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** Copyright (C) 2016 Intel Corporation.
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** ensure the GNU Lesser General Public License version 3 requirements
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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, errorOccurred() 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::UnconnectedState, 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 errorOccurred(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::errorOccurred(QAbstractSocket::SocketError socketError)
    \since 5.15

    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 SctpSocket SCTP
    \value UnknownSocketType Other than TCP, UDP and SCTP

    \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()
    \sa QAbstractSocket::errorOccurred()
*/

/*!
    \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.

    \value PathMtuSocketOption Retrieves the Path Maximum Transmission Unit
    (PMTU) value currently known by the IP stack, if any. Some IP stacks also
    allow setting the MTU for transmission.
    This enum value was introduced in Qt 5.11.

    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 is the default behavior, so 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 \macos, 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 and Unix, this is equivalent to the SO_REUSEADDR
    socket option.

    \value DefaultForPlatform The default option for the current platform.
    On Unix and \macos, this is equivalent to (DontShareAddress
    + ReuseAddressHint), and on Windows, it is 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 behavior of Qt 4.
    \value PauseOnSslErrors Pause data transfer on the socket upon receiving an
    SSL error notification. I.E. QSslSocket::sslErrors().
*/

#include <QtNetwork/private/qtnetworkglobal_p.h>

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

#include "private/qhostinfo_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>
#include <qvarlengtharray.h>

#include <private/qthread_p.h>

#ifdef QABSTRACTSOCKET_DEBUG
#include <qdebug.h>
#include <private/qdebug_p.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_TRANSFER_TIMEOUT 120000

QT_BEGIN_NAMESPACE

static const int DefaultConnectTimeout = 30000;

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()
    : emittedReadyRead(false),
      emittedBytesWritten(false),
      abortCalled(false),
      pendingClose(false),
      pauseMode(QAbstractSocket::PauseNever),
      port(0),
      localPort(0),
      peerPort(0),
      socketEngine(nullptr),
      cachedSocketDescriptor(-1),
      readBufferMaxSize(0),
      isBuffered(false),
      hasPendingData(false),
      connectTimer(nullptr),
      hostLookupId(-1),
      socketType(QAbstractSocket::UnknownSocketType),
      state(QAbstractSocket::UnconnectedState),
      socketError(QAbstractSocket::UnknownSocketError),
      preferredNetworkLayerProtocol(QAbstractSocket::UnknownNetworkLayerProtocol)
{
    writeBufferChunkSize = QABSTRACTSOCKET_BUFFERSIZE;
}

/*! \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

    hasPendingData = false;
    if (socketEngine) {
        socketEngine->close();
        socketEngine->disconnect();
        delete socketEngine;
        socketEngine = nullptr;
        cachedSocketDescriptor = -1;
    }
    if (connectTimer)
        connectTimer->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 if (q->socketType() == QAbstractSocket::SctpSocket) typeStr = QLatin1String("SctpSocket");
    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) {
        setError(QAbstractSocket::UnsupportedSocketOperationError,
                 QAbstractSocket::tr("Operation on socket is not supported"));
        return false;
    }
    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
        setError(socketEngine->error(), socketEngine->errorString());
        return false;
    }

    configureCreatedSocket();

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

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

/*! \internal
*/
void QAbstractSocketPrivate::configureCreatedSocket()
{
#ifndef QT_NO_SCTP
    Q_Q(QAbstractSocket);
    // Set single stream mode for unbuffered SCTP socket
    if (socketEngine && q->socketType() == QAbstractSocket::SctpSocket)
        socketEngine->setOption(QAbstractSocketEngine::MaxStreamsSocketOption, 1);
#endif
}

/*! \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

    // If buffered, read data from the socket into the read buffer
    if (isBuffered) {
        const qint64 oldBufferSize = buffer.size();

        // Return if there is no space in the buffer
        if (readBufferMaxSize && oldBufferSize >= readBufferMaxSize) {
            socketEngine->setReadNotificationEnabled(false);
#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.
        if (!readFromSocket()) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocketPrivate::canReadNotification() disconnecting socket");
#endif
            q->disconnectFromHost();
            return false;
        }

        // Return if there is no new data available.
        if (buffer.size() == oldBufferSize) {
            // If the socket is opened only for writing, return true
            // to indicate that the data was discarded.
            return !q->isReadable();
        }
    } else {
        if (hasPendingData) {
            socketEngine->setReadNotificationEnabled(false);
            return true;
        }
        hasPendingData = true;
    }

    emitReadyRead();

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

    return true;
}

/*! \internal

    Slot connected to the close socket notifier. It's called when the
    socket is closed.
*/
void QAbstractSocketPrivate::canCloseNotification()
{
    Q_Q(QAbstractSocket);
    // Note that this method is only called on Windows. Other platforms close in the canReadNotification()

#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();
        qint64 oldReadBufferMaxSize = readBufferMaxSize;
        readBufferMaxSize = 0; // temporarily disable max read buffer, we want to empty the OS buffer
        bool hadReadFromSocket = readFromSocket();
        readBufferMaxSize = oldReadBufferMaxSize;
        if (!hadReadFromSocket) {
            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.
            emitReadyRead();

            QMetaObject::invokeMethod(socketEngine, "closeNotification", Qt::QueuedConnection);
        }
    } else if ((socketType == QAbstractSocket::TcpSocket ||
                socketType == QAbstractSocket::SctpSocket) && socketEngine) {
        emitReadyRead();
    }
}


/*! \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 (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::canWriteNotification() flushing");
#endif

    return writeToSocket();
}

/*! \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 one pending data block in the write buffer to the socket.

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

    Emits bytesWritten().
*/
bool QAbstractSocketPrivate::writeToSocket()
{
    Q_Q(QAbstractSocket);
    if (!socketEngine || !socketEngine->isValid() || (writeBuffer.isEmpty()
        && socketEngine->bytesToWrite() == 0)) {
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::writeToSocket() 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();
        } else {
            if (socketEngine)
                socketEngine->setWriteNotificationEnabled(false);
        }

        return false;
    }

    qint64 nextSize = writeBuffer.nextDataBlockSize();
    const char *ptr = writeBuffer.readPointer();

    // Attempt to write it all in one chunk.
    qint64 written = nextSize ? socketEngine->write(ptr, nextSize) : Q_INT64_C(0);
    if (written < 0) {
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug() << "QAbstractSocketPrivate::writeToSocket() write error, aborting."
                 << socketEngine->errorString();
#endif
        setErrorAndEmit(socketEngine->error(), socketEngine->errorString());
        // an unexpected error so close the socket.
        q->abort();
        return false;
    }

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

    if (written > 0) {
        // Remove what we wrote so far.
        writeBuffer.free(written);

        // Emit notifications.
        emitBytesWritten(written);
    }

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

    return written > 0;
}

/*! \internal

    Writes pending data in the write buffers to the socket. The function
    writes as much as it can without blocking. If any data was written,
    this function returns true; otherwise false is returned.
*/
bool QAbstractSocketPrivate::flush()
{
    bool dataWasWritten = false;

    while (!allWriteBuffersEmpty() && writeToSocket())
        dataWasWritten = true;

    return dataWasWritten;
}

#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, protocolTag,
                                 socketType == QAbstractSocket::TcpSocket ?
                                 QNetworkProxyQuery::TcpSocket :
                                 socketType == QAbstractSocket::SctpSocket ?
                                 QNetworkProxyQuery::SctpSocket :
                                 QNetworkProxyQuery::UdpSocket);
        proxies = QNetworkProxyFactory::proxyForQuery(query);
    }

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

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

        if (socketType == QAbstractSocket::SctpSocket &&
            (p.capabilities() & QNetworkProxy::SctpTunnelingCapability) == 0)
            continue;

        proxyInUse = p;
        return;
    }

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

#if !defined(QT_NO_NETWORKPROXY)
/*!
    \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);

    if (cachedSocketDescriptor != -1 || initSocketLayer(QAbstractSocket::UnknownNetworkLayerProtocol)) {
        // Try to connect to the host. If it succeeds immediately
        // (e.g. QSocks5SocketEngine in UDPASSOCIATE mode), emit
        // connected() and return.
        if (socketEngine->connectToHostByName(host, port)) {
            fetchConnectionParameters();
            return;
        }

        if (socketEngine->state() == QAbstractSocket::ConnectingState)
            return;

        // failed to connect
        setError(socketEngine->error(), socketEngine->errorString());
    }

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

#endif // !QT_NO_NETWORKPROXY

/*! \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 {
        const auto candidates = hostInfo.addresses();
        for (const QHostAddress &address : candidates) {
            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;
        setError(QAbstractSocket::HostNotFoundError, QAbstractSocket::tr("Host not found"));
        emit q->stateChanged(state);
        emit q->errorOccurred(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();

    // 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, errorOccurred(ConnectionRefusedError) or
    errorOccurred(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) {
                    setError(QAbstractSocket::ConnectionRefusedError,
                             QAbstractSocket::tr("Connection refused"));
                } else {
                    setError(socketEngine->error(), socketEngine->errorString());
                }
            } else {
//                socketError = QAbstractSocket::ConnectionRefusedError;
//                q->setErrorString(QAbstractSocket::tr("Connection refused"));
            }
            emit q->stateChanged(state);
            emit q->errorOccurred(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 (cachedSocketDescriptor == -1 && !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;
        }

        // 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.loadRelaxed()->hasEventDispatcher()) {
            if (!connectTimer) {
                connectTimer = new QTimer(q);
                QObject::connect(connectTimer, SIGNAL(timeout()),
                                 q, SLOT(_q_abortConnectionAttempt()),
                                 Qt::DirectConnection);
            }
            int connectTimeout = DefaultConnectTimeout;
            connectTimer->start(connectTimeout);
        }

        // 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 (connectTimer)
        connectTimer->stop();

    if (socketEngine) {
        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 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;
        setError(QAbstractSocket::SocketTimeoutError,
                 QAbstractSocket::tr("Connection timed out"));
        emit q->stateChanged(state);
        emit q->errorOccurred(socketError);
    } else {
        _q_connectToNextAddress();
    }
}

/*! \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 (q->isReadable()) {
        if (readBufferMaxSize && bytesToRead > (readBufferMaxSize - buffer.size()))
            bytesToRead = readBufferMaxSize - buffer.size();

#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::readFromSocket() about to read %lld bytes",
               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(bytesToRead - (readBytes < 0 ? qint64(0) : readBytes));
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::readFromSocket() got %lld bytes, buffer size = %lld",
               readBytes, buffer.size());
#endif
    } else {
        // Discard unwanted data if opened in WriteOnly mode
        QVarLengthArray<char, 4096> discardBuffer(bytesToRead);

#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocketPrivate::readFromSocket() about to discard %lld bytes",
               bytesToRead);
#endif
        socketEngine->read(discardBuffer.data(), bytesToRead);
    }

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

    return true;
}

/*! \internal

    Emits readyRead(), protecting against recursion.
*/
void QAbstractSocketPrivate::emitReadyRead(int channel)
{
    Q_Q(QAbstractSocket);
    // Only emit readyRead() when not recursing.
    if (!emittedReadyRead && channel == currentReadChannel) {
        QScopedValueRollback<bool> r(emittedReadyRead);
        emittedReadyRead = true;
        emit q->readyRead();
    }
    // channelReadyRead() can be emitted recursively - even for the same channel.
    emit q->channelReadyRead(channel);
}

/*! \internal

    Emits bytesWritten(), protecting against recursion.
*/
void QAbstractSocketPrivate::emitBytesWritten(qint64 bytes, int channel)
{
    Q_Q(QAbstractSocket);
    // Only emit bytesWritten() when not recursing.
    if (!emittedBytesWritten && channel == currentWriteChannel) {
        QScopedValueRollback<bool> r(emittedBytesWritten);
        emittedBytesWritten = true;
        emit q->bytesWritten(bytes);
    }
    // channelBytesWritten() can be emitted recursively - even for the same channel.
    emit q->channelBytesWritten(channel, bytes);
}

/*! \internal

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

    peerName = hostName;
    if (socketEngine) {
        if (q->isReadable()) {
            const int inboundStreamCount = socketEngine->inboundStreamCount();
            setReadChannelCount(qMax(1, inboundStreamCount));
            if (inboundStreamCount == 0)
                readChannelCount = 0;
        }
        if (q->isWritable()) {
            const int outboundStreamCount = socketEngine->outboundStreamCount();
            setWriteChannelCount(qMax(1, outboundStreamCount));
            if (outboundStreamCount == 0)
                writeChannelCount = 0;
        }
        socketEngine->setReadNotificationEnabled(true);
        socketEngine->setWriteNotificationEnabled(true);
        localPort = socketEngine->localPort();
        peerPort = socketEngine->peerPort();
        localAddress = socketEngine->localAddress();
        peerAddress = socketEngine->peerAddress();
        cachedSocketDescriptor = socketEngine->socketDescriptor();
    }

    state = QAbstractSocket::ConnectedState;
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocketPrivate::fetchConnectionParameters() connection to %s:%i established",
           host.toString().toLatin1().constData(), port);
#endif
    emit q->stateChanged(state);
    emit q->connected();
}

/*! \reimp
*/
qint64 QAbstractSocket::skipData(qint64 maxSize)
{
    Q_D(const QAbstractSocket);

    // if we're not connected, return -1 indicating EOF
    if (!d->socketEngine || !d->socketEngine->isValid()
        || d->state != QAbstractSocket::ConnectedState)
        return -1;

    // Caller, QIODevice::skip(), has ensured buffer is empty. So, wait
    // for more data in buffered mode.
    if (d->isBuffered)
        return 0;

    return QIODevice::skipData(maxSize);
}

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

    Sets the socket error state to \c errorCode and \a errorString.
*/
void QAbstractSocketPrivate::setError(QAbstractSocket::SocketError errorCode,
                                      const QString &errStr)
{
    socketError = errorCode;
    errorString = errStr;
}

/*!
    \internal

    Sets the socket error state to \c errorCode and \a errorString,
    and emits the QAbstractSocket::errorOccurred() signal.
*/
void QAbstractSocketPrivate::setErrorAndEmit(QAbstractSocket::SocketError errorCode,
                                             const QString &errorString)
{
    Q_Q(QAbstractSocket);
    setError(errorCode, errorString);
    emit q->errorOccurred(errorCode);
}

/*! \internal

    Constructs a new abstract socket of type \a socketType. The \a
    parent argument is passed to QObject's constructor.
*/
QAbstractSocket::QAbstractSocket(SocketType socketType,
                                 QAbstractSocketPrivate &dd, QObject *parent)
    : QIODevice(dd, parent)
{
    Q_D(QAbstractSocket);
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::QAbstractSocket(%sSocket, QAbstractSocketPrivate == %p, parent == %p)",
           socketType == TcpSocket ? "Tcp" : socketType == UdpSocket ? "Udp"
           : socketType == SctpSocket ? "Sctp" : "Unknown", &dd, parent);
#endif
    d->socketType = socketType;
}

/*!
    Creates a new abstract socket of type \a socketType. The \a
    parent argument is passed to QObject's constructor.

    \sa socketType(), QTcpSocket, QUdpSocket
*/
QAbstractSocket::QAbstractSocket(SocketType socketType, QObject *parent)
    : QAbstractSocket(socketType, *new QAbstractSocketPrivate, parent)
{
}

/*!
    Destroys the socket.
*/
QAbstractSocket::~QAbstractSocket()
{
    Q_D(QAbstractSocket);
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::~QAbstractSocket()");
#endif
    if (d->state != UnconnectedState)
        abort();
}

/*!
    \since 5.0

    Continues data transfer on the socket. This method should only be used
    after the socket has been set to pause upon notifications and a
    notification has been received.
    The only notification currently supported is QSslSocket::sslErrors().
    Calling this method if the socket is not paused results in undefined
    behavior.

    \sa pauseMode(), setPauseMode()
*/
void QAbstractSocket::resume()
{
    QAbstractSocketPrivate::resumeSocketNotifiers(this);
}

/*!
    \since 5.0

    Returns the pause mode of this socket.

    \sa setPauseMode(), resume()
*/
QAbstractSocket::PauseModes QAbstractSocket::pauseMode() const
{
    return d_func()->pauseMode;
}


/*!
    \since 5.0

    Controls whether to pause upon receiving a notification. The \a pauseMode parameter
    specifies the conditions in which the socket should be paused. The only notification
    currently supported is QSslSocket::sslErrors(). If set to PauseOnSslErrors,
    data transfer on the socket will be paused and needs to be enabled explicitly
    again by calling resume().
    By default this option is set to PauseNever.
    This option must be called before connecting to the server, otherwise it will
    result in undefined behavior.

    \sa pauseMode(), resume()
*/
void QAbstractSocket::setPauseMode(PauseModes pauseMode)
{
    d_func()->pauseMode = pauseMode;
}

/*!
    \since 5.0

    Binds to \a address on port \a port, using the BindMode \a mode.

    For UDP sockets, after binding, the signal QUdpSocket::readyRead() is emitted
    whenever a UDP datagram arrives on the specified address and port.
    Thus, this function is useful to write UDP servers.

    For TCP sockets, this function may be used to specify which interface to use
    for an outgoing connection, which is useful in case of multiple network
    interfaces.

    By default, the socket is bound using the DefaultForPlatform BindMode.
    If a port is not specified, a random port is chosen.

    On success, the function returns \c true and the socket enters
    BoundState; otherwise it returns \c false.

*/
bool QAbstractSocket::bind(const QHostAddress &address, quint16 port, BindMode mode)
{
    Q_D(QAbstractSocket);
    return d->bind(address, port, mode);
}

bool QAbstractSocketPrivate::bind(const QHostAddress &address, quint16 port, QAbstractSocket::BindMode mode)
{
    Q_Q(QAbstractSocket);

    // now check if the socket engine is initialized and to the right type
    if (!socketEngine || !socketEngine->isValid()) {
        QHostAddress nullAddress;
        resolveProxy(nullAddress.toString(), port);

        QAbstractSocket::NetworkLayerProtocol protocol = address.protocol();
        if (protocol == QAbstractSocket::UnknownNetworkLayerProtocol)
            protocol = nullAddress.protocol();

        if (!initSocketLayer(protocol))
            return false;
    }

    if (mode != QAbstractSocket::DefaultForPlatform) {
#ifdef Q_OS_UNIX
    if ((mode & QAbstractSocket::ShareAddress) || (mode & QAbstractSocket::ReuseAddressHint))
        socketEngine->setOption(QAbstractSocketEngine::AddressReusable, 1);
    else
        socketEngine->setOption(QAbstractSocketEngine::AddressReusable, 0);
#endif
#ifdef Q_OS_WIN
    if (mode & QAbstractSocket::ReuseAddressHint)
        socketEngine->setOption(QAbstractSocketEngine::AddressReusable, 1);
    else
        socketEngine->setOption(QAbstractSocketEngine::AddressReusable, 0);
    if (mode & QAbstractSocket::DontShareAddress)
        socketEngine->setOption(QAbstractSocketEngine::BindExclusively, 1);
    else
        socketEngine->setOption(QAbstractSocketEngine::BindExclusively, 0);
#endif
    }
    bool result = socketEngine->bind(address, port);
    cachedSocketDescriptor = socketEngine->socketDescriptor();

    if (!result) {
        setErrorAndEmit(socketEngine->error(), socketEngine->errorString());
        return false;
    }

    state = QAbstractSocket::BoundState;
    localAddress = socketEngine->localAddress();
    localPort = socketEngine->localPort();

    emit q->stateChanged(state);
    // A slot attached to stateChanged() signal can break our invariant:
    // by closing the socket it will reset its socket engine - thus we
    // have additional check (isValid()) ...
    if (q->isValid() && socketType == QAbstractSocket::UdpSocket)
        socketEngine->setReadNotificationEnabled(true);
    return true;
}

/*!
    \fn bool QAbstractSocket::bind(QHostAddress::SpecialAddress addr, quint16 port, BindMode mode)
    \since 6.2
    \overload

    Binds to the special address \a addr on port \a port, using the BindMode \a
    mode.

    By default, the socket is bound using the DefaultForPlatform BindMode.
    If a port is not specified, a random port is chosen.
*/

/*!
    \fn bool QAbstractSocket::bind(quint16 port, BindMode mode)
    \since 5.0
    \overload

    Binds to QHostAddress:Any on port \a port, using the BindMode \a mode.

    By default, the socket is bound using the DefaultForPlatform BindMode.
    If a port is not specified, a random port is chosen.
*/
#if QT_VERSION < QT_VERSION_CHECK(7, 0, 0)
bool QAbstractSocket::bind(quint16 port, BindMode mode)
{
    return bind(QHostAddress::Any, port, mode);
}
#endif

/*!
    Returns \c true if the socket is valid and ready for use; otherwise
    returns \c false.

    \note The socket's state must be ConnectedState before reading and
    writing can occur.

    \sa state()
*/
bool QAbstractSocket::isValid() const
{
    return d_func()->socketEngine ? d_func()->socketEngine->isValid() : isOpen();
}

/*!
    Attempts to make a connection to \a hostName on the given \a port.
    The \a protocol parameter can be used to specify which network
    protocol to use (eg. IPv4 or IPv6).

    The socket is opened in the given \a openMode and first enters
    HostLookupState, then performs a host name lookup of \a hostName.
    If the lookup succeeds, hostFound() is emitted and QAbstractSocket
    enters ConnectingState. It then attempts to connect to the address
    or addresses returned by the lookup. Finally, if a connection is
    established, QAbstractSocket enters ConnectedState and
    emits connected().

    At any point, the socket can emit errorOccurred() to signal that an error
    occurred.

    \a hostName may be an IP address in string form (e.g.,
    "43.195.83.32"), or it may be a host name (e.g.,
    "example.com"). QAbstractSocket will do a lookup only if
    required. \a port is in native byte order.

    \sa state(), peerName(), peerAddress(), peerPort(), waitForConnected()
*/
void QAbstractSocket::connectToHost(const QString &hostName, quint16 port,
                                    OpenMode openMode,
                                    NetworkLayerProtocol protocol)
{
    Q_D(QAbstractSocket);
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::connectToHost(\"%s\", %i, %i)...", qPrintable(hostName), port,
           (int) openMode);
#endif

    if (d->state == ConnectedState || d->state == ConnectingState
        || d->state == ClosingState || d->state == HostLookupState) {
        qWarning("QAbstractSocket::connectToHost() called when already looking up or connecting/connected to \"%s\"", qPrintable(hostName));
        d->setErrorAndEmit(OperationError, tr("Trying to connect while connection is in progress"));
        return;
    }

    d->preferredNetworkLayerProtocol = protocol;
    d->hostName = hostName;
    d->port = port;
    d->setReadChannelCount(0);
    d->setWriteChannelCount(0);
    d->abortCalled = false;
    d->pendingClose = false;
    if (d->state != BoundState) {
        d->state = UnconnectedState;
        d->localPort = 0;
        d->localAddress.clear();
    }
    d->peerPort = 0;
    d->peerAddress.clear();
    d->peerName = hostName;
    if (d->hostLookupId != -1) {
        QHostInfo::abortHostLookup(d->hostLookupId);
        d->hostLookupId = -1;
    }

#ifndef QT_NO_NETWORKPROXY
    // Get the proxy information
    d->resolveProxy(hostName, port);
    if (d->proxyInUse.type() == QNetworkProxy::DefaultProxy) {
        // failed to setup the proxy
        d->setErrorAndEmit(UnsupportedSocketOperationError,
                           tr("Operation on socket is not supported"));
        return;
    }
#endif

    // Sync up with error string, which open() shall clear.
    d->socketError = UnknownSocketError;
    if (openMode & QIODevice::Unbuffered)
        d->isBuffered = false;
    else if (!d_func()->isBuffered)
        openMode |= QAbstractSocket::Unbuffered;

    QIODevice::open(openMode);
    d->readChannelCount = d->writeChannelCount = 0;

    d->state = HostLookupState;
    emit stateChanged(d->state);

    QHostAddress temp;
    if (temp.setAddress(hostName)) {
        QHostInfo info;
        info.setAddresses(QList<QHostAddress>() << temp);
        d->_q_startConnecting(info);
#ifndef QT_NO_NETWORKPROXY
    } else if (d->proxyInUse.capabilities() & QNetworkProxy::HostNameLookupCapability) {
        // the proxy supports connection by name, so use it
        d->startConnectingByName(hostName);
        return;
#endif
    } else {
        if (d->threadData.loadRelaxed()->hasEventDispatcher()) {
            // this internal API for QHostInfo either immediately gives us the desired
            // QHostInfo from cache or later calls the _q_startConnecting slot.
            bool immediateResultValid = false;
            QHostInfo hostInfo = qt_qhostinfo_lookup(hostName,
                                                     this,
                                                     SLOT(_q_startConnecting(QHostInfo)),
                                                     &immediateResultValid,
                                                     &d->hostLookupId);
            if (immediateResultValid) {
                d->hostLookupId = -1;
                d->_q_startConnecting(hostInfo);
            }
        }
    }

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::connectToHost(\"%s\", %i) == %s%s", hostName.toLatin1().constData(), port,
           (d->state == ConnectedState) ? "true" : "false",
           (d->state == ConnectingState || d->state == HostLookupState)
           ? " (connection in progress)" : "");
#endif
}

/*! \overload

    Attempts to make a connection to \a address on port \a port.
*/
void QAbstractSocket::connectToHost(const QHostAddress &address, quint16 port,
                                    OpenMode openMode)
{
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::connectToHost([%s], %i, %i)...",
           address.toString().toLatin1().constData(), port, (int) openMode);
#endif
    connectToHost(address.toString(), port, openMode);
}

/*!
    Returns the number of bytes that are waiting to be written. The
    bytes are written when control goes back to the event loop or
    when flush() is called.

    \sa bytesAvailable(), flush()
*/
qint64 QAbstractSocket::bytesToWrite() const
{
    const qint64 pendingBytes = QIODevice::bytesToWrite();
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::bytesToWrite() == %lld", pendingBytes);
#endif
    return pendingBytes;
}

/*!
    Returns the number of incoming bytes that are waiting to be read.

    \sa bytesToWrite(), read()
*/
qint64 QAbstractSocket::bytesAvailable() const
{
    Q_D(const QAbstractSocket);
    qint64 available = QIODevice::bytesAvailable();

    if (!d->isBuffered && d->socketEngine && d->socketEngine->isValid())
        available += d->socketEngine->bytesAvailable();

#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::bytesAvailable() == %lld", available);
#endif
    return available;
}

/*!
    Returns the host port number (in native byte order) of the local
    socket if available; otherwise returns 0.

    \sa localAddress(), peerPort(), setLocalPort()
*/
quint16 QAbstractSocket::localPort() const
{
    Q_D(const QAbstractSocket);
    return d->localPort;
}

/*!
    Returns the host address of the local socket if available;
    otherwise returns QHostAddress::Null.

    This is normally the main IP address of the host, but can be
    QHostAddress::LocalHost (127.0.0.1) for connections to the
    local host.

    \sa localPort(), peerAddress(), setLocalAddress()
*/
QHostAddress QAbstractSocket::localAddress() const
{
    Q_D(const QAbstractSocket);
    return d->localAddress;
}

/*!
    Returns the port of the connected peer if the socket is in
    ConnectedState; otherwise returns 0.

    \sa peerAddress(), localPort(), setPeerPort()
*/
quint16 QAbstractSocket::peerPort() const
{
    Q_D(const QAbstractSocket);
    return d->peerPort;
}

/*!
    Returns the address of the connected peer if the socket is in
    ConnectedState; otherwise returns QHostAddress::Null.

    \sa peerName(), peerPort(), localAddress(), setPeerAddress()
*/
QHostAddress QAbstractSocket::peerAddress() const
{
    Q_D(const QAbstractSocket);
    return d->peerAddress;
}

/*!
    Returns the name of the peer as specified by connectToHost(), or
    an empty QString if connectToHost() has not been called.

    \sa peerAddress(), peerPort(), setPeerName()
*/
QString QAbstractSocket::peerName() const
{
    Q_D(const QAbstractSocket);
    return d->peerName.isEmpty() ? d->hostName : d->peerName;
}

/*!
    Returns the native socket descriptor of the QAbstractSocket object
    if this is available; otherwise returns -1.

    If the socket is using QNetworkProxy, the returned descriptor
    may not be usable with native socket functions.

    The socket descriptor is not available when QAbstractSocket is in
    UnconnectedState.

    \sa setSocketDescriptor()
*/
qintptr QAbstractSocket::socketDescriptor() const
{
    Q_D(const QAbstractSocket);
    return d->cachedSocketDescriptor;
}

/*!
    Initializes QAbstractSocket with the native socket descriptor \a
    socketDescriptor. Returns \c true if \a socketDescriptor is accepted
    as a valid socket descriptor; otherwise returns \c false.
    The socket is opened in the mode specified by \a openMode, and
    enters the socket state specified by \a socketState.
    Read and write buffers are cleared, discarding any pending data.

    \b{Note:} It is not possible to initialize two abstract sockets
    with the same native socket descriptor.

    \sa socketDescriptor()
*/
bool QAbstractSocket::setSocketDescriptor(qintptr socketDescriptor, SocketState socketState,
                                          OpenMode openMode)
{
    Q_D(QAbstractSocket);

    d->resetSocketLayer();
    d->setReadChannelCount(0);
    d->setWriteChannelCount(0);
    d->socketEngine = QAbstractSocketEngine::createSocketEngine(socketDescriptor, this);
    if (!d->socketEngine) {
        d->setError(UnsupportedSocketOperationError, tr("Operation on socket is not supported"));
        return false;
    }
    bool result = d->socketEngine->initialize(socketDescriptor, socketState);
    if (!result) {
        d->setError(d->socketEngine->error(), d->socketEngine->errorString());
        return false;
    }

    // Sync up with error string, which open() shall clear.
    d->socketError = UnknownSocketError;
    if (d->threadData.loadRelaxed()->hasEventDispatcher())
        d->socketEngine->setReceiver(d);

    QIODevice::open(openMode);

    if (socketState == ConnectedState) {
        if (isReadable()) {
            const int inboundStreamCount = d->socketEngine->inboundStreamCount();
            d->setReadChannelCount(qMax(1, inboundStreamCount));
            if (inboundStreamCount == 0)
                d->readChannelCount = 0;
        }
        if (isWritable()) {
            const int outboundStreamCount = d->socketEngine->outboundStreamCount();
            d->setWriteChannelCount(qMax(1, outboundStreamCount));
            if (outboundStreamCount == 0)
                d->writeChannelCount = 0;
        }
    } else {
        d->readChannelCount = d->writeChannelCount = 0;
    }

    if (d->state != socketState) {
        d->state = socketState;
        emit stateChanged(d->state);
    }

    d->pendingClose = false;
    d->socketEngine->setReadNotificationEnabled(true);
    d->localPort = d->socketEngine->localPort();
    d->peerPort = d->socketEngine->peerPort();
    d->localAddress = d->socketEngine->localAddress();
    d->peerAddress = d->socketEngine->peerAddress();
    d->cachedSocketDescriptor = socketDescriptor;

    return true;
}

/*!
    \since 4.6
    Sets the given \a option to the value described by \a value.

    \note On Windows Runtime, QAbstractSocket::KeepAliveOption must be set
    before the socket is connected.

    \sa socketOption()
*/
void QAbstractSocket::setSocketOption(QAbstractSocket::SocketOption option, const QVariant &value)
{
    if (!d_func()->socketEngine)
        return;

    switch (option) {
        case LowDelayOption:
            d_func()->socketEngine->setOption(QAbstractSocketEngine::LowDelayOption, value.toInt());
            break;

        case KeepAliveOption:
            d_func()->socketEngine->setOption(QAbstractSocketEngine::KeepAliveOption, value.toInt());
            break;

        case MulticastTtlOption:
                d_func()->socketEngine->setOption(QAbstractSocketEngine::MulticastTtlOption, value.toInt());
                break;

        case MulticastLoopbackOption:
                d_func()->socketEngine->setOption(QAbstractSocketEngine::MulticastLoopbackOption, value.toInt());
                break;

        case TypeOfServiceOption:
            d_func()->socketEngine->setOption(QAbstractSocketEngine::TypeOfServiceOption, value.toInt());
            break;

        case SendBufferSizeSocketOption:
            d_func()->socketEngine->setOption(QAbstractSocketEngine::SendBufferSocketOption, value.toInt());
            break;

        case ReceiveBufferSizeSocketOption:
            d_func()->socketEngine->setOption(QAbstractSocketEngine::ReceiveBufferSocketOption, value.toInt());
            break;

        case PathMtuSocketOption:
            d_func()->socketEngine->setOption(QAbstractSocketEngine::PathMtuInformation, value.toInt());
            break;
    }
}

/*!
    \since 4.6
    Returns the value of the \a option option.

    \sa setSocketOption()
*/
QVariant QAbstractSocket::socketOption(QAbstractSocket::SocketOption option)
{
    if (!d_func()->socketEngine)
        return QVariant();

    int ret = -1;
    switch (option) {
        case LowDelayOption:
            ret = d_func()->socketEngine->option(QAbstractSocketEngine::LowDelayOption);
            break;

        case KeepAliveOption:
            ret = d_func()->socketEngine->option(QAbstractSocketEngine::KeepAliveOption);
            break;

        case MulticastTtlOption:
                ret = d_func()->socketEngine->option(QAbstractSocketEngine::MulticastTtlOption);
                break;
        case MulticastLoopbackOption:
                ret = d_func()->socketEngine->option(QAbstractSocketEngine::MulticastLoopbackOption);
                break;

        case TypeOfServiceOption:
                ret = d_func()->socketEngine->option(QAbstractSocketEngine::TypeOfServiceOption);
                break;

        case SendBufferSizeSocketOption:
                ret = d_func()->socketEngine->option(QAbstractSocketEngine::SendBufferSocketOption);
                break;

        case ReceiveBufferSizeSocketOption:
                ret = d_func()->socketEngine->option(QAbstractSocketEngine::ReceiveBufferSocketOption);
                break;

        case PathMtuSocketOption:
                ret = d_func()->socketEngine->option(QAbstractSocketEngine::PathMtuInformation);
                break;
    }
    if (ret == -1)
        return QVariant();
    else
        return QVariant(ret);
}

/*!
    Waits until the socket is connected, up to \a msecs
    milliseconds. If the connection has been established, this
    function returns \c true; otherwise it returns \c false. In the case
    where it returns \c false, you can call error() to determine
    the cause of the error.

    The following example waits up to one second for a connection
    to be established:

    \snippet code/src_network_socket_qabstractsocket.cpp 0

    If msecs is -1, this function will not time out.

    \note This function may wait slightly longer than \a msecs,
    depending on the time it takes to complete the host lookup.

    \note Multiple calls to this functions do not accumulate the time.
    If the function times out, the connecting process will be aborted.

    \note This function may fail randomly on Windows. Consider using the event
    loop and the connected() signal if your software will run on Windows.

    \sa connectToHost(), connected()
*/
bool QAbstractSocket::waitForConnected(int msecs)
{
    Q_D(QAbstractSocket);
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::waitForConnected(%i)", msecs);
#endif

    if (state() == ConnectedState) {
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::waitForConnected(%i) already connected", msecs);
#endif
        return true;
    }

    bool wasPendingClose = d->pendingClose;
    d->pendingClose = false;
    QElapsedTimer stopWatch;
    stopWatch.start();

    if (d->state == HostLookupState) {
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::waitForConnected(%i) doing host name lookup", msecs);
#endif
        QHostInfo::abortHostLookup(d->hostLookupId);
        d->hostLookupId = -1;
        QHostAddress temp;
        if (temp.setAddress(d->hostName)) {
            QHostInfo info;
            info.setAddresses(QList<QHostAddress>() << temp);
            d->_q_startConnecting(info);
        } else {
            d->_q_startConnecting(QHostInfo::fromName(d->hostName));
        }
    }
    if (state() == UnconnectedState)
        return false; // connect not im progress anymore!

    int connectTimeout = DefaultConnectTimeout;
    bool timedOut = true;
#if defined (QABSTRACTSOCKET_DEBUG)
    int attempt = 1;
#endif
    while (state() == ConnectingState && (msecs == -1 || stopWatch.elapsed() < msecs)) {
        int timeout = qt_subtract_from_timeout(msecs, stopWatch.elapsed());
        if (msecs != -1 && timeout > connectTimeout)
            timeout = connectTimeout;
#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::waitForConnected(%i) waiting %.2f secs for connection attempt #%i",
               msecs, timeout / 1000.0, attempt++);
#endif
        timedOut = false;

        if (d->socketEngine && d->socketEngine->waitForWrite(timeout, &timedOut) && !timedOut) {
            d->_q_testConnection();
        } else {
            d->_q_connectToNextAddress();
        }
    }

    if ((timedOut && state() != ConnectedState) || state() == ConnectingState) {
        d->setError(SocketTimeoutError, tr("Socket operation timed out"));
        d->state = UnconnectedState;
        emit stateChanged(d->state);
        d->resetSocketLayer();
    }

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::waitForConnected(%i) == %s", msecs,
           state() == ConnectedState ? "true" : "false");
#endif
    if (state() != ConnectedState)
        return false;
    if (wasPendingClose)
        disconnectFromHost();
    return true;
}

/*!
    This function blocks until new data is available for reading and the
    \l{QIODevice::}{readyRead()} signal has been emitted. The function
    will timeout after \a msecs milliseconds; the default timeout is
    30000 milliseconds.

    The function returns \c true if the readyRead() signal is emitted and
    there is new data available for reading; otherwise it returns \c false
    (if an error occurred or the operation timed out).

    \note This function may fail randomly on Windows. Consider using the event
    loop and the readyRead() signal if your software will run on Windows.

    \sa waitForBytesWritten()
*/
bool QAbstractSocket::waitForReadyRead(int msecs)
{
    Q_D(QAbstractSocket);
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::waitForReadyRead(%i)", msecs);
#endif

    // require calling connectToHost() before waitForReadyRead()
    if (state() == UnconnectedState) {
        /* If all you have is a QIODevice pointer to an abstractsocket, you cannot check
           this, so you cannot avoid this warning. */
//        qWarning("QAbstractSocket::waitForReadyRead() is not allowed in UnconnectedState");
        return false;
    }

    QElapsedTimer stopWatch;
    stopWatch.start();

    // handle a socket in connecting state
    if (state() == HostLookupState || state() == ConnectingState) {
        if (!waitForConnected(msecs))
            return false;
    }

    do {
        if (state() != ConnectedState && state() != BoundState)
            return false;
        Q_ASSERT(d->socketEngine);

        bool readyToRead = false;
        bool readyToWrite = false;
        if (!d->socketEngine->waitForReadOrWrite(&readyToRead, &readyToWrite, true, !d->writeBuffer.isEmpty(),
                                               qt_subtract_from_timeout(msecs, stopWatch.elapsed()))) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::waitForReadyRead(%i) failed (%i, %s)",
                   msecs, d->socketEngine->error(), d->socketEngine->errorString().toLatin1().constData());
#endif
            d->setErrorAndEmit(d->socketEngine->error(), d->socketEngine->errorString());
            if (d->socketError != SocketTimeoutError)
                close();
            return false;
        }

        if (readyToRead) {
            if (d->canReadNotification())
                return true;
        }

        if (readyToWrite)
            d->canWriteNotification();
    } while (msecs == -1 || qt_subtract_from_timeout(msecs, stopWatch.elapsed()) > 0);
    return false;
}

/*! \reimp

    This function blocks until at least one byte has been written on the socket
    and the \l{QIODevice::}{bytesWritten()} signal has been emitted. The
    function will timeout after \a msecs milliseconds; the default timeout is
    30000 milliseconds.

    The function returns \c true if the bytesWritten() signal is emitted;
    otherwise it returns \c false (if an error occurred or the operation timed
    out).

    \note This function may fail randomly on Windows. Consider using the event
    loop and the bytesWritten() signal if your software will run on Windows.

    \sa waitForReadyRead()
 */
bool QAbstractSocket::waitForBytesWritten(int msecs)
{
    Q_D(QAbstractSocket);
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::waitForBytesWritten(%i)", msecs);
#endif

    // require calling connectToHost() before waitForBytesWritten()
    if (state() == UnconnectedState) {
        qWarning("QAbstractSocket::waitForBytesWritten() is not allowed in UnconnectedState");
        return false;
    }

    if (d->writeBuffer.isEmpty())
        return false;

    QElapsedTimer stopWatch;
    stopWatch.start();

    // handle a socket in connecting state
    if (state() == HostLookupState || state() == ConnectingState) {
        if (!waitForConnected(msecs))
            return false;
    }

    forever {
        bool readyToRead = false;
        bool readyToWrite = false;
        if (!d->socketEngine->waitForReadOrWrite(&readyToRead, &readyToWrite,
                                  !d->readBufferMaxSize || d->buffer.size() < d->readBufferMaxSize,
                                  !d->writeBuffer.isEmpty(),
                                  qt_subtract_from_timeout(msecs, stopWatch.elapsed()))) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::waitForBytesWritten(%i) failed (%i, %s)",
                   msecs, d->socketEngine->error(), d->socketEngine->errorString().toLatin1().constData());
#endif
            d->setErrorAndEmit(d->socketEngine->error(), d->socketEngine->errorString());
            if (d->socketError != SocketTimeoutError)
                close();
            return false;
        }

        if (readyToRead) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::waitForBytesWritten calls canReadNotification");
#endif
            d->canReadNotification();
        }


        if (readyToWrite) {
            if (d->canWriteNotification()) {
#if defined (QABSTRACTSOCKET_DEBUG)
                qDebug("QAbstractSocket::waitForBytesWritten returns true");
#endif
                return true;
            }
        }

        if (state() != ConnectedState)
            return false;
    }
    return false;
}

/*!
    Waits until the socket has disconnected, up to \a msecs milliseconds. If the
    connection was successfully disconnected, this function returns \c true;
    otherwise it returns \c false (if the operation timed out, if an error
    occurred, or if this QAbstractSocket is already disconnected). In the case
    where it returns \c false, you can call error() to determine the cause of
    the error.

    The following example waits up to one second for a connection
    to be closed:

    \snippet code/src_network_socket_qabstractsocket.cpp 1

    If msecs is -1, this function will not time out.

    \note This function may fail randomly on Windows. Consider using the event
    loop and the disconnected() signal if your software will run on Windows.

    \sa disconnectFromHost(), close()
*/
bool QAbstractSocket::waitForDisconnected(int msecs)
{
    Q_D(QAbstractSocket);

    // require calling connectToHost() before waitForDisconnected()
    if (state() == UnconnectedState) {
        qWarning("QAbstractSocket::waitForDisconnected() is not allowed in UnconnectedState");
        return false;
    }

    QElapsedTimer stopWatch;
    stopWatch.start();

    // handle a socket in connecting state
    if (state() == HostLookupState || state() == ConnectingState) {
        if (!waitForConnected(msecs))
            return false;
        if (state() == UnconnectedState)
            return true;
    }

    forever {
        bool readyToRead = false;
        bool readyToWrite = false;
        if (!d->socketEngine->waitForReadOrWrite(&readyToRead, &readyToWrite, state() == ConnectedState,
                                               !d->writeBuffer.isEmpty(),
                                               qt_subtract_from_timeout(msecs, stopWatch.elapsed()))) {
#if defined (QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::waitForReadyRead(%i) failed (%i, %s)",
                   msecs, d->socketEngine->error(), d->socketEngine->errorString().toLatin1().constData());
#endif
            d->setErrorAndEmit(d->socketEngine->error(), d->socketEngine->errorString());
            if (d->socketError != SocketTimeoutError)
                close();
            return false;
        }

        if (readyToRead)
            d->canReadNotification();
        if (readyToWrite)
            d->canWriteNotification();

        if (state() == UnconnectedState)
            return true;
    }
    return false;
}

/*!
    Aborts the current connection and resets the socket. Unlike disconnectFromHost(),
    this function immediately closes the socket, discarding any pending data in the
    write buffer.

    \sa disconnectFromHost(), close()
*/
void QAbstractSocket::abort()
{
    Q_D(QAbstractSocket);
#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::abort()");
#endif
    d->setWriteChannelCount(0);
    d->abortCalled = true;
    close();
}

/*! \reimp
*/
bool QAbstractSocket::isSequential() const
{
    return true;
}

/*!
    This function writes as much as possible from the internal write buffer to
    the underlying network socket, without blocking. If any data was written,
    this function returns \c true; otherwise false is returned.

    Call this function if you need QAbstractSocket to start sending buffered
    data immediately. The number of bytes successfully written depends on the
    operating system. In most cases, you do not need to call this function,
    because QAbstractSocket will start sending data automatically once control
    goes back to the event loop. In the absence of an event loop, call
    waitForBytesWritten() instead.

    \sa write(), waitForBytesWritten()
*/
bool QAbstractSocket::flush()
{
    return d_func()->flush();
}

/*! \reimp
*/
qint64 QAbstractSocket::readData(char *data, qint64 maxSize)
{
    Q_D(QAbstractSocket);

    // if we're not connected, return -1 indicating EOF
    if (!d->socketEngine || !d->socketEngine->isValid() || d->state != QAbstractSocket::ConnectedState)
        return maxSize ? qint64(-1) : qint64(0);

    qint64 readBytes = (maxSize && !d->isBuffered) ? d->socketEngine->read(data, maxSize)
                                                   : qint64(0);
    if (readBytes == -2) {
        // -2 from the engine means no bytes available (EAGAIN) so read more later
        readBytes = 0;
    }
    if (readBytes < 0) {
        d->setError(d->socketEngine->error(), d->socketEngine->errorString());
        d->resetSocketLayer();
        d->state = QAbstractSocket::UnconnectedState;
    } else {
        // Only do this when there was no error
        d->hasPendingData = false;
        d->socketEngine->setReadNotificationEnabled(true);
    }

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::readData(%p \"%s\", %lli) == %lld [engine]", data,
           QtDebugUtils::toPrintable(data, readBytes, 32).constData(), maxSize, readBytes);
#endif
    return readBytes;
}

/*! \reimp
*/
qint64 QAbstractSocket::readLineData(char *data, qint64 maxlen)
{
    return QIODevice::readLineData(data, maxlen);
}

/*! \reimp
*/
qint64 QAbstractSocket::writeData(const char *data, qint64 size)
{
    Q_D(QAbstractSocket);
    if (d->state == QAbstractSocket::UnconnectedState
        || (!d->socketEngine && d->socketType != TcpSocket && !d->isBuffered)) {
        d->setError(UnknownSocketError, tr("Socket is not connected"));
        return -1;
    }

    if (!d->isBuffered && d->socketType == TcpSocket
        && d->socketEngine && d->writeBuffer.isEmpty()) {
        // This code is for the new Unbuffered QTcpSocket use case
        qint64 written = size ? d->socketEngine->write(data, size) : Q_INT64_C(0);
        if (written < 0) {
            d->setError(d->socketEngine->error(), d->socketEngine->errorString());
        } else if (written < size) {
            // Buffer what was not written yet
            d->writeBuffer.append(data + written, size - written);
            written = size;
            d->socketEngine->setWriteNotificationEnabled(true);
        }

#if defined (QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::writeData(%p \"%s\", %lli) == %lli", data,
               QtDebugUtils::toPrintable(data, size, 32).constData(), size, written);
#endif
        return written; // written = actually written + what has been buffered
    } else if (!d->isBuffered && d->socketType != TcpSocket) {
        // This is for a QUdpSocket that was connect()ed
        qint64 written = d->socketEngine->write(data, size);
        if (written < 0)
            d->setError(d->socketEngine->error(), d->socketEngine->errorString());

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::writeData(%p \"%s\", %lli) == %lli", data,
           QtDebugUtils::toPrintable(data, size, 32).constData(), size, written);
#endif
        if (written >= 0)
            d->emitBytesWritten(written);
        return written;
    }

    // This is the code path for normal buffered QTcpSocket or
    // unbuffered QTcpSocket when there was already something in the
    // write buffer and therefore we could not do a direct engine write.
    // We just write to our write buffer and enable the write notifier
    // The write notifier then flush()es the buffer.

    d->write(data, size);
    qint64 written = size;

    if (d->socketEngine && !d->writeBuffer.isEmpty())
        d->socketEngine->setWriteNotificationEnabled(true);

#if defined (QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::writeData(%p \"%s\", %lli) == %lli", data,
           QtDebugUtils::toPrintable(data, size, 32).constData(), size, written);
#endif
    return written;
}

/*!
    \since 4.1

    Sets the port on the local side of a connection to \a port.

    You can call this function in a subclass of QAbstractSocket to
    change the return value of the localPort() function after a
    connection has been established. This feature is commonly used by
    proxy connections for virtual connection settings.

    Note that this function does not bind the local port of the socket
    prior to a connection (e.g., QAbstractSocket::bind()).

    \sa localAddress(), setLocalAddress(), setPeerPort()
*/
void QAbstractSocket::setLocalPort(quint16 port)
{
    Q_D(QAbstractSocket);
    d->localPort = port;
}

/*!
    \since 4.1

    Sets the address on the local side of a connection to
    \a address.

    You can call this function in a subclass of QAbstractSocket to
    change the return value of the localAddress() function after a
    connection has been established. This feature is commonly used by
    proxy connections for virtual connection settings.

    Note that this function does not bind the local address of the socket
    prior to a connection (e.g., QAbstractSocket::bind()).

    \sa localAddress(), setLocalPort(), setPeerAddress()
*/
void QAbstractSocket::setLocalAddress(const QHostAddress &address)
{
    Q_D(QAbstractSocket);
    d->localAddress = address;
}

/*!
    \since 4.1

    Sets the port of the remote side of the connection to
    \a port.

    You can call this function in a subclass of QAbstractSocket to
    change the return value of the peerPort() function after a
    connection has been established. This feature is commonly used by
    proxy connections for virtual connection settings.

    \sa peerPort(), setPeerAddress(), setLocalPort()
*/
void QAbstractSocket::setPeerPort(quint16 port)
{
    Q_D(QAbstractSocket);
    d->peerPort = port;
}

/*!
    \since 4.1

    Sets the address of the remote side of the connection
    to \a address.

    You can call this function in a subclass of QAbstractSocket to
    change the return value of the peerAddress() function after a
    connection has been established. This feature is commonly used by
    proxy connections for virtual connection settings.

    \sa peerAddress(), setPeerPort(), setLocalAddress()
*/
void QAbstractSocket::setPeerAddress(const QHostAddress &address)
{
    Q_D(QAbstractSocket);
    d->peerAddress = address;
}

/*!
    \since 4.1

    Sets the host name of the remote peer to \a name.

    You can call this function in a subclass of QAbstractSocket to
    change the return value of the peerName() function after a
    connection has been established. This feature is commonly used by
    proxy connections for virtual connection settings.

    \sa peerName()
*/
void QAbstractSocket::setPeerName(const QString &name)
{
    Q_D(QAbstractSocket);
    d->peerName = name;
}

/*!
    Closes the I/O device for the socket and calls disconnectFromHost()
    to close the socket's connection.

    See QIODevice::close() for a description of the actions that occur when an I/O
    device is closed.

    \sa abort()
*/
void QAbstractSocket::close()
{
    Q_D(QAbstractSocket);
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::close()");
#endif
    QIODevice::close();
    if (d->state != UnconnectedState)
        disconnectFromHost();
}

/*!
    Attempts to close the socket. If there is pending data waiting to
    be written, QAbstractSocket will enter ClosingState and wait
    until all data has been written. Eventually, it will enter
    UnconnectedState and emit the disconnected() signal.

    \sa connectToHost()
*/
void QAbstractSocket::disconnectFromHost()
{
    Q_D(QAbstractSocket);
#if defined(QABSTRACTSOCKET_DEBUG)
    qDebug("QAbstractSocket::disconnectFromHost()");
#endif

    if (d->state == UnconnectedState) {
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::disconnectFromHost() was called on an unconnected socket");
#endif
        return;
    }

    if (!d->abortCalled && (d->state == ConnectingState || d->state == HostLookupState)) {
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::disconnectFromHost() but we're still connecting");
#endif
        d->pendingClose = true;
        return;
    }

    // Disable and delete read notification
    if (d->socketEngine)
        d->socketEngine->setReadNotificationEnabled(false);

    if (d->abortCalled) {
#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::disconnectFromHost() aborting immediately");
#endif
        if (d->state == HostLookupState) {
            QHostInfo::abortHostLookup(d->hostLookupId);
            d->hostLookupId = -1;
        }
    } else {
        // Perhaps emit closing()
        if (d->state != ClosingState) {
            d->state = ClosingState;
#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::disconnectFromHost() emits stateChanged()(ClosingState)");
#endif
            emit stateChanged(d->state);
        } else {
#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::disconnectFromHost() return from delayed close");
#endif
        }

        // Wait for pending data to be written.
        if (d->socketEngine && d->socketEngine->isValid() && (!d->allWriteBuffersEmpty()
            || d->socketEngine->bytesToWrite() > 0)) {
            d->socketEngine->setWriteNotificationEnabled(true);

#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::disconnectFromHost() delaying disconnect");
#endif
            return;
        } else {
#if defined(QABSTRACTSOCKET_DEBUG)
            qDebug("QAbstractSocket::disconnectFromHost() disconnecting immediately");
#endif
        }
    }

    SocketState previousState = d->state;
    d->resetSocketLayer();
    d->state = UnconnectedState;
    emit stateChanged(d->state);
    emit readChannelFinished();       // we got an EOF

    // only emit disconnected if we were connected before
    if (previousState == ConnectedState || previousState == ClosingState)
        emit disconnected();

    d->localPort = 0;
    d->peerPort = 0;
    d->localAddress.clear();
    d->peerAddress.clear();
    d->peerName.clear();
    d->setWriteChannelCount(0);

#if defined(QABSTRACTSOCKET_DEBUG)
        qDebug("QAbstractSocket::disconnectFromHost() disconnected!");
#endif

}

/*!
    Returns the size of the internal read buffer. This limits the
    amount of data that the client can receive before you call read()
    or readAll().

    A read buffer size of 0 (the default) means that the buffer has
    no size limit, ensuring that no data is lost.

    \sa setReadBufferSize(), read()
*/
qint64 QAbstractSocket::readBufferSize() const
{
    return d_func()->readBufferMaxSize;
}

/*!
    Sets the size of QAbstractSocket's internal read buffer to be \a
    size bytes.

    If the buffer size is limited to a certain size, QAbstractSocket
    won't buffer more than this size of data. Exceptionally, a buffer
    size of 0 means that the read buffer is unlimited and all
    incoming data is buffered. This is the default.

    This option is useful if you only read the data at certain points
    in time (e.g., in a real-time streaming application) or if you
    want to protect your socket against receiving too much data,
    which may eventually cause your application to run out of memory.

    Only QTcpSocket uses QAbstractSocket's internal buffer; QUdpSocket
    does not use any buffering at all, but rather relies on the
    implicit buffering provided by the operating system.
    Because of this, calling this function on QUdpSocket has no
    effect.

    \sa readBufferSize(), read()
*/
void QAbstractSocket::setReadBufferSize(qint64 size)
{
    Q_D(QAbstractSocket);

    if (d->readBufferMaxSize == size)
        return;
    d->readBufferMaxSize = size;

    // Do not change the notifier unless we are connected.
    if (d->socketEngine && d->state == QAbstractSocket::ConnectedState) {
        // Ensure that the read notification is enabled if we've now got
        // room in the read buffer.
        d->socketEngine->setReadNotificationEnabled(size == 0 || d->buffer.size() < size);
    }
}

/*!
    Returns the state of the socket.

    \sa error()
*/
QAbstractSocket::SocketState QAbstractSocket::state() const
{
    return d_func()->state;
}

/*!
    Sets the state of the socket to \a state.

    \sa state()
*/
void QAbstractSocket::setSocketState(SocketState state)
{
    d_func()->state = state;
}

/*!
    Returns the socket type (TCP, UDP, or other).

    \sa QTcpSocket, QUdpSocket
*/
QAbstractSocket::SocketType QAbstractSocket::socketType() const
{
    return d_func()->socketType;
}

/*!
    Returns the type of error that last occurred.

    \sa state(), errorString()
*/
QAbstractSocket::SocketError QAbstractSocket::error() const
{
    return d_func()->socketError;
}

/*!
    Sets the type of error that last occurred to \a socketError.

    \sa setSocketState(), setErrorString()
*/
void QAbstractSocket::setSocketError(SocketError socketError)
{
    d_func()->socketError = socketError;
}

#ifndef QT_NO_NETWORKPROXY
/*!
    \since 4.1

    Sets the explicit network proxy for this socket to \a networkProxy.

    To disable the use of a proxy for this socket, use the
    QNetworkProxy::NoProxy proxy type:

    \snippet code/src_network_socket_qabstractsocket.cpp 2

    The default value for the proxy is QNetworkProxy::DefaultProxy,
    which means the socket will use the application settings: if a
    proxy is set with QNetworkProxy::setApplicationProxy, it will use
    that; otherwise, if a factory is set with
    QNetworkProxyFactory::setApplicationProxyFactory, it will query
    that factory with type QNetworkProxyQuery::TcpSocket.

    \sa proxy(), QNetworkProxy, QNetworkProxyFactory::queryProxy()
*/
void QAbstractSocket::setProxy(const QNetworkProxy &networkProxy)
{
    Q_D(QAbstractSocket);
    d->proxy = networkProxy;
}

/*!
    \since 4.1

    Returns the network proxy for this socket.
    By default QNetworkProxy::DefaultProxy is used, which means this
    socket will query the default proxy settings for the application.

    \sa setProxy(), QNetworkProxy, QNetworkProxyFactory
*/
QNetworkProxy QAbstractSocket::proxy() const
{
    Q_D(const QAbstractSocket);
    return d->proxy;
}

/*!
    \since 5.13

    Returns the protocol tag for this socket.
    If the protocol tag is set then this is passed to QNetworkProxyQuery
    when this is created internally to indicate the protocol tag to be
    used.

    \sa setProtocolTag(), QNetworkProxyQuery
*/

QString QAbstractSocket::protocolTag() const
{
    Q_D(const QAbstractSocket);
    return d->protocolTag;
}

/*!
    \since 5.13

    Sets the protocol tag for this socket to \a tag.

    \sa protocolTag()
*/

void QAbstractSocket::setProtocolTag(const QString &tag)
{
    Q_D(QAbstractSocket);
    d->protocolTag = tag;
}

#endif // QT_NO_NETWORKPROXY

#ifndef QT_NO_DEBUG_STREAM
Q_NETWORK_EXPORT QDebug operator<<(QDebug debug, QAbstractSocket::SocketError error)
{
    QDebugStateSaver saver(debug);
    debug.resetFormat().nospace();
    switch (error) {
    case QAbstractSocket::ConnectionRefusedError:
        debug << "QAbstractSocket::ConnectionRefusedError";
        break;
    case QAbstractSocket::RemoteHostClosedError:
        debug << "QAbstractSocket::RemoteHostClosedError";
        break;
    case QAbstractSocket::HostNotFoundError:
        debug << "QAbstractSocket::HostNotFoundError";
        break;
    case QAbstractSocket::SocketAccessError:
        debug << "QAbstractSocket::SocketAccessError";
        break;
    case QAbstractSocket::SocketResourceError:
        debug << "QAbstractSocket::SocketResourceError";
        break;
    case QAbstractSocket::SocketTimeoutError:
        debug << "QAbstractSocket::SocketTimeoutError";
        break;
    case QAbstractSocket::DatagramTooLargeError:
        debug << "QAbstractSocket::DatagramTooLargeError";
        break;
    case QAbstractSocket::NetworkError:
        debug << "QAbstractSocket::NetworkError";
        break;
    case QAbstractSocket::AddressInUseError:
        debug << "QAbstractSocket::AddressInUseError";
        break;
    case QAbstractSocket::SocketAddressNotAvailableError:
        debug << "QAbstractSocket::SocketAddressNotAvailableError";
        break;
    case QAbstractSocket::UnsupportedSocketOperationError:
        debug << "QAbstractSocket::UnsupportedSocketOperationError";
        break;
    case QAbstractSocket::UnfinishedSocketOperationError:
        debug << "QAbstractSocket::UnfinishedSocketOperationError";
        break;
    case QAbstractSocket::ProxyAuthenticationRequiredError:
        debug << "QAbstractSocket::ProxyAuthenticationRequiredError";
        break;
    case QAbstractSocket::UnknownSocketError:
        debug << "QAbstractSocket::UnknownSocketError";
        break;
    case QAbstractSocket::ProxyConnectionRefusedError:
        debug << "QAbstractSocket::ProxyConnectionRefusedError";
        break;
    case QAbstractSocket::ProxyConnectionClosedError:
        debug << "QAbstractSocket::ProxyConnectionClosedError";
        break;
    case QAbstractSocket::ProxyConnectionTimeoutError:
        debug << "QAbstractSocket::ProxyConnectionTimeoutError";
        break;
    case QAbstractSocket::ProxyNotFoundError:
        debug << "QAbstractSocket::ProxyNotFoundError";
        break;
    case QAbstractSocket::ProxyProtocolError:
        debug << "QAbstractSocket::ProxyProtocolError";
        break;
    default:
        debug << "QAbstractSocket::SocketError(" << int(error) << ')';
        break;
    }
    return debug;
}

Q_NETWORK_EXPORT QDebug operator<<(QDebug debug, QAbstractSocket::SocketState state)
{
    QDebugStateSaver saver(debug);
    debug.resetFormat().nospace();
    switch (state) {
    case QAbstractSocket::UnconnectedState:
        debug << "QAbstractSocket::UnconnectedState";
        break;
    case QAbstractSocket::HostLookupState:
        debug << "QAbstractSocket::HostLookupState";
        break;
    case QAbstractSocket::ConnectingState:
        debug << "QAbstractSocket::ConnectingState";
        break;
    case QAbstractSocket::ConnectedState:
        debug << "QAbstractSocket::ConnectedState";
        break;
    case QAbstractSocket::BoundState:
        debug << "QAbstractSocket::BoundState";
        break;
    case QAbstractSocket::ListeningState:
        debug << "QAbstractSocket::ListeningState";
        break;
    case QAbstractSocket::ClosingState:
        debug << "QAbstractSocket::ClosingState";
        break;
    default:
        debug << "QAbstractSocket::SocketState(" << int(state) << ')';
        break;
    }
    return debug;
}
#endif

QT_END_NAMESPACE

#include "moc_qabstractsocket.cpp"
