In a follow up to my previous post on Proper URL Construction, I am going to dive more deeply in to the Status Codes that control the redirects that were talked about in my previous article.
Most developers are familiar with the HTTP 1.0 Status Codes, that have been recently popularized by the SEO guys. We have all heard that you should use 301 Moved Permanently instead of 302 Temporary Redirect. What many of the SEO guys won't tell you, because they don't know any better, is that they are using the RFC 1945 HTTP/1.0 Standard that was released in May 1996, that is right it is about 12 years old. The newest HTTP/1.1 Standard, RFC 2616, was released in June 1999, and made some pretty drastic changes the the 3xx Redirect Status Codes. The goal of this post is to inform and familiarize developers with the HTTP/1.1 Standard, specifically the 3xx Redirect Status Code changes. This can have drastic effect on how you handle requests on your website and optimize your site for search engines.
In the middle-to-late 1990's 302 Moved Temporarily was the most popular redirect code, but also an example of industrial practice contradicting the standard. HTTP/1.0 specification (RFC 1945) required the client to perform a temporary redirect (the original describing phrase was "Moved Temporarily"), but popular browsers implemented it as though it was a 303 See Other.
Note from 302 Found: RFC 1945 and RFC 2068 specify that the client is not allowed to change the method on the redirected request. However, most existing user agent implementations treat 302 as if it were a 303 response, performing a GET on the Location field-value regardless of the original request method. The status codes 303 and 307 have been added for servers that wish to make unambiguously clear which kind of reaction is expected of the client.
Therefore, HTTP/1.1 added status codes 303 and 307 to disambiguate between the two behaviors. However, majority of Web applications and frameworks still use the 302 status code as if it were the 303.
Proper Use of HTTP Redirects
The next part will be a guide of the conditions that should be met in order to use the specific redirect.
301 Moved Permanently
- The URL (or page) is going to permanently reside in a differently location
- The domain should always be displayed a certain way, (i.e. This domain is always displayed as coderjoural.com, so any traffic to www.coderjournal.com gets a 301 redirect to coderjoural.com).
- This should be used for most static redirects that are not generated programmatically.
- *NEW* This status was mostly designed to be used with GET and HEAD requests.
303 See Other
- This is going to be the most common type of redirect that you want to use when you are programmatically changing where the user is located in your site during a POST back.
- Any time you want to redirect a user to another URL after a POST from a form has occurred (i.e. The visitor to your site registers with your site and after they are done registering you want to direct them back to the home page, this is when you would use a 303 redirect).
- *NEW* This status was designed to be used with POST requests specifically, so it should not be used for GET or HEAD requests.
307 Temporary Redirect
- Anytime that you want to put up a temporary page (i.e. your site is under construction and you want all traffic temporarily redirected to a static HTML page).
- *NEW* This should be used when you want to redirect a GET request to different location each time the URL is requested.
- *NEW* This should be not be used with POST requests, because of this statement in the specification:
the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
- Use this for any condition not met above.
- This should be used sparingly because there is a search engine penalty if used too much, because of some spammers that used an Exploit called Page Hijacking.
- This is sort of the antithesis to 404 Not Found and should be used in a similar way. So if you have a page that is referenced but no longer exists, but you do not want to return a 404 and just redirect the user to a random (not static as defined in a 301) site you would use a 302 redirect. (note this argument is very weak and there is very little reason in a HTTP/1.1 world to use a 302 redirect)
- *NEW* This status should be used during GET requests for any semi-static URL's that may change in the future, but don't change with each and every request. A good example of this on Coder Journal is my Essential Software Every Developer Needs which I publish annually, and is located at http://www.coderjournal.com/essential-software/. It changes but it only changes once a year, so it is semi-static in terms of the internet.
- *NEW* The 302 Found falls right between 301 Moved Permanently and 307 Temporary Redirect in terms of how permanent the URL is for GET requests.
An example of an HTTP Redirect Response will look something like the following, this was take from my own site when somebody queries www.coderjournal.com:
HTTP/1.1 301 Moved Permanently Date: Tue, 24 Apr 2007 18:12:55 GMT Server: Apache Location: http://www.coderjournal.com/ Keep-Alive: timeout=15, max=99 Connection: Keep-Alive Transfer-Encoding: chunked Content-Type: text/html; charset=iso-8859-1131
If you would like to learn more about how to perform these redirects, that I have talked about above, in your favorite language please read this article from Steven Hargrove.
Update (2008-5-20): I have updated my understanding of the different types of redirects that developers may want to use. See above for my new understandings.