HTTP conditional GET
hendrik.hardeman at hotmail.com
Sat Aug 1 17:39:32 MSD 2009
The semantics of the GET method change to a "conditional GET" if the request message includes an If-Modified-Since, If-Unmodified-Since, If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already held by the client.
>From Nginx Wiki (directive in HTTP Core):
syntax: if_modified_since [off|exact|before]
default: if_modified_since exact
context: http, server, location
The directive (0.7.24) defines how to compare time of file modification and time in request header "If-Modified-Since":
off — don't check "If-Modified-Since" request header (0.7.34);
exact — exact match;
before — file modification time should be less than time in "If-Modified-Since" request header.
Hope this helps to clarify what conditional GET is about.
> I have just test my website with bing's tools: http://www.microsoft.com/search/Tools/default.aspx
> The test result is
> HTTP compression and conditional GET results
> URL: http://www.shijile.com
> HTTP status code: 200 OK
> HTTP conditional GET: not enabled for the date selected
> HTTP compression enabled using gzip
> HTTP headers:
> Transfer-Encoding: chunked
> Connection: keep-alive
> Pragma: no-cache
> Cache-Control: max-age=86400,private
> Content-Type: text/html
> Date: Sat, 01 Aug 2009 12:57:43 GMT
> Expires: Sun, 02 Aug 2009 12:57:43 GMT
> Set-Cookie: PHPSESSID=e86i00j7mn1f88jm6mqlogjqd6; path=/
> Server: nginx/0.7.61
> X-Powered-By: PHP/5.1.6
> Content-Encoding: gzip
> For more information
> Find the information you need to enhance your website with HTTP compression and conditional GET:
> Blog: Announcing Crawler Improvements for bing
> Blog: Optimizing your very large site for search - Part 2
> Webmaster Center
> I am curious about this info: HTTP conditional GET not enabled. It is said that HTTP conditional GET will greatly improve the website performance.
> I have searched Nginx wiki and this forum but get no result for this feature. Is there any setting equivalent to enable HTTP conditional GET? Or Nginx will implement it in the future?
> Posted at Nginx Forum: http://forum.nginx.org/read.php?2,4669,4669#msg-4669
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