main.dart

  void main() => runApp(DemoApp());

  class DemoApp extends StatelessWidget {
    const DemoApp();

    @override
    Widget build(BuildContext context) {
      return MaterialApp(
        home: Scaffold(
          appBar: AppBar(
            title: const Text("SVG Download"),
          ),
          body: const Center(
            child: SvgFromWeb(),
          )
        ),
      );
    }
  }
  

downloader.dart

  class Downloader {
    final String url;
    const Downloader({ required this.url });

    static final _opt = BaseOptions(
        baseUrl: "https://fluttercompletereference.com/",
        connectTimeout: 3000,
        responseType: ResponseType.bytes
    );

    static final _client = Dio(_opt);

    Future<List<int>> start() async {
      final request = await _client.get<List<int>>(url);
      return request.data;
    }
  }
  

svg_widget.dart

  class SvgFromWeb extends StatefulWidget {
    const SvgFromWeb();

    @override
    _SvgFromWebState createState() => _SvgFromWebState();
  }

  class _SvgFromWebState extends State<SvgFromWeb> {
    late final Downloader downloader;
    late final Future<List<int>> svgImage;

    @override
    void initState() {
      super.initState();
      downloader = const Downloader(url: "/demoimages/firefox.svg");
      svgImage = downloader.start();
    }

    @override
    Widget build(BuildContext context) {
      return FutureBuilder<List<int>>(
        future: svgImage,
        builder: (context, snapshot) {
          if (snapshot.hasError) {
            return const ErrorWidget();
          }

          if (snapshot.hasData) {
            if (snapshot.data != null) {
              return SvgPicture.memory(
                Uint8List.fromList(snapshot.data!),
                placeholderBuilder: (_) => const DecoderLoader(),
              );
            } else {
              return const ErrorWidget();
            }
          }

          return const NetworkLoader();
        },
      );
    }
  }
  

network_loader.dart

  class NetworkLoader extends StatelessWidget {
    const NetworkLoader();

    @override
    Widget build(BuildContext context) {
      return Column(
        mainAxisSize: MainAxisSize.min,
        children: const [
          CircularProgressIndicator(),

          Padding(
            padding: EdgeInsets.only(top: 10),
            child: Text("Downloading..."),
          )
        ],
      );
    }

  }
  

decoder_loader.dart

  class DecoderLoader extends StatelessWidget {
    const DecoderLoader();

    @override
    Widget build(BuildContext context) {
      return Column(
        mainAxisSize: MainAxisSize.min,
        children: const [
          CircularProgressIndicator(),

          Padding(
            padding: EdgeInsets.only(top: 10),
            child: Text("Decoding SVG..."),
          )
        ],
      );
    }

  }
  

error_widget.dart

  class ErrorWidget extends StatelessWidget {
    const ErrorWidget();

    @override
    Widget build(BuildContext context) {
      return const Icon(
        Icons.error,
        size: 25,
        color: Colors.red,
      );
    }

  }