The HTTP Location header field is returned in responses from an HTTP server under two circumstances:
An obsolete version of the HTTP 1.1 specifications (IETF RFC 2616) required a complete absolute URI for redirection.[2] The IETF HTTP working group found that the most popular web browsers tolerate the passing of a relative URL[3] and, consequently, the updated HTTP 1.1 specifications (IETF RFC 7231) relaxed the original constraint, allowing the use of relative URLs in Location headers.[4]
Absolute URLs are URLs that start with a scheme[5] (e.g., http:, https:, telnet:, mailto:)[6] and conform to scheme-specific syntax and semantics. For example, the HTTP scheme-specific syntax and semantics for HTTP URLs requires a "host" (web server address) and "absolute path", with optional components of "port" and "query".
A client requesting
https://www.example.com/index.html
using
GET /index.html HTTP/1.1
Host: www.example.com
may get the server response
HTTP/1.1 302 Found
Location: https://www.example.org/index.php
Relative URLs are URLs that do not include a scheme or a host. In order to be understood they must be combined with the URL of the original request.
A client request for
https://www.example.com/blog/all:
may get a server response with a path that is absolute because it starts with a slash:[7]
HTTP/1.1 302 Found
Location: /articles/
The URL of the location is expanded by the client to
https://www.example.com/articles/.[8]
A client request for
https://www.example.com/blog/latest
may get a server response with a path that is relative because it doesn't start with a slash:[7]
HTTP/1.1 302 Found
Location: 2020/zoo
The client removes the path segment after the last slash of the original URL and appends the relative path resulting in
https://www.example.com/blog/2020/zoo.[10][8]