[web] consolidate network code into httpFetch

lib/web_ui/dev/test_platform.dart

@@ -90,6 +90,12 @@ class BrowserPlatform extends PlatformPlugin {
         // This handler goes last, after all more specific handlers failed to handle the request.
         .add(_createAbsolutePackageUrlHandler())
         .add(_screenshotHandler)
+
+        // Generates and serves a test payload of given length, split into chunks
+        // of given size. Reponds to requests to /long_test_payload.
+        .add(_testPayloadGenerator)
+
+        // If none of the handlers above handled the request, return 404.
         .add(_fileNotFoundCatcher);
 
     server.mount(cascade.handler);
@@ -320,6 +326,46 @@ class BrowserPlatform extends PlatformPlugin {
     };
   }
 
+  Future<shelf.Response> _testPayloadGenerator(shelf.Request request) async {
+    if (!request.requestedUri.path.endsWith('/long_test_payload')) {
+      return shelf.Response.notFound(
+          'This request is not handled by the screenshot handler');
+    }
+
+    final int payloadLength = int.parse(request.requestedUri.queryParameters['length']!);
+    final int chunkLength = int.parse(request.requestedUri.queryParameters['chunk']!);
+
+    final StreamController<List<int>> controller = StreamController<List<int>>();
+
+    Future<void> fillPayload() async {
+      int remainingByteCount = payloadLength;
+      int byteCounter = 0;
+      while (remainingByteCount > 0) {
+        final int currentChunkLength = min(chunkLength, remainingByteCount);
+        final List<int> chunk = List<int>.generate(
+          currentChunkLength,
+          (int i) => (byteCounter + i) & 0xFF,
+        );
+        byteCounter = (byteCounter + currentChunkLength) & 0xFF;
+        remainingByteCount -= currentChunkLength;
+        controller.add(chunk);
+        await Future<void>.delayed(const Duration(milliseconds: 100));
+      }
+      await controller.close();
+    }
+
+    // Kick off payload filling function but don't block on it. The stream should
+    // be returned immediately, and the client should receive data in chunks.
+    unawaited(fillPayload());
+    return shelf.Response.ok(
+      controller.stream,
+      headers: <String, String>{
+        'Content-Type': 'application/octet-stream',
+        'Content-Length': '$payloadLength',
+      },
+    );
+  }
+
   Future<shelf.Response> _screenshotHandler(shelf.Request request) async {
     if (!request.requestedUri.path.endsWith('/screenshot')) {
       return shelf.Response.notFound(

lib/web_ui/lib/src/engine/assets.dart

@@ -63,52 +63,23 @@ class AssetManager {
     return Uri.encodeFull('${_baseUrl ?? ''}$assetsDir/$asset');
   }
 
+  /// Loads an asset and returns the server response.
+  Future<HttpFetchResponse> loadAsset(String asset) {
+    return httpFetch(getAssetUrl(asset));
+  }
+
   /// Loads an asset using an [DomXMLHttpRequest] and returns data as [ByteData].
   Future<ByteData> load(String asset) async {
     final String url = getAssetUrl(asset);
-    try {
-      final DomXMLHttpRequest request =
-          await domHttpRequest(url, responseType: 'arraybuffer');
-
-      final ByteBuffer response = request.response as ByteBuffer;
-      return response.asByteData();
-    } catch (e) {
-      if (!domInstanceOfString(e, 'ProgressEvent')){
-        rethrow;
-      }
-      final DomProgressEvent p = e as DomProgressEvent;
-      final DomEventTarget? target = p.target;
-      if (domInstanceOfString(target,'XMLHttpRequest')) {
-        final DomXMLHttpRequest request = target! as DomXMLHttpRequest;
-        if (request.status == 404 && asset == 'AssetManifest.json') {
-          printWarning('Asset manifest does not exist at `$url` – ignoring.');
-          return Uint8List.fromList(utf8.encode('{}')).buffer.asByteData();
-        }
-        throw AssetManagerException(url, request.status!.toInt());
-      }
-
-      final String? constructorName = target == null ? 'null' :
-          domGetConstructorName(target);
-      printWarning('Caught ProgressEvent with unknown target: '
-          '$constructorName');
-      rethrow;
-    }
-  }
-}
+    final HttpFetchResponse response = await httpFetch(url);
 
-/// Thrown to indicate http failure during asset loading.
-class AssetManagerException implements Exception {
-  /// Initializes exception with request url and http status.
-  AssetManagerException(this.url, this.httpStatus);
-
-  /// Http request url for asset.
-  final String url;
-
-  /// Http status of response.
-  final int httpStatus;
+    if (response.status == 404 && asset == 'AssetManifest.json') {
+      printWarning('Asset manifest does not exist at `$url` - ignoring.');
+      return Uint8List.fromList(utf8.encode('{}')).buffer.asByteData();
+    }
 
-  @override
-  String toString() => 'Failed to load asset at "$url" ($httpStatus)';
+    return (await response.payload.asByteBuffer()).asByteData();
+  }
 }
 
 /// An asset manager that gives fake empty responses for assets.
@@ -141,6 +112,33 @@ class WebOnlyMockAssetManager implements AssetManager {
   @override
   String getAssetUrl(String asset) => asset;
 
+  @override
+  Future<HttpFetchResponse> loadAsset(String asset) async {
+    if (asset == getAssetUrl('AssetManifest.json')) {
+      return MockHttpFetchResponse(
+        url: asset,
+        status: 200,
+        payload: MockHttpFetchPayload(
+          byteBuffer: _toByteData(utf8.encode(defaultAssetManifest)).buffer,
+        )
+      );
+    }
+    if (asset == getAssetUrl('FontManifest.json')) {
+      return MockHttpFetchResponse(
+        url: asset,
+        status: 200,
+        payload: MockHttpFetchPayload(
+          byteBuffer: _toByteData(utf8.encode(defaultFontManifest)).buffer,
+        )
+      );
+    }
+
+    return MockHttpFetchResponse(
+      url: asset,
+      status: 404,
+    );
+  }
+
   @override
   Future<ByteData> load(String asset) {
     if (asset == getAssetUrl('AssetManifest.json')) {
@@ -151,7 +149,7 @@ class WebOnlyMockAssetManager implements AssetManager {
       return Future<ByteData>.value(
           _toByteData(utf8.encode(defaultFontManifest)));
     }
-    throw AssetManagerException(asset, 404);
+    throw HttpFetchNoPayloadError(asset, status: 404);
   }
 
   ByteData _toByteData(List<int> bytes) {

lib/web_ui/lib/src/engine/canvaskit/font_fallbacks.dart

@@ -488,37 +488,33 @@ class NotoDownloader {
   /// Downloads the [url] and returns it as a [ByteBuffer].
   ///
   /// Override this for testing.
-  Future<ByteBuffer> downloadAsBytes(String url, {String? debugDescription}) {
+  Future<ByteBuffer> downloadAsBytes(String url, {String? debugDescription}) async {
     if (assertionsEnabled) {
       _debugActiveDownloadCount += 1;
     }
-    final Future<ByteBuffer> result = httpFetch(url).then(
-        (DomResponse fetchResult) => fetchResult
-            .arrayBuffer()
-            .then<ByteBuffer>((dynamic x) => x as ByteBuffer));
+    final Future<ByteBuffer> data = httpFetchByteBuffer(url);
     if (assertionsEnabled) {
-      result.whenComplete(() {
+      unawaited(data.whenComplete(() {
         _debugActiveDownloadCount -= 1;
-      });
+      }));
     }
-    return result;
+    return data;
   }
 
   /// Downloads the [url] and returns is as a [String].
   ///
   /// Override this for testing.
-  Future<String> downloadAsString(String url, {String? debugDescription}) {
+  Future<String> downloadAsString(String url, {String? debugDescription}) async {
     if (assertionsEnabled) {
       _debugActiveDownloadCount += 1;
     }
-    final Future<String> result = httpFetch(url).then((DomResponse response) =>
-        response.text().then<String>((dynamic x) => x as String));
+    final Future<String> data = httpFetchText(url);
     if (assertionsEnabled) {
-      result.whenComplete(() {
+      unawaited(data.whenComplete(() {
         _debugActiveDownloadCount -= 1;
-      });
+      }));
     }
-    return result;
+    return data;
   }
 }
 

lib/web_ui/lib/src/engine/canvaskit/fonts.dart

@@ -93,21 +93,15 @@ class SkiaFontCollection implements FontCollection {
   /// Loads fonts from `FontManifest.json`.
   @override
   Future<void> downloadAssetFonts(AssetManager assetManager) async {
-    ByteData byteData;
+    final HttpFetchResponse response = await assetManager.loadAsset('FontManifest.json');
 
-    try {
-      byteData = await assetManager.load('FontManifest.json');
-    } on AssetManagerException catch (e) {
-      if (e.httpStatus == 404) {
-        printWarning('Font manifest does not exist at `${e.url}` – ignoring.');
-        return;
-      } else {
-        rethrow;
-      }
+    if (!response.hasPayload) {
+      printWarning('Font manifest does not exist at `${response.url}` - ignoring.');
+      return;
     }
 
-    final List<dynamic>? fontManifest =
-        json.decode(utf8.decode(byteData.buffer.asUint8List())) as List<dynamic>?;
+    final Uint8List data = await response.asUint8List();
+    final List<dynamic>? fontManifest = json.decode(utf8.decode(data)) as List<dynamic>?;
     if (fontManifest == null) {
       throw AssertionError(
           'There was a problem trying to load FontManifest.json');
@@ -206,10 +200,11 @@ class SkiaFontCollection implements FontCollection {
     String family
   ) {
     Future<UnregisteredFont?> downloadFont() async {
-      ByteBuffer buffer;
+      // Try to get the font leniently. Do not crash the app when failing to
+      // fetch the font in the spirit of "gradual degradation of functionality".
       try {
-        buffer = await httpFetch(url).then(_getArrayBuffer);
-        return UnregisteredFont(buffer, url, family);
+        final ByteBuffer data = await httpFetchByteBuffer(url);
+        return UnregisteredFont(data, url, family);
       } catch (e) {
         printWarning('Failed to load font $family at $url');
         printWarning(e.toString());
@@ -230,12 +225,6 @@ class SkiaFontCollection implements FontCollection {
     return actualFamily;
   }
 
-  Future<ByteBuffer> _getArrayBuffer(DomResponse fetchResult) {
-    return fetchResult
-        .arrayBuffer()
-        .then<ByteBuffer>((dynamic x) => x as ByteBuffer);
-  }
-
   TypefaceFontProvider? fontProvider;
 
   @override

lib/web_ui/lib/src/engine/canvaskit/image.dart

@@ -167,12 +167,6 @@ class ImageCodecException implements Exception {
 
 const String _kNetworkImageMessage = 'Failed to load network image.';
 
-typedef HttpRequestFactory = DomXMLHttpRequest Function();
-HttpRequestFactory httpRequestFactory = () => createDomXMLHttpRequest();
-void debugRestoreHttpRequestFactory() {
-  httpRequestFactory = () => createDomXMLHttpRequest();
-}
-
 /// Instantiates a [ui.Codec] backed by an `SkAnimatedImage` from Skia after
 /// requesting from URI.
 Future<ui.Codec> skiaInstantiateWebImageCodec(
@@ -186,49 +180,48 @@ Future<ui.Codec> skiaInstantiateWebImageCodec(
 }
 
 /// Sends a request to fetch image data.
-Future<Uint8List> fetchImage(
-    String url, WebOnlyImageCodecChunkCallback? chunkCallback) {
-  final Completer<Uint8List> completer = Completer<Uint8List>();
-
-  final DomXMLHttpRequest request = httpRequestFactory();
-  request.open('GET', url, true);
-  request.responseType = 'arraybuffer';
-  if (chunkCallback != null) {
-    request.addEventListener('progress', allowInterop((DomEvent event)  {
-      event = event as DomProgressEvent;
-      chunkCallback.call(event.loaded!.toInt(), event.total!.toInt());
-    }));
-  }
-
-  request.addEventListener('error', allowInterop((DomEvent event) {
-    completer.completeError(ImageCodecException('$_kNetworkImageMessage\n'
+Future<Uint8List> fetchImage(String url, WebOnlyImageCodecChunkCallback? chunkCallback) async {
+  try {
+    final HttpFetchResponse response = await httpFetch(url);
+    final int? contentLength = response.contentLength;
+
+    if (!response.hasPayload) {
+      throw ImageCodecException(
+        '$_kNetworkImageMessage\n'
         'Image URL: $url\n'
-        'Trying to load an image from another domain? Find answers at:\n'
-        'https://flutter.dev/docs/development/platform-integration/web-images'));
-  }));
-
-  request.addEventListener('load', allowInterop((DomEvent event) {
-    final int status = request.status!.toInt();
-    final bool accepted = status >= 200 && status < 300;
-    final bool fileUri = status == 0; // file:// URIs have status of 0.
-    final bool notModified = status == 304;
-    final bool unknownRedirect = status > 307 && status < 400;
-    final bool success = accepted || fileUri || notModified || unknownRedirect;
-
-    if (!success) {
-      completer.completeError(
-        ImageCodecException('$_kNetworkImageMessage\n'
-            'Image URL: $url\n'
-            'Server response code: $status'),
+        'Server response code: ${response.status}',
       );
-      return;
     }
 
-    completer.complete(Uint8List.view(request.response as ByteBuffer));
-  }));
+    if (chunkCallback != null && contentLength != null) {
+      return readChunked(response.payload, contentLength, chunkCallback);
+    } else {
+      return await response.asUint8List();
+    }
+  } on HttpFetchError catch (_) {
+    throw ImageCodecException(
+      '$_kNetworkImageMessage\n'
+      'Image URL: $url\n'
+      'Trying to load an image from another domain? Find answers at:\n'
+      'https://flutter.dev/docs/development/platform-integration/web-images',
+    );
+  }
+}
 
-  request.send();
-  return completer.future;
+/// Reads the [payload] in chunks using the browser's Streams API
+///
+/// See: https://developer.mozilla.org/en-US/docs/Web/API/Streams_API
+Future<Uint8List> readChunked(HttpFetchPayload payload, int contentLength, WebOnlyImageCodecChunkCallback chunkCallback) async {
+  final Uint8List result = Uint8List(contentLength);
+  int position = 0;
+  int cumulativeBytesLoaded = 0;
+  await payload.read<Uint8List>((Uint8List chunk) {
+    cumulativeBytesLoaded += chunk.lengthInBytes;
+    chunkCallback(cumulativeBytesLoaded, contentLength);
+    result.setAll(position, chunk);
+    position += chunk.lengthInBytes;
+  });
+  return result;
 }
 
 /// A [ui.Image] backed by an `SkImage` from Skia.