# 读取和发送Headers

REST API通常使用头读取和发送非内容信息。例如，对GitHub的API的任何请求都将返回详细描述当前用户速率限制状态的头。

```
X-RateLimit-Limit: 5000
X-RateLimit-Remaining: 4987
X-RateLimit-Reset: 1350085394
```

**X-\* Headers**

您可能想知道为什么Github速率限制头的前缀是x-，特别是当您在同一请求返回的其他头的上下文中看到它们时。

```
HTTP/1.1 200 OK
Server: nginx
Date: Fri, 12 Oct 2012 23:33:14 GMT
Content-Type: application/json; charset=utf-8
Connection: keep-alive
Status: 200 OK
ETag: "a00049ba79152d03380c34652f2cb612"
X-GitHub-Media-Type: github.v3
X-RateLimit-Limit: 5000
X-RateLimit-Remaining: 4987
X-RateLimit-Reset: 1350085394
Content-Length: 5
Cache-Control: max-age=0, private, must-revalidate
X-Content-Type-Options: nosniff
```

> 以X开头的头并不在HTTP标准中，它可能是完全捏造的(例如，X-How-Much-Matt-Loves-This-Page)，或者尚未成为规范的一部分(例如，X-Requested-With)。

同样需要API允许开发人员使用头自定义请求，例如，GitHub的API可以很容易地定义你要使用Accept标头的API的哪个版本。

```
Accept: application/vnd.github.v3+json
```

如果你想更改v3到v2，Github将传递你的请求到第二版本。

让我们学习如何在Laravel中快速的实现这两种


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://liseen315.gitbook.io/laravel/bian-xie-apis/du-qu-he-fa-song-headers.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.