301Moved Permanently

请求的资源已经被移动到了由 Location 头部指定的 url 上，是固定的不会再改变。搜索引擎会根据该响应修正。

The target resource has been assigned a new permanent URI and any future references to this resource ought to use one of the enclosed URIs.

Clients with link-editing capabilities ought to automatically re-link references to the effective request URI to one or more of the new references sent by the server, where possible.

The server SHOULD generate a Location header field in the response containing a preferred URI reference for the new permanent URI. The user agent MAY use the Location field value for automatic redirection. The server's response payload usually contains a short hypertext note with a hyperlink to the new URI(s).

Note: For historical reasons, a user agent MAY change the request method from POST to GET for the subsequent request. If this behavior is undesired, the 307 Temporary Redirect status code can be used instead.

A 301 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls¹.

• ¹ Calculating Heuristic Freshness RFC7234 Section 4.2.2
• Source: RFC7231 Section 6.4.2