/src/qt/qtbase/src/network/socket/qabstractsocket.cpp

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//#define QABSTRACTSOCKET_DEBUG

/*!
    \class QAbstractSocket

    \brief The QAbstractSocket class provides the base functionality
    common to all socket types.

    \reentrant
    \ingroup network
    \inmodule QtNetwork

    QAbstractSocket is the base class for QTcpSocket and QUdpSocket
    and contains all common functionality of these two classes. If
    you need a socket, you have two options:

    \list
    \li  Instantiate QTcpSocket or QUdpSocket.
    \li  Create a native socket descriptor, instantiate
        QAbstractSocket, and call setSocketDescriptor() to wrap the
        native socket.
    \endlist

    TCP (Transmission Control Protocol) is a reliable,
    stream-oriented, connection-oriented transport protocol. UDP
    (User Datagram Protocol) is an unreliable, datagram-oriented,
    connectionless protocol. In practice, this means that TCP is
    better suited for continuous transmission of data, whereas the
    more lightweight UDP can be used when reliability isn't
    important.

    QAbstractSocket's API unifies most of the differences between the
    two protocols. For example, although UDP is connectionless,
    connectToHost() establishes a virtual connection for UDP sockets,
    enabling you to use QAbstractSocket in more or less the same way
    regardless of the underlying protocol. Internally,
    QAbstractSocket remembers the address and port passed to
    connectToHost(), and functions like read() and write() use these
    values.

    At any time, QAbstractSocket has a state (returned by
    state()). The initial state is UnconnectedState. After
    calling connectToHost(), the socket first enters
    HostLookupState. If the host is found, QAbstractSocket enters
    ConnectingState and emits the hostFound() signal. When the
    connection has been established, it enters ConnectedState and
    emits connected(). If an error occurs at any stage, error() is
    emitted. Whenever the state changes, stateChanged() is emitted.
    For convenience, isValid() returns \c true if the socket is ready for
    reading and writing, but note that the socket's state must be
    ConnectedState before reading and writing can occur.

    Read or write data by calling read() or write(), or use the
    convenience functions readLine() and readAll(). QAbstractSocket
    also inherits getChar(), putChar(), and ungetChar() from
    QIODevice, which work on single bytes. The bytesWritten() signal
    is emitted when data has been written to the socket. Note that Qt does
    not limit the write buffer size. You can monitor its size by listening
    to this signal.

    The readyRead() signal is emitted every time a new chunk of data
    has arrived. bytesAvailable() then returns the number of bytes
    that are available for reading. Typically, you would connect the
    readyRead() signal to a slot and read all available data there.
    If you don't read all the data at once, the remaining data will
    still be available later, and any new incoming data will be
    appended to QAbstractSocket's internal read buffer. To limit the
    size of the read buffer, call setReadBufferSize().

    To close the socket, call disconnectFromHost(). QAbstractSocket enters
    QAbstractSocket::ClosingState. After all pending data has been written to
    the socket, QAbstractSocket actually closes the socket, enters
    QAbstractSocket::ClosedState, and emits disconnected(). If you want to
    abort a connection immediately, discarding all pending data, call abort()
    instead. If the remote host closes the connection, QAbstractSocket will
    emit error(QAbstractSocket::RemoteHostClosedError), during which the socket
    state will still be ConnectedState, and then the disconnected() signal
    will be emitted.

    The port and address of the connected peer is fetched by calling
    peerPort() and peerAddress(). peerName() returns the host name of
    the peer, as passed to connectToHost(). localPort() and
    localAddress() return the port and address of the local socket.

    QAbstractSocket provides a set of functions that suspend the
    calling thread until certain signals are emitted. These functions
    can be used to implement blocking sockets:

    \list
    \li waitForConnected() blocks until a connection has been established.

    \li waitForReadyRead() blocks until new data is available for
    reading.

    \li waitForBytesWritten() blocks until one payload of data has been
    written to the socket.

    \li waitForDisconnected() blocks until the connection has closed.
    \endlist

    We show an example:

    \snippet network/tcpwait.cpp 0

    If \l{QIODevice::}{waitForReadyRead()} returns \c false, the
    connection has been closed or an error has occurred.

    Programming with a blocking socket is radically different from
    programming with a non-blocking socket. A blocking socket doesn't
    require an event loop and typically leads to simpler code.
    However, in a GUI application, blocking sockets should only be
    used in non-GUI threads, to avoid freezing the user interface.
    See the \l fortuneclient and \l blockingfortuneclient
    examples for an overview of both approaches.

    \note We discourage the use of the blocking functions together
    with signals. One of the two possibilities should be used.

    QAbstractSocket can be used with QTextStream and QDataStream's
    stream operators (operator<<() and operator>>()). There is one
    issue to be aware of, though: You must make sure that enough data
    is available before attempting to read it using operator>>().

    \sa QNetworkAccessManager, QTcpServer
*/

/*!
    \fn void QAbstractSocket::hostFound()

    This signal is emitted after connectToHost() has been called and
    the host lookup has succeeded.

    \note Since Qt 4.6.3 QAbstractSocket may emit hostFound()
    directly from the connectToHost() call since a DNS result could have been
    cached.

    \sa connected()
*/

/*!
    \fn void QAbstractSocket::connected()

    This signal is emitted after connectToHost() has been called and
    a connection has been successfully established.

    \note On some operating systems the connected() signal may
    be directly emitted from the connectToHost() call for connections
    to the localhost.

    \sa connectToHost(), disconnected()
*/

/*!
    \fn void QAbstractSocket::disconnected()

    This signal is emitted when the socket has been disconnected.

    \warning If you need to delete the sender() of this signal in a slot connected
    to it, use the \l{QObject::deleteLater()}{deleteLater()} function.

    \sa connectToHost(), disconnectFromHost(), abort()
*/

/*!
    \fn void QAbstractSocket::error(QAbstractSocket::SocketError socketError)

    This signal is emitted after an error occurred. The \a socketError
    parameter describes the type of error that occurred.

    When this signal is emitted, the socket may not be ready for a reconnect
    attempt. In that case, attempts to reconnect should be done from the event
    loop. For example, use a QTimer::singleShot() with 0 as the timeout.

    QAbstractSocket::SocketError is not a registered metatype, so for queued
    connections, you will have to register it with Q_DECLARE_METATYPE() and
    qRegisterMetaType().

    \sa error(), errorString(), {Creating Custom Qt Types}
*/

/*!
    \fn void QAbstractSocket::stateChanged(QAbstractSocket::SocketState socketState)

    This signal is emitted whenever QAbstractSocket's state changes.
    The \a socketState parameter is the new state.

    QAbstractSocket::SocketState is not a registered metatype, so for queued
    connections, you will have to register it with Q_DECLARE_METATYPE() and
    qRegisterMetaType().

    \sa state(), {Creating Custom Qt Types}
*/

/*!
    \fn void QAbstractSocket::proxyAuthenticationRequired(const QNetworkProxy &proxy, QAuthenticator *authenticator)
    \since 4.3

    This signal can be emitted when a \a proxy that requires
    authentication is used. The \a authenticator object can then be
    filled in with the required details to allow authentication and
    continue the connection.

    \note It is not possible to use a QueuedConnection to connect to
    this signal, as the connection will fail if the authenticator has
    not been filled in with new information when the signal returns.

    \sa QAuthenticator, QNetworkProxy
*/

/*!
    \enum QAbstractSocket::NetworkLayerProtocol

    This enum describes the network layer protocol values used in Qt.

    \value IPv4Protocol IPv4
    \value IPv6Protocol IPv6
    \value AnyIPProtocol Either IPv4 or IPv6
    \value UnknownNetworkLayerProtocol Other than IPv4 and IPv6

    \sa QHostAddress::protocol()
*/

/*!
    \enum QAbstractSocket::SocketType

    This enum describes the transport layer protocol.

    \value TcpSocket TCP
    \value UdpSocket UDP
    \value UnknownSocketType Other than TCP and UDP

    \sa QAbstractSocket::socketType()
*/

/*!
    \enum QAbstractSocket::SocketError

    This enum describes the socket errors that can occur.

    \value ConnectionRefusedError The connection was refused by the
           peer (or timed out).
    \value RemoteHostClosedError The remote host closed the
           connection. Note that the client socket (i.e., this socket)
           will be closed after the remote close notification has
           been sent.
    \value HostNotFoundError The host address was not found.
    \value SocketAccessError The socket operation failed because the
           application lacked the required privileges.
    \value SocketResourceError The local system ran out of resources
           (e.g., too many sockets).
    \value SocketTimeoutError The socket operation timed out.
    \value DatagramTooLargeError The datagram was larger than the
           operating system's limit (which can be as low as 8192
           bytes).
    \value NetworkError An error occurred with the network (e.g., the
           network cable was accidentally plugged out).
    \value AddressInUseError The address specified to QAbstractSocket::bind() is
           already in use and was set to be exclusive.
    \value SocketAddressNotAvailableError The address specified to
           QAbstractSocket::bind() does not belong to the host.
    \value UnsupportedSocketOperationError The requested socket operation is
           not supported by the local operating system (e.g., lack of
           IPv6 support).
    \value ProxyAuthenticationRequiredError The socket is using a proxy, and
           the proxy requires authentication.
    \value SslHandshakeFailedError The SSL/TLS handshake failed, so
           the connection was closed (only used in QSslSocket)
    \value UnfinishedSocketOperationError Used by QAbstractSocketEngine only,
           The last operation attempted has not finished yet (still in progress in
            the background).
    \value ProxyConnectionRefusedError Could not contact the proxy server because
           the connection to that server was denied
    \value ProxyConnectionClosedError The connection to the proxy server was closed
           unexpectedly (before the connection to the final peer was established)
    \value ProxyConnectionTimeoutError The connection to the proxy server timed out
           or the proxy server stopped responding in the authentication phase.
    \value ProxyNotFoundError The proxy address set with setProxy() (or the application
           proxy) was not found.
    \value ProxyProtocolError The connection negotiation with the proxy server failed,
           because the response from the proxy server could not be understood.
    \value OperationError An operation was attempted while the socket was in a state that
           did not permit it.
    \value SslInternalError The SSL library being used reported an internal error. This is
           probably the result of a bad installation or misconfiguration of the library.
    \value SslInvalidUserDataError Invalid data (certificate, key, cypher, etc.) was
           provided and its use resulted in an error in the SSL library.
    \value TemporaryError A temporary error occurred (e.g., operation would block and socket
           is non-blocking).

    \value UnknownSocketError An unidentified error occurred.
    \sa QAbstractSocket::error()
*/

/*!
    \enum QAbstractSocket::SocketState

    This enum describes the different states in which a socket can be.

    \value UnconnectedState The socket is not connected.
    \value HostLookupState The socket is performing a host name lookup.
    \value ConnectingState The socket has started establishing a connection.
    \value ConnectedState A connection is established.
    \value BoundState The socket is bound to an address and port.
    \value ClosingState The socket is about to close (data may still
    be waiting to be written).
    \value ListeningState For internal use only.

    \sa QAbstractSocket::state()
*/

/*!
    \enum QAbstractSocket::SocketOption
    \since 4.6

    This enum represents the options that can be set on a socket.  If
    desired, they can be set after having received the connected()
    signal from the socket or after having received a new socket from
    a QTcpServer.

    \value LowDelayOption Try to optimize the socket for low
    latency. For a QTcpSocket this would set the TCP_NODELAY option
    and disable Nagle's algorithm. Set this to 1 to enable.

    \value KeepAliveOption Set this to 1 to enable the SO_KEEPALIVE
    socket option

    \value MulticastTtlOption Set this to an integer value to set
    IP_MULTICAST_TTL (TTL for multicast datagrams) socket option.

    \value MulticastLoopbackOption Set this to 1 to enable the
    IP_MULTICAST_LOOP (multicast loopback) socket option.

    \value TypeOfServiceOption This option is not supported on
    Windows. This maps to the IP_TOS socket option. For possible values,
    see table below.

    \value SendBufferSizeSocketOption Sets the socket send buffer size
    in bytes at the OS level. This maps to the SO_SNDBUF socket option.
    This option does not affect the QIODevice or QAbstractSocket buffers.
    This enum value has been introduced in Qt 5.3.

    \value ReceiveBufferSizeSocketOption Sets the socket receive
    buffer size in bytes at the OS level.
    This maps to the SO_RCVBUF socket option.
    This option does not affect the QIODevice or QAbstractSocket buffers
    (see \l{QAbstractSocket::}{setReadBufferSize()}).
    This enum value has been introduced in Qt 5.3.

    Possible values for \e{TypeOfServiceOption} are:

    \table
    \header \li Value \li Description
    \row \li 224 \li Network control
    \row \li 192 \li Internetwork control
    \row \li 160 \li CRITIC/ECP
    \row \li 128 \li Flash override
    \row \li 96 \li Flash
    \row \li 64 \li Immediate
    \row \li 32 \li Priority
    \row \li 0 \li Routine
    \endtable

    \sa QAbstractSocket::setSocketOption(), QAbstractSocket::socketOption()
*/

/*! \enum QAbstractSocket::BindFlag
    \since 5.0

    This enum describes the different flags you can pass to modify the
    behavior of QAbstractSocket::bind().

    \value ShareAddress Allow other services to bind to the same address
    and port. This is useful when multiple processes share
    the load of a single service by listening to the same address and port
    (e.g., a web server with several pre-forked listeners can greatly
    improve response time). However, because any service is allowed to
    rebind, this option is subject to certain security considerations.
    Note that by combining this option with ReuseAddressHint, you will
    also allow your service to rebind an existing shared address. On
    Unix, this is equivalent to the SO_REUSEADDR socket option. On Windows,
    this option is ignored.

    \value DontShareAddress Bind the address and port exclusively, so that
    no other services are allowed to rebind. By passing this option to
    QAbstractSocket::bind(), you are guaranteed that on successs, your service
    is the only one that listens to the address and port. No services are
    allowed to rebind, even if they pass ReuseAddressHint. This option
    provides more security than ShareAddress, but on certain operating
    systems, it requires you to run the server with administrator privileges.
    On Unix and Mac OS X, not sharing is the default behavior for binding
    an address and port, so this option is ignored. On Windows, this
    option uses the SO_EXCLUSIVEADDRUSE socket option.

    \value ReuseAddressHint Provides a hint to QAbstractSocket that it should try
    to rebind the service even if the address and port are already bound by
    another socket. On Windows, this is equivalent to the SO_REUSEADDR
    socket option. On Unix, this option is ignored.

    \value DefaultForPlatform The default option for the current platform.
    On Unix and Mac OS X, this is equivalent to (DontShareAddress
    + ReuseAddressHint), and on Windows, its equivalent to ShareAddress.
*/

/*! \enum QAbstractSocket::PauseMode
    \since 5.0

    This enum describes the behavior of when the socket should hold
    back with continuing data transfer.
    The only notification currently supported is QSslSocket::sslErrors().

    \value PauseNever Do not pause data transfer on the socket. This is the
    default and matches the behaviour of Qt 4.
    \value PauseOnSslErrors Pause data transfer on the socket upon receiving an
    SSL error notification. I.E. QSslSocket::sslErrors().
*/

#include "qabstractsocket.h"
#include "qabstractsocket_p.h"

#include "private/qhostinfo_p.h"
#include "private/qnetworksession_p.h"

#include <qabstracteventdispatcher.h>
#include <qhostaddress.h>
#include <qhostinfo.h>
#include <qmetaobject.h>
#include <qpointer.h>
#include <qtimer.h>
#include <qelapsedtimer.h>
#include <qscopedvaluerollback.h>

#ifndef QT_NO_SSL
#include <QtNetwork/qsslsocket.h>
#endif

#include <private/qthread_p.h>

#ifdef QABSTRACTSOCKET_DEBUG
#include <qdebug.h>
#endif

#include <time.h>

#define Q_CHECK_SOCKETENGINE(returnValue) do { \
    if (!d->socketEngine) { \
        return returnValue; \
    } } while (0)

#ifndef QABSTRACTSOCKET_BUFFERSIZE
#define QABSTRACTSOCKET_BUFFERSIZE 32768
#endif
#define QT_CONNECT_TIMEOUT 30000
#define QT_TRANSFER_TIMEOUT 120000

QT_BEGIN_NAMESPACE

#if defined QABSTRACTSOCKET_DEBUG
QT_BEGIN_INCLUDE_NAMESPACE
#include <qstring.h>
#include <ctype.h>
QT_END_INCLUDE_NAMESPACE

/*
    Returns a human readable representation of the first \a len
    characters in \a data.
*/
static QByteArray qt_prettyDebug(const char *data, int len, int maxLength)
{
    if (!data) return "(null)";
    QByteArray out;
    for (int i = 0; i < len; ++i) {
        char c = data[i];
        if (isprint(int(uchar(c)))) {
            out += c;
        } else switch (c) {
        case '\n': out += "\\n"; break;
        case '\r': out += "\\r"; break;
        case '\t': out += "\\t"; break;
        default:
            QString tmp;
            tmp.sprintf("\\%o", c);
            out += tmp.toLatin1();
        }
    }

    if (len < maxLength)
        out += "...";

    return out;
}
#endif

static bool isProxyError(QAbstractSocket::SocketError error)
{
    switch (error) {
    case QAbstractSocket::ProxyAuthenticationRequiredError:
    case QAbstractSocket::ProxyConnectionRefusedError:
    case QAbstractSocket::ProxyConnectionClosedError:
    case QAbstractSocket::ProxyConnectionTimeoutError:
    case QAbstractSocket::ProxyNotFoundError:
    case QAbstractSocket::ProxyProtocolError:
        return true;
    default:
        return false;
    }
}

/*! \internal

    Constructs a QAbstractSocketPrivate. Initializes all members.
*/
QAbstractSocketPrivate::QAbstractSocketPrivate()
    : readSocketNotifierCalled(false),
      readSocketNotifierState(false),
      readSocketNotifierStateSet(false),
      emittedReadyRead(false),
      emittedBytesWritten(false),
      abortCalled(false),
      closeCalled(false),
      pendingClose(false),
      pauseMode(QAbstractSocket::PauseNever),
      port(0),
      localPort(0),
      peerPort(0),
      socketEngine(0),
      cachedSocketDescriptor(-1),
      readBufferMaxSize(0),
      writeBuffer(QABSTRACTSOCKET_BUFFERSIZE),
      isBuffered(false),
      blockingTimeout(30000),
      connectTimer(0),
      disconnectTimer(0),
      connectTimeElapsed(0),
      hostLookupId(-1),
      socketType(QAbstractSocket::UnknownSocketType),
      state(QAbstractSocket::UnconnectedState),
      socketError(QAbstractSocket::UnknownSocketError),
      preferredNetworkLayerProtocol(QAbstractSocket::UnknownNetworkLayerProtocol)
{
}

/*! \internal

    Destructs the QAbstractSocket. If the socket layer is open, it
    will be reset.
*/
QAbstractSocketPrivate::~QAbstractSocketPrivate()
{
}

/*! \internal

    Resets the socket layer and deletes any socket notifiers.
*/
void QAbstractSocketPrivate::resetSocketLayer()
{
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::resetSocketLayer()");
#endif

    if (socketEngine) {
        socketEngine->close();
        socketEngine->disconnect();
        delete socketEngine;
        socketEngine = 0;
        cachedSocketDescriptor = -1;
    }
    if (connectTimer)
        connectTimer->stop();
    if (disconnectTimer)
        disconnectTimer->stop();
}

/*! \internal

    Initializes the socket layer to by of type \a type, using the
    network layer protocol \a protocol. Resets the socket layer first
    if it's already initialized. Sets up the socket notifiers.
*/
bool QAbstractSocketPrivate::initSocketLayer(QAbstractSocket::NetworkLayerProtocol protocol)
{
#ifdef QT_NO_NETWORKPROXY
    // this is here to avoid a duplication of the call to createSocketEngine below
    static const QNetworkProxy &proxyInUse = *(QNetworkProxy *)0;
#endif

    Q_Q(QAbstractSocket);
#if defined (QABSTRACTSOCKET_DEBUG)
    QString typeStr;
    if (q->socketType() == QAbstractSocket::TcpSocket) typeStr = QLatin1String("TcpSocket");
    else if (q->socketType() == QAbstractSocket::UdpSocket) typeStr = QLatin1String("UdpSocket");
    else typeStr = QLatin1String("UnknownSocketType");
    QString protocolStr;
    if (protocol == QAbstractSocket::IPv4Protocol) protocolStr = QLatin1String("IPv4Protocol");
    else if (protocol == QAbstractSocket::IPv6Protocol) protocolStr = QLatin1String("IPv6Protocol");
    else protocolStr = QLatin1String("UnknownNetworkLayerProtocol");
#endif

    resetSocketLayer();
    socketEngine = QAbstractSocketEngine::createSocketEngine(q->socketType(), proxyInUse, q);
    if (!socketEngine) {
        socketError = QAbstractSocket::UnsupportedSocketOperationError;
        q->setErrorString(QAbstractSocket::tr("Operation on socket is not supported"));
        return false;
    }
#ifndef QT_NO_BEARERMANAGEMENT
    //copy network session down to the socket engine (if it has been set)
    socketEngine->setProperty("_q_networksession", q->property("_q_networksession"));
#endif
    if (!socketEngine->initialize(q->socketType(), protocol)) {
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::initSocketLayer(%s, %s) failed (%s)",
               typeStr.toLatin1().constData(), protocolStr.toLatin1().constData(),
               socketEngine->errorString().toLatin1().constData());
#endif
        socketError = socketEngine->error();
        q->setErrorString(socketEngine->errorString());
        return false;
    }

    if (threadData->hasEventDispatcher())
        socketEngine->setReceiver(this);

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::initSocketLayer(%s, %s) success",
           typeStr.toLatin1().constData(), protocolStr.toLatin1().constData());
#endif
    return true;
}

/*! \internal

    Slot connected to the read socket notifier. This slot is called
    when new data is available for reading, or when the socket has
    been closed. Handles recursive calls.
*/
bool QAbstractSocketPrivate::canReadNotification()
{
    Q_Q(QAbstractSocket);
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::canReadNotification()");
#endif

    // Prevent recursive calls
    if (readSocketNotifierCalled) {
        if (!readSocketNotifierStateSet) {
            readSocketNotifierStateSet = true;
            readSocketNotifierState = socketEngine->isReadNotificationEnabled();
            socketEngine->setReadNotificationEnabled(false);
        }
    }
    QScopedValueRollback<bool> rsncrollback(readSocketNotifierCalled);
    readSocketNotifierCalled = true;

    if (!isBuffered)
        socketEngine->setReadNotificationEnabled(false);

    // If buffered, read data from the socket into the read buffer
    qint64 newBytes = 0;
    if (isBuffered) {
        // Return if there is no space in the buffer
        if (readBufferMaxSize && buffer.size() >= readBufferMaxSize) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocketPrivate::canReadNotification() buffer is full");
#endif
            return false;
        }

        // If reading from the socket fails after getting a read
        // notification, close the socket.
        newBytes = buffer.size();
        if (!readFromSocket()) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocketPrivate::canReadNotification() disconnecting socket");
#endif
            q->disconnectFromHost();
            return false;
        }
        newBytes = buffer.size() - newBytes;

        // If read buffer is full, disable the read socket notifier.
        if (readBufferMaxSize && buffer.size() == readBufferMaxSize) {
            socketEngine->setReadNotificationEnabled(false);
        }
    }

    // only emit readyRead() when not recursing, and only if there is data available
    bool hasData = newBytes > 0
#ifndef QT_NO_UDPSOCKET
        || (!isBuffered && socketType != QAbstractSocket::TcpSocket && socketEngine && socketEngine->hasPendingDatagrams())
#endif
        || (!isBuffered && socketType == QAbstractSocket::TcpSocket && socketEngine)
        ;

    if (!emittedReadyRead && hasData) {
        QScopedValueRollback<bool> r(emittedReadyRead);
        emittedReadyRead = true;
        emit q->readyRead();
    }

    // If we were closed as a result of the readyRead() signal,
    // return.
    if (state == QAbstractSocket::UnconnectedState || state == QAbstractSocket::ClosingState) {
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::canReadNotification() socket is closing - returning");
#endif
        return true;
    }

    if ((isBuffered || socketType != QAbstractSocket::TcpSocket) && socketEngine)
        socketEngine->setReadNotificationEnabled(readBufferMaxSize == 0 || readBufferMaxSize > q->bytesAvailable());

    // reset the read socket notifier state if we reentered inside the
    // readyRead() connected slot.
    if (readSocketNotifierStateSet && socketEngine &&
        readSocketNotifierState != socketEngine->isReadNotificationEnabled()) {
        socketEngine->setReadNotificationEnabled(readSocketNotifierState);
        readSocketNotifierStateSet = false;
    }
    return true;
}

/*! \internal

    Slot connected to the close socket notifier. It's called when the
    socket is closed.
*/
void QAbstractSocketPrivate::canCloseNotification()
{
    Q_Q(QAbstractSocket);

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::canCloseNotification()");
#endif

    qint64 newBytes = 0;
    if (isBuffered) {
        // Try to read to the buffer, if the read fail we can close the socket.
        newBytes = buffer.size();
        if (!readFromSocket()) {
            q->disconnectFromHost();
            return;
        }
        newBytes = buffer.size() - newBytes;
        if (newBytes) {
            // If there was still some data to be read from the socket
            // then we could get another FD_READ. The disconnect will
            // then occur when we read from the socket again and fail
            // in canReadNotification or by the manually created
            // closeNotification below.
            emit q->readyRead();

            QMetaObject::invokeMethod(socketEngine, "closeNotification", Qt::QueuedConnection);
        }
    } else if (socketType == QAbstractSocket::TcpSocket && socketEngine) {
        emit q->readyRead();
    }
}


/*! \internal

    Slot connected to the write socket notifier. It's called during a
    delayed connect or when the socket is ready for writing.
*/
bool QAbstractSocketPrivate::canWriteNotification()
{
#if defined (Q_OS_WIN)
    if (socketEngine && socketEngine->isWriteNotificationEnabled())
        socketEngine->setWriteNotificationEnabled(false);
#endif

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::canWriteNotification() flushing");
#endif
    int tmp = writeBuffer.size();
    flush();

    if (socketEngine) {
#if defined (Q_OS_WIN)
        if (!writeBuffer.isEmpty())
            socketEngine->setWriteNotificationEnabled(true);
#else
        if (writeBuffer.isEmpty() && socketEngine->bytesToWrite() == 0)
            socketEngine->setWriteNotificationEnabled(false);
#endif
    }

    return (writeBuffer.size() < tmp);
}

/*! \internal

    Slot connected to a notification of connection status
    change. Either we finished connecting or we failed to connect.
*/
void QAbstractSocketPrivate::connectionNotification()
{
    // If in connecting state, check if the connection has been
    // established, otherwise flush pending data.
    if (state == QAbstractSocket::ConnectingState) {
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::connectionNotification() testing connection");
#endif
        _q_testConnection();
    }
}

/*! \internal

    Writes pending data in the write buffers to the socket. The
    function writes as much as it can without blocking.

    It is usually invoked by canWriteNotification after one or more
    calls to write().

    Emits bytesWritten().
*/
bool QAbstractSocketPrivate::flush()
{
    Q_Q(QAbstractSocket);
    if (!socketEngine || !socketEngine->isValid() || (writeBuffer.isEmpty()
        && socketEngine->bytesToWrite() == 0)) {
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::flush() nothing to do: valid ? %s, writeBuffer.isEmpty() ? %s",
           (socketEngine && socketEngine->isValid()) ? "yes" : "no", writeBuffer.isEmpty() ? "yes" : "no");
#endif

        // this covers the case when the buffer was empty, but we had to wait for the socket engine to finish
        if (state == QAbstractSocket::ClosingState)
            q->disconnectFromHost();

        return false;
    }

    int nextSize = writeBuffer.nextDataBlockSize();
    const char *ptr = writeBuffer.readPointer();

    // Attempt to write it all in one chunk.
    qint64 written = socketEngine->write(ptr, nextSize);
    if (written < 0) {
        socketError = socketEngine->error();
        q->setErrorString(socketEngine->errorString());
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug() << "QAbstractSocketPrivate::flush() write error, aborting." << socketEngine->errorString();
#endif
        emit q->error(socketError);
        // an unexpected error so close the socket.
        q->abort();
        return false;
    }

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::flush() %lld bytes written to the network",
           written);
#endif

    // Remove what we wrote so far.
    writeBuffer.free(written);
    if (written > 0) {
        // Don't emit bytesWritten() recursively.
        if (!emittedBytesWritten) {
            QScopedValueRollback<bool> r(emittedBytesWritten);
            emittedBytesWritten = true;
            emit q->bytesWritten(written);
        }
    }

    if (writeBuffer.isEmpty() && socketEngine && socketEngine->isWriteNotificationEnabled()
        && !socketEngine->bytesToWrite())
        socketEngine->setWriteNotificationEnabled(false);
    if (state == QAbstractSocket::ClosingState)
        q->disconnectFromHost();

    return true;
}

#ifndef QT_NO_NETWORKPROXY
/*! \internal

    Resolve the proxy to its final value.
*/
void QAbstractSocketPrivate::resolveProxy(const QString &hostname, quint16 port)
{
    QList<QNetworkProxy> proxies;

    if (proxy.type() != QNetworkProxy::DefaultProxy) {
        // a non-default proxy was set with setProxy
        proxies << proxy;
    } else {
        // try the application settings instead
        QNetworkProxyQuery query(hostname, port, QString(),
                                 socketType == QAbstractSocket::TcpSocket ?
                                 QNetworkProxyQuery::TcpSocket :
                                 QNetworkProxyQuery::UdpSocket);
        proxies = QNetworkProxyFactory::proxyForQuery(query);
    }

    // return the first that we can use
    foreach (const QNetworkProxy &p, proxies) {
        if (socketType == QAbstractSocket::UdpSocket &&
            (p.capabilities() & QNetworkProxy::UdpTunnelingCapability) == 0)
            continue;

        if (socketType == QAbstractSocket::TcpSocket &&
            (p.capabilities() & QNetworkProxy::TunnelingCapability) == 0)
            continue;

        proxyInUse = p;
        return;
    }

    // no proxy found
    // DefaultProxy here will raise an error
    proxyInUse = QNetworkProxy();
}

/*!
    \internal

    Starts the connection to \a host, like _q_startConnecting below,
    but without hostname resolution.
*/
void QAbstractSocketPrivate::startConnectingByName(const QString &host)
{
    Q_Q(QAbstractSocket);
    if (state == QAbstractSocket::ConnectingState || state == QAbstractSocket::ConnectedState)
        return;

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::startConnectingByName(host == %s)", qPrintable(host));
#endif

    // ### Let the socket engine drive this?
    state = QAbstractSocket::ConnectingState;
    emit q->stateChanged(state);

    connectTimeElapsed = 0;

    if (initSocketLayer(QAbstractSocket::UnknownNetworkLayerProtocol)) {
        if (socketEngine->connectToHostByName(host, port) ||
            socketEngine->state() == QAbstractSocket::ConnectingState) {
            cachedSocketDescriptor = socketEngine->socketDescriptor();

            return;
        }

        // failed to connect
        socketError = socketEngine->error();
        q->setErrorString(socketEngine->errorString());
    }

    state = QAbstractSocket::UnconnectedState;
    emit q->error(socketError);
    emit q->stateChanged(state);
}

#endif

/*! \internal

    Slot connected to QHostInfo::lookupHost() in connectToHost(). This
    function starts the process of connecting to any number of
    candidate IP addresses for the host, if it was found. Calls
    _q_connectToNextAddress().
*/
void QAbstractSocketPrivate::_q_startConnecting(const QHostInfo &hostInfo)
{
    Q_Q(QAbstractSocket);
    addresses.clear();
    if (state != QAbstractSocket::HostLookupState)
        return;

    if (hostLookupId != -1 && hostLookupId != hostInfo.lookupId()) {
        qWarning("QAbstractSocketPrivate::_q_startConnecting() received hostInfo for wrong lookup ID %d expected %d", hostInfo.lookupId(), hostLookupId);
    }

    // Only add the addresses for the preferred network layer.
    // Or all if preferred network layer is not set.
    if (preferredNetworkLayerProtocol == QAbstractSocket::UnknownNetworkLayerProtocol || preferredNetworkLayerProtocol == QAbstractSocket::AnyIPProtocol) {
        addresses = hostInfo.addresses();
    } else {
        foreach (const QHostAddress &address, hostInfo.addresses())
            if (address.protocol() == preferredNetworkLayerProtocol)
                addresses += address;
    }


#if defined(QABSTRACTSOCKET_DEBUG)
    QString s = QLatin1String("{");
    for (int i = 0; i < addresses.count(); ++i) {
        if (i != 0) s += QLatin1String(", ");
        s += addresses.at(i).toString();
    }
    s += QLatin1Char('}');
    qDebug("QAbstractSocketPrivate::_q_startConnecting(hostInfo == %s)", s.toLatin1().constData());
#endif

    // Try all addresses twice.
    addresses += addresses;

    // If there are no addresses in the host list, report this to the
    // user.
    if (addresses.isEmpty()) {
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::_q_startConnecting(), host not found");
#endif
        state = QAbstractSocket::UnconnectedState;
        socketError = QAbstractSocket::HostNotFoundError;
        q->setErrorString(QAbstractSocket::tr("Host not found"));
        emit q->stateChanged(state);
        emit q->error(QAbstractSocket::HostNotFoundError);
        return;
    }

    // Enter Connecting state (see also sn_write, which is called by
    // the write socket notifier after connect())
    state = QAbstractSocket::ConnectingState;
    emit q->stateChanged(state);

    // Report the successful host lookup
    emit q->hostFound();

    // Reset the total time spent connecting.
    connectTimeElapsed = 0;

    // The addresses returned by the lookup will be tested one after
    // another by _q_connectToNextAddress().
    _q_connectToNextAddress();
}

/*! \internal

    Called by a queued or direct connection from _q_startConnecting() or
    _q_testConnection(), this function takes the first address of the
    pending addresses list and tries to connect to it. If the
    connection succeeds, QAbstractSocket will emit
    connected(). Otherwise, error(ConnectionRefusedError) or
    error(SocketTimeoutError) is emitted.
*/
void QAbstractSocketPrivate::_q_connectToNextAddress()
{
    Q_Q(QAbstractSocket);
    do {
        // Check for more pending addresses
        if (addresses.isEmpty()) {
#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocketPrivate::_q_connectToNextAddress(), all addresses failed.");
#endif
            state = QAbstractSocket::UnconnectedState;
            if (socketEngine) {
                if ((socketEngine->error() == QAbstractSocket::UnknownSocketError
#ifdef Q_OS_AIX
                     // On AIX, the second connect call will result in EINVAL and not
                     // ECONNECTIONREFUSED; although the meaning is the same.
                     || socketEngine->error() == QAbstractSocket::UnsupportedSocketOperationError
#endif
                    ) && socketEngine->state() == QAbstractSocket::ConnectingState) {
                    socketError = QAbstractSocket::ConnectionRefusedError;
                    q->setErrorString(QAbstractSocket::tr("Connection refused"));
                } else {
                    socketError = socketEngine->error();
                    q->setErrorString(socketEngine->errorString());
                }
            } else {
//                socketError = QAbstractSocket::ConnectionRefusedError;
//                q->setErrorString(QAbstractSocket::tr("Connection refused"));
            }
            emit q->stateChanged(state);
            emit q->error(socketError);
            return;
        }

        // Pick the first host address candidate
        host = addresses.takeFirst();
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::_q_connectToNextAddress(), connecting to %s:%i, %d left to try",
               host.toString().toLatin1().constData(), port, addresses.count());
#endif

        if (!initSocketLayer(host.protocol())) {
            // hope that the next address is better
#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocketPrivate::_q_connectToNextAddress(), failed to initialize sock layer");
#endif
            continue;
        }

        // Tries to connect to the address. If it succeeds immediately
        // (localhost address on BSD or any UDP connect), emit
        // connected() and return.
        if (socketEngine->connectToHost(host, port)) {
            //_q_testConnection();
            fetchConnectionParameters();
            return;
        }

        // cache the socket descriptor even if we're not fully connected yet
        cachedSocketDescriptor = socketEngine->socketDescriptor();

        // Check that we're in delayed connection state. If not, try
        // the next address
        if (socketEngine->state() != QAbstractSocket::ConnectingState) {
#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocketPrivate::_q_connectToNextAddress(), connection failed (%s)",
                   socketEngine->errorString().toLatin1().constData());
#endif
            continue;
        }

        // Start the connect timer.
        if (threadData->hasEventDispatcher()) {
            if (!connectTimer) {
                connectTimer = new QTimer(q);
                QObject::connect(connectTimer, SIGNAL(timeout()),
                                 q, SLOT(_q_abortConnectionAttempt()),
                                 Qt::DirectConnection);
            }
            connectTimer->start(QT_CONNECT_TIMEOUT);
        }

        // Wait for a write notification that will eventually call
        // _q_testConnection().
        socketEngine->setWriteNotificationEnabled(true);
        break;
    } while (state != QAbstractSocket::ConnectedState);
}

/*! \internal

    Tests if a connection has been established. If it has, connected()
    is emitted. Otherwise, _q_connectToNextAddress() is invoked.
*/
void QAbstractSocketPrivate::_q_testConnection()
{
    if (socketEngine) {
        if (threadData->hasEventDispatcher()) {
            if (connectTimer)
                connectTimer->stop();
        }

        if (socketEngine->state() == QAbstractSocket::ConnectedState) {
            // Fetch the parameters if our connection is completed;
            // otherwise, fall out and try the next address.
            fetchConnectionParameters();
            if (pendingClose) {
                q_func()->disconnectFromHost();
                pendingClose = false;
            }
            return;
        }

        // don't retry the other addresses if we had a proxy error
        if (isProxyError(socketEngine->error()))
            addresses.clear();
    }

    if (threadData->hasEventDispatcher()) {
        if (connectTimer)
            connectTimer->stop();
    }

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::_q_testConnection() connection failed,"
           " checking for alternative addresses");
#endif
    _q_connectToNextAddress();
}

/*! \internal

    This function is called after a certain number of seconds has
    passed while waiting for a connection. It simply tests the
    connection, and continues to the next address if the connection
    failed.
*/
void QAbstractSocketPrivate::_q_abortConnectionAttempt()
{
    Q_Q(QAbstractSocket);
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::_q_abortConnectionAttempt() (timed out)");
#endif
    if (socketEngine)
        socketEngine->setWriteNotificationEnabled(false);

    connectTimer->stop();

    if (addresses.isEmpty()) {
        state = QAbstractSocket::UnconnectedState;
        socketError = QAbstractSocket::SocketTimeoutError;
        q->setErrorString(QAbstractSocket::tr("Connection timed out"));
        emit q->stateChanged(state);
        emit q->error(socketError);
    } else {
        _q_connectToNextAddress();
    }
}

void QAbstractSocketPrivate::_q_forceDisconnect()
{
    Q_Q(QAbstractSocket);
    if (socketEngine && socketEngine->isValid() && state == QAbstractSocket::ClosingState) {
        socketEngine->close();
        q->disconnectFromHost();
    }
}

/*! \internal

    Reads data from the socket layer into the read buffer. Returns
    true on success; otherwise false.
*/
bool QAbstractSocketPrivate::readFromSocket()
{
    Q_Q(QAbstractSocket);
    // Find how many bytes we can read from the socket layer.
    qint64 bytesToRead = socketEngine->bytesAvailable();
    if (bytesToRead == 0) {
        // Under heavy load, certain conditions can trigger read notifications
        // for socket notifiers on which there is no activity. If we continue
        // to read 0 bytes from the socket, we will trigger behavior similar
        // to that which signals a remote close. When we hit this condition,
        // we try to read 4k of data from the socket, which will give us either
        // an EAGAIN/EWOULDBLOCK if the connection is alive (i.e., the remote
        // host has _not_ disappeared).
        bytesToRead = 4096;
    }
    if (readBufferMaxSize && bytesToRead > (readBufferMaxSize - buffer.size()))
        bytesToRead = readBufferMaxSize - buffer.size();

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::readFromSocket() about to read %d bytes",
           int(bytesToRead));
#endif

    // Read from the socket, store data in the read buffer.
    char *ptr = buffer.reserve(bytesToRead);
    qint64 readBytes = socketEngine->read(ptr, bytesToRead);
    if (readBytes == -2) {
        // No bytes currently available for reading.
        buffer.chop(bytesToRead);
        return true;
    }
    buffer.chop(int(bytesToRead - (readBytes < 0 ? qint64(0) : readBytes)));
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::readFromSocket() got %d bytes, buffer size = %d",
           int(readBytes), buffer.size());
#endif

    if (!socketEngine->isValid()) {
        socketError = socketEngine->error();
        q->setErrorString(socketEngine->errorString());
        emit q->error(socketError);
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::readFromSocket() read failed: %s",
               q->errorString().toLatin1().constData());
#endif
        resetSocketLayer();
        return false;
    }

    return true;
}

/*! \internal

    Sets up the internal state after the connection has succeeded.
*/
void QAbstractSocketPrivate::fetchConnectionParameters()
{
    Q_Q(QAbstractSocket);

    peerName = hostName;
    if (socketEngine) {
        socketEngine->setReadNotificationEnabled(true);
        socketEngine->setWriteNotificationEnabled(true);
        localPort = socketEngine->localPort();
        peerPort = socketEngine->peerPort();
        localAddress = socketEngine->localAddress();
        peerAddress = socketEngine->peerAddress();
        cachedSocketDescriptor = socketEngine->socketDescriptor();
    }

    state = QAbstractSocket::ConnectedState;
    emit q->stateChanged(state);
    emit q->connected();

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::fetchConnectionParameters() connection to %s:%i established",
           host.toString().toLatin1().constData(), port);
#endif
}


void QAbstractSocketPrivate::pauseSocketNotifiers(QAbstractSocket *socket)
{
    QAbstractSocketEngine *socketEngine = socket->d_func()->socketEngine;
    if (!socketEngine)
        return;
    socket->d_func()->prePauseReadSocketNotifierState = socketEngine->isReadNotificationEnabled();
    socket->d_func()->prePauseWriteSocketNotifierState = socketEngine->isWriteNotificationEnabled();
    socket->d_func()->prePauseExceptionSocketNotifierState = socketEngine->isExceptionNotificationEnabled();
    socketEngine->setReadNotificationEnabled(false);
    socketEngine->setWriteNotificationEnabled(false);
    socketEngine->setExceptionNotificationEnabled(false);
}

void QAbstractSocketPrivate::resumeSocketNotifiers(QAbstractSocket *socket)
{
    QAbstractSocketEngine *socketEngine = socket->d_func()->socketEngine;
    if (!socketEngine)
        return;
    socketEngine->setReadNotificationEnabled(socket->d_func()->prePauseReadSocketNotifierState);
    socketEngine->setWriteNotificationEnabled(socket->d_func()->prePauseWriteSocketNotifierState);
    socketEngine->setExceptionNotificationEnabled(socket->d_func()->prePauseExceptionSocketNotifierState);
}

QAbstractSocketEngine* QAbstractSocketPrivate::getSocketEngine(QAbstractSocket *socket)
{
    return socket->d_func()->socketEngine;
}


/*! \internal

    Constructs a new abstract socket of type \a socketType. The \a
    parent …

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