In debug mode i got different msquic packet

[vitoo]

Hello :)

I am building a C++ windows app that use msquic as client, and a go app that serve a quic server

I build my c++ client with cmake, CMAKE_GENERATOR "Visual Studio 17 2022"

When i build and run in Release mode, it works.

But when i do it in Debug mode, my server receive a packet length of : 3722304989 (it is normally 10 or 11 bytes)

I read that : "The value 3722304989 in hexadecimal is 0xDDDDDDDD, which is a common pattern used by some debug memory allocators to fill uninitialized memory."

am i doing something wrong ?

here is how i send data :

bool QuicClient::sendData(const QByteArray &data, const HQUIC &stream, int screenIndex)
{
    QUIC_STATUS status;
    QByteArray prefixedData;
    QDataStream prefixStream(&prefixedData, QIODevice::WriteOnly);
    prefixStream.setByteOrder(QDataStream::BigEndian);
    
    quint32 dataSize = static_cast<quint32>(data.size());
    quint32 screenIndexUint = static_cast<quint32>(screenIndex);
   
    // Write data length (4 bytes)
    prefixStream << dataSize;
    
    // Write screen index (4 bytes)
    prefixStream << screenIndexUint;
    
    // Append the actual msgpack data
    prefixedData.append(data);

    QUIC_BUFFER *buffer = new QUIC_BUFFER();
    buffer->Buffer = reinterpret_cast<uint8_t *>(const_cast<char *>(prefixedData.constData()));
    buffer->Length = prefixedData.size();

    if (QUIC_FAILED(status = msQuicApi->StreamSend(stream, buffer, 1, QUIC_SEND_FLAG_ALLOW_0_RTT, nullptr)))
    {
        qDebug() << "Failed to send data with status:" << status;
        return false;
    }

    return true;
}

Thanks for your help

[nibanks]

prefixedData is a local variable in this function and does not stay allocated for the lifetime of the StreamSend. The API call returns PENDING, and you need to keep the buffer and all memory it points to allocated until you get a SEND_COMPLETE event for this. Currently, you return immediately and free the memory. So MsQuic ends doing a use-after-free and tries to send junk...

[vitoo]

Thanks you @nibanks, now it works in debug !

//edited, wrong code

[vitoo]

So i have done like this to handle pending change and it works

if you have any recommendation @nibanks, i am listening, thanks

Sending :

    uint64_t sendId = nextSendId++;
    // Create a new PendingSend object
    PendingSend pendingSend;
    pendingSend.buffer = new QUIC_BUFFER();
    pendingSend.buffer->Buffer = reinterpret_cast<uint8_t *>(const_cast<char *>(prefixedData.constData()));
    pendingSend.buffer->Length = prefixedData.size();
    pendingSend.data = prefixedData; // Store a copy of the data
    // Store the PendingSend object in the map
    pendingSends[sendId] = std::move(pendingSend);

    if (QUIC_FAILED(status = msQuicApi->StreamSend(stream, pendingSends[sendId].buffer, 1, QUIC_SEND_FLAG_ALLOW_0_RTT, reinterpret_cast<void *>(sendId))))
    {
        qDebug() << "Failed to send data with status:" << status;
        delete pendingSends[sendId].buffer;
        pendingSends.remove(sendId);
        return false;
    }

send complete :

    case QUIC_STREAM_EVENT_SEND_COMPLETE:
    {
        uint64_t sendId = reinterpret_cast<uint64_t>(event->SEND_COMPLETE.ClientContext);
        auto it = client->pendingSends.find(sendId);
        if (it != client->pendingSends.end())
        {
            delete it->buffer;              // Free the QUIC_BUFFER
            client->pendingSends.erase(it); // Remove from map, which will also free the QByteArray
            // qDebug() << "Send completed for sendId:" << sendId;
        }
        else
        {
            qDebug() << "Received SEND_COMPLETE for unknown sendId:" << sendId;
        }
    }