[flutter_tools] added base-href command in web (#80519)

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -35,6 +35,12 @@ const String kDart2jsOptimization = 'Dart2jsOptimization';
 /// Whether to disable dynamic generation code to satisfy csp policies.
 const String kCspMode = 'cspMode';
 
+/// Base href to set in index.html in flutter build command
+const String kBaseHref = 'baseHref';
+
+/// Placeholder for base href
+const String kBaseHrefPlaceholder = r'$FLUTTER_BASE_HREF';
+
 /// The caching strategy to use for service worker generation.
 const String kServiceWorkerStrategy = 'ServiceWorkerStrategy';
 
@@ -356,7 +362,7 @@ class WebReleaseBundle extends Target {
       // in question.
       if (environment.fileSystem.path.basename(inputFile.path) == 'index.html') {
         final String randomHash = Random().nextInt(4294967296).toString();
-        final String resultString = inputFile.readAsStringSync()
+        String resultString = inputFile.readAsStringSync()
           .replaceFirst(
             'var serviceWorkerVersion = null',
             "var serviceWorkerVersion = '$randomHash'",
@@ -367,6 +373,13 @@ class WebReleaseBundle extends Target {
             "navigator.serviceWorker.register('flutter_service_worker.js')",
             "navigator.serviceWorker.register('flutter_service_worker.js?v=$randomHash')",
           );
+        if (resultString.contains(kBaseHrefPlaceholder) &&
+            environment.defines[kBaseHref] == null) {
+          resultString = resultString.replaceAll(kBaseHrefPlaceholder, '/');
+        } else if (resultString.contains(kBaseHrefPlaceholder) &&
+            environment.defines[kBaseHref] != null) {
+          resultString = resultString.replaceAll(kBaseHrefPlaceholder, environment.defines[kBaseHref]);
+        }
         outputFile.writeAsStringSync(resultString);
         continue;
       }

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -10,6 +10,7 @@ import '../base/common.dart';
 import '../build_info.dart';
 import '../build_system/targets/web.dart';
 import '../features.dart';
+import '../globals.dart' as globals;
 import '../project.dart';
 import '../runner/flutter_command.dart'
     show DevelopmentArtifact, FlutterCommandResult;
@@ -42,6 +43,7 @@ class BuildWebCommand extends BuildSubCommand {
             'to view and debug the original source code of a compiled and minified Dart '
             'application.'
     );
+
     argParser.addOption('pwa-strategy',
       defaultsTo: kOfflineFirst,
       help: 'The caching strategy to be used by the PWA service worker.',
@@ -59,6 +61,13 @@ class BuildWebCommand extends BuildSubCommand {
                        'is not desirable',
       },
     );
+    argParser.addOption('base-href',
+      help: 'Overrides the href attribute of the <base> tag in web/index.html. '
+          'No change is done to web/index.html file if this flag is not provided. '
+          'The value has to start and end with a slash "/". '
+          'For more information: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base'
+    );
+
   }
 
   @override
@@ -87,6 +96,20 @@ class BuildWebCommand extends BuildSubCommand {
     if (buildInfo.isDebug) {
       throwToolExit('debug builds cannot be built directly for the web. Try using "flutter run"');
     }
+    if (stringArg('base-href') != null && !(stringArg('base-href').startsWith('/') && stringArg('base-href').endsWith('/'))) {
+      throwToolExit('base-href should start and end with /');
+    }
+    if (!globals.fs.currentDirectory
+        .childDirectory('web')
+        .childFile('index.html')
+        .readAsStringSync()
+        .contains(kBaseHrefPlaceholder) &&
+        stringArg('base-href') != null) {
+      throwToolExit(
+        "Couldn't find the placeholder for base href. "
+        r'Please add `<base href="$FLUTTER_BASE_HREF">` to web/index.html'
+      );
+    }
     displayNullSafetyMode(buildInfo);
     await buildWeb(
       flutterProject,
@@ -96,6 +119,7 @@ class BuildWebCommand extends BuildSubCommand {
       stringArg('pwa-strategy'),
       boolArg('source-maps'),
       boolArg('native-null-assertions'),
+      stringArg('base-href'),
     );
     return FlutterCommandResult.success();
   }

packages/flutter_tools/lib/src/isolated/devfs_web.dart

@@ -28,6 +28,7 @@ import '../base/logger.dart';
 import '../base/net.dart';
 import '../base/platform.dart';
 import '../build_info.dart';
+import '../build_system/targets/web.dart';
 import '../bundle.dart';
 import '../cache.dart';
 import '../compile.dart';
@@ -488,6 +489,12 @@ class WebAssetServer implements AssetReader {
         .childFile('index.html');
 
     if (indexFile.existsSync()) {
+      String indexFileContent =  indexFile.readAsStringSync();
+      if (indexFileContent.contains(kBaseHrefPlaceholder)) {
+          indexFileContent =  indexFileContent.replaceAll(kBaseHrefPlaceholder, '/');
+          headers[HttpHeaders.contentLengthHeader] = indexFileContent.length.toString();
+          return shelf.Response.ok(indexFileContent,headers: headers);
+        }
       headers[HttpHeaders.contentLengthHeader] =
           indexFile.lengthSync().toString();
       return shelf.Response.ok(indexFile.openRead(), headers: headers);
@@ -1025,13 +1032,12 @@ String _stripTrailingSlashes(String path) {
 String _parseBasePathFromIndexHtml(File indexHtml) {
   final String htmlContent =
       indexHtml.existsSync() ? indexHtml.readAsStringSync() : _kDefaultIndex;
-
   final Document document = parse(htmlContent);
   final Element baseElement = document.querySelector('base');
   String baseHref =
       baseElement?.attributes == null ? null : baseElement.attributes['href'];
 
-  if (baseHref == null) {
+  if (baseHref == null || baseHref == kBaseHrefPlaceholder) {
     baseHref = '';
   } else if (!baseHref.startsWith('/')) {
     throw ToolExit(

packages/flutter_tools/lib/src/isolated/resident_web_runner.dart

@@ -297,6 +297,7 @@ class ResidentWebRunner extends ResidentRunner {
             kNoneWorker,
             true,
             debuggingOptions.nativeNullAssertions,
+            null,
           );
         }
         await device.device.startApp(
@@ -365,6 +366,7 @@ class ResidentWebRunner extends ResidentRunner {
           kNoneWorker,
           true,
           debuggingOptions.nativeNullAssertions,
+          kBaseHref,
         );
       } on ToolExit {
         return OperationResult(1, 'Failed to recompile application.');

packages/flutter_tools/lib/src/web/compile.dart

@@ -26,6 +26,7 @@ Future<void> buildWeb(
   String serviceWorkerStrategy,
   bool sourceMaps,
   bool nativeNullAssertions,
+  String baseHref,
 ) async {
   if (!flutterProject.web.existsSync()) {
     throwToolExit('Missing index.html.');
@@ -49,6 +50,7 @@ Future<void> buildWeb(
         kTargetFile: target,
         kHasWebPlugins: hasWebPlugins.toString(),
         kCspMode: csp.toString(),
+        kBaseHref : baseHref,
         kSourceMapsEnabled: sourceMaps.toString(),
         kNativeNullAssertions: nativeNullAssertions.toString(),
         if (serviceWorkerStrategy != null)

packages/flutter_tools/templates/app/web/index.html.tmpl

@@ -10,8 +10,11 @@
 
     For more details:
     * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
+
+    This is a placeholder for base href that will be replaced by the value of
+    the `--base-href` argument provided to `flutter build`.
   -->
-  <base href="/">
+  <base href="$FLUTTER_BASE_HREF">
 
   <meta charset="UTF-8">
   <meta content="IE=Edge" http-equiv="X-UA-Compatible">

packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart

@@ -60,6 +60,7 @@ void main() {
       null,
       true,
       true,
+      null,
     ), throwsToolExit());
   }, overrides: <Type, Generator>{
     Platform: () => fakePlatform,
@@ -119,6 +120,7 @@ void main() {
         'DartObfuscation': 'false',
         'TrackWidgetCreation': 'false',
         'TreeShakeIcons': 'false',
+        'baseHref': null,
       });
     }),
   });

packages/flutter_tools/test/general.shard/build_system/targets/web_test.dart

@@ -101,6 +101,33 @@ void main() {
     expect(environment.outputDir.childFile('version.json'), exists);
   }));
 
+  test('Base href is created in index.html with given base-href after release build', () => testbed.run(() async {
+    environment.defines[kBuildMode] = 'release';
+    environment.defines[kBaseHref] = '/basehreftest/';
+    final Directory webResources = environment.projectDir.childDirectory('web');
+    webResources.childFile('index.html').createSync(recursive: true);
+    webResources.childFile('index.html').writeAsStringSync('''
+<!DOCTYPE html><html><base href="$kBaseHrefPlaceholder"><head></head></html>
+    ''');
+    environment.buildDir.childFile('main.dart.js').createSync();
+    await const WebReleaseBundle().build(environment);
+
+    expect(environment.outputDir.childFile('index.html').readAsStringSync(), contains('/basehreftest/'));
+  }));
+
+  test('null base href does not override existing base href in index.html', () => testbed.run(() async {
+    environment.defines[kBuildMode] = 'release';
+    final Directory webResources = environment.projectDir.childDirectory('web');
+    webResources.childFile('index.html').createSync(recursive: true);
+    webResources.childFile('index.html').writeAsStringSync('''
+<!DOCTYPE html><html><head><base href='/basehreftest/'></head></html>
+    ''');
+    environment.buildDir.childFile('main.dart.js').createSync();
+    await const WebReleaseBundle().build(environment);
+
+    expect(environment.outputDir.childFile('index.html').readAsStringSync(), contains('/basehreftest/'));
+  }));
+
   test('WebReleaseBundle copies dart2js output and resource files to output directory', () => testbed.run(() async {
     environment.defines[kBuildMode] = 'release';
     final Directory webResources = environment.projectDir.childDirectory('web');

packages/flutter_tools/test/general.shard/web/devfs_web_test.dart

@@ -10,6 +10,7 @@ import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/build_info.dart';
+import 'package:flutter_tools/src/build_system/targets/web.dart';
 import 'package:flutter_tools/src/compile.dart';
 import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
@@ -209,6 +210,19 @@ void main() {
     expect(await response.readAsString(), htmlContent);
   }));
 
+  test('serves index.html at / if href attribute is $kBaseHrefPlaceholder', () => testbed.run(() async {
+    const String htmlContent = '<html><head><base href ="$kBaseHrefPlaceholder"></head><body id="test"></body></html>';
+    final Directory webDir = globals.fs.currentDirectory.childDirectory('web')
+      ..createSync();
+    webDir.childFile('index.html').writeAsStringSync(htmlContent);
+
+    final Response response = await webAssetServer
+      .handleRequest(Request('GET', Uri.parse('http://foobar/')));
+
+    expect(response.statusCode, HttpStatus.ok);
+    expect(await response.readAsString(), htmlContent.replaceAll(kBaseHrefPlaceholder, '/'));
+  }));
+
   test('does not serve outside the base path', () => testbed.run(() async {
     webAssetServer.basePath = 'base/path';