packages/flutter/lib/src/painting/_network_image_web.dart

// Copyright 2019 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:async';
import 'dart:ui' as ui;

import 'package:flutter/foundation.dart';

import 'image_provider.dart' as image_provider;
import 'image_stream.dart';

/// The dart:html implementation of [image_provider.NetworkImage].
///
/// NetworkImage on the web does not support decoding to a specified size.
class NetworkImage extends image_provider.ImageProvider<image_provider.NetworkImage> implements image_provider.NetworkImage {
  /// Creates an object that fetches the image at the given URL.
  ///
  /// The arguments [url] and [scale] must not be null.
  const NetworkImage(this.url, {this.scale = 1.0, this.headers})
      : assert(url != null),
        assert(scale != null);

  @override
  final String url;

  @override
  final double scale;

  @override
  final Map<String, String> headers;

  @override
  Future<NetworkImage> obtainKey(image_provider.ImageConfiguration configuration) {
    return SynchronousFuture<NetworkImage>(this);
  }

  @override
  ImageStreamCompleter load(image_provider.NetworkImage key, image_provider.DecoderCallback decode) {
    return MultiFrameImageStreamCompleter(
      codec: _loadAsync(key, decode),
      scale: key.scale,
      informationCollector: () {
        return <DiagnosticsNode>[
          DiagnosticsProperty<image_provider.ImageProvider>('Image provider', this),
          DiagnosticsProperty<NetworkImage>('Image key', key),
        ];
      },
    );
  }

  // TODO(garyq): We should eventually support custom decoding of network images on Web as
  // well, see https://github.com/flutter/flutter/issues/42789.
  //
  // Web does not support decoding network images to a specified size. The decode parameter
  // here is ignored and the web-only `ui.webOnlyInstantiateImageCodecFromUrl` will be used
  // directly in place of the typical `instantiateImageCodec` method.
  Future<ui.Codec> _loadAsync(NetworkImage key, image_provider.DecoderCallback decode) async {
    assert(key == this);

    final Uri resolved = Uri.base.resolve(key.url);
    // This API only exists in the web engine implementation and is not
    // contained in the analyzer summary for Flutter.
    return ui.webOnlyInstantiateImageCodecFromUrl(resolved); // ignore: undefined_function
  }

  @override
  bool operator ==(dynamic other) {
    if (other.runtimeType != runtimeType) {
      return false;
    }
    final NetworkImage typedOther = other;
    return url == typedOther.url && scale == typedOther.scale;
  }

  @override
  int get hashCode => ui.hashValues(url, scale);

  @override
  String toString() => '$runtimeType("$url", scale: $scale)';
}