Fix dead slow animated QR code reader

__tests__/animatedQrThroughput.test.ts

@@ -0,0 +1,52 @@
+/**
+ * Animated QR (UR) throughput.
+ *
+ * Scanning a token used to take minutes because react-native-camera-kit defaults
+ * scanThrottleDelay to 2000 ms — one accepted part every 2 s. ScanScreen now passes
+ * scanThrottleDelay={0}, so the QRCode display interval is the only limit.
+ *
+ * This pins the part budget the timing estimate rests on: if the fountain encoder or
+ * the fragment length regresses, the wall-clock time goes up with it.
+ */
+import { UR, UREncoder, URDecoder } from '@gandlaf21/bc-ur'
+
+// Must mirror src/screens/Wallet/QRCode.tsx.
+const ANIMATED_QR_FRAGMENT_LENGTH = 150
+const ANIMATED_QR_INTERVAL = 250
+
+const partsToDecode = (payload: string) => {
+  const encoder = new UREncoder(UR.fromBuffer(Buffer.from(payload)), ANIMATED_QR_FRAGMENT_LENGTH, 0)
+  const decoder = new URDecoder()
+  let parts = 0
+
+  while (!decoder.isComplete()) {
+    decoder.receivePart(encoder.nextPart())
+    parts++
+    if (parts > 1000) throw new Error('decoder never completed')
+  }
+
+  expect(decoder.isSuccess()).toBe(true)
+  return {parts, decoded: Buffer.from(decoder.resultUR().decodeCBOR()).toString('utf8')}
+}
+
+test('a ~3 kB token round-trips within a few seconds of display time', () => {
+  const token = 'cashuB' + 'a'.repeat(3000)
+  const {parts, decoded} = partsToDecode(token)
+
+  expect(decoded).toBe(token)
+
+  // 3000 bytes / 150 = 20 fragments; the fountain encoder sends those in order first,
+  // so a lossless reader needs no more than a handful of extra parts.
+  expect(parts).toBeLessThanOrEqual(25)
+  // The number that actually matters to the user: seconds, not minutes.
+  expect(parts * ANIMATED_QR_INTERVAL).toBeLessThan(8000)
+})
+
+test('every displayed part is distinct, so the scanner-side dedupe never stalls', () => {
+  const encoder = new UREncoder(UR.fromBuffer(Buffer.from('x'.repeat(1500))), ANIMATED_QR_FRAGMENT_LENGTH, 0)
+  const seen = Array.from({length: 30}, () => encoder.nextPart())
+
+  // ScanScreen skips a read equal to the previous one. Consecutive repeats from the
+  // encoder would make that dedupe drop real parts.
+  seen.forEach((part, i) => expect(part).not.toBe(seen[i - 1]))
+})

jest.config.js

@@ -7,13 +7,17 @@ module.exports = {
   // The `(.*/)?` makes the allowlist apply at any depth: nostr-tools carries its
   // own ESM-only @noble copies in a nested node_modules, and those need babel too.
   transformIgnorePatterns: [
-    'node_modules/(?!(.*/)?((jest-)?react-native|@react-native|@react-native-community|@cashu|@noble|@scure|react-native-flash-message)/)',
+    'node_modules/(?!(.*/)?((jest-)?react-native|@react-native|@react-native-community|@cashu|@noble|@scure|cborg|react-native-flash-message)/)',
   ],
   // Several native or source-shipped packages are unusable under jest, and the
   // MODEL layer reaches all of them at import time (Mint -> services barrel ->
   // mmkvStorage / keyChain / db). That is what made MST stores impossible to
   // instantiate in a test at all; these mappings are what make store tests possible.
   moduleNameMapper: {
+    // cborg (via @gandlaf21/bc-ur) is ESM-only and its exports map has an "import"
+    // condition only, which jest's CJS resolver cannot satisfy. Point at the entry
+    // file directly and let babel transform it (see transformIgnorePatterns above).
+    '^cborg$': '<rootDir>/node_modules/cborg/cborg.js',
     // Same shape as the @scure/bip39 mapping below: the package's exports map
     // names only the suffixed path, so app code imports it that way. This accepts
     // both spellings, for transitive dependencies still using the bare one.

src/screens/ScanScreen.tsx

@@ -41,10 +41,16 @@ export const ScanScreen = function ScanScreen({ route }: Props) {
     const {mintsStore} = useStores()
 
     const [shouldLoad, setShouldLoad] = useState<boolean>(false)        
-    const [isScanned, setIsScanned] = useState<boolean>(false)
     const [prevRouteName, setPrevRouteName] = useState<string>('')
-    const [urDecoder, setUrDecoder] = useState<URDecoder | undefined>(undefined)
     const [urDecoderProgress, setUrDecoderProgress] = useState<number>(0)
+    /*
+     * Refs, not state: with scanThrottleDelay={0} onReadCode fires on every camera
+     * frame (~30/s), so a state flag would still be stale on the next few frames and
+     * let a completed scan navigate several times.
+     */
+    const urDecoder = useRef<URDecoder>(new URDecoder())
+    const isScanned = useRef<boolean>(false)
+    const lastPart = useRef<string>('')
     const [unit, setUnit] = useState<MintUnit>('sat')
     const [mint, setMint] = useState<Mint | undefined>(undefined) 
     const [error, setError] = useState<AppError | undefined>()
@@ -62,8 +68,6 @@ export const ScanScreen = function ScanScreen({ route }: Props) {
               setPrevRouteName(prevRoute)
           }
 
-          const decoder = new URDecoder()
-          setUrDecoder(decoder)
         }
         load()
     }, [])
@@ -93,23 +97,28 @@ export const ScanScreen = function ScanScreen({ route }: Props) {
 
 
     const onReadCode = async function(event: any) {
+        if (isScanned.current) { return }
+
         const scanned = event.nativeEvent.codeStringValue
-        
+
+        // The camera reads the same QR many times while it is on screen. Skipping the
+        // repeats keeps receivePart() and the progress re-render off the hot path.
+        if (scanned === lastPart.current) { return }
+        lastPart.current = scanned
+
         if (scanned.toLowerCase().startsWith("ur:")) {
-            if(!urDecoder) { return }
+            urDecoder.current.receivePart(scanned)
+            setUrDecoderProgress(Math.floor(urDecoder.current.estimatedPercentComplete() * 100))
 
-            urDecoder.receivePart(scanned)
-            setUrDecoderProgress(Math.floor(urDecoder.estimatedPercentComplete() * 100))
-
-            if (!urDecoder.isComplete()) {
+            if (!urDecoder.current.isComplete()) {
 				return;
 			}
 
-            if (urDecoder.isSuccess()) {
-                setIsScanned(true) 
+            if (urDecoder.current.isSuccess()) {
+                isScanned.current = true
                 setUrDecoderProgress(0)
 
-                const ur = urDecoder.resultUR()
+                const ur = urDecoder.current.resultUR()
                 const decodedBuffer = ur.decodeCBOR()                
 
                 const decodedData = Buffer.from(decodedBuffer).toString('utf8')
@@ -118,11 +127,11 @@ export const ScanScreen = function ScanScreen({ route }: Props) {
 
                 return onIncomingData(decodedData)
             } else {
-                setError(new AppError(Err.SCAN_ERROR, urDecoder.resultError()))
+                setError(new AppError(Err.SCAN_ERROR, urDecoder.current.resultError()))
             }
         }
 
-        setIsScanned(true)        
+        isScanned.current = true        
         log.trace('Scanned', {scanned})
 
         return onIncomingData(scanned)
@@ -307,7 +316,8 @@ export const ScanScreen = function ScanScreen({ route }: Props) {
             <Camera
                 cameraType={CameraType.Back}                      
                 scanBarcode
-                onReadCode={(event: any) => (isScanned ? undefined : onReadCode(event))}                
+                scanThrottleDelay={0}
+                onReadCode={onReadCode}                
                 style={{flex: 1}}            
             />
             <View style={$bottomContainer}>                

src/screens/Wallet/QRCode.tsx

@@ -27,6 +27,10 @@ import AppError, { Err } from '../../utils/AppError';
 export type QRCodeBlockTypes = 'EncodedV3Token' | 'EncodedV4Token' | 'Bolt11Invoice' | 'URL' | 'NWC' | 'PUBKEY' | 'PaymentRequest' | 'BitcoinAddress'
 
 const ANIMATED_QR_FRAGMENT_LENGTH = 150
+// ScanScreen passes scanThrottleDelay={0}, so our own scanner reads every camera
+// frame and the display rate is the only limit. 4 fps is kept deliberately: it is
+// what other cashu wallets animate at, and it survives a low-end camera that cannot
+// decode a frame in less than ~200ms. Do not raise it without device testing.
 const ANIMATED_QR_INTERVAL = 250
 
 export const QRCodeBlock = function (props: {