传入Webhook松弛：在飞行前响应中，Access-Control-Allow-Headers不允许请求标头字段Content-type

问题描述

我尝试通过浏览器中的访存API发布松弛消息：

I try to post a slack message via the fetch API in a browser:

fetch('https://hooks.slack.com/services/xxx/xxx/xx', {
  method: 'post',
  headers: {
    'Accept': 'application/json, text/plain, */*',
    'Content-type': 'application/json'
  },
  body: JSON.stringify({text: 'Hi there'})
})
  .then(response => console.log)
  .catch(error => console.error);
};

我收到以下错误消息：

Fetch API cannot load:
https://hooks.slack.com/services/xxxxxxx/xxxxx.
Request header field Content-type is not allowed by Access-Control-Allow-Headers in preflight response.

该怎么办？

推荐答案

不幸的是，Slack API终结点在处理来自前端JavaScript代码的跨域请求时似乎已被破坏，因为它无法处理CORS预检 OPTIONS 请求，因此唯一的解决方案似乎是忽略 Content-Type 标头。

That Slack API endpoint unfortunately appears to be broken in its handling of cross-origin requests from frontend JavaScript code—in that it doesn’t handle the CORS preflight OPTIONS request as it should—so the only solution seems to be to omit the Content-Type header.

因此，您似乎需要从请求代码的标头部分中删除以下内容：

So it looks like you need to remove the following from the headers part of your request code:

'Content-type': 'application/json'

那个'Content-type'：'application / json'部分触发您的浏览器执行。因此，要让您的浏览器允许您的前端JavaScript代码发送您要执行的 POST 请求，请使用 https：//hooks.slack .com / services API终结点必须返回 Access-Control-Allow-Headers 响应标头，其中包含 Content-Type 的值。

That 'Content-type': 'application/json' part triggers your browser to do a CORS preflight OPTIONS request. So, for your browser to allow your frontend JavaScript code to send the POST request you’re trying to do, the https://hooks.slack.com/services API endpoint must return an Access-Control-Allow-Headers response header that contains Content-Type in its value.

但是该端点不会返回该标头，因此预检失败并且浏览器就在那里停止。

But that endpoint doesn’t return that header, so the preflight fails and the browser stops right there.

通常从前端JavaScript发布到需要JSON的API端点时，将 Content-Type：application / json 标头添加到请求正是您需要做的，应该做的。但不是这种情况-因为特定的API端点无法正确处理它。

Normally when posting from frontend JavaScript to an API endpoint that expects JSON, adding that Content-Type: application/json header to the request is exactly what you need to do and should do. But not in this case—because that particular API endpoint doesn’t handle it properly.

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