QT分析之网络编程（二）

 QT分析之网络编程（二）

程序人生 2010-01-31 11:08:42 阅读547 评论0 字号：大中小

前面分析（一）之前没有看QT自带的文档，看了doc之后对QT的网络体系有一个大致的了解：
QNatvieSocketEnginePrivate是OS相关的API封装，和QNativeSocketEngine一起构成具体平台SOCKET实现；
QTcpSocket、QUdpSocket、QTcpServer构成底层的应用API；QSslSocket是SSL加密相关API；
QHttp、QFtp构成高层次应该API；
QNetworkAccessManager、QNetworkRequest、QNetworkReply是高度抽象的网络层。
分析TCP的例子fortuneclient，运行起来按了[Get Fortune]按钮之后，调用的是Client::requestNewFortune()。
void Client::requestNewFortune()
{
    getFortuneButton->setEnabled(false);
    blockSize = 0;
    tcpSocket->abort();
    tcpSocket->connectToHost(hostLineEdit->text(), portLineEdit->text().toInt());
}
具体看QTcpSocket::connectToHost()的代码：
void QAbstractSocket::connectToHost(const QString &hostName, quint16 port,
                                    OpenMode openMode)
{
    QMetaObject::invokeMethod(this, "connectToHostImplementation",
                              Qt::DirectConnection,
                              Q_ARG(QString, hostName),
                              Q_ARG(quint16, port),
                              Q_ARG(OpenMode, openMode));
}
调用的是QAbstractSocket::connectToHostImplementation()。
void QAbstractSocket::connectToHostImplementation(const QString &hostName, quint16 port,
                                                  OpenMode openMode)
{
    Q_D(QAbstractSocket);
    if (d->state == ConnectedState || d->state == ConnectingState || d->state == ClosingState) {
        qWarning("QAbstractSocket::connectToHost() called when already connecting/connected to \"%s\"", qPrintable(hostName));
        return;
    }
    d->hostName = hostName;
    d->port = port;
    d->state = UnconnectedState;
    d->readBuffer.clear();
    d->writeBuffer.clear();
    d->abortCalled = false;
    d->closeCalled = false;
    d->pendingClose = false;
    d->localPort = 0;
    d->peerPort = 0;
    d->localAddress.clear();
    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->socketError = QAbstractSocket::UnsupportedSocketOperationError;
        setErrorString(QAbstractSocket::tr("Operation on socket is not supported"));
        emit error(d->socketError);
        return;
    }
#endif
    if (!d_func()->isBuffered)
        openMode |= QAbstractSocket::Unbuffered;
    QIODevice::open(openMode);  // ？？
    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->eventDispatcher)
            d->hostLookupId = QHostInfo::lookupHost(hostName, this, SLOT(_q_startConnecting(QHostInfo)));
    }
}
继续调用QAbstractSocket::_q_startConnecting()，是QAbstractSocket的私有信号。简单来说，_q_startConnecting()就是调用了_q_connectToNextAddress()而已。
void QAbstractSocketPrivate::_q_connectToNextAddress()
{
    Q_Q(QAbstractSocket);
    do {
        // Check for more pending addresses
        if (addresses.isEmpty()) {
            state = QAbstractSocket::UnconnectedState;
            if (socketEngine) {
                if ((socketEngine->error() == QAbstractSocket::UnknownSocketError
                    ) && socketEngine->state() == QAbstractSocket::ConnectingState) {
                    socketError = QAbstractSocket::ConnectionRefusedError;
                    q->setErrorString(QAbstractSocket::tr("Connection refused"));
                } else {
                    socketError = socketEngine->error();
                    q->setErrorString(socketEngine->errorString());
                }
            } else {
//                socketError = QAbstractSocket::ConnectionRefusedError;
//                q->setErrorString(QAbstractSocket::tr("Connection refused"));
            }
            emit q->stateChanged(state);
            emit q->error(socketError);
            return;
        }
        // Pick the first host address candidate
        host = addresses.takeFirst();
#if defined(QT_NO_IPV6)
        if (host.protocol() == QAbstractSocket::IPv6Protocol) {
            // If we have no IPv6 support, then we will not be able to
            // connect. So we just pretend we didn't see this address.
            continue;
        }
#endif
        if (!initSocketLayer(host.protocol())) {
            // hope that the next address is better
            continue;
        }
        // Tries to connect to the address. If it succeeds immediately
        // (localhost address on BSD or any UDP connect), emit
        // connected() and return.
        if (socketEngine->connectToHost(host, port)) {
            //_q_testConnection();
            fetchConnectionParameters();
            return;
        }
        // cache the socket descriptor even if we're not fully connected yet
        cachedSocketDescriptor = socketEngine->socketDescriptor();
        // Check that we're in delayed connection state. If not, try
        // the next address
        if (socketEngine->state() != QAbstractSocket::ConnectingState) {
            continue;
        }
        // Start the connect timer.
        if (threadData->eventDispatcher) {
            if (!connectTimer) {
                connectTimer = new QTimer(q);
                QObject::connect(connectTimer, SIGNAL(timeout()),
                                 q, SLOT(_q_abortConnectionAttempt()),
                                 Qt::DirectConnection);
            }
            connectTimer->start(QT_CONNECT_TIMEOUT);
        }
        // Wait for a write notification that will eventually call
        // _q_testConnection().
        socketEngine->setWriteNotificationEnabled(true);
        break;
    } while (state != QAbstractSocket::ConnectedState);
}
上面关键的三句，实际是把WinSocket编程中的简单过程分成三个阶段：socket初始化；connect到远程目标；设定Timer定时查看并处理Select的情况（收发数据或者关闭socket）。这里主要看前面两个：初始化和连接，select的处理放到明天分析。
1、初始化
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);
    resetSocketLayer();
    socketEngine = QAbstractSocketEngine::createSocketEngine(q->socketType(), proxyInUse, q);
    if (!socketEngine) {
        socketError = QAbstractSocket::UnsupportedSocketOperationError;
        q->setErrorString(QAbstractSocket::tr("Operation on socket is not supported"));
        return false;
    }
    if (!socketEngine->initialize(q->socketType(), protocol)) {
        socketError = socketEngine->error();
    q->setErrorString(socketEngine->errorString());
        return false;
    }
    if (threadData->eventDispatcher)
        socketEngine->setReceiver(this);
    return true;
}
QAbstractSocketEngine *QAbstractSocketEngine::createSocketEngine(QAbstractSocket::SocketType socketType, const QNetworkProxy &proxy, QObject *parent)
{
#ifndef QT_NO_NETWORKPROXY
    // proxy type must have been resolved by now
    if (proxy.type() == QNetworkProxy::DefaultProxy)
        return 0;
#endif
    QMutexLocker locker(&socketHandlers()->mutex);
    for (int i = 0; i < socketHandlers()->size(); i++) {
        if (QAbstractSocketEngine *ret = socketHandlers()->at(i)->createSocketEngine(socketType, proxy, parent))
            return ret;
    }
    return new QNativeSocketEngine(parent);
}
上面可以知道socketEngine->initialize()实际调用的是QNativeSocketEngine::initialize()
bool QNativeSocketEngine::initialize(QAbstractSocket::SocketType socketType, QAbstractSocket::NetworkLayerProtocol protocol)
{
    Q_D(QNativeSocketEngine);
    if (isValid())
        close();
#if defined(QT_NO_IPV6)
    if (protocol == QAbstractSocket::IPv6Protocol) {
        d->setError(QAbstractSocket::UnsupportedSocketOperationError,
                    QNativeSocketEnginePrivate::NoIpV6ErrorString);
        return false;
    }
#endif
    // Create the socket
    if (!d->createNewSocket(socketType, protocol)) {
        return false;
    }
    // Make the socket nonblocking.
    if (!setOption(NonBlockingSocketOption, 1)) {
        d->setError(QAbstractSocket::UnsupportedSocketOperationError,
                    QNativeSocketEnginePrivate::NonBlockingInitFailedErrorString);
        close();
        return false;
    }
    // Set the broadcasting flag if it's a UDP socket.
    if (socketType == QAbstractSocket::UdpSocket
        && !setOption(BroadcastSocketOption, 1)) {
        d->setError(QAbstractSocket::UnsupportedSocketOperationError,
                    QNativeSocketEnginePrivate::BroadcastingInitFailedErrorString);
        close();
        return false;
    }
    // Make sure we receive out-of-band da ta
    if (socketType == QAbstractSocket::TcpSocket
        && !setOption(ReceiveOutOfBandData, 1)) {
        qWarning("QNativeSocketEngine::initialize unable to inline out-of-band da ta");
    }
    // Set the send and receive buffer sizes to a magic size, found
    // most optimal for our platforms.
    setReceiveBufferSize(49152);
    setSendBufferSize(49152);
    d->socketType = socketType;
    d->socketProtocol = protocol;
    return true;
}
至此，初始化过程完成，socket被设定为非阻塞模式（也就是Select会超时方式）。
2、connect到远程目标
bool QNativeSocketEngine::connectToHost(const QHostAddress &address, quint16 port)
{
    Q_D(QNativeSocketEngine);
    Q_CHECK_VALID_SOCKETLAYER(QNativeSocketEngine::connectToHost(), false);
#if defined (QT_NO_IPV6)
    if (address.protocol() == QAbstractSocket::IPv6Protocol) {
        d->setError(QAbstractSocket::UnsupportedSocketOperationError,
                    QNativeSocketEnginePrivate::NoIpV6ErrorString);
        return false;
    }
#endif
    if (!d->checkProxy(address))
        return false;
    Q_CHECK_STATES(QNativeSocketEngine::connectToHost(),
                   QAbstractSocket::UnconnectedState, QAbstractSocket::ConnectingState, false);
    d->peerAddress = address;
    d->peerPort = port;
    bool connected = d->nativeConnect(address, port);
    if (connected)
        d->fetchConnectionParameters();
    return connected;
}
连接相对简单。