fix: Zeus-to-Zeus NFC scan (update react-native-hce + empty NDEF guard)

components/NFCButton.tsx

@@ -3,7 +3,11 @@ import { Platform, TouchableOpacity } from 'react-native';
 import { inject, observer } from 'mobx-react';
 import { checkNfcEnabled } from '../utils/NFCUtils';
 
-import HCESession, { NFCContentType, NFCTagType4 } from 'react-native-hce';
+import {
+    HCESession,
+    NFCTagType4,
+    NFCTagType4NDEFContentType
+} from 'react-native-hce';
 
 import NfcIcon from '../assets/images/SVG/NFC-alt.svg';
 
@@ -69,12 +73,20 @@ export default class NFCButton extends React.Component<
     };
 
     startSimulation = async () => {
-        const tag = new NFCTagType4(NFCContentType.Text, this.props.value);
-        this.simulation = await new HCESession(tag).start();
+        const tag = new NFCTagType4({
+            type: NFCTagType4NDEFContentType.Text,
+            content: this.props.value,
+            writable: false
+        });
+        this.simulation = await HCESession.getInstance();
+        await this.simulation.setApplication(tag);
+        await this.simulation.setEnabled(true);
     };
 
     stopSimulation = async () => {
-        await this.simulation.terminate();
+        if (this.simulation) {
+            await this.simulation.setEnabled(false);
+        }
     };
 
     render() {

package.json

@@ -11,7 +11,7 @@
       "<rootDir>/node_modules"
     ],
     "transformIgnorePatterns": [
-      "node_modules/(?!(react-native|@react-native|react-native-blob-util|react-native-randombytes|dateformat|nostr-tools|@nostr|@noble|@scure|uuid)/)"
+      "node_modules/(?!(react-native|@react-native|react-native-blob-util|react-native-randombytes|react-native-nfc-manager|dateformat|nostr-tools|@nostr|@noble|@scure|uuid)/)"
     ],
     "testPathIgnorePatterns": [
       "check-styles.test.ts"
@@ -124,7 +124,7 @@
     "react-native-gesture-handler": "2.30.0",
     "react-native-get-random-values": "1.9.0",
     "react-native-haptic-feedback": "2.3.3",
-    "react-native-hce": "0.1.2",
+    "react-native-hce": "0.3.0",
     "react-native-image-picker": "8.2.1",
     "react-native-keychain": "10.0.0",
     "react-native-nfc-manager": "3.17.2",

utils/NFCUtils.test.ts

@@ -0,0 +1,56 @@
+// Explicit jest type reference required: the import chain goes through
+// react-native-nfc-manager's ambient module declaration, which causes
+// tsserver to lose automatic @types/jest inclusion (tsc is unaffected).
+/// <reference types="jest" />
+
+jest.mock('react-native-nfc-manager', () => ({
+    __esModule: true,
+    default: {
+        isEnabled: () => {},
+        setEventListener: () => {},
+        start: () => {},
+        registerTagEvent: () => {},
+        unregisterTagEvent: () => {}
+    },
+    NfcEvents: { DiscoverTag: 'DiscoverTag', SessionClosed: 'SessionClosed' },
+    Ndef: { text: { decodePayload: () => {} } }
+}));
+
+import { decodeNdefTextPayload } from './NFCUtils';
+
+// NDEF Text Record payload structure:
+//   byte 0:   status byte — lower 6 bits = language code length
+//   bytes 1–N: language code (e.g. "en" = 2 bytes)
+//   remaining: actual text (UTF-8)
+const withHeader = (...textBytes: number[]) =>
+    new Uint8Array([0x02, 0x65, 0x6e, ...textBytes]); // 0x02 = 2-char lang, "en"
+
+describe('decodeNdefTextPayload', () => {
+    it('returns empty string for empty input', () => {
+        expect(decodeNdefTextPayload(new Uint8Array([]))).toBe('');
+    });
+
+    it('returns empty string when payload contains only the header', () => {
+        expect(decodeNdefTextPayload(withHeader())).toBe('');
+    });
+
+    it('decodes a plain ASCII payload', () => {
+        // "hello" = 0x68 0x65 0x6c 0x6c 0x6f
+        expect(
+            decodeNdefTextPayload(withHeader(0x68, 0x65, 0x6c, 0x6c, 0x6f))
+        ).toBe('hello');
+    });
+
+    it('decodes a multi-byte UTF-8 character (ü = 0xC3 0xBC)', () => {
+        expect(decodeNdefTextPayload(withHeader(0xc3, 0xbc))).toBe('ü');
+    });
+
+    it('returns null for an invalid UTF-8 sequence', () => {
+        expect(decodeNdefTextPayload(withHeader(0xff))).toBeNull();
+    });
+
+    it('returns null for a truncated multi-byte sequence', () => {
+        // 0xC3 starts a 2-byte sequence but has no continuation byte
+        expect(decodeNdefTextPayload(withHeader(0xc3))).toBeNull();
+    });
+});

utils/NFCUtils.ts

@@ -1,6 +1,24 @@
-import NfcManager from 'react-native-nfc-manager';
+import { Platform } from 'react-native';
+import NfcManager, {
+    NfcEvents,
+    TagEvent,
+    Ndef
+} from 'react-native-nfc-manager';
 import ModalStore from '../stores/ModalStore';
 
+export function decodeNdefTextPayload(data: Uint8Array): string | null {
+    if (data.length === 0) return '';
+    const langCodeLen = data[0] & 0x3f;
+    const textData = data.slice(1 + langCodeLen);
+    try {
+        return new global.TextDecoder('utf-8', { fatal: true }).decode(
+            textData
+        );
+    } catch {
+        return null;
+    }
+}
+
 /**
  * Checks whether NFC is enabled on the device.
  * If not, shows the AndroidNfcModal with the disabled state and returns false.
@@ -18,37 +36,54 @@ export async function checkNfcEnabled(
     return true;
 }
 
-class NFCUtils {
-    nfcUtf8ArrayToStr = (data: any) => {
-        const extraByteMap = [1, 1, 1, 1, 2, 2, 3, 0];
-        const count = data.length;
-        let str = '';
-
-        for (let index = 0; index < count; ) {
-            let ch = data[index++];
-            if (ch & 0x80) {
-                let extra = extraByteMap[(ch >> 3) & 0x07];
-                if (!(ch & 0x40) || !extra || index + extra > count) {
-                    return null;
-                }
-
-                ch = ch & (0x3f >> extra);
-                for (; extra > 0; extra -= 1) {
-                    const chx = data[index++];
-                    if ((chx & 0xc0) !== 0x80) {
-                        return null;
-                    }
-
-                    ch = (ch << 6) | (chx & 0x3f);
-                }
+export async function scanNfcTag(
+    modalStore: ModalStore
+): Promise<string | undefined> {
+    if (!(await checkNfcEnabled(modalStore))) return undefined;
+
+    NfcManager.setEventListener(NfcEvents.DiscoverTag, null);
+    NfcManager.setEventListener(NfcEvents.SessionClosed, null);
+    await NfcManager.start().catch((e) => console.warn(e.message));
+
+    return new Promise((resolve) => {
+        let tagFound: TagEvent | null = null;
+
+        if (Platform.OS === 'android') modalStore.toggleAndroidNfcModal(true);
+
+        NfcManager.setEventListener(NfcEvents.DiscoverTag, (tag: TagEvent) => {
+            if (!tag.ndefMessage?.[0]?.payload) {
+                if (Platform.OS === 'android')
+                    modalStore.toggleAndroidNfcModal(false);
+                resolve(undefined);
+                NfcManager.unregisterTagEvent().catch(() => 0);
+                return;
             }
 
-            str += String.fromCharCode(ch);
-        }
+            tagFound = tag;
+            const bytes = new Uint8Array(tag.ndefMessage[0].payload);
 
-        return str.slice(3);
-    };
-}
+            let str: string;
+            const decoded = Ndef.text.decodePayload(bytes);
+            if (decoded.match(/^(https?|lnurl)/)) {
+                str = decoded;
+            } else {
+                str = decodeNdefTextPayload(bytes) || '';
+            }
+
+            if (Platform.OS === 'android')
+                modalStore.toggleAndroidNfcModal(false);
+
+            resolve(str);
+            NfcManager.unregisterTagEvent().catch(() => 0);
+        });
 
-const nfcUtils = new NFCUtils();
-export default nfcUtils;
+        NfcManager.setEventListener(NfcEvents.SessionClosed, () => {
+            if (Platform.OS === 'android')
+                modalStore.toggleAndroidNfcModal(false);
+
+            if (!tagFound) resolve(undefined);
+        });
+
+        NfcManager.registerTagEvent();
+    });
+}

views/Cashu/ReceiveEcash.tsx

@@ -10,11 +10,7 @@ import {
 import { LNURLWithdrawParams } from 'js-lnurl';
 import { ButtonGroup, Icon } from '@rneui/themed';
 import { inject, observer } from 'mobx-react';
-import NfcManager, {
-    NfcEvents,
-    TagEvent,
-    Ndef
-} from 'react-native-nfc-manager';
+import NfcManager from 'react-native-nfc-manager';
 import { Route } from '@react-navigation/native';
 import { NativeStackNavigationProp } from '@react-navigation/native-stack';
 import Clipboard from '@react-native-clipboard/clipboard';
@@ -56,7 +52,7 @@ import UnitsStore from '../../stores/UnitsStore';
 import CashuInvoice from '../../models/CashuInvoice';
 
 import { localeString } from '../../utils/LocaleUtils';
-import NFCUtils, { checkNfcEnabled } from '../../utils/NFCUtils';
+import { scanNfcTag } from '../../utils/NFCUtils';
 import { themeColor } from '../../utils/ThemeUtils';
 import { getAmountFromSats } from '../../utils/AmountUtils';
 
@@ -262,63 +258,9 @@ export default class ReceiveEcash extends React.Component<
         });
     };
 
-    disableNfc = () => {
-        NfcManager.setEventListener(NfcEvents.DiscoverTag, null);
-        NfcManager.setEventListener(NfcEvents.SessionClosed, null);
-    };
-
-    enableNfc = async () => {
-        const { ModalStore } = this.props;
-
-        if (!(await checkNfcEnabled(ModalStore))) return;
-
-        this.disableNfc();
-        await NfcManager.start().catch((e) => console.warn(e.message));
-
-        return new Promise((resolve: any) => {
-            let tagFound: TagEvent | null = null;
-
-            // enable NFC
-            if (Platform.OS === 'android')
-                ModalStore.toggleAndroidNfcModal(true);
-
-            NfcManager.setEventListener(
-                NfcEvents.DiscoverTag,
-                (tag: TagEvent) => {
-                    tagFound = tag;
-                    const bytes = new Uint8Array(
-                        tagFound.ndefMessage[0].payload
-                    );
-
-                    let str;
-                    const decoded = Ndef.text.decodePayload(bytes);
-                    if (decoded.match(/^(https?|lnurl)/)) {
-                        str = decoded;
-                    } else {
-                        str = NFCUtils.nfcUtf8ArrayToStr(bytes) || '';
-                    }
-
-                    // close NFC
-                    if (Platform.OS === 'android')
-                        ModalStore.toggleAndroidNfcModal(false);
-
-                    resolve(this.validateAddress(str));
-                    NfcManager.unregisterTagEvent().catch(() => 0);
-                }
-            );
-
-            NfcManager.setEventListener(NfcEvents.SessionClosed, () => {
-                // close NFC
-                if (Platform.OS === 'android')
-                    ModalStore.toggleAndroidNfcModal(false);
-
-                if (!tagFound) {
-                    resolve();
-                }
-            });
-
-            NfcManager.registerTagEvent();
-        });
+    scanNfc = async () => {
+        const str = await scanNfcTag(this.props.ModalStore);
+        if (str) this.validateAddress(str);
     };
 
     validateAddress = (text: string) => {
@@ -830,7 +772,7 @@ export default class ReceiveEcash extends React.Component<
                                                                 />
                                                             }
                                                             onPress={() =>
-                                                                this.enableNfc()
+                                                                this.scanNfc()
                                                             }
                                                             secondary
                                                         />