feat(#11281): bring up the wifi hotspot and pairing

build.gradle

@@ -488,6 +488,11 @@ android {
 }
 
 dependencies {
+  // Offline sync over WiFi hotspot (#11281): NanoHTTPD is a single-file HTTP server, ZXing does QR both ways
+  implementation 'org.nanohttpd:nanohttpd:2.3.1'
+  implementation 'com.google.zxing:core:3.5.3'
+  implementation 'com.journeyapps:zxing-android-embedded:4.3.0'
+
   implementation fileTree(dir: 'libs', include: ['*.jar'])
   implementation platform('org.jetbrains.kotlin:kotlin-bom:1.9.24')
   implementation 'androidx.browser:browser:1.8.0'

src/main/AndroidManifest.xml

@@ -26,6 +26,16 @@
   <uses-permission android:name="android.permission.SEND_SMS"/>
   -->
 
+  <!-- Offline sync over WiFi hotspot. NEARBY_WIFI_DEVICES only exists from 33, and below it the
+       platform requires location permission for wifi scanning, which is already declared above. -->
+  <uses-permission android:name="android.permission.ACCESS_WIFI_STATE"/>
+  <uses-permission android:name="android.permission.CHANGE_WIFI_STATE"/>
+  <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
+  <uses-permission android:name="android.permission.CAMERA"/>
+  <uses-permission android:name="android.permission.NEARBY_WIFI_DEVICES" android:minSdkVersion="33"/>
+  <uses-feature android:name="android.hardware.wifi" android:required="false"/>
+  <uses-feature android:name="android.hardware.camera" android:required="false"/>
+
   <application android:label="@string/app_name"
       android:icon="@mipmap/ic_launcher"
       android:allowBackup="false"
@@ -99,6 +109,19 @@
         android:permission="android.permission.BIND_JOB_SERVICE"
         android:exported="true"
         tools:targetApi="23" />
+
+    <!-- Offline sync over WiFi hotspot (#11281). No cleartext config is declared and none is needed: the
+         only outbound call is the peer's probe of the host, and that is https against a pinned
+         per-session certificate. -->
+    <activity android:name="RequestOfflineSyncPermissionsActivity"
+        android:screenOrientation="portrait"
+        android:exported="false"
+        tools:ignore="DiscouragedApi,LockedOrientationActivity"/>
+    <activity android:name=".offlinesync.QrScannerActivity"
+        android:screenOrientation="portrait"
+        android:exported="false"
+        tools:ignore="DiscouragedApi"/>
+
   </application>
 
   <queries>

src/main/java/org/medicmobile/webapp/mobile/EmbeddedBrowserActivity.java

@@ -41,6 +41,10 @@
 import java.util.Arrays;
 import java.util.Optional;
 
+import org.medicmobile.webapp.mobile.offlinesync.OfflineSyncManager;
+import org.medicmobile.webapp.mobile.offlinesync.OfflineSyncPeer;
+import org.medicmobile.webapp.mobile.offlinesync.QrScannerActivity;
+
 @SuppressWarnings({ "PMD.GodClass", "PMD.TooManyMethods" })
 public class EmbeddedBrowserActivity extends Activity {
 
@@ -50,6 +54,8 @@ public class EmbeddedBrowserActivity extends Activity {
 	private MrdtSupport mrdt;
 	private FilePickerHandler filePickerHandler;
 	private SmsSender smsSender;
+	private OfflineSyncManager offlineSyncManager;
+	private OfflineSyncPeer offlineSyncPeer;
 	private ChtExternalAppHandler chtExternalAppHandler;
 	private boolean isMigrationRunning = false;
 
@@ -82,6 +88,19 @@ public void onReceiveValue(String result) {
 			error(ex, "Failed to create SmsSender.");
 		}
 
+		// Hosting and joining have different Android version floors, so each is created only where
+		// it can actually work and the webapp asks before offering either.
+		if(OfflineSyncManager.isHostSupported()) {
+			try {
+				this.offlineSyncManager = OfflineSyncManager.create(this, Build.MODEL);
+			} catch(Exception ex) {
+				error(ex, "Failed to create OfflineSyncManager.");
+			}
+		}
+		if(OfflineSyncPeer.isJoinSupported()) {
+			this.offlineSyncPeer = OfflineSyncPeer.create(this);
+		}
+
 		this.settings = SettingsStore.in(this);
 		this.appUrl = settings.getAppUrl();
 
@@ -228,6 +247,12 @@ protected void onActivityResult(int requestCd, int resultCode, Intent intent) {
 				case ACCESS_SEND_SMS_PERMISSION:
 					this.smsSender.resumeProcess(resultCode);
 					return;
+				case ACCESS_OFFLINE_SYNC_PERMISSIONS:
+					offlineSyncPermissionsResolved(resultCode == RESULT_OK);
+					return;
+				case SCAN_OFFLINE_SYNC_QR_CODE:
+					offlineSyncQrCodeScanned(resultCode, intent);
+					return;
 				default:
 					trace(this, "onActivityResult() :: no handling for requestCode=%s", requestCode.name());
 			}
@@ -268,6 +293,22 @@ SmsSender getSmsSender() {
 		return this.smsSender;
 	}
 
+	OfflineSyncManager getOfflineSyncManager() {
+		return this.offlineSyncManager;
+	}
+
+	OfflineSyncPeer getOfflineSyncPeer() {
+		return this.offlineSyncPeer;
+	}
+
+	/** Opens the scanner so the user can read a host's QR code. */
+	void scanOfflineSyncQrCode() {
+		startActivityForResult(
+			new Intent(this, QrScannerActivity.class),
+			RequestCode.SCAN_OFFLINE_SYNC_QR_CODE.getCode()
+		);
+	}
+
 	ChtExternalAppHandler getChtExternalAppHandler() {
 		return this.chtExternalAppHandler;
 	}
@@ -302,6 +343,25 @@ public void setMigrationRunning(boolean migrationRunning) {
 		isMigrationRunning = migrationRunning;
 	}
 
+	/**
+	 * Whether an offline sync session may start, asking for the permissions if it may not.
+	 *
+	 * Returns false while the request is in flight; the webapp retries once the user has answered.
+	 */
+	public boolean getOfflineSyncPermissions() {
+		if (RequestOfflineSyncPermissionsActivity.hasOfflineSyncPermissions(this)) {
+			trace(this, "getOfflineSyncPermissions() :: Offline sync permissions already granted");
+			return true;
+		}
+
+		trace(this, "getOfflineSyncPermissions() :: Offline sync permissions not granted before, requesting access...");
+		startActivityForResult(
+			new Intent(this, RequestOfflineSyncPermissionsActivity.class),
+			RequestCode.ACCESS_OFFLINE_SYNC_PERMISSIONS.getCode()
+		);
+		return false;
+	}
+
 	public boolean getLocationPermissions() {
 		boolean hasFineLocation = ContextCompat.checkSelfPermission(this, ACCESS_FINE_LOCATION) == PERMISSION_GRANTED;
 		boolean hasCoarseLocation = ContextCompat.checkSelfPermission(this, ACCESS_COARSE_LOCATION) == PERMISSION_GRANTED;
@@ -320,6 +380,55 @@ public boolean getLocationPermissions() {
 	}
 
 //> PRIVATE HELPERS
+	/**
+		* Why the scan ended without a code. The scanner reports this; without it every bad code
+		* would look to the user like they had cancelled the scan themselves.
+		*/
+	private static String scanFailureCode(Intent intent) {
+		if (intent == null) {
+			return "scan_cancelled";
+		}
+		String reason = intent.getStringExtra(QrScannerActivity.EXTRA_QR_ERROR);
+		return reason == null ? "scan_cancelled" : reason;
+	}
+
+	/** Hands a scanned code to the peer, which joins and then checks the host is who it claims. */
+	private void offlineSyncQrCodeScanned(int resultCode, Intent intent) {
+		if(resultCode != RESULT_OK || intent == null) {
+			resolveOfflineSyncPairing(false, scanFailureCode(intent));
+			return;
+		}
+
+		String payload = intent.getStringExtra(QrScannerActivity.EXTRA_QR_RESULT);
+		this.offlineSyncPeer.pair(payload, new OfflineSyncPeer.PairCallback() {
+			@Override public void onPaired(String hostLabel) {
+				resolveOfflineSyncPairing(true, hostLabel);
+			}
+
+			@Override public void onFailed(String reason) {
+				resolveOfflineSyncPairing(false, reason);
+			}
+		});
+	}
+
+	private void resolveOfflineSyncPairing(boolean ok, String detail) {
+		evaluateJavascript(String.format(
+			"try {" +
+				"const api = window.CHTCore.AndroidApi;" +
+				"if (api && api.v1 && api.v1.resolveOfflineSyncPairing) {" +
+				"  api.v1.resolveOfflineSyncPairing(%s, %s);" +
+				"}" +
+				"} catch (error) {" +
+				"  console.error('EmbeddedBrowserActivity :: Offline sync pairing result not delivered', error);" +
+				"}",
+			ok, org.json.JSONObject.quote(detail)));
+	}
+
+	private void offlineSyncPermissionsResolved(boolean granted) {
+		evaluateJavascript(String.format(
+			"window.CHTCore.AndroidApi.v1.offlineSyncPermissionsResolved(%s);", granted));
+	}
+
 	private void locationRequestResolved() {
 		evaluateJavascript("window.CHTCore.AndroidApi.v1.locationPermissionRequestResolved();");
 	}
@@ -451,7 +560,9 @@ public enum RequestCode {
 		ACCESS_SEND_SMS_PERMISSION(102),
 		CHT_EXTERNAL_APP_ACTIVITY(103),
 		GRAB_MRDT_PHOTO_ACTIVITY(104),
-		FILE_PICKER_ACTIVITY(105);
+		FILE_PICKER_ACTIVITY(105),
+		ACCESS_OFFLINE_SYNC_PERMISSIONS(106),
+		SCAN_OFFLINE_SYNC_QR_CODE(107);
 
 		private final int requestCode;