ClickHouse/base/poco/Net/include/Poco/Net/SocketConnector.h

//
// SocketConnector.h
//
// Library: Net
// Package: Reactor
// Module:  SocketConnector
//
// Definition of the SocketConnector class.
//
// Copyright (c) 2005-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Net_SocketConnector_INCLUDED
#define Net_SocketConnector_INCLUDED


#include "Poco/Net/Net.h"
#include "Poco/Net/SocketAddress.h"
#include "Poco/Net/SocketNotification.h"
#include "Poco/Net/StreamSocket.h"
#include "Poco/Observer.h"


namespace Poco
{
namespace Net
{


    template <class ServiceHandler>
    class SocketConnector
    /// This class implements the Connector part of the
    /// Acceptor-Connector design pattern.
    ///
    /// The Acceptor-Connector pattern has been described in the book
    /// "Pattern Languages of Program Design 3", edited by Robert Martin,
    /// Frank Buschmann and Dirk Riehle (Addison Wesley, 1997).
    ///
    /// The Acceptor-Connector design pattern decouples connection
    /// establishment and service initialization in a distributed system
    /// from the processing performed once a service is initialized.
    /// This decoupling is achieved with three components: Acceptors,
    /// Connectors and Service Handlers.
    /// The Connector actively establishes a connection with a remote
    /// server socket (usually managed by an Acceptor) and initializes
    /// a Service Handler to manage the connection.
    ///
    /// The SocketConnector sets up a StreamSocket, initiates a non-blocking
    /// connect operation and registers itself for ReadableNotification, WritableNotification
    /// and ErrorNotification. ReadableNotification or WritableNotification denote the successful
    /// establishment of the connection.
    ///
    /// When the StreamSocket becomes readable or writeable, the SocketConnector
    /// creates a ServiceHandler to service the connection and unregisters
    /// itself.
    ///
    /// In case of an error (ErrorNotification), the SocketConnector unregisters itself
    /// and calls the onError() method, which can be overridden by subclasses
    /// to perform custom error handling.
    ///
    /// The ServiceHandler class must provide a constructor that
    /// takes a StreamSocket and a SocketReactor as arguments,
    /// e.g.:
    ///     MyServiceHandler(const StreamSocket& socket, ServiceReactor& reactor)
    ///
    /// When the ServiceHandler is done, it must destroy itself.
    ///
    /// Subclasses can override the createServiceHandler() factory method
    /// if special steps are necessary to create a ServiceHandler object.
    {
    public:
        explicit SocketConnector(SocketAddress & address) : _pReactor(0)
        /// Creates a SocketConnector, using the given Socket.
        {
            _socket.connectNB(address);
        }

        SocketConnector(SocketAddress & address, SocketReactor & reactor) : _pReactor(0)
        /// Creates an acceptor, using the given ServerSocket.
        /// The SocketConnector registers itself with the given SocketReactor.
        {
            _socket.connectNB(address);
            registerConnector(reactor);
        }

        virtual ~SocketConnector()
        /// Destroys the SocketConnector.
        {
            try
            {
                unregisterConnector();
            }
            catch (...)
            {
                poco_unexpected();
            }
        }

        virtual void registerConnector(SocketReactor & reactor)
        /// Registers the SocketConnector with a SocketReactor.
        ///
        /// A subclass can override this and, for example, also register
        /// an event handler for a timeout event.
        ///
        /// The overriding method must call the baseclass implementation first.
        {
            _pReactor = &reactor;
            _pReactor->addEventHandler(_socket, Poco::Observer<SocketConnector, ReadableNotification>(*this, &SocketConnector::onReadable));
            _pReactor->addEventHandler(_socket, Poco::Observer<SocketConnector, WritableNotification>(*this, &SocketConnector::onWritable));
            _pReactor->addEventHandler(_socket, Poco::Observer<SocketConnector, ErrorNotification>(*this, &SocketConnector::onError));
        }

        virtual void unregisterConnector()
        /// Unregisters the SocketConnector.
        ///
        /// A subclass can override this and, for example, also unregister
        /// its event handler for a timeout event.
        ///
        /// The overriding method must call the baseclass implementation first.
        {
            if (_pReactor)
            {
                _pReactor->removeEventHandler(
                    _socket, Poco::Observer<SocketConnector, ReadableNotification>(*this, &SocketConnector::onReadable));
                _pReactor->removeEventHandler(
                    _socket, Poco::Observer<SocketConnector, WritableNotification>(*this, &SocketConnector::onWritable));
                _pReactor->removeEventHandler(
                    _socket, Poco::Observer<SocketConnector, ErrorNotification>(*this, &SocketConnector::onError));
            }
        }

        void onReadable(ReadableNotification * pNotification)
        {
            pNotification->release();
            int err = _socket.impl()->socketError();
            if (err)
            {
                onError(err);
                unregisterConnector();
            }
            else
            {
                onConnect();
            }
        }

        void onWritable(WritableNotification * pNotification)
        {
            pNotification->release();
            onConnect();
        }

        void onConnect()
        {
            _socket.setBlocking(true);
            createServiceHandler();
            unregisterConnector();
        }

        void onError(ErrorNotification * pNotification)
        {
            pNotification->release();
            onError(_socket.impl()->socketError());
            unregisterConnector();
        }

    protected:
        virtual ServiceHandler * createServiceHandler()
        /// Create and initialize a new ServiceHandler instance.
        ///
        /// Subclasses can override this method.
        {
            return new ServiceHandler(_socket, *_pReactor);
        }

        virtual void onError(int errorCode)
        /// Called when the socket cannot be connected.
        ///
        /// Subclasses can override this method.
        {
        }

        SocketReactor * reactor()
        /// Returns a pointer to the SocketReactor where
        /// this SocketConnector is registered.
        ///
        /// The pointer may be null.
        {
            return _pReactor;
        }

        StreamSocket & socket()
        /// Returns a reference to the SocketConnector's socket.
        {
            return _socket;
        }

    private:
        SocketConnector();
        SocketConnector(const SocketConnector &);
        SocketConnector & operator=(const SocketConnector &);

        StreamSocket _socket;
        SocketReactor * _pReactor;
    };


}
} // namespace Poco::Net


#endif // Net_SocketConnector_INCLUDED