Question

我经常在Dart中收到错误“HTTP标头不可变”。

我想要做的是当用户在“packages”文件夹中询问某些内容时，它会获取它。

我的错误代码是这样的：

if(new RegExp("/packages/(.*)").hasMatch(request.uri.toString())){
    new File(request.uri.toString().substring(1)).readAsString().then((String contents){
      request.response.headers.contentType = new ContentType("text", "css", charset: "utf-8");
      request.response.write(contents);
      request.response.close();
    });
  }

我的整个代码是这样的：

import "dart:io";

void main() {
  HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, 8000).then((HttpServer server){
    print("Listening on localhost on {$server.port}");

    server.listen((HttpRequest request){
      switch(request.uri.toString()){
        case "/":
          request.response.headers.contentType = ContentType.HTML;

          new File("static/taskbar.html").readAsString().then((String contents){
            request.response.write(contents);
            request.response.close();

            new File("static/index.html").readAsString().then((String contents){
              request.response.write(contents);
              request.response.close();
            });
          });
          break;
        default:
          request.response.statusCode = HttpStatus.NOT_FOUND;
          request.response.write("404 Not Found.");
          request.response.close();
          break;
      }

      if(new RegExp("/packages/(.*)").hasMatch(request.uri.toString())){
        new File(request.uri.toString().substring(1)).readAsString().then((String contents){
          request.response.headers.contentType = new ContentType("text", "css", charset: "utf-8");
          request.response.write(contents);
          request.response.close();
        });
      }
    });
  });
}

Answer 1

基本上，当您收到“HTTP标头不可变”错误时，这意味着您在写入响应后尝试修改标头。

在您的代码中，当请求与/packages/(.*)模式匹配时，它还会执行交换机的default子句，从而产生404响应。因此，当您尝试再次写入响应时，服务器会抛出异常。

要解决此问题，您可以使用if else表达式替换开关。例如：

HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, 8000).then((HttpServer server){
  print("Listening on localhost on {$server.port}");

  server.listen((HttpRequest request){
    var uri = request.uri.toString();
    if (uri == "/") {

      request.response.headers.contentType = ContentType.HTML;

      new File("static/taskbar.html").readAsString().then((String contents){
        request.response.write(contents);
        request.response.close();

        new File("static/index.html").readAsString().then((String contents){
          request.response.write(contents);
          request.response.close();
        });
      });

    } else if(new RegExp("/packages/(.*)").hasMatch(uri)){

      new File(uri.substring(1)).readAsString().then((String contents){
        request.response.headers.contentType = new ContentType("text", "css", charset: "utf-8");
        request.response.write(contents);
        request.response.close();
      });

    } else {

      request.response.statusCode = HttpStatus.NOT_FOUND;
      request.response.write("404 Not Found.");
      request.response.close();

    }
  });
});

Dart：HTTP标头不可变

1 个答案: