Avoiding 301 redirect caching

Question

This is a follow up question to Using 301/303/307 redirects for dynamic short urls, where I try to determine the best method for implementing short url redirection when the destination url will change on a frequent basis.

While it seems that 301 and 307 redirects both perform the same way, the issue that concerns me is 301 redirect caching (as documented here)- is the best way to avoid this to use 307 redirects instead (I'm assuming 307 redirects will never cache?), or to explicitly send a no-cache header ("Cache-Control: no-cache, must-revalidate")?

Windowpane

related: #12193090 – Kildare

Answer 1

Don't try to avoid 301 caching. If you don't want any user agent to cache your redirect, then simply don't use a 301 redirect. In other words, 301 caching is here to stay, and semantically, it's a permanent redirect, so if you're planning to change the destination URL, 301 is not the right status code to use. On the other hand, 307 responses are not cached by default.

Sosthina

Your interpretation violates the HTTP specification. Clients must follow Cache-Control when it's present on a 301. – Dail

@Dail yes, clients must honor Cache-Control, but a 301 is still permanent, and shouldn't be used if the redirect is not intended to be permanent. Because it's permanent, it's cachable by default as defined in tools.ietf.org/html/rfc2616#section-10.3.2 – Sosthina

301 does not have to be permanent (that's just the default caching rule). According to tools.ietf.org/html/… A 301 response is cacheable unless otherwise indicated by [...] explicit cache controls where explicit cache controls means Cache-Control and related headers. – Dail

The RFC says "The 301 (Moved Permanently) status code indicates that the target resource has been assigned a new permanent URI", so yes, that means it's permanent. Of course you can technically use it for other purposes, but then you're misusing HTTP semantics. – Sosthina

You're reading too much into the name. Nothing is forever. Domain names get sold. Companies go bankrupt. There are even technical limitations preventing this: tools.ietf.org/html/draft-ietf-httpbis-p6-cache-24#page-28 [...] extremely large values have been demonstrated to cause problems [...] In conclusion: Forever just means until the resource is deleted, or a reasonably long time. – Dail

There is a final point you're missing: 301 is the only reasonable response for URI canonicalization. Codes 303 and 307 require clients to repeat requests on the original URI (defeating the point of URI canonicalization): tools.ietf.org/html/… Since the redirection can change over time, the client ought to continue using the original effective request URI for future requests. URI canonicalization means clients should be able to use the canonical URI instead of the alias that redirected to them. Codes 303 and 307 prevent this. – Dail

You're right about one thing though: OP wants to redirect without caching. In such a case, 307 is a better solution. I'm just saying that 301 with Cache-Control headers is perfectly reasonable and should not be ruled out for other uses. – Dail

Answer 2

In situations where you want the behaviour that a 301 redirect brings, like the updating of browser bookmarks and the change of URL in google bot, but at the same time want to track the redirects or perform some other kind of functionality you can always add the cache control headers to "no cache"

HTTP/1.0 301 Moved Permanently
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Expires: Sat, 26 Jul 1997 05:00:00 GMT
Location: http://example.com

In php it looks like this:

header('Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0');
header('Expires: Sat, 26 Jul 1997 05:00:00 GMT');
header('Location:'.$url, true, 301);

Related: https://mcmap.net/q/659562/-how-to-do-a-non-cached-301-redirect

Kildare