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Merge pull request #9 from algorandfoundation/feat/prevent-screenshots
feat: prevent screenshots of sensitive data.
2 parents 8f8ae36 + 9b7908c commit a288fbf

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‎__tests__/lib/screenshotManager-test.ts‎

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/**
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* Tests for lib/screenshotManager.ts
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*
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* Because screenshotManager is a singleton, each test uses jest.resetModules()
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* + a fresh require() so state never leaks between cases.
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*
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* enable() / disable() / reset() return the internal queue promise, so tests
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* can await the returned value directly instead of relying on setImmediate.
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*/
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import type { screenshotManager as ScreenshotManagerType } from "../../lib/screenshotManager";
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describe("ScreenshotManager", () => {
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let manager: typeof ScreenshotManagerType;
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let mockPrevent: jest.Mock;
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let mockAllow: jest.Mock;
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beforeEach(() => {
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jest.resetModules();
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mockPrevent = jest.fn().mockResolvedValue(undefined);
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mockAllow = jest.fn().mockResolvedValue(undefined);
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// Register fresh mock factory after resetting the module registry.
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jest.mock("expo-screen-capture", () => ({
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preventScreenCaptureAsync: mockPrevent,
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allowScreenCaptureAsync: mockAllow,
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}));
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({ screenshotManager: manager } =
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// eslint-disable-next-line @typescript-eslint/no-require-imports
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require("../../lib/screenshotManager") as {
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screenshotManager: typeof ScreenshotManagerType;
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});
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});
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// ── basic enable / disable ────────────────────────────────────────────────
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it("single enable() calls preventScreenCaptureAsync once", async () => {
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await manager.enable();
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expect(mockPrevent).toHaveBeenCalledTimes(1);
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expect(mockAllow).not.toHaveBeenCalled();
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});
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it("multiple enable() calls only invoke preventScreenCaptureAsync once", async () => {
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await manager.enable();
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await manager.enable();
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await manager.enable();
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expect(mockPrevent).toHaveBeenCalledTimes(1);
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expect(mockAllow).not.toHaveBeenCalled();
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});
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it("enable() × 2 then disable() × 1 does not call allowScreenCaptureAsync", async () => {
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await manager.enable();
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await manager.enable();
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await manager.disable();
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expect(mockAllow).not.toHaveBeenCalled();
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});
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it("enable() × 2 then disable() × 2 calls allowScreenCaptureAsync once", async () => {
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await manager.enable();
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await manager.enable();
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await manager.disable();
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await manager.disable();
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expect(mockPrevent).toHaveBeenCalledTimes(1);
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expect(mockAllow).toHaveBeenCalledTimes(1);
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});
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it("disable() when count is already 0 does not call any API", async () => {
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await manager.disable();
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expect(mockPrevent).not.toHaveBeenCalled();
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expect(mockAllow).not.toHaveBeenCalled();
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});
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// ── failure resilience ────────────────────────────────────────────────────
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it("preventScreenCaptureAsync failure leaves enabled=false so next enable() retries", async () => {
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mockPrevent.mockRejectedValueOnce(new Error("permission denied"));
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await manager.enable();
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expect(mockPrevent).toHaveBeenCalledTimes(1);
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// enabled is still false internally — a subsequent enable() must retry.
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await manager.enable();
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expect(mockPrevent).toHaveBeenCalledTimes(2);
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});
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it("allowScreenCaptureAsync failure leaves enabled=true so next disable() retries", async () => {
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await manager.enable();
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mockAllow.mockRejectedValueOnce(new Error("system error"));
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await manager.disable();
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expect(mockAllow).toHaveBeenCalledTimes(1);
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// enabled is still true internally — a subsequent disable() must retry.
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await manager.disable();
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expect(mockAllow).toHaveBeenCalledTimes(2);
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});
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// ── queue serialisation ───────────────────────────────────────────────────
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it("rapid enable/disable/enable settles with prevention active", async () => {
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// All three must be enqueued synchronously so the queue coalesces them.
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// By the time all updates run, count=1 and the intermediate disable
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// transition is a no-op (enabled stays true after the first enable).
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manager.enable();
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manager.disable();
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await manager.enable();
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expect(mockPrevent).toHaveBeenCalledTimes(1);
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expect(mockAllow).not.toHaveBeenCalled();
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});
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// ── reset ─────────────────────────────────────────────────────────────────
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it("reset() while enabled forces allowScreenCaptureAsync and clears count", async () => {
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await manager.enable();
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await manager.enable(); // count=2, enabled=true
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await manager.reset(); // count=0 → should disable
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expect(mockAllow).toHaveBeenCalledTimes(1);
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// Further disable() should be a no-op (count already 0, enabled already false).
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await manager.disable();
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expect(mockAllow).toHaveBeenCalledTimes(1);
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});
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it("reset() when already disabled is a no-op", async () => {
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await manager.reset();
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expect(mockPrevent).not.toHaveBeenCalled();
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expect(mockAllow).not.toHaveBeenCalled();
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});
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});

‎app/_layout.tsx‎

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@@ -15,6 +15,7 @@ import {registerGlobals} from "react-native-webrtc";
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import { globalPolyfill, setupNavigatorPolyfill } from "@/lib/polyfill";
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import ReactNativePasskeyAutofill from "@algorandfoundation/react-native-passkey-autofill";
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import { CredentialProviderService } from "@/lib/credentialProvider";
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import { PreventScreenshotProvider } from "@/providers/PreventScreenshotProvider";
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import React from "react";
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globalPolyfill()
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});
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return (
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<WalletProvider
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provider={provider}
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>
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<Stack />
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</WalletProvider>
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<PreventScreenshotProvider>
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<WalletProvider
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provider={provider}
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>
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<Stack />
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</WalletProvider>
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</PreventScreenshotProvider>
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)
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}

‎app/import.tsx‎

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@@ -7,6 +7,7 @@ import { MaterialIcons } from '@expo/vector-icons';
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import { wordlist } from '@scure/bip39/wordlists/english.js';
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import { validateMnemonic, mnemonicToSeed } from '@scure/bip39';
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import { useProvider } from '@/hooks/useProvider';
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import { PreventScreenshot } from '@/components/PreventScreenshot';
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// Extract provider configuration from expo-constants
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const config = Constants.expoConfig?.extra?.provider || {
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<View style={styles.importInputContainer}>
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<Text style={styles.importLabel}>Recovery Phrase (24 words)</Text>
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<TextInput
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style={styles.importTextInput}
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multiline
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numberOfLines={8}
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placeholder="Enter your 24-word recovery phrase here...&#10;word1 word2 word3 ..."
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placeholderTextColor="#94A3B8"
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value={importText}
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onChangeText={setImportText}
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autoCapitalize="none"
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autoCorrect={false}
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textAlignVertical="top"
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/>
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<PreventScreenshot>
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<TextInput
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style={styles.importTextInput}
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multiline
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numberOfLines={8}
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placeholder="Enter your 24-word recovery phrase here...&#10;word1 word2 word3 ..."
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placeholderTextColor="#94A3B8"
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value={importText}
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onChangeText={setImportText}
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autoCapitalize="none"
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autoCorrect={false}
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textAlignVertical="top"
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/>
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</PreventScreenshot>
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<Text style={styles.importHelper}>
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Words entered: {importText.split(/\s+/).filter(w => w.length > 0).length} / 24
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</Text>

‎app/onboarding.tsx‎

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@@ -13,6 +13,7 @@ import * as bip39 from '@scure/bip39';
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import { useProvider } from '@/hooks/useProvider'
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import { mnemonicToSeed } from '@scure/bip39'
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import ReactNativePasskeyAutofill from "@algorandfoundation/react-native-passkey-autofill";
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import { PreventScreenshot } from '@/components/PreventScreenshot';
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// Extract provider configuration from expo-constants
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</View>
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{!isBackupVerified && (
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<>
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<PreventScreenshot enabled={isPhraseVisible}>
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<SeedPhrase
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recoveryPhrase={recoveryPhrase || []}
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showSeed={isPhraseVisible}
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}
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primaryColor={primaryColor}
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/>
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</>
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</PreventScreenshot>
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)}
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</ScrollView>
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‎components/PreventScreenshot.tsx‎

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import { usePreventScreenshot } from "@/hooks/usePreventScreenshot";
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type Props = {
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enabled?: boolean;
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children: React.ReactNode;
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};
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export function PreventScreenshot({ enabled = true, children }: Props) {
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usePreventScreenshot(enabled);
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return <>{children}</>;
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}

‎hooks/usePreventScreenshot.ts‎

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import { screenshotManager } from "@/lib/screenshotManager";
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import { useEffect } from "react";
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export function usePreventScreenshot(enabled = true) {
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useEffect(() => {
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if (!enabled) return;
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void screenshotManager.enable().catch((error) => {
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console.error("Failed to enable screenshot prevention: ", error);
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});
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return () => {
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void screenshotManager.disable().catch((error) => {
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console.error("Failed to disable screenshot prevention: ", error);
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});
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};
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}, [enabled]);
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}

‎lib/screenshotManager.ts‎

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import * as ScreenCapture from "expo-screen-capture";
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class ScreenshotManager {
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private count = 0;
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private enabled = false;
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private queue: Promise<void> = Promise.resolve();
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private async update() {
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const shouldEnable = this.count > 0;
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if (shouldEnable === this.enabled) return;
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const currentCount = this.count; // Capture the current count for logging
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if (shouldEnable) {
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await ScreenCapture.preventScreenCaptureAsync();
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this.enabled = true;
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console.debug("Screenshot prevention enabled. Count:", currentCount);
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} else {
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await ScreenCapture.allowScreenCaptureAsync();
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this.enabled = false;
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console.debug("Screenshot prevention disabled. Count:", currentCount);
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}
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}
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private enqueue(): Promise<void> {
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this.queue = this.queue
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.then(() => this.update())
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.catch((error) => {
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// Swallow the error so that subsequent operations are not blocked.
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console.error("Failed to update screenshot capture state: ", error);
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});
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return this.queue;
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}
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enable(): Promise<void> {
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this.count++;
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return this.enqueue();
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}
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disable(): Promise<void> {
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this.count = Math.max(0, this.count - 1);
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return this.enqueue();
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}
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reset(): Promise<void> {
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this.count = 0;
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return this.enqueue();
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}
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}
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export const screenshotManager = new ScreenshotManager();

‎package-lock.json‎

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‎package.json‎

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"expo-image": "~3.0.11",
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"expo-linking": "~8.0.11",
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"expo-router": "~6.0.23",
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"expo-screen-capture": "~8.0.9",
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"expo-splash-screen": "~31.0.13",
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"expo-status-bar": "~3.0.9",
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"expo-symbols": "~1.0.8",

‎providers/PreventScreenshotProvider.tsx‎

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import { screenshotManager } from "@/lib/screenshotManager";
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import React, { useEffect } from "react";
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// Not really a provider, but this is where we can do the safety reset on unmount
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export function PreventScreenshotProvider({
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children,
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}: {
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children: React.ReactNode;
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}) {
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useEffect(() => {
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return () => {
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// Safety reset when app unmounts
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screenshotManager.reset().catch((error) => {
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console.error("Failed to reset screenshot manager on unmount: ", error);
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});
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};
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}, []);
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return <>{children}</>;
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}

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