import 'dart:io'; not support on the web application

问题

when I use the dart: io library on the flutter web, a warning appears when debugging .like that

[WARNING]build_web_compilers:entrypoint on web/main.dart: Skipping compiling retgoo_internal|web/main.dart with ddc because some of its transitive libraries have sdk dependencies that not supported on this platform:

retgoo_internal|lib/protocol/http_aiframework.dart

but when I use import 'package: flutter_web / io.dart'; there is an error code, in code .transform here is the http_aiframework.dart code

import 'dart:async';
import 'dart:convert';
import 'dart:io';
//import 'package:flutter_web/io.dart';

import '../main.dart';

typedef HttpProgressListener(int totalBytes, int receivedBytes, bool done);

class Http {
  static String baseURL;

  static bool loadAccessToken() {
    return accessToken != null;
  }

  static bool setAccessToken(String token) {
    accessToken = token;
    return accessToken != null;
  }

  static bool removeAccessToken() {
    accessToken = null;
    return accessToken == null;
  }

  static _processHeader(
      {HttpClientRequest request, Map<String, dynamic> headers}) {
    if (headers != null) {
      headers.forEach((key, value) {
        request.headers.add(key, value);
      });
    }

    if (accessToken != null) {
      request.headers.set("Authorization", "Bearer " + accessToken);
    }
  }

  static _processResponse(
      {HttpClientResponse response,
      HttpProgressListener progressListener}) async {
    final int totalBytes = response.contentLength;
    int receivedBytes = 0;

    String body = await response
        .transform( //this is the error code when I use import 'package: flutter_web / io.dart';
          StreamTransformer.fromHandlers(
            handleData: (data, sink) {
              sink.add(data);

              if (progressListener != null) {
                receivedBytes += data.length;
                progressListener(totalBytes, receivedBytes, false);
              }
            },
            handleDone: (sink) {
              sink.close();
              if (progressListener != null) {
                progressListener(totalBytes, receivedBytes, true);
              }
            },
          ),
        )
        .map((v) => utf8.decoder.convert(v))
        .join();

    return body;
  }

  static getData({
    String baseURL,
    String endpoint,
    Map<String, dynamic> headers,
    HttpProgressListener downloadProgressListener,
    dynamic data,
  }) async {
    final client = HttpClient();
    client.userAgent = "AIFramework/";
    client.connectionTimeout = Duration(seconds: 30);

    HttpClientRequest request;
    String mBaseURL = baseURL ?? Http.baseURL;

    var uri = Uri.parse("$mBaseURL$endpoint");

    if (data == null) {
      request = await client.getUrl(uri);
    } else {
      request = await client.postUrl(uri);
    }

    _processHeader(
      request: request,
      headers: headers,
    );

    if (data != null) {
      String payload = json.encode(data);
      request.write(payload);
    }

    final response = await request.close();
    if (response.statusCode == 200) {
      return json.decode(
        await _processResponse(
          response: response,
          progressListener: downloadProgressListener,
        ),
      );
    }

    return null;
  }
}

回答1:

I just ran into this problem myself, looks like the dart:io library won't work with web applications.

From: https://api.flutter.dev/flutter/dart-io/dart-io-library.html

Important: Browser-based applications can't use this library. Only servers, command-line scripts, and Flutter mobile apps can import and use dart:io.

回答2:

If what you want to use from io.dart is WebSocket, you can use HtmlWebSocketChannel from the html package (import 'package:web_socket_channel/html.dart';)

回答3:

You can use the universal_io package. It supports the web in addition to Android and iOS.

dependencies:
  universal_io: ^1.0.1

Do the following import instead of dart:io:

import 'package:universal_io/io.dart';

It works the same way.

Related question: Avoid using web-only libraries outside Flutter web plugin packages

回答4:

StreamTransformer has two generic type, specific them like this

StreamTransformer<List<int>, String>

ps: Dart is a type-safe & dynamic-type language.

来源：https://stackoverflow.com/questions/56945106/import-dartio-not-support-on-the-web-application