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// Copyright (C) 2013-2021 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef DNS_CLIENT_H
#define DNS_CLIENT_H
#include <asiolink/io_service.h>
#include <asiodns/io_fetch.h>
#include <d2srv/d2_tsig_key.h>
#include <d2srv/d2_update_message.h>
#include <util/buffer.h>
namespace isc {
namespace d2 {
class DNSClient;
typedef boost::shared_ptr<DNSClient> DNSClientPtr;
/// DNSClient class implementation.
class DNSClientImpl;
/// @brief The @c DNSClient class handles communication with the DNS server.
///
/// Communication with the DNS server is asynchronous. Caller must provide a
/// callback, which will be invoked when the response from the DNS server is
/// received, a timeout has occurred or IO service has been stopped for any
/// reason. The caller-supplied callback is called by the internal callback
/// operator implemented by @c DNSClient. This callback is responsible for
/// initializing the @c D2UpdateMessage instance which encapsulates the response
/// from the DNS. This initialization does not take place if the response from
/// DNS is not received.
///
/// Caller must supply a pointer to the @c D2UpdateMessage object, which will
/// encapsulate DNS response, through class constructor. An exception will be
/// thrown if the pointer is not initialized by the caller.
///
/// @todo Ultimately, this class will support both TCP and UDP Transport.
/// Currently only UDP is supported and can be specified as a preferred
/// protocol. @c DNSClient constructor will throw an exception if TCP is
/// specified. Once both protocols are supported, the @c DNSClient logic will
/// try to obey caller's preference. However, it may use the other protocol if
/// on its own discretion, when there is a legitimate reason to do so. For
/// example, if communication with the server using preferred protocol fails.
class DNSClient {
public:
/// @brief Transport layer protocol used by a DNS Client to communicate
/// with a server.
enum Protocol {
UDP,
TCP
};
/// @brief A status code of the DNSClient.
enum Status {
SUCCESS, ///< Response received and is ok.
TIMEOUT, ///< No response, timeout.
IO_STOPPED, ///< IO was stopped.
INVALID_RESPONSE, ///< Response received but invalid.
OTHER ///< Other, unclassified error.
};
/// @brief Callback for the @c DNSClient class.
///
/// This is an abstract class which represents the external callback for the
/// @c DNSClient. Caller must implement this class and supply its instance
/// in the @c DNSClient constructor to get callbacks when the DNS Update
/// exchange is complete (@see @c DNSClient).
class Callback {
public:
/// @brief Virtual destructor.
virtual ~Callback() { }
/// @brief Function operator implementing a callback.
///
/// @param status a @c DNSClient::Status enum representing status code
/// of DNSClient operation.
virtual void operator()(DNSClient::Status status) = 0;
};
/// @brief Constructor.
///
/// @param response_placeholder Message object pointer which will be updated
/// with dynamically allocated object holding the DNS server's response.
/// @param callback Pointer to an object implementing @c DNSClient::Callback
/// class. This object will be called when DNS message exchange completes or
/// if an error occurs. NULL value disables callback invocation.
/// @param proto caller's preference regarding Transport layer protocol to
/// be used by DNS Client to communicate with a server.
DNSClient(D2UpdateMessagePtr& response_placeholder, Callback* callback,
const Protocol proto = UDP);
/// @brief Virtual destructor, does nothing.
~DNSClient();
/// @brief Stop the client.
void stop();
///
/// @name Copy constructor and assignment operator
///
/// Copy constructor and assignment operator are private because there are
/// no use cases when a DNSClient instance will need to be copied. Also, it
/// is desired to avoid copying a DNSClient::impl_ pointer and external
/// callbacks.
///
//@{
private:
DNSClient(const DNSClient& source);
DNSClient& operator=(const DNSClient& source);
//@}
public:
/// @brief Returns maximal allowed timeout value accepted by
/// @c DNSClient::doUpdate.
///
/// @return maximal allowed timeout value accepted by @c DNSClient::doUpdate
static unsigned int getMaxTimeout();
/// @brief Start asynchronous DNS Update with TSIG.
///
/// This function starts asynchronous DNS Update and returns. The DNS Update
/// will be executed by the specified IO service. Once the message exchange
/// with a DNS server is complete, timeout occurs or IO operation is
/// interrupted, the caller-supplied callback function will be invoked.
///
/// An address and port of the DNS server is specified through the function
/// arguments so as the same instance of the @c DNSClient can be used to
/// initiate multiple message exchanges.
///
/// @param io_service IO service to be used to run the message exchange.
/// @param ns_addr DNS server address.
/// @param ns_port DNS server port.
/// @param update A DNS Update message to be sent to the server.
/// @param wait A timeout (in milliseconds) for the response. If a response
/// is not received within the timeout, exchange is interrupted. This value
/// must not exceed maximal value for 'int' data type.
/// @param tsig_key A pointer to an @c D2TsigKeyPtr object that will
/// (if not null) be used to sign the DNS Update message and verify the
/// response.
void doUpdate(const asiolink::IOServicePtr& io_service,
const asiolink::IOAddress& ns_addr,
const uint16_t ns_port,
D2UpdateMessage& update,
const unsigned int wait,
const D2TsigKeyPtr& tsig_key = D2TsigKeyPtr());
private:
/// @brief Pointer to DNSClient implementation.
std::unique_ptr<DNSClientImpl> impl_;
};
} // namespace d2
} // namespace isc
#endif // DNS_CLIENT_H
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