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XModemAdapter: ensure file truncation before receiving and add isBusy() method to prevent concurrent writes

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This commit is contained in:
Ben Meadors
2026-05-12 15:38:04 -05:00
parent 7ff6641f97
commit d9cb74e4dd
2 changed files with 20 additions and 1 deletions
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15
src/xmodem.cpp
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@@ -123,15 +123,24 @@ void XModemAdapter::handlePacket(meshtastic_XModem xmodemPacket)
filename[sizeof(filename) - 1] = '\0';
if (xmodemPacket.control == meshtastic_XModem_Control_SOH) { // Receive this file and put to Flash
// Truncate the destination before opening. On Adafruit_LittleFS,
// `open(path, FILE_O_WRITE)` is *append* semantics (O_RDWR|O_CREAT +
// seek-to-EOF), so without a prior remove, our XModem-streamed
// payload would be concatenated onto whatever was there, producing
// a corrupt mixed file.
spiLock->lock();
if (FSCom.exists(filename))
FSCom.remove(filename);
file = FSCom.open(filename, FILE_O_WRITE);
spiLock->unlock();
if (file) {
LOG_INFO("XModem: receiving %s", filename);
sendControl(meshtastic_XModem_Control_ACK);
isReceiving = true;
packetno = 1;
break;
}
LOG_WARN("XModem: open(%s, WRITE) failed", filename);
sendControl(meshtastic_XModem_Control_NAK);
isReceiving = false;
break;
@@ -169,8 +178,12 @@ void XModemAdapter::handlePacket(meshtastic_XModem xmodemPacket)
check(xmodemPacket.buffer.bytes, xmodemPacket.buffer.size, xmodemPacket.crc16)) {
// valid packet
spiLock->lock();
file.write(xmodemPacket.buffer.bytes, xmodemPacket.buffer.size);
size_t written = file.write(xmodemPacket.buffer.bytes, xmodemPacket.buffer.size);
spiLock->unlock();
if (written != xmodemPacket.buffer.size) {
LOG_WARN("XModem: short write seq=%d expected=%d wrote=%d (LittleFS partition full?)",
(int)xmodemPacket.seq, (int)xmodemPacket.buffer.size, (int)written);
}
sendControl(meshtastic_XModem_Control_ACK);
packetno++;
break;

6
src/xmodem.h
View File

@@ -52,6 +52,12 @@ class XModemAdapter
meshtastic_XModem getForPhone();
void resetForPhone();
// True while a file is being received from or transmitted to the phone.
// Callers (e.g. NodeDB::saveNodeDatabaseToDisk) consult this to avoid
// opening the same on-disk file for write in parallel, which races our
// long-lived xmodem `file` handle and ends up producing a 0-byte file.
bool isBusy() const { return isReceiving || isTransmitting; }
private:
bool isReceiving = false;
bool isTransmitting = false;