)
  {
    m_resolver.cancel();
    // ensure the Resolver isn't destructed while callbacks are still pending, see #2653
    m_resolver.get_io_service().post(bind([] (const shared_ptr<Resolver>&) {}, self));

    if (m_onError)
      m_onError("Hostname resolution timed out");
  }

  iterator
  selectAddress(iterator it) const
  {
    while (it != iterator() &&
           !m_addressSelector(it->endpoint().address())) {
      ++it;
    }

    return it;
  }

private:
  protocol::resolver m_resolver;

  AddressSelector m_addressSelector;
  SuccessCallback m_onSuccess;
  ErrorCallback m_onError;

  util::scheduler::Scheduler m_scheduler;
  util::scheduler::EventId m_resolveTimeout;
};

void
asyncResolve(const std::string& host,
             const SuccessCallback& onSuccess,
             const ErrorCallback& onError,
             boost::asio::io_service& ioService,
             const AddressSelector& addressSelector,
             time::nanoseconds timeout)
{
  auto resolver = make_shared<Resolver>(ref(ioService), addressSelector);
  resolver->asyncResolve(Resolver::query(host, ""), onSuccess, onError, timeout, resolver);
  // resolver will be destroyed when async operation finishes or ioService stops
}

IpAddress
syncResolve(const std::string& host,
            boost::asio::io_service& ioService,
            const AddressSelector& addressSelector)
{
  Resolver resolver(ioService, addressSelector);
  auto it = resolver.syncResolve(Resolver::query(host, ""));

  if (it == Resolver::iterator()) {
    BOOST_THROW_EXCEPTION(Error("No endpoints match the specified address selector"));
  }

  return it->endpoint().address();
}

} // namespace dns
} // namespace ndn