MockLinkFTP.cc

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#include "MockLinkFTP.h"
#include "MockLink.h"
#include "QGCLoggingCategory.h"
 
#include <QtCore/QDataStream>
#include <QtCore/QDir>
#include <QtCore/QTemporaryFile>
 
QGC_LOGGING_CATEGORY(MockLinkFTPLog, "Comms.MockLink.MockLinkFTP")
 
MockLinkFTP::MockLinkFTP(uint8_t systemIdServer, uint8_t componentIdServer, MockLink *mockLink)
    : QObject(mockLink)
    , _systemIdServer(systemIdServer)
    , _componentIdServer(componentIdServer)
    , _mockLink(mockLink)
{
    // qCDebug(MockLinkFTPLog) << Q_FUNC_INFO << this;
}
 
MockLinkFTP::~MockLinkFTP()
{
    if (!_paramPckTempFile.isEmpty()) {
        QFile::remove(_paramPckTempFile);
    }
}
 
void MockLinkFTP::ensureNullTemination(MavlinkFTP::Request *request)
{
    if (request->hdr.size < sizeof(request->data)) {
        request->data[request->hdr.size] = '\0';
    } else {
        request->data[sizeof(request->data) - 1] = '\0';
    }
}
 
void MockLinkFTP::_listCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber, bool withTime)
{
    MavlinkFTP::Request ackResponse{};
    ensureNullTemination(request);
 
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
    const MavlinkFTP::OpCode_t listOpCode = withTime ? MavlinkFTP::kCmdListDirectoryWithTime : MavlinkFTP::kCmdListDirectory;
 
    if (withTime && !_listDirectoryWithTimeSupported) {
        // Simulate a server which doesn't implement the command. The client should fall back to kCmdListDirectory.
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrUnknownCommand, outgoingSeqNumber, listOpCode);
        return;
    }
 
    // We only support root path
    const QString path = reinterpret_cast<char*>(&request->data[0]);
    if (!path.isEmpty() && path != "/") {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, listOpCode);
        return;
    }
 
    if (request->hdr.offset > 0) {
        if (_errMode == errModeNakSecondResponse) {
            // Nak error all subsequent requests
            _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, listOpCode);
            return;
        }
 
        if (_errMode == errModeNoSecondResponse) {
            // No response for all subsequent requests
            return;
        }
 
        if (_errMode == errModeNoSecondResponseAllowRetry) {
            // No response to this request, subsequent requests will succeed
            _errMode = errModeNone;
            return;
        }
    }
 
    ackResponse.hdr.opcode = MavlinkFTP::kRspAck;
    ackResponse.hdr.req_opcode = listOpCode;
    ackResponse.hdr.session = 0;
    ackResponse.hdr.offset = request->hdr.offset;
    ackResponse.hdr.size = 0;
 
    // Entry format is "F<name>\t<size>", plus a trailing "\t<modification time>" for kCmdListDirectoryWithTime.
    const auto makeEntry = [withTime](uint32_t index) {
        QString entry = QStringLiteral("Ffile%1.txt\t%2").arg(index).arg(1024 + index);
        if (withTime) {
            entry += QStringLiteral("\t%1").arg(kMockModificationTime + index);
        }
        return entry;
    };
 
    // MockLink sends two directory entries per packet for a maximum of 3 packets, 6 total entries
    if (request->hdr.offset <= 5) {
        char *bufPtr = reinterpret_cast<char*>(&ackResponse.data[0]);
        QString dirEntry = makeEntry(request->hdr.offset);
        auto cchDirEntry = dirEntry.length();
        (void) strncpy(bufPtr, dirEntry.toStdString().c_str(), cchDirEntry);
        ackResponse.hdr.size += dirEntry.length() + 1;
        bufPtr += cchDirEntry + 1;
        dirEntry = makeEntry(request->hdr.offset + 1);
        cchDirEntry = dirEntry.length();
        (void) strncpy(bufPtr, dirEntry.toStdString().c_str(), cchDirEntry);
        ackResponse.hdr.size += dirEntry.length() + 1;
    } else {
        ackResponse.hdr.opcode = MavlinkFTP::kRspNak;
        ackResponse.data[0] = MavlinkFTP::kErrEOF;
        ackResponse.hdr.size = 1;
    }
 
    _sendResponse(senderSystemId, senderComponentId, &ackResponse, outgoingSeqNumber);
}
 
void MockLinkFTP::_openCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    MavlinkFTP::Request response{};
    ensureNullTemination(request);
    const QString path = reinterpret_cast<char*>(request->data);
 
    _uploadSession.reset();
 
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    const size_t cchPath = strnlen(reinterpret_cast<char*>(request->data), sizeof(request->data));
    Q_ASSERT(cchPath != sizeof(request->data));
    Q_UNUSED(cchPath); // Fix initialized-but-not-referenced warning on release builds
 
    _currentFile.close();
 
    QString tmpFilename;
    const QString sizePrefix = sizeFilenamePrefix;
    if (path.startsWith(sizePrefix)) {
        const QString sizeString = path.right(path.length() - sizePrefix.length());
        tmpFilename = _createTestTempFile(sizeString.toInt());
    } else if (path == "/general.json") {
        tmpFilename = QStringLiteral(":MockLink/General.MetaData.json");
    } else if (path == "/general.json.xz") {
        tmpFilename = QStringLiteral(":MockLink/General.MetaData.json.xz");
    } else if (path == "/parameter.json") {
        tmpFilename = QStringLiteral(":MockLink/Parameter.MetaData.json");
    } else if (path == "/parameter.json.xz") {
        tmpFilename = QStringLiteral(":MockLink/Parameter.MetaData.json.xz");
    } else if (path == "@PARAM/param.pck" || path.startsWith("@PARAM/param.pck?")) {
        const bool withDefaults = path.contains(QStringLiteral("withdefaults=1"));
        tmpFilename = _generateParamPck(withDefaults);
    }
 
    if (!tmpFilename.isEmpty()) {
        _currentFile.setFileName(tmpFilename);
        if (!_currentFile.open(QIODevice::ReadOnly)) {
            _sendNakErrno(senderSystemId, senderComponentId, _currentFile.error(), outgoingSeqNumber, MavlinkFTP::kCmdOpenFileRO);
            return;
        }
    } else {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFailFileNotFound, outgoingSeqNumber, MavlinkFTP::kCmdOpenFileRO);
        return;
    }
 
    response.hdr.opcode = MavlinkFTP::kRspAck;
    response.hdr.req_opcode = MavlinkFTP::kCmdOpenFileRO;
    response.hdr.session = _sessionId;
 
    // Data contains file length
    response.hdr.size = sizeof(uint32_t);
 
    // Ardupilot sends constant wrong file size for parameter file due to dynamic on the fly generation
    response.openFileLength = ((path == "@PARAM/param.pck" || path.startsWith("@PARAM/param.pck?")) ? qPow(1024, 2) : _currentFile.size());
 
    _sendResponse(senderSystemId, senderComponentId, &response, outgoingSeqNumber);
}
 
void MockLinkFTP::_createFileCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    ensureNullTemination(request);
 
    const QString path = reinterpret_cast<char*>(request->data);
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    if (path.isEmpty()) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdCreateFile);
        return;
    }
 
    _uploadSession.reset();
    _uploadSession.active = true;
    _uploadSession.remotePath = path;
 
    MavlinkFTP::Request response{};
    response.hdr.opcode = MavlinkFTP::kRspAck;
    response.hdr.req_opcode = MavlinkFTP::kCmdCreateFile;
    response.hdr.session = _sessionId;
    response.hdr.size = 0;
 
    _sendResponse(senderSystemId, senderComponentId, &response, outgoingSeqNumber);
}
 
void MockLinkFTP::_openFileWOCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    ensureNullTemination(request);
 
    const QString path = reinterpret_cast<char*>(request->data);
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    if (path.isEmpty()) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdOpenFileWO);
        return;
    }
 
    _uploadSession.reset();
    _uploadSession.active = true;
    _uploadSession.remotePath = path;
 
    MavlinkFTP::Request response{};
    response.hdr.opcode = MavlinkFTP::kRspAck;
    response.hdr.req_opcode = MavlinkFTP::kCmdOpenFileWO;
    response.hdr.session = _sessionId;
    response.hdr.size = 0;
 
    _sendResponse(senderSystemId, senderComponentId, &response, outgoingSeqNumber);
}
 
void MockLinkFTP::_readCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    MavlinkFTP::Request response{};
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    if (request->hdr.session != _sessionId) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrInvalidSession, outgoingSeqNumber, MavlinkFTP::kCmdReadFile);
        return;
    }
 
    const uint32_t readOffset = request->hdr.offset;  // offset into file for reading
    if (readOffset != 0) {
        // If we get here it means the client is requesting additional data past the first request
        if (_errMode == errModeNakSecondResponse) {
            // Nak error all subsequent requests
            _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdReadFile);
            return;
        }
 
        if (_errMode == errModeNoSecondResponse) {
            // No rsponse for all subsequent requests
            return;
        }
    }
 
    if (readOffset >= _currentFile.size()) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrEOF, outgoingSeqNumber, MavlinkFTP::kCmdReadFile);
        return;
    }
 
    const uint8_t cBytesToRead = static_cast<uint8_t>(qMin(static_cast<qint64>(sizeof(response.data)), _currentFile.size() - readOffset));
    (void) _currentFile.seek(readOffset);
    const QByteArray bytes = _currentFile.read(cBytesToRead);
    (void) memcpy(response.data, bytes.constData(), cBytesToRead);
 
    // We should always have written something, otherwise there is something wrong with the code above
    Q_ASSERT(cBytesToRead);
 
    response.hdr.session = _sessionId;
    response.hdr.size = cBytesToRead;
    response.hdr.offset = request->hdr.offset;
    response.hdr.opcode = MavlinkFTP::kRspAck;
    response.hdr.req_opcode = MavlinkFTP::kCmdReadFile;
 
    _sendResponse(senderSystemId, senderComponentId, &response, outgoingSeqNumber);
}
 
void MockLinkFTP::_burstReadCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    MavlinkFTP::Request response{};
    uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    if (request->hdr.session != _sessionId) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdBurstReadFile);
        return;
    }
 
    constexpr int burstMax = 10;
    int burstCount = 1;
    uint32_t burstOffset = request->hdr.offset;
 
    while ((burstOffset < _currentFile.size()) && (burstCount++ < burstMax)) {
        _currentFile.seek(burstOffset);
 
        const uint8_t cBytes = static_cast<uint8_t>(qMin(static_cast<qint64>(sizeof(response.data)), _currentFile.size() - burstOffset));
        const QByteArray bytes = _currentFile.read(cBytes);
        Q_ASSERT(cBytes); // We should always have written something, otherwise there is something wrong with the code above
 
        (void) memcpy(response.data, bytes.constData(), cBytes);
 
        response.hdr.session = _sessionId;
        response.hdr.size = cBytes;
        response.hdr.offset = burstOffset;
        response.hdr.opcode = MavlinkFTP::kRspAck;
        response.hdr.req_opcode = MavlinkFTP::kCmdBurstReadFile;
        response.hdr.burstComplete = (burstCount == burstMax) ? 1 : 0;
 
        _sendResponse(senderSystemId, senderComponentId, &response, outgoingSeqNumber);
 
        outgoingSeqNumber = _nextSeqNumber(outgoingSeqNumber);
        burstOffset += cBytes;
    }
 
    if (burstOffset >= _currentFile.size()) {
        // Burst is fully complete
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrEOF, outgoingSeqNumber, MavlinkFTP::kCmdBurstReadFile);
    }
}
 
void MockLinkFTP::_terminateCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    if (request->hdr.session != _sessionId) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrInvalidSession, outgoingSeqNumber, MavlinkFTP::kCmdTerminateSession);
        return;
    }
 
    _currentFile.close();
    _sendAck(senderSystemId, senderComponentId, outgoingSeqNumber, MavlinkFTP::kCmdTerminateSession);
 
    _finalizeActiveUpload();
 
    emit terminateCommandReceived();
}
 
void MockLinkFTP::_resetCommand(uint8_t senderSystemId, uint8_t senderComponentId, uint16_t seqNumber)
{
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    _currentFile.close();
    _sendAck(senderSystemId, senderComponentId, outgoingSeqNumber, MavlinkFTP::kCmdResetSessions);
 
    _finalizeActiveUpload();
 
    emit resetCommandReceived();
}
 
void MockLinkFTP::_writeCommand(uint8_t senderSystemId, uint8_t senderComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    const uint16_t outgoingSeqNumber = _nextSeqNumber(seqNumber);
 
    if ((request->hdr.session != _sessionId) || !_uploadSession.active) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrInvalidSession, outgoingSeqNumber, MavlinkFTP::kCmdWriteFile);
        return;
    }
 
    if (request->hdr.offset > static_cast<uint32_t>(_uploadSession.buffer.size())) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdWriteFile);
        return;
    }
 
    if (request->hdr.offset != 0) {
        if (_errMode == errModeNakSecondResponse) {
            _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdWriteFile);
            return;
        }
 
        if (_errMode == errModeNoSecondResponse) {
            return;
        }
 
        if (_errMode == errModeNoSecondResponseAllowRetry) {
            _errMode = errModeNone;
            return;
        }
    }
 
    const uint32_t bytesToWrite = request->hdr.size;
    if (bytesToWrite > sizeof(request->data)) {
        _sendNak(senderSystemId, senderComponentId, MavlinkFTP::kErrFail, outgoingSeqNumber, MavlinkFTP::kCmdWriteFile);
        return;
    }
 
    const uint32_t requiredSize = request->hdr.offset + bytesToWrite;
    if (requiredSize > static_cast<uint32_t>(_uploadSession.buffer.size())) {
        _uploadSession.buffer.resize(requiredSize);
    }
 
    if (bytesToWrite > 0) {
        (void) memcpy(_uploadSession.buffer.data() + request->hdr.offset, request->data, bytesToWrite);
    }
 
    MavlinkFTP::Request response{};
    response.hdr.opcode = MavlinkFTP::kRspAck;
    response.hdr.req_opcode = MavlinkFTP::kCmdWriteFile;
    response.hdr.session = _sessionId;
    response.hdr.size = 0;
    response.hdr.offset = request->hdr.offset;
 
    _sendResponse(senderSystemId, senderComponentId, &response, outgoingSeqNumber);
}
 
void MockLinkFTP::_finalizeActiveUpload()
{
    if (!_uploadSession.active) {
        return;
    }
 
    if (!_uploadSession.remotePath.isEmpty()) {
        _uploadedFiles.insert(_uploadSession.remotePath, _uploadSession.buffer);
    }
 
    _uploadSession.reset();
}
 
void MockLinkFTP::mavlinkMessageReceived(const mavlink_message_t &message)
{
    if (message.msgid != MAVLINK_MSG_ID_FILE_TRANSFER_PROTOCOL) {
        return;
    }
 
    mavlink_file_transfer_protocol_t requestFTP{};
    mavlink_msg_file_transfer_protocol_decode(&message, &requestFTP);
 
    if (requestFTP.target_system != _systemIdServer) {
        return;
    }
 
    MavlinkFTP::Request *request = reinterpret_cast<MavlinkFTP::Request*>(&requestFTP.payload[0]);
 
    // kCmdOpenFileRO and kCmdResetSessions don't support retry so we can't drop those
    if (_randomDropsEnabled && (request->hdr.opcode != MavlinkFTP::kCmdOpenFileRO) && (request->hdr.opcode != MavlinkFTP::kCmdResetSessions)) {
        if ((rand() % 5) == 0) {
            qCDebug(MockLinkFTPLog) << "MockLinkFTP: Random drop of incoming packet";
            return;
        }
    }
 
    if (_lastReplyValid && (request->hdr.seqNumber == (_lastReplySequence - 1))) {
        // This is the same request as the one we replied to last. It means the (n)ack got lost, and the GCS
        // resent the request
        qCDebug(MockLinkFTPLog) << "MockLinkFTP: resending response";
        _mockLink->respondWithMavlinkMessage(_lastReply);
        return;
    }
 
    const uint16_t incomingSeqNumber = request->hdr.seqNumber;
    const uint16_t outgoingSeqNumber = _nextSeqNumber(incomingSeqNumber);
 
    if ((request->hdr.opcode != MavlinkFTP::kCmdResetSessions) && (request->hdr.opcode != MavlinkFTP::kCmdTerminateSession)) {
        if (_errMode == errModeNoResponse) {
            // Don't respond to any requests, this shold cause the client to eventually timeout waiting for the ack
            return;
        }
 
        if (_errMode == errModeNakResponse) {
            // Nak all requests, the actual error send back doesn't really matter as long as it's an error
            _sendNak(message.sysid, message.compid, MavlinkFTP::kErrFail, outgoingSeqNumber, static_cast<MavlinkFTP::OpCode_t>(request->hdr.opcode));
            return;
        }
    }
 
    MavlinkFTP::Request ackResponse{};
    switch (request->hdr.opcode) {
    case MavlinkFTP::kCmdNone:
        // ignored, always acked
        ackResponse.hdr.opcode = MavlinkFTP::kRspAck;
        ackResponse.hdr.session = 0;
        ackResponse.hdr.size = 0;
        _sendResponse(message.sysid, message.compid, &ackResponse, outgoingSeqNumber);
        break;
    case MavlinkFTP::kCmdListDirectory:
        _listCommand(message.sysid, message.compid, request, incomingSeqNumber, false /* withTime */);
        break;
    case MavlinkFTP::kCmdListDirectoryWithTime:
        _listCommand(message.sysid, message.compid, request, incomingSeqNumber, true /* withTime */);
        break;
    case MavlinkFTP::kCmdOpenFileRO:
        _openCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdCreateFile:
        _createFileCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdOpenFileWO:
        _openFileWOCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdReadFile:
        _readCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdBurstReadFile:
        _burstReadCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdWriteFile:
        _writeCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdTerminateSession:
        _terminateCommand(message.sysid, message.compid, request, incomingSeqNumber);
        break;
    case MavlinkFTP::kCmdResetSessions:
        _resetCommand(message.sysid, message.compid, incomingSeqNumber);
        break;
    default:
        // nack for all NYI opcodes
        _sendNak(message.sysid, message.compid, MavlinkFTP::kErrUnknownCommand, outgoingSeqNumber, static_cast<MavlinkFTP::OpCode_t>(request->hdr.opcode));
        break;
    }
}
 
void MockLinkFTP::_sendAck(uint8_t targetSystemId, uint8_t targetComponentId, uint16_t seqNumber, MavlinkFTP::OpCode_t reqOpcode)
{
    MavlinkFTP::Request ackResponse{};
 
    ackResponse.hdr.opcode = MavlinkFTP::kRspAck;
    ackResponse.hdr.req_opcode = reqOpcode;
    ackResponse.hdr.session = _sessionId;
    ackResponse.hdr.size = 0;
 
    _sendResponse(targetSystemId, targetComponentId, &ackResponse, seqNumber);
}
 
void MockLinkFTP::_sendNak(uint8_t targetSystemId, uint8_t targetComponentId, MavlinkFTP::ErrorCode_t error, uint16_t seqNumber, MavlinkFTP::OpCode_t reqOpcode)
{
    MavlinkFTP::Request nakResponse{};
 
    nakResponse.hdr.opcode = MavlinkFTP::kRspNak;
    nakResponse.hdr.req_opcode = reqOpcode;
    nakResponse.hdr.session = _sessionId;
    nakResponse.hdr.size = 1;
    nakResponse.data[0] = error;
 
    _sendResponse(targetSystemId, targetComponentId, &nakResponse, seqNumber);
}
 
void MockLinkFTP::_sendNakErrno(uint8_t targetSystemId, uint8_t targetComponentId, uint8_t nakErrno, uint16_t seqNumber, MavlinkFTP::OpCode_t reqOpcode)
{
    MavlinkFTP::Request nakResponse{};
 
    nakResponse.hdr.opcode = MavlinkFTP::kRspNak;
    nakResponse.hdr.req_opcode = reqOpcode;
    nakResponse.hdr.session = _sessionId;
    nakResponse.hdr.size = 2;
    nakResponse.data[0] = MavlinkFTP::kErrFailErrno;
    nakResponse.data[1] = nakErrno;
 
    _sendResponse(targetSystemId, targetComponentId, &nakResponse, seqNumber);
}
 
 
void MockLinkFTP::_sendResponse(uint8_t targetSystemId, uint8_t targetComponentId, MavlinkFTP::Request *request, uint16_t seqNumber)
{
    request->hdr.seqNumber = seqNumber;
    _lastReplySequence = seqNumber;
    _lastReplyValid = true;
 
    (void) mavlink_msg_file_transfer_protocol_pack_chan(
        _systemIdServer,                    // System ID
        _componentIdServer,                 // Component ID
        _mockLink->mavlinkChannel(),
        &_lastReply,                        // Mavlink Message to pack into
        0,                                  // Target network
        targetSystemId,
        targetComponentId,
        reinterpret_cast<uint8_t*>(request) // Payload
    );
 
    // kCmdOpenFileRO and kCmdResetSessions don't support retry so we can't drop those
    if (_randomDropsEnabled && (request->hdr.req_opcode != MavlinkFTP::kCmdOpenFileRO) && (request->hdr.req_opcode != MavlinkFTP::kCmdResetSessions)) {
        if ((rand() % 5) == 0) {
            qCDebug(MockLinkFTPLog) << "MockLinkFTP: Random drop of outgoing packet";
            return;
        }
    }
 
    _mockLink->respondWithMavlinkMessage(_lastReply);
}
 
 
uint16_t MockLinkFTP::_nextSeqNumber(uint16_t seqNumber) const
{
    uint16_t outgoingSeqNumber = seqNumber + 1;
 
    if (_errMode == errModeBadSequence) {
        outgoingSeqNumber++;
    }
 
    return outgoingSeqNumber;
}
 
QString MockLinkFTP::_createTestTempFile(int size)
{
    QTemporaryFile tmpFile(QDir::tempPath() + QStringLiteral("/MockLinkFTPTestCaseXXXXXX"));
    tmpFile.setAutoRemove(false);
 
    if (tmpFile.open()) {
        for (int i = 0; i < size; i++) {
            (void) tmpFile.write(QByteArray(1, static_cast<char>(i % 255)));
        }
        tmpFile.close();
    }
 
    return tmpFile.fileName();
}
 
QString MockLinkFTP::_generateParamPck(bool withDefaults)
{
    // AP_PARAM types used in the binary param.pck format
    enum APParamType : quint8 {
        AP_PARAM_INT8  = 1,
        AP_PARAM_INT16 = 2,
        AP_PARAM_INT32 = 3,
        AP_PARAM_FLOAT = 4,
    };
 
    // ArduPilot binary param.pck format magic numbers.
    // See AP_Filesystem_Param.cpp in ArduPilot source (AP_PARAM_HEADER_MAGIC / AP_PARAM_HEADER_MAGIC_DEFAULT).
    constexpr quint16 magicStandard     = 0x671B; // param.pck without defaults
    constexpr quint16 magicWithDefaults = 0x671C; // param.pck?withdefaults=1
    constexpr int readSize = 239; // Max data bytes per MAVLink FTP burst: MAVLink payload (251 bytes) minus FTP header (12 bytes) = 239.
                                 // This matches the MAVLink FTP spec / PX4-ArduPilot implementations and is critical to correct chunking and padding.
 
    // Get params for component 1 (MAV_COMP_ID_AUTOPILOT1)
    constexpr int compId = 1;
    const auto &valueMap = _mockLink->_mapParamName2Value;
    const auto &typeMap  = _mockLink->_mapParamName2MavParamType;
    if (!valueMap.contains(compId) || !typeMap.contains(compId)) {
        qCWarning(MockLinkFTPLog) << "_generateParamPck: no parameters for component" << compId;
        return QString();
    }
 
    const auto &values = valueMap[compId];
    const auto &types  = typeMap[compId];
 
    // Sort parameter names alphabetically (matching ArduPilot behavior)
    QStringList paramNames = values.keys();
    paramNames.sort();
 
    const quint16 numParams = static_cast<quint16>(paramNames.size());
 
    // Map MAV_PARAM_TYPE to AP_PARAM type and value size
    auto mapType = [](MAV_PARAM_TYPE mavType, quint8 &apType, int &valueSize) {
        switch (mavType) {
        case MAV_PARAM_TYPE_UINT8:
        case MAV_PARAM_TYPE_INT8:
            apType = AP_PARAM_INT8;
            valueSize = 1;
            break;
        case MAV_PARAM_TYPE_UINT16:
        case MAV_PARAM_TYPE_INT16:
            apType = AP_PARAM_INT16;
            valueSize = 2;
            break;
        case MAV_PARAM_TYPE_UINT32:
        case MAV_PARAM_TYPE_INT32:
            apType = AP_PARAM_INT32;
            valueSize = 4;
            break;
        case MAV_PARAM_TYPE_REAL32:
            apType = AP_PARAM_FLOAT;
            valueSize = 4;
            break;
        default:
            apType = AP_PARAM_FLOAT;
            valueSize = 4;
            break;
        }
    };
 
    QByteArray data;
    QDataStream stream(&data, QIODevice::WriteOnly);
    stream.setByteOrder(QDataStream::LittleEndian);
 
    // Write header
    const quint16 magic = withDefaults ? magicWithDefaults : magicStandard;
    stream << magic << numParams << numParams;
 
    QByteArray previousName;
    constexpr int headerSize = 6; // 2 bytes magic + 2 bytes numParams + 2 bytes totalParams
 
    for (const QString &name : paramNames) {
        const QVariant &value = values[name];
        const MAV_PARAM_TYPE mavType = types[name];
        const QByteArray nameBytes = name.toLatin1();
 
        quint8 apType = 0;
        int valueSize = 0;
        mapType(mavType, apType, valueSize);
 
        // Compute common prefix with previous parameter name
        const int previousNameLen = previousName.size();
        const int currentNameLen = nameBytes.size();
        int commonLen = 0;
        // common_len is limited to 15 because common_len + name_len <= 16 and name_len must be >= 1
        const int maxCommon = std::min({previousNameLen, currentNameLen, 15});
        while (commonLen < maxCommon && nameBytes[commonLen] == previousName[commonLen]) {
            commonLen++;
        }
 
        int nameLen = currentNameLen - commonLen;
        // name_len is encoded as (name_len - 1) in 4 bits, so it must be >= 1.
        // If the entire name matched the common prefix, steal one char back.
        if (nameLen == 0 && commonLen > 0) {
            nameLen = 1;
            commonLen--;
        }
        // Ensure name_len + common_len <= 16
        if (nameLen + commonLen > 16) {
            commonLen = 16 - nameLen;
        }
        // name_len must fit in 4 bits as (name_len - 1)
        if (nameLen > 16) {
            nameLen = 16;
            commonLen = 0;
        }
 
        // For ArduPilot, calibration-indicator parameters have a firmware default of 0
        // (uncalibrated). All other parameters use their current value as the default,
        // since MockLink params are loaded from a snapshot and we have no separate
        // defaults file.
        const bool useZeroDefault = withDefaults
            && (_mockLink->getFirmwareType() == MAV_AUTOPILOT_ARDUPILOTMEGA)
            && MockLink::kAPMCalOffsetParams.contains(name);
        const bool addDefault = withDefaults;
        const quint8 flags = addDefault ? 0x01 : 0x00;
        const int packedLen = 2 + nameLen + valueSize + (addDefault ? valueSize : 0);
 
        // FTP reads data in fixed-size blocks (readSize = 239 bytes, the MAVLink FTP
        // payload). If a multi-byte value straddles a block boundary, a retransmitted
        // block could overwrite part of the value with stale data, corrupting it.
        // To prevent this, ArduPilot inserts zero-byte padding before the entry so
        // the value bytes land entirely within one block. The parser skips leading
        // zeros between entries. See AP_Filesystem_Param::pack_param.
        if (valueSize > 1) {
            const quint32 dataOfs = static_cast<quint32>(data.size()) - headerSize;
            const quint32 endOfs = dataOfs + static_cast<quint32>(packedLen);
            const quint32 endMod = endOfs % readSize;
            if (endMod > 0 && endMod < static_cast<quint32>(valueSize)) {
                const int pad = valueSize - static_cast<int>(endMod);
                for (int i = 0; i < pad; i++) {
                    stream << static_cast<quint8>(0);
                }
            }
        }
 
        // Type + flags byte
        stream << static_cast<quint8>(apType | (flags << 4));
        // Name encoding byte: upper 4 bits = (name_len - 1), lower 4 bits = common_len
        stream << static_cast<quint8>(((nameLen - 1) << 4) | commonLen);
        // Write the unique suffix of the name
        stream.writeRawData(nameBytes.constData() + commonLen, nameLen);
 
        // Write parameter value
        switch (apType) {
        case AP_PARAM_INT8: {
            const qint8 v = static_cast<qint8>(value.toInt());
            stream << v;
            if (addDefault) stream << (useZeroDefault ? qint8(0) : v);
            break;
        }
        case AP_PARAM_INT16: {
            const qint16 v = static_cast<qint16>(value.toInt());
            stream << v;
            if (addDefault) stream << (useZeroDefault ? qint16(0) : v);
            break;
        }
        case AP_PARAM_INT32: {
            const qint32 v = value.toInt();
            stream << v;
            if (addDefault) stream << (useZeroDefault ? qint32(0) : v);
            break;
        }
        case AP_PARAM_FLOAT: {
            const float f = value.toFloat();
            qint32 raw;
            memcpy(&raw, &f, sizeof(raw));
            stream << raw;
            if (addDefault) {
                if (useZeroDefault) {
                    stream << qint32(0);
                } else {
                    stream << raw;
                }
            }
            break;
        }
        }
 
        previousName = nameBytes;
    }
 
    // Clean up previous temp file
    if (!_paramPckTempFile.isEmpty()) {
        QFile::remove(_paramPckTempFile);
        _paramPckTempFile.clear();
    }
 
    // Write to temp file
    QTemporaryFile tmpFile(QDir::temp().filePath(QStringLiteral("MockLinkParamPckXXXXXX")));
    tmpFile.setAutoRemove(false);
 
    if (!tmpFile.open()) {
        qCWarning(MockLinkFTPLog) << "_generateParamPck: failed to create temp file";
        return QString();
    }
 
    tmpFile.write(data);
    tmpFile.close();
    _paramPckTempFile = tmpFile.fileName();
 
    qCDebug(MockLinkFTPLog) << "_generateParamPck: generated" << numParams << "params,"
                            << data.size() << "bytes, withDefaults:" << withDefaults
                            << "file:" << tmpFile.fileName();
 
    return tmpFile.fileName();
}