corelib/io/qwindowspipereader.cpp

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#include "qwindowspipereader_p.h"
#include "qiodevice_p.h"
#include <qelapsedtimer.h>
#include <qscopedvaluerollback.h>

QT_BEGIN_NAMESPACE

QWindowsPipeReader::Overlapped::Overlapped(QWindowsPipeReader *reader)
    : pipeReader(reader)
{
}

void QWindowsPipeReader::Overlapped::clear()
{
    ZeroMemory(this, sizeof(OVERLAPPED));
}


QWindowsPipeReader::QWindowsPipeReader(QObject *parent)
    : QObject(parent),
      handle(INVALID_HANDLE_VALUE),
      overlapped(this),
      readBufferMaxSize(0),
      actualReadBufferSize(0),
      stopped(true),
      readSequenceStarted(false),
      notifiedCalled(false),
      pipeBroken(false),
      readyReadPending(false),
      inReadyRead(false)
{
    connect(this, &QWindowsPipeReader::_q_queueReadyRead,
            this, &QWindowsPipeReader::emitPendingReadyRead, Qt::QueuedConnection);
}

QWindowsPipeReader::~QWindowsPipeReader()
{
    stop();
}

/*!
    Sets the handle to read from. The handle must be valid.
 */
void QWindowsPipeReader::setHandle(HANDLE hPipeReadEnd)
{
    readBuffer.clear();
    actualReadBufferSize = 0;
    handle = hPipeReadEnd;
    pipeBroken = false;
}

/*!
    Stops the asynchronous read sequence.
    If the read sequence is running then the I/O operation is canceled.
 */
void QWindowsPipeReader::stop()
{
    stopped = true;
    if (readSequenceStarted) {
        if (!CancelIoEx(handle, &overlapped)) {
            const DWORD dwError = GetLastError();
            if (dwError != ERROR_NOT_FOUND) {
                qErrnoWarning(dwError, "QWindowsPipeReader: CancelIoEx on handle %p failed.",
                              handle);
            }
        }
        waitForNotification(-1);
    }
}

/*!
    Returns the number of bytes we've read so far.
 */
qint64 QWindowsPipeReader::bytesAvailable() const
{
    return actualReadBufferSize;
}

/*!
    Copies at most \c{maxlen} bytes from the internal read buffer to \c{data}.
 */
qint64 QWindowsPipeReader::read(char *data, qint64 maxlen)
{
    if (pipeBroken && actualReadBufferSize == 0)
        return 0;  // signal EOF

    qint64 readSoFar;
    // If startAsyncRead() has read data, copy it to its destination.
    if (maxlen == 1 && actualReadBufferSize > 0) {
        *data = readBuffer.getChar();
        actualReadBufferSize--;
        readSoFar = 1;
    } else {
        readSoFar = readBuffer.read(data, qMin(actualReadBufferSize, maxlen));
        actualReadBufferSize -= readSoFar;
    }

    if (!pipeBroken) {
        if (!readSequenceStarted && !stopped)
            startAsyncRead();
        if (readSoFar == 0)
            return -2;      // signal EWOULDBLOCK
    }

    return readSoFar;
}

bool QWindowsPipeReader::canReadLine() const
{
    return readBuffer.indexOf('\n', actualReadBufferSize) >= 0;
}

/*!
    \internal
    Will be called whenever the read operation completes.
 */
void QWindowsPipeReader::notified(DWORD errorCode, DWORD numberOfBytesRead)
{
    notifiedCalled = true;
    readSequenceStarted = false;

    switch (errorCode) {
    case ERROR_SUCCESS:
        break;
    case ERROR_MORE_DATA:
        // This is not an error. We're connected to a message mode
        // pipe and the message didn't fit into the pipe's system
        // buffer. We will read the remaining data in the next call.
        break;
    case ERROR_BROKEN_PIPE:
    case ERROR_PIPE_NOT_CONNECTED:
        pipeBroken = true;
        break;
    case ERROR_OPERATION_ABORTED:
        if (stopped)
            break;
        Q_FALLTHROUGH();
    default:
        emit winError(errorCode, QLatin1String("QWindowsPipeReader::notified"));
        pipeBroken = true;
        break;
    }

    // After the reader was stopped, the only reason why this function can be called is the
    // completion of a cancellation. No signals should be emitted, and no new read sequence should
    // be started in this case.
    if (stopped)
        return;

    if (pipeBroken) {
        emit pipeClosed();
        return;
    }

    actualReadBufferSize += numberOfBytesRead;
    readBuffer.truncate(actualReadBufferSize);
    startAsyncRead();
    if (!readyReadPending) {
        readyReadPending = true;
        emit _q_queueReadyRead(QWindowsPipeReader::QPrivateSignal());
    }
}

/*!
    \internal
    Reads data from the pipe into the readbuffer.
 */
void QWindowsPipeReader::startAsyncRead()
{
    const DWORD minReadBufferSize = 4096;
    qint64 bytesToRead = qMax(checkPipeState(), minReadBufferSize);
    if (pipeBroken)
        return;

    if (readBufferMaxSize && bytesToRead > (readBufferMaxSize - readBuffer.size())) {
        bytesToRead = readBufferMaxSize - readBuffer.size();
        if (bytesToRead <= 0) {
            // Buffer is full. User must read data from the buffer
            // before we can read more from the pipe.
            return;
        }
    }

    char *ptr = readBuffer.reserve(bytesToRead);

    stopped = false;
    readSequenceStarted = true;
    overlapped.clear();
    if (!ReadFileEx(handle, ptr, bytesToRead, &overlapped, &readFileCompleted)) {
        readSequenceStarted = false;

        const DWORD dwError = GetLastError();
        switch (dwError) {
        case ERROR_BROKEN_PIPE:
        case ERROR_PIPE_NOT_CONNECTED:
            // It may happen, that the other side closes the connection directly
            // after writing data. Then we must set the appropriate socket state.
            pipeBroken = true;
            emit pipeClosed();
            break;
        default:
            emit winError(dwError, QLatin1String("QWindowsPipeReader::startAsyncRead"));
            break;
        }
    }
}

/*!
    \internal
    Called when ReadFileEx finished the read operation.
 */
void QWindowsPipeReader::readFileCompleted(DWORD errorCode, DWORD numberOfBytesTransfered,
                                           OVERLAPPED *overlappedBase)
{
    Overlapped *overlapped = static_cast<Overlapped *>(overlappedBase);
    overlapped->pipeReader->notified(errorCode, numberOfBytesTransfered);
}

/*!
    \internal
    Returns the number of available bytes in the pipe.
    Sets QWindowsPipeReader::pipeBroken to true if the connection is broken.
 */
DWORD QWindowsPipeReader::checkPipeState()
{
    DWORD bytes;
    if (PeekNamedPipe(handle, nullptr, 0, nullptr, &bytes, nullptr))
        return bytes;
    if (!pipeBroken) {
        pipeBroken = true;
        emit pipeClosed();
    }
    return 0;
}

bool QWindowsPipeReader::waitForNotification(int timeout)
{
    QElapsedTimer t;
    t.start();
    notifiedCalled = false;
    int msecs = timeout;
    while (SleepEx(msecs == -1 ? INFINITE : msecs, TRUE) == WAIT_IO_COMPLETION) {
        if (notifiedCalled)
            return true;

        // Some other I/O completion routine was called. Wait some more.
        msecs = qt_subtract_from_timeout(timeout, t.elapsed());
        if (!msecs)
            break;
    }
    return notifiedCalled;
}

void QWindowsPipeReader::emitPendingReadyRead()
{
    if (readyReadPending) {
        readyReadPending = false;
        QScopedValueRollback<bool> guard(inReadyRead, true);
        emit readyRead();
    }
}

/*!
    Waits for the completion of the asynchronous read operation.
    Returns \c true, if we've emitted the readyRead signal (non-recursive case)
    or readyRead will be emitted by the event loop (recursive case).
 */
bool QWindowsPipeReader::waitForReadyRead(int msecs)
{
    if (readyReadPending) {
        if (!inReadyRead)
            emitPendingReadyRead();
        return true;
    }

    if (!readSequenceStarted)
        return false;

    if (!waitForNotification(msecs))
        return false;

    if (readyReadPending) {
        if (!inReadyRead)
            emitPendingReadyRead();
        return true;
    }

    return false;
}

/*!
    Waits until the pipe is closed.
 */
bool QWindowsPipeReader::waitForPipeClosed(int msecs)
{
    const int sleepTime = 10;
    QElapsedTimer stopWatch;
    stopWatch.start();
    forever {
        waitForReadyRead(0);
        checkPipeState();
        if (pipeBroken)
            return true;
        if (stopWatch.hasExpired(msecs - sleepTime))
            return false;
        Sleep(sleepTime);
    }
}

QT_END_NAMESPACE