http - HTTP 服务器应该如何响应它不想处理的代理请求？

Question

HTTP 请求的第一行包含一个“目标”，它是以下之一:

request-target = origin-form
               / absolute-form
               / authority-form
               / asterisk-form

origin-form 是典型的形式，例如 GET/hello-world HTTP/1.1。代理请求使用绝对形式:

GET https://example.com/ HTTP/1.1

假设该请求到达源服务器，它只是试图服务于一些其他 域。 (例如，假设我们向 en.wikipedia.org 发送了上述请求。)手头的服务器不希望成为代理服务器，并且不希望完成发出的请求。它应该返回什么？ (理想情况下，为什么？HTTP RFC 中是否有任何地方说明了这一点？)

(我查询了一些服务器以查看根据经验发生了什么。我得到了大部分 500 和 200(但内容错误)、409 冲突 和在一个特殊情况下的 301 Moved Permanently 形成了一个无限循环。我感觉客户端向服务器发送代理请求是一个错误，服务器不能也不会满足它。服务器及其行为都没有问题，应该影响更改的区域直接位于客户端，因此，4xx，但我不清楚哪个是合适的。)

Answer 1

好问题。来自 RFC 2616 :

5.1.2 Request-URI

...

To allow for transition to absoluteURIs in all requests in future versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI form in requests, even though HTTP/1.1 clients will only generate them in requests to proxies.

和:

5.2 The Resource Identified by a Request

The exact resource identified by an Internet request is determined by examining both the Request-URI and the Host header field.

An origin server that does not allow resources to differ by the requested host MAY ignore the Host header field value when determining the resource identified by an HTTP/1.1 request. (But see section 19.6.1.1 for other requirements on Host support in HTTP/1.1.)

An origin server that does differentiate resources based on the host requested (sometimes referred to as virtual hosts or vanity host names) MUST use the following rules for determining the requested resource on an HTTP/1.1 request:

1. If Request-URI is an absoluteURI, the host is part of the Request-URI. Any Host header field value in the request MUST be ignored.

2. If the Request-URI is not an absoluteURI, and the request includes a Host header field, the host is determined by the Host header field value.

3. If the host as determined by rule 1 or 2 is not a valid host on the server, the response MUST be a 400 (Bad Request) error message.

所以看起来正确的答案是要么忽略主机并尝试在本地完成请求，让它产生任何可能的错误，要么发送 400。这不是完全确定的，因为错误是在 GET 行中，而不是 HOST 行中，并且您的不是“根据请求的主机区分资源的原始服务器”，但它看起来与 RFC 一样接近。

在后续的 RFC 中，RFC 7230与上文5.1.2措辞相同；它没有我能找到的第 5.2 节之类的内容，但它确实有:

Recipients of an invalid request-line SHOULD respond with either a 400 (Bad Request) error or a 301 (Moved Permanently) redirect with the request-target properly encoded.