Flutter Web通过Golang Chi路由部署时MIME类型错误求助

用Golang编写后端代码，Flutter Web作为前端，通过Chi路由部署后功能看似正常，但浏览器控制台出现以下错误：

来自“http://localhost:8282/flutter.js”的脚本已加载，但其MIME类型（“text/plain”）不是有效的JavaScript MIME类型。localhost:8282
Uncaught (in promise) DOMException: 操作不安全。无法从Service Worker加载应用，回退到普通标签。flutter.js:145:23
来自“http://localhost:8282/main.dart.js”的脚本已加载，但其MIME类型（“text/plain”）不是有效的JavaScript MIME类型。localhost:8282

现有代码 #

Golang服务器代码 #

package main

import (
    "github.com/go-chi/chi/v5"
    "log"
    "net/http"
    "os"
)

func main() {
    port := os.Getenv("PORT")

    if port == "" {
        port = "8282"
    }

    router := chi.NewRouter()

    //Status router for testing if server is working
    router.Get("/status", func(w http.ResponseWriter, r *http.Request) {
        _, _ = w.Write([]byte("It is working!!!!!!!!!!!!!!!!!"))
    })

    //Configuring frontend
    fs := http.FileServer(http.Dir("web"))

    router.Handle("/*", http.StripPrefix("/", fs))

    log.Printf("connect to http://localhost:%s/ for viewing flutter web", port)
    log.Fatal(http.ListenAndServe("127.0.0.1:"+port, router))
}

Flutter Web的index.html代码 #

<!DOCTYPE html>
<html>
<head>
  <!--
    If you are serving your web app in a path other than the root, change the
    href value below to reflect the base path you are serving from.

    The path provided below has to start and end with a slash "/" in order for
    it to work correctly.

    For more details:
    * https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base

    This is a placeholder for base href that will be replaced by the value of
    the `--base-href` argument provided to `flutter build`.
  -->
  <base href="/">

  <meta charset="UTF-8">
  <meta content="IE=Edge" http-equiv="X-UA-Compatible">
  <meta name="description" content="A new Flutter project.">

  <!-- iOS meta tags & icons -->
  <meta name="apple-mobile-web-app-capable" content="yes">
  <meta name="apple-mobile-web-app-status-bar-style" content="black">
  <meta name="apple-mobile-web-app-title" content="futa_web">
  <link rel="apple-touch-icon" href="icons/Icon-192.png">

  <!-- Favicon -->
  <link rel="icon" type="image/png" href="favicon.png"/>

  <title>futa_web</title>
  <link rel="manifest" href="manifest.json">

  <script>
    // The value below is injected by flutter build, do not touch.
    var serviceWorkerVersion = '532060023';
  </script>
  <!-- This script adds the flutter initialization JS code -->
  <script src="flutter.js" defer></script>
</head>
<body>
  <script>
    window.addEventListener('load', function(ev) {
      // Download main.dart.js
      _flutter.loader.loadEntrypoint({
        serviceWorker: {
          serviceWorkerVersion: serviceWorkerVersion,
        }
      }).then(function(engineInitializer) {
        return engineInitializer.initializeEngine();
      }).then(function(appRunner) {
        return appRunner.runApp();
      });
    });
  </script>
</body>
</html>

解决方案 #

问题根源是Golang默认的http.FileServer无法正确识别部分文件的MIME类型，导致.js文件被标记为text/plain，触发浏览器安全限制。需要自定义文件处理器，根据文件扩展名设置正确的Content-Type头：

修改后的Golang代码：

package main

import (
    "github.com/go-chi/chi/v5"
    "log"
    "net/http"
    "os"
    "path/filepath"
    "mime"
)

// 自定义文件处理函数，修复MIME类型问题
func customFileServer(fs http.FileSystem) http.Handler {
    fileServer := http.FileServer(fs)
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        ext := filepath.Ext(r.URL.Path)
        if ext != "" {
            mimeType := mime.TypeByExtension(ext)
            if mimeType != "" {
                w.Header().Set("Content-Type", mimeType)
            }
        }
        fileServer.ServeHTTP(w, r)
    })
}

func main() {
    port := os.Getenv("PORT")

    if port == "" {
        port = "8282"
    }

    router := chi.NewRouter()

    router.Get("/status", func(w http.ResponseWriter, r *http.Request) {
        _, _ = w.Write([]byte("It is working!!!!!!!!!!!!!!!!!"))
    })

    // 使用自定义文件服务器替代默认实现
    fs := http.Dir("web")
    router.Handle("/*", http.StripPrefix("/", customFileServer(fs)))

    log.Printf("connect to http://localhost:%s/ for viewing flutter web", port)
    log.Fatal(http.ListenAndServe("127.0.0.1:"+port, router))
}

说明 #

• 自定义customFileServer函数会根据请求文件的扩展名，通过mime.TypeByExtension获取正确的MIME类型并设置到响应头中，比如.js文件会被设置为application/javascript
• 确保web目录是flutter build web生成的产物目录，路径配置正确

内容的提问来源于stack exchange，提问作者Kateile