binding: Add packageInfo getter

This is a preparatory commit for the work of embedding the
device info in user-agent header.

Author: rajveermalviya

lib/model/binding.dart

@@ -3,6 +3,7 @@ import 'package:firebase_core/firebase_core.dart' as firebase_core;
 import 'package:firebase_messaging/firebase_messaging.dart' as firebase_messaging;
 import 'package:flutter/foundation.dart';
 import 'package:flutter_local_notifications/flutter_local_notifications.dart';
+import 'package:package_info_plus/package_info_plus.dart' as package_info_plus;
 import 'package:url_launcher/url_launcher.dart' as url_launcher;
 
 import '../host/android_notifications.dart';
@@ -81,6 +82,20 @@ abstract class ZulipBinding {
   /// or an error occured while fetching the data.
   BaseDeviceInfo? get maybeDeviceInfo;
 
+  /// Provides application package information,
+  /// via package:package_info_plus.
+  ///
+  /// The returned Future resolves to null if an error is
+  /// encountered while fetching the data.
+  Future<PackageInfo?> get packageInfo;
+
+  /// Provides application package information,
+  /// via package:package_info_plus.
+  ///
+  /// May return null if prefetching hasn't completed yet,
+  /// or an error occured while fetching the data.
+  PackageInfo? get maybePackageInfo;
+
   /// Prepare the app's [GlobalStore], loading the necessary data.
   ///
   /// Generally the app should call this function only once.
@@ -161,6 +176,17 @@ class IosDeviceInfo extends BaseDeviceInfo {
   IosDeviceInfo({required this.systemVersion});
 }
 
+/// Like [package_info_plus.PackageInfo], but without things we don't use.
+class PackageInfo {
+  final String version;
+  final String buildNumber;
+
+  PackageInfo({
+    required this.version,
+    required this.buildNumber,
+  });
+}
+
 /// A concrete binding for use in the live application.
 ///
 /// The global store returned by [loadGlobalStore], and consequently by
@@ -175,6 +201,7 @@ class LiveZulipBinding extends ZulipBinding {
     if (ZulipBinding._instance == null) {
       final binding = LiveZulipBinding();
       binding._deviceInfo = binding._prefetchDeviceInfo();
+      binding._packageInfo = binding._prefetchPackageInfo();
     }
     return ZulipBinding.instance as LiveZulipBinding;
   }
@@ -187,6 +214,14 @@ class LiveZulipBinding extends ZulipBinding {
   BaseDeviceInfo? get maybeDeviceInfo => _maybeDeviceInfo;
   BaseDeviceInfo? _maybeDeviceInfo;
 
+  @override
+  Future<PackageInfo?> get packageInfo => _packageInfo;
+  late Future<PackageInfo?> _packageInfo;
+
+  @override
+  PackageInfo? get maybePackageInfo => _maybePackageInfo;
+  PackageInfo? _maybePackageInfo;
+
   Future<BaseDeviceInfo?> _prefetchDeviceInfo() async {
     try {
       final info = await device_info_plus.DeviceInfoPlugin().deviceInfo;
@@ -202,6 +237,20 @@ class LiveZulipBinding extends ZulipBinding {
     return _maybeDeviceInfo;
   }
 
+  Future<PackageInfo?> _prefetchPackageInfo() async {
+    try {
+      final info = await package_info_plus.PackageInfo.fromPlatform();
+      _maybePackageInfo = PackageInfo(
+        version: info.version,
+        buildNumber: info.buildNumber,
+      );
+    } catch (e) {
+      assert(debugLog('Failed to prefetch package info: $e'));
+      // TODO(log)
+    }
+    return _maybePackageInfo;
+  }
+
   @override
   Future<GlobalStore> loadGlobalStore() {
     return LiveGlobalStore.load();

test/model/binding.dart

@@ -70,6 +70,7 @@ class TestZulipBinding extends ZulipBinding {
     _resetLaunchUrl();
     _resetCloseInAppWebView();
     _resetDeviceInfo();
+    _resetPackageInfo();
     _resetFirebase();
     _resetNotifications();
   }
@@ -218,6 +219,20 @@ class TestZulipBinding extends ZulipBinding {
     deviceInfoResult = _defaultDeviceInfoResult;
   }
 
+  @override
+  Future<PackageInfo?> get packageInfo async => packageInfoResult;
+
+  @override
+  PackageInfo? get maybePackageInfo => packageInfoResult;
+
+  /// The value that `ZulipBinding.instance.packageInfo` should return.
+  PackageInfo packageInfoResult = _defaultPackageInfo;
+  static final _defaultPackageInfo = PackageInfo(version: '0.0.1', buildNumber: '1');
+
+  void _resetPackageInfo() {
+    packageInfoResult = _defaultPackageInfo;
+  }
+
   void _resetFirebase() {
     _firebaseInitialized = false;
     _firebaseMessaging = null;