QT分析之網路編程（三）

 QT分析之網路編程（三）

程式人生 2010-01-31 21:45:47 閱讀229 評論0 字型大小：大中小

3、讀取資訊
在QAbstractSocket中，有兩個成員是收發資料用的：readData()、writeData()
readData()有兩種讀取方式：有緩衝和無緩衝方式。基本原理是一致的，簡單其見只分析無緩衝直接讀取方式。
qint64 QAbstractSocket::readData(char *data, qint64 maxSize)
{
    Q_D(QAbstractSocket);
    if (d->socketEngine && !d->socketEngine->isReadNotificationEnabled() && d->socketEngine->isValid())
        d->socketEngine->setReadNotificationEnabled(true);
    if (!d->isBuffered) {
        if (!d->socketEngine)
            return -1;          // no socket engine is probably EOF
        qint64 readBytes = d->socketEngine->read(data, maxSize);
        if (readBytes < 0) {
            d->socketError = d->socketEngine->error();
            setErrorString(d->socketEngine->errorString());
        }
        if (!d->socketEngine->isReadNotificationEnabled())
            d->socketEngine->setReadNotificationEnabled(true);
        return readBytes;
    }
    if (d->readBuffer.isEmpty())
        // if we're still connected, return 0 indicating there may be more data in the future
        // if we're not connected, return -1 indicating EOF
        return d->state == QAbstractSocket::ConnectedState ? qint64(0) : qint64(-1);
    // If readFromSocket() read data, copy it to its destination.
    if (maxSize == 1) {
        *data = d->readBuffer.getChar();
        return 1;
    }
    qint64 bytesToRead = qMin(qint64(d->readBuffer.size()), maxSize);
    qint64 readSoFar = 0;
    while (readSoFar < bytesToRead) {
        const char *ptr = d->readBuffer.readPointer();
        int bytesToReadFromThisBlock = qMin(int(bytesToRead - readSoFar),
                                            d->readBuffer.nextDataBlockSize());
        memcpy(data + readSoFar, ptr, bytesToReadFromThisBlock);
        readSoFar += bytesToReadFromThisBlock;
        d->readBuffer.free(bytesToReadFromThisBlock);
    }
    return readSoFar;
}
從前面（二）可以知道，socketEngine->read()實際調用的是QNativeSocketEngine::read()
qint64 QNativeSocketEngine::read(char *data, qint64 maxSize)
{
    Q_D(QNativeSocketEngine);
    Q_CHECK_VALID_SOCKETLAYER(QNativeSocketEngine::read(), -1);
    Q_CHECK_STATES(QNativeSocketEngine::read(), QAbstractSocket::ConnectedState, QAbstractSocket::BoundState, -1);
    qint64 readBytes = d->nativeRead(data, maxSize);
    // Handle remote close
    if (readBytes == 0 && d->socketType == QAbstractSocket::TcpSocket) {
        d->setError(QAbstractSocket::RemoteHostClosedError,
                    QNativeSocketEnginePrivate::RemoteHostClosedErrorString);
        close();
        return -1;
    }
    return readBytes;
}
除了一些相關的檢查，就是調用QNativeSocketPrivate::nativeRead()
qint64 QNativeSocketEnginePrivate::nativeRead(char *data, qint64 maxSize)
{
    Q_Q(QNativeSocketEngine);
    if (!q->isValid()) {
        qWarning("QNativeSocketEngine::unbufferedRead: Invalid socket");
        return -1;
    }

    ssize_t r = 0;
#ifdef Q_OS_SYMBIAN
    r = ::read(socketDescriptor, data, maxSize);
#else
    r = qt_safe_read(socketDescriptor, data, maxSize);
#endif

    if (r < 0) {
        r = -1;
        switch (errno) {
#if EWOULDBLOCK-0 && EWOULDBLOCK != EAGAIN
        case EWOULDBLOCK:
#endif
        case EAGAIN:
            // No data was available for reading
            r = -2;
            break;
        case EBADF:
        case EINVAL:
        case EIO:
            //error string is now set in read(), not here in nativeRead()
            break;
#ifdef Q_OS_SYMBIAN
        case EPIPE:
#endif
        case ECONNRESET:
#if defined(Q_OS_VXWORKS)
        case ESHUTDOWN:
#endif
            r = 0;
            break;
        default:
            break;
        }
    }

#if defined (QNATIVESOCKETENGINE_DEBUG)
    qDebug("QNativeSocketEnginePrivate::nativeRead(%p \"%s\", %llu) == %i",
           data, qt_prettyDebug(data, qMin(r, ssize_t(16)), r).data(),
           maxSize, r);
#endif

    return qint64(r);
}
至此，調用API讀取資料。
4、發送資料
同樣分有緩衝與無緩衝方式，對無緩衝方式：
qint64 QAbstractSocket::writeData(const char *data, qint64 size)
{
    Q_D(QAbstractSocket);
    if (d->state == QAbstractSocket::UnconnectedState) {
        d->socketError = QAbstractSocket::UnknownSocketError;
        setErrorString(tr("Socket is not connected"));
        return -1;
    }
    if (!d->isBuffered) {
        qint64 written = d->socketEngine->write(data, size);
        if (written < 0) {
            d->socketError = d->socketEngine->error();
            setErrorString(d->socketEngine->errorString());
        } else if (!d->writeBuffer.isEmpty()) {
            d->socketEngine->setWriteNotificationEnabled(true);
        }
        if (written >= 0)
            emit bytesWritten(written);
        return written;
    }
    char *ptr = d->writeBuffer.reserve(size);
    if (size == 1)
        *ptr = *data;
    else
        memcpy(ptr, data, size);
    qint64 written = size;
    if (d->socketEngine && !d->writeBuffer.isEmpty())
        d->socketEngine->setWriteNotificationEnabled(true);
    return written;
}
查看QNativeSocketEngine::write()：
qint64 QNativeSocketEngine::write(const char *data, qint64 size)
{
    Q_D(QNativeSocketEngine);
    Q_CHECK_VALID_SOCKETLAYER(QNativeSocketEngine::write(), -1);
    Q_CHECK_STATE(QNativeSocketEngine::write(), QAbstractSocket::ConnectedState, -1);
    return d->nativeWrite(data, size);
}
qint64 QNativeSocketEnginePrivate::nativeWrite(const char *data, qint64 len)
{
    Q_Q(QNativeSocketEngine);
    qint64 ret = 0;
    // don't send more than 49152 per call to WSASendTo to avoid getting a WSAENOBUFS
    for (;;) {
        qint64 bytesToSend = qMin<qint64>(49152, len - ret);
        WSABUF buf;
        buf.buf = (char*)data + ret;
        buf.len = bytesToSend;
        DWORD flags = 0;
        DWORD bytesWritten = 0;
        int socketRet = ::WSASend(socketDescriptor, &buf, 1, &bytesWritten, flags, 0,0);
        ret += qint64(bytesWritten);
        if (socketRet != SOCKET_ERROR) {
            if (ret == len)
                break;
            else
                continue;
        } else if (WSAGetLastError() == WSAEWOULDBLOCK) {
            break;
        } else {
            int err = WSAGetLastError();
            WS_ERROR_DEBUG(err);
            switch (err) {
            case WSAECONNRESET:
            case WSAECONNABORTED:
                ret = -1;
                setError(QAbstractSocket::NetworkError, WriteErrorString);
                q->close();
                break;
            default:
                break;
            }
            break;
        }
    }
    return ret;
}
至此分析完畢。