fix(nfc): auto-recover a wedged CCID reader via USB power-cycle
The Feitian R502-CL (and cheap CCID readers generally) can wedge: it keeps detecting a card but every APDU returns "card absent or mute", and ONLY a USB power-cycle clears it — restarting pcscd or the app does not (confirmed on-device). Until now that left cash-out/cash-in taps dead until a manual replug. - nfc-service.ts: count consecutive read failures; after 3 (gated by a 30s cooldown so a still-wedged reader can't reset-loop) trigger nfc-reader-reset.service. nfc-pcsc then re-detects the reader on USB hotplug with no app restart (verified live). - batm3.nix: nfc-reader-reset.service (oneshot, root) re-binds the reader's USB device (a software replug); reader-agnostic via the CCID interface class (0x0B) so it also covers a future ACR1252U. A polkit rule lets the unprivileged `bitspire` app start just that one unit. Hardware track (separate): the durable fix is a better reader (ACR1252U — large antenna for behind-panel, firmware-upgradable). This change makes any reader's wedge a ~2s self-heal in the meantime. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Patrick Mulligan
parent
d00f3c0bbd
commit
ffbacafe39
2 changed files with 96 additions and 4 deletions
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@ -13,6 +13,8 @@
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* QR path keeps working — cash-out never depends on this.
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*/
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import { execFile } from 'node:child_process'
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export type NfcState = 'ready' | 'reading' | 'error' | 'card-removed' | 'unavailable'
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export interface NfcStatus {
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state: NfcState
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@ -83,7 +85,11 @@ export async function readNdefLnurlw(
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const send = (bytes: number[]) => transmit(Buffer.from(bytes), 256)
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// Select the NDEF Tag Application (AID D2760000850101).
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if (!swOk(await send([0x00, 0xa4, 0x04, 0x00, 0x07, 0xd2, 0x76, 0x00, 0x00, 0x85, 0x01, 0x01, 0x00]))) {
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if (
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!swOk(
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await send([0x00, 0xa4, 0x04, 0x00, 0x07, 0xd2, 0x76, 0x00, 0x00, 0x85, 0x01, 0x01, 0x00])
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)
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) {
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return null
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}
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@ -107,6 +113,29 @@ export async function readNdefLnurlw(
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let stopFn: (() => void) | null = null
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// ── Wedge auto-recovery ───────────────────────────────────────────────────
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// Cheap CCID readers (the Feitian R502-CL especially) occasionally wedge: they
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// keep detecting a card but every APDU returns "card absent or mute", and ONLY
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// a USB power-cycle clears it — pcscd/app restarts do NOT. When we see a run of
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// consecutive read failures we trigger nfc-reader-reset.service (a root oneshot
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// that re-binds the reader's USB device = a software replug); nfc-pcsc then
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// re-detects the reader on hotplug with no app restart. The trigger is gated by
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// a cooldown so a still-wedged reader can't reset-loop. A quality reader (e.g.
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// ACR1252U) wedges far less; this is belt-and-suspenders for any reader.
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const WEDGE_FAILURE_THRESHOLD = 3
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const RESET_COOLDOWN_MS = 30_000
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// Persist across reader re-enumerations (a reset spawns a fresh reader closure).
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let lastReaderResetAt = 0
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/** Trigger the privileged USB power-cycle of the reader. Best-effort. */
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function resetWedgedReader(): void {
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// NixOS: the app runs unprivileged as `bitspire`; a polkit rule authorises it
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// to start this one unit. systemctl lives at a stable path on the device.
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execFile('/run/current-system/sw/bin/systemctl', ['start', 'nfc-reader-reset.service'], () => {
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/* best-effort — if it fails the reader stays wedged until a manual reset */
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})
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}
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/**
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* Start listening for Bolt Card taps. Idempotent. Returns a stop function.
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* Never throws — failures surface via onStatus.
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@ -159,6 +188,10 @@ export async function startNfcReader(
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// a present↔empty storm when hammered, so ignore re-detections for a beat
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// after a failure. Successful reads don't cool down.
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let cooldownUntil = 0
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// Consecutive failed reads → wedge detection (see resetWedgedReader above).
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// A completed read (Bolt Card or not) proves the reader is healthy and
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// clears the count; only a run of thrown transmits trips the reset.
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let consecutiveFailures = 0
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r.on('card', async () => {
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if (Date.now() < cooldownUntil) return
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onStatus({ state: 'reading', reader: name })
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@ -167,13 +200,30 @@ export async function startNfcReader(
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// user simply re-taps.
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try {
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const lnurlw = await readNdefLnurlw((apdu, maxLen) => r.transmit(apdu, maxLen))
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consecutiveFailures = 0
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if (lnurlw) {
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onCard(lnurlw)
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return
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}
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onStatus({ state: 'error', reader: name, message: 'not a Bolt Card' })
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} catch (e) {
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onStatus({ state: 'error', reader: name, message: 'card read failed — hold steady & retap' })
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consecutiveFailures++
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if (
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consecutiveFailures >= WEDGE_FAILURE_THRESHOLD &&
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Date.now() - lastReaderResetAt > RESET_COOLDOWN_MS
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) {
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// Reader looks wedged — auto power-cycle it (only fix that works).
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lastReaderResetAt = Date.now()
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consecutiveFailures = 0
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onStatus({ state: 'error', reader: name, message: 'reader stuck — auto-resetting…' })
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resetWedgedReader()
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} else {
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onStatus({
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state: 'error',
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reader: name,
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message: 'card read failed — hold steady & retap',
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})
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}
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void e
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}
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cooldownUntil = Date.now() + 1500
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@ -182,7 +232,9 @@ export async function startNfcReader(
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r.on('error', (err: unknown) =>
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onStatus({ state: 'error', reader: name, message: errMsg(err) })
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)
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r.on('end', () => onStatus({ state: 'unavailable', reader: name, message: 'reader disconnected' }))
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r.on('end', () =>
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onStatus({ state: 'unavailable', reader: name, message: 'reader disconnected' })
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)
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})
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nfc.on('error', (err: unknown) => onStatus({ state: 'error', message: errMsg(err) }))
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@ -94,7 +94,8 @@
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# pcscd gates client access via polkit; without a rule the sandboxed
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# `bitspire` service user is "Rejected unauthorized PC/SC client". Authorize
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# it to talk to the daemon and the card.
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# it to talk to the daemon and the card. The second rule lets the app trigger
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# the NFC reader wedge-recovery service (see nfc-reader-reset below).
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security.polkit.extraConfig = ''
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polkit.addRule(function(action, subject) {
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if ((action.id == "org.debian.pcsc-lite.access_pcsc" ||
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@ -103,8 +104,47 @@
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return polkit.Result.YES;
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}
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});
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polkit.addRule(function(action, subject) {
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if (action.id == "org.freedesktop.systemd1.manage-units" &&
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action.lookup("unit") == "nfc-reader-reset.service" &&
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subject.user == "bitspire") {
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return polkit.Result.YES;
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}
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});
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'';
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# NFC reader wedge-recovery. The Feitian R502-CL CCID reader (and, less often,
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# any CCID reader) can wedge: it keeps detecting a card but every APDU returns
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# "card absent or mute", and ONLY a USB power-cycle clears it — restarting
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# pcscd or the app does not. This oneshot re-binds the reader's USB device (a
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# software replug); pcscd + nfc-pcsc then re-detect it on hotplug with no app
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# restart (verified on-device). The app (unprivileged `bitspire`) starts it via
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# the polkit rule above when it sees repeated read failures. Reader-agnostic:
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# it matches the USB CCID interface class (0x0B), so it also covers a future
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# ACR1252U swap without a config change.
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systemd.services.nfc-reader-reset = {
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description = "Power-cycle a wedged CCID NFC reader (USB re-bind)";
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serviceConfig = {
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Type = "oneshot";
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ExecStart = pkgs.writeShellScript "reset-nfc-reader" ''
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set -u
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found=0
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for iface in /sys/bus/usb/devices/*:*/bInterfaceClass; do
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[ -f "$iface" ] || continue
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[ "$(${pkgs.coreutils}/bin/cat "$iface" 2>/dev/null)" = "0b" ] || continue
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ifname=$(${pkgs.coreutils}/bin/basename "$(${pkgs.coreutils}/bin/dirname "$iface")")
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dev=''${ifname%%:*}
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echo "reset-nfc-reader: power-cycling CCID reader USB device $dev" >&2
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echo -n "$dev" > /sys/bus/usb/drivers/usb/unbind 2>/dev/null || true
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${pkgs.coreutils}/bin/sleep 2
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echo -n "$dev" > /sys/bus/usb/drivers/usb/bind 2>/dev/null || true
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found=1
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done
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[ "$found" = 1 ] || { echo "reset-nfc-reader: no CCID reader found" >&2; exit 1; }
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'';
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};
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};
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# Disable suspend/hibernate for kiosk
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systemd.targets = {
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sleep.enable = false;
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