commit 6008d0e82624c04facdfbb8bc80e0518d4b089c9
parent 5a50c1764be2f885469db3816853ae0beea7a8f1
Author: Iván Ávalos <avalos@disroot.org>
Date: Wed, 22 Jul 2026 12:20:14 +0200
[wallet] implement writing xTOTP codes via NFC
Diffstat:
3 files changed, 161 insertions(+), 4 deletions(-)
diff --git a/wallet/src/main/java/net/taler/wallet/payment/NfcTotpWriter.kt b/wallet/src/main/java/net/taler/wallet/payment/NfcTotpWriter.kt
@@ -0,0 +1,155 @@
+/*
+ * This file is part of GNU Taler
+ * (C) 2026 Taler Systems S.A.
+ *
+ * GNU Taler is free software; you can redistribute it and/or modify it under the
+ * terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3, or (at your option) any later version.
+ *
+ * GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ * A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * GNU Taler; see the file COPYING. If not, see <http://www.gnu.org/licenses/>
+ */
+
+package net.taler.wallet.payment
+
+import android.app.Activity
+import android.nfc.NdefMessage
+import android.nfc.NdefRecord
+import android.nfc.NfcAdapter
+import android.nfc.tech.Ndef
+import android.nfc.tech.NfcA
+import android.widget.Toast
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.material3.Button
+import androidx.compose.material3.ButtonDefaults
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment.Companion.CenterHorizontally
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.font.FontFamily
+import androidx.compose.ui.unit.dp
+import net.taler.wallet.R
+import java.io.ByteArrayOutputStream
+
+private const val NFC_READER_FLAGS = NfcAdapter.FLAG_READER_NFC_A or NfcAdapter.FLAG_READER_NFC_V
+
+private fun formatTotpPayload(totpString: String): ByteArray {
+ val codes = totpString.split("\n").mapNotNull { it.toUIntOrNull() }
+ val out = ByteArrayOutputStream()
+ out.write(0x42)
+ for (code in codes) {
+ val v = code.toInt()
+ out.write(v shr 0 and 0xFF)
+ out.write(v shr 8 and 0xFF)
+ out.write(v shr 16 and 0xFF)
+ out.write(v shr 24 and 0xFF)
+ }
+ return out.toByteArray()
+}
+
+@Composable
+fun TotpNfcWriter(
+ totpString: String,
+ modifier: Modifier = Modifier,
+) {
+ val context = LocalContext.current
+ val activity = context as? Activity
+ var isWriting by remember { mutableStateOf(false) }
+
+ DisposableEffect(activity) {
+ onDispose {
+ if (isWriting && activity != null) {
+ NfcAdapter.getDefaultAdapter(context)?.disableReaderMode(activity)
+ }
+ }
+ }
+
+ val ndefMessage = remember(totpString) {
+ val payload = formatTotpPayload(totpString)
+ val record = NdefRecord(
+ NdefRecord.TNF_WELL_KNOWN,
+ "T".encodeToByteArray(),
+ ByteArray(0),
+ payload,
+ )
+ NdefMessage(arrayOf(record))
+ }
+
+ Column(modifier = modifier, horizontalAlignment = CenterHorizontally) {
+ Text(
+ modifier = Modifier.padding(top = 16.dp, start = 16.dp, end = 16.dp),
+ text = stringResource(R.string.payment_confirmation_code),
+ style = MaterialTheme.typography.bodyMedium,
+ )
+
+ Text(
+ modifier = Modifier.padding(top = 8.dp, start = 16.dp, end = 16.dp, bottom = 8.dp),
+ text = totpString,
+ fontFamily = FontFamily.Monospace,
+ fontSize = MaterialTheme.typography.titleLarge.fontSize,
+ )
+
+ Button(
+ onClick = {
+ val nfcAdapter = NfcAdapter.getDefaultAdapter(context)
+ val act = activity
+ if (nfcAdapter == null || act == null) {
+ Toast.makeText(context, R.string.nfc_not_available, Toast.LENGTH_SHORT).show()
+ return@Button
+ }
+ isWriting = true
+ nfcAdapter.enableReaderMode(act, { tag ->
+ val ndef = Ndef.get(tag)
+ if (ndef != null) {
+ try {
+ ndef.connect()
+ ndef.writeNdefMessage(ndefMessage)
+ act.runOnUiThread {
+ Toast.makeText(context, R.string.nfc_write_success, Toast.LENGTH_SHORT).show()
+ }
+ } catch (e: Exception) {
+ act.runOnUiThread {
+ Toast.makeText(context, "${e.message}", Toast.LENGTH_SHORT).show()
+ }
+ } finally {
+ act.runOnUiThread {
+ isWriting = false
+ nfcAdapter.disableReaderMode(act)
+ }
+ }
+ } else {
+ act.runOnUiThread {
+ isWriting = false
+ nfcAdapter.disableReaderMode(act)
+ Toast.makeText(context, R.string.nfc_tag_not_ndef, Toast.LENGTH_SHORT).show()
+ }
+ }
+ }, NFC_READER_FLAGS, null)
+ },
+ modifier = Modifier.fillMaxWidth().padding(horizontal = 32.dp).padding(top = 4.dp),
+ enabled = !isWriting,
+ ) {
+ Text(if (isWriting) stringResource(R.string.nfc_writing) else stringResource(R.string.nfc_write_button))
+ }
+
+ if (!isWriting) {
+ Spacer(Modifier.height(ButtonDefaults.IconSpacing))
+ }
+ }
+}
diff --git a/wallet/src/main/java/net/taler/wallet/payment/TransactionPaymentComposable.kt b/wallet/src/main/java/net/taler/wallet/payment/TransactionPaymentComposable.kt
@@ -143,10 +143,7 @@ fun TransactionPaymentComposable(
}
if (t.posConfirmation != null) {
- TransactionInfoComposable(
- label = stringResource(id = R.string.payment_confirmation_code),
- info = t.posConfirmation,
- )
+ TotpNfcWriter(totpString = t.posConfirmation)
}
if (t.info != null) PurchaseDetails(info = t.info) {
diff --git a/wallet/src/main/res/values/strings.xml b/wallet/src/main/res/values/strings.xml
@@ -71,6 +71,11 @@ GNU Taler is immune to many types of fraud such as credit card data theft, phish
<string name="millisecond">%1$d ms</string>
<string name="offline">Operation requires internet access. Please ensure your internet connection works and try again.</string>
<string name="offline_banner">No internet access</string>
+ <string name="nfc_not_available">NFC is not available on this device</string>
+ <string name="nfc_tag_not_ndef">NFC tag does not support NDEF</string>
+ <string name="nfc_write_button">Write NFC</string>
+ <string name="nfc_write_success">Confirmation code written to terminal</string>
+ <string name="nfc_writing">Tap phone to terminal…</string>
<string name="ok">OK</string>
<string name="open">Open</string>
<string name="paste">Paste</string>
