Dart http包设置followRedirects=false仍自动重定向，如何解决？

我尝试用Flutter和Dart实现一个小型HTTP封装类，希望手动处理重定向以避免CORS问题，于是设置了request.followRedirects = false，但发现该设置完全无效，客户端仍会自动跟随重定向。

复现代码及场景 #

Dart HTTP封装类 #

import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;

class HttpWrapper {
  http.Client httpClient = http.Client();

  Future<http.StreamedResponse> backendHttpRequest(
      String method, String endpoint) async {
    String backendUrlBase = const String.fromEnvironment("backend_url_base");

    var uri = Uri.parse(backendUrlBase + endpoint);
    http.Request request = http.Request(method, uri);
    request.followRedirects = false;

    var response = await httpClient.send(request);

    if (response.isRedirect) {
      debugPrint("Redirecting...");
      // handle redirect
      return response;
    } else {
      return response;
    }
  }
}

Express示例服务器 #

const express = require('express');
const app = express();
var cors = require('cors')
const logger = require('morgan');
const PORT = 3000;

app.use(logger('dev'));
app.use(cors()) 

// Without middleware
app.get('/endpointwhichredirects', function (req, res) {
    console.log("Redirecting...");
    res.redirect('/user');
});
 
app.get('/user', function (req, res) {
    res.send("This is the user-page");
});
 
app.listen(PORT, function (err) {
    if (err) console.log(err);
    console.log("Server listening on PORT", PORT);
});

调用代码 #

HttpWrapper httpWp = HttpWrapper();
res = httpWp.backendHttpRequest('Get', '/endpointwhichredirects');

服务器日志输出 #

> GET /endpointwhichredirects 302 3.051 ms - 27
> GET /user 304 2.986 ms - -

代码中的debugPrint("Redirecting...")从未触发，断点只进入非重定向分支。

原因及解决办法 #

核心原因 #

默认的http.Client()在Flutter不同环境下（移动端/Web）的底层实现会忽略请求对象的followRedirects设置，自动处理重定向，导致你的配置不生效。

解决步骤 #

根据运行环境选择对应的自定义客户端，全局禁用自动跟随重定向：

1. 移动端/桌面端（使用IOClient）

import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'package:http/io_client.dart';
import 'dart:io';

class HttpWrapper {
  late http.Client httpClient;

  HttpWrapper() {
    // 创建自定义HttpClient并禁用自动跟随重定向
    final ioClient = HttpClient()
      ..followRedirects = false;
    httpClient = IOClient(ioClient);
  }

  Future<http.StreamedResponse> backendHttpRequest(
      String method, String endpoint) async {
    String backendUrlBase = const String.fromEnvironment("backend_url_base");

    var uri = Uri.parse(backendUrlBase + endpoint);
    http.Request request = http.Request(method, uri);

    var response = await httpClient.send(request);

    if (response.isRedirect) {
      debugPrint("Redirecting...");
      // 在这里手动处理重定向逻辑，比如读取Location头发起新请求
      return response;
    } else {
      return response;
    }
  }
}

2. Web环境（使用BrowserClient）

import 'package:flutter/foundation.dart';
import 'package:http/http.dart' as http;
import 'package:http/browser_client.dart';

class HttpWrapper {
  late http.Client httpClient;

  HttpWrapper() {
    // 创建BrowserClient并禁用自动跟随重定向
    httpClient = BrowserClient()..followRedirects = false;
  }

  Future<http.StreamedResponse> backendHttpRequest(
      String method, String endpoint) async {
    String backendUrlBase = const String.fromEnvironment("backend_url_base");

    var uri = Uri.parse(backendUrlBase + endpoint);
    http.Request request = http.Request(method, uri);

    var response = await httpClient.send(request);

    if (response.isRedirect) {
      debugPrint("Redirecting...");
      // 手动处理重定向逻辑
      return response;
    } else {
      return response;
    }
  }
}

补充说明 #

• 修改后，客户端会直接返回302响应，response.isRedirect会变为true，触发你的手动处理逻辑。
• 手动处理重定向时，记得读取响应头中的Location字段，自行构造新请求，同时注意处理CORS相关配置。

内容的提问来源于stack exchange，提问作者di-math