Method loadPipeSource

src/core/PipeWireAudioBridge.cpp:231–293

}

bool PipeWireAudioBridge::loadPipeSource(int index)
{
    // FIFO lives in the per-user XDG runtime directory with mode 0600.
    // Pre-fix code used /tmp/aethersdr-dax-%1.pipe with mode 0666, which
    // any local user could read (operator RX audio) or write (operator
    // TX audio with the licensed callsign — an FCC liability).
    // See GHSA-x8xf-4g5v-ppf9.
    const QString fifoDir = daxFifoDir();
    if (fifoDir.isEmpty()) return false;
    auto pipePath = QStringLiteral("%1/dax-%2.pipe").arg(fifoDir).arg(index + 1);
    auto sourceName = QStringLiteral("aethersdr-dax-%1").arg(index + 1);
    auto sourceDesc = QStringLiteral("AetherSDR DAX %1").arg(index + 1);

    if (!makeOwnedFifo(pipePath)) return false;

    // Load PulseAudio pipe-source module.
    // Format/rate match the PipeWire graph (48 kHz float32) so PipeWire does
    // not insert a resampler on this node — that resampler is the dominant
    // remaining latency source after pipe_size was reduced (see issue #1008).
    // node.latency=256/48000 (~5.3 ms quantum) tells PipeWire to negotiate a
    // small quantum for this node instead of falling back to clock.quantum-limit.
    uint32_t modIdx = runPactl({
        "load-module", "module-pipe-source",
        QStringLiteral("file=%1").arg(pipePath),
        QStringLiteral("source_name=%1").arg(sourceName),
        // Single-quoted: the pipewire-pulse pulse-module argument parser splits
        // the property value on unescaped whitespace, so unquoted the space in
        // "AetherSDR DAX N" truncates device.description to "AetherSDR" and
        // orphans node.latency. node.description is derived from
        // device.description, so this also labels the node in qpwgraph / JACK.
        QStringLiteral("source_properties='device.description=\"%1\" node.latency=256/48000'").arg(sourceDesc),
        QStringLiteral("format=float32le"),
        QStringLiteral("rate=%1").arg(PIPE_RATE),
        QStringLiteral("channels=%1").arg(PIPE_CHANNELS),
    });

    if (modIdx == 0) {
        ::unlink(pipePath.toUtf8().constData());
        return false;
    }

    // Open the pipe for writing (non-blocking to avoid hanging if no reader)
    int fd = ::open(pipePath.toUtf8().constData(), O_WRONLY | O_NONBLOCK);
    if (fd < 0) {
        qCWarning(lcDax) << "PipeWireAudioBridge: open pipe failed:" << strerror(errno);
        runPactl({"unload-module", QString::number(modIdx)});
        ::unlink(pipePath.toUtf8().constData());
        return false;
    }

    // Cap kernel FIFO capacity so back-pressure surfaces quickly instead of
    // accumulating ~1.3 s of audio in the default 64 KB pipe buffer.
    if (::fcntl(fd, F_SETPIPE_SZ, PIPE_KERNEL_BUF) < 0) {
        qCDebug(lcDax) << "PipeWireAudioBridge: F_SETPIPE_SZ failed (non-fatal):" << strerror(errno);
    }

    m_rx[index].fd = fd;
    m_rx[index].moduleIndex = modIdx;