如何更改请求的标头？

Question

是否可以更改fetch 事件接收到的Request 对象的标头？

两次尝试：

1. 修改现有标题：

   self.addEventListener('fetch', function (event) {
     event.request.headers.set("foo", "bar");
     event.respondWith(fetch(event.request));
   });
   

   Failed to execute 'set' on 'Headers': Headers are immutable 失败。

2. 创建新的Request 对象：

   self.addEventListener('fetch', function (event) {
     var req = new Request(event.request, {
       headers: { "foo": "bar" }
     });
     event.respondWith(fetch(req));
   });
   

   Failed to construct 'Request': Cannot construct a Request with a Request whose mode is 'navigate' and a non-empty RequestInit. 失败

（另见How to alter the headers of a Response?）

Answer 1

只要您设置了所有选项，就可以创建一个新的请求对象：

// request is event.request sent by browser here 
var req = new Request(request.url, {
    method: request.method,
    headers: request.headers,
    mode: 'same-origin', // need to set this properly
    credentials: request.credentials,
    redirect: 'manual'   // let browser handle redirects
});

如果原来的mode 是navigate（这就是您遇到异常的原因），则您不能使用原始mode，并且您可能希望将重定向传递回浏览器以使其更改其URL，而不是让fetch 处理它.

确保您没有在 GET 请求上设置正文 - fetch 不喜欢它，但浏览器有时会在响应来自 POST 请求的重定向时生成带有正文的 GET 请求。 fetch 不喜欢。

Answer 2

您可以在原始请求的基础上创建一个新请求并覆盖标头：

new Request(originalRequest, {
  headers: {
    ...originalRequest.headers,
    foo: 'bar'
  }
})

另请参阅：https://developer.mozilla.org/en-US/docs/Web/API/Request/Request

Answer 3

您是否尝试过类似于您提到的问题 (How to alter the headers of a Response?) 中的解决方案？

在 Service Worker Cookbook 中，我们手动复制 Request 对象以将它们存储在 IndexedDB (https://serviceworke.rs/request-deferrer_service-worker_doc.html) 中。这是出于不同的原因（我们想将它们存储在缓存中，但由于https://github.com/slightlyoff/ServiceWorker/issues/693，我们无法存储 POST 请求），但它应该也适用于您想做的事情。

// Serialize is a little bit convolved due to headers is not a simple object.
function serialize(request) {
  var headers = {};
  // `for(... of ...)` is ES6 notation but current browsers supporting SW, support this
  // notation as well and this is the only way of retrieving all the headers.
  for (var entry of request.headers.entries()) {
    headers[entry[0]] = entry[1];
  }
  var serialized = {
    url: request.url,
    headers: headers,
    method: request.method,
    mode: request.mode,
    credentials: request.credentials,
    cache: request.cache,
    redirect: request.redirect,
    referrer: request.referrer
  };



  // Only if method is not `GET` or `HEAD` is the request allowed to have body.
  if (request.method !== 'GET' && request.method !== 'HEAD') {
    return request.clone().text().then(function(body) {
      serialized.body = body;
      return Promise.resolve(serialized);
    });
  }
  return Promise.resolve(serialized);
}

// Compared, deserialize is pretty simple.
function deserialize(data) {
  return Promise.resolve(new Request(data.url, data));
}

Answer 4

如果未来的读者还需要删除不可变的 Request/Response 标头中的键，并且还希望对不可变标头具有高保真度，您可以有效地克隆 Header 对象：

const mutableHeaders = new Headers();
immutableheaders.forEach((value, key, parent) => mutableHeaders.set(key, value));

mutableHeaders.delete('content-encoding');
mutableHeaders.delete('vary');
mutableHeaders['host'] = 'example.com';
// etc.

然后您可以创建一个新的Request 并传入您的mutableHeaders。

这比已接受的答案更受欢迎，因为如果您需要代理 Request，您不想手动指定每个可能的标头，同时包括 Cloudflare、AWS、Azure、Google 等自定义 CDN 标头.

---

背景资料

Request 中的标头不可变或只读的原因是：

interface Request extends Body {
  readonly cache: RequestCache;
  readonly credentials: RequestCredentials;
  readonly destination: RequestDestination;
  readonly headers: Headers;
  readonly integrity: string;
    ...

Headers的接口是：

interface Headers {
    append(name: string, value: string): void;
    delete(name: string): void;
    get(name: string): string | null;
    has(name: string): boolean;
    set(name: string, value: string): void;
    forEach(callbackfn: (value: string, key: string, parent: Headers) => void, thisArg?: any): void;
}