CODEWITHSUNDEEP
http
Rouki
Rouki

Reputation: 2345

If modified since - HTTP protocol

If my browser uses cache (local cache), does it GUARANTEE that each HTTP request it sends contains "IF MODIFIED SINCE" header line?

If not, how do I define that it will ? and what if I define a proxy server to the browser ? will it add it automatically then?

thanks in advance

Upvotes: 1

Views: 1172

Answers (1)

whitestryder
whitestryder

Reputation: 461

I was just working on this with my RESTful web service and ran a few tests for a particular resource. First of all I was trying to control the browser cache from my web server by setting the following HTTP headers on the HTTP response for the resource:

Cache-Control: must-revalidate, max-age=30
Last-Modified: Mon May 19 11:21:05 GMT 2014
Expires: Mon May 19 11:51:05 GMT 2014

Then from my web UI I have a timer that periodically (every 5 seconds) does a GET on the resource that I've said is cacheable. Since the resource in the browser cache has not yet expired the GET request for the resource is served from the browser cache, however, once the "max-age" has expired the next GET request goes to the server and the browser adds the "If-Modified-Since" header with the "Last-Modified" date as the value like this:

[GET] - /cms_cm_web/api/notification
referer: http://localhost:8080/cms_ui/#/
accept: application/json, text/plain, */*
accept-language: en-us
ua-cpu: AMD64
accept-encoding: gzip, deflate
user-agent: Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Win64; x64; Trident/5.0)
host: localhost:8080
if-modified-since: Mon, May 19 11:21:05 GMT 2014
connection: Keep-Alive

This came from IE9 browser. I get the same from latest Firefox and Chrome browsers as well. From here the server can look for the "If-Modified-Since" header and if it determines the resource has not been modified then it returns a 304 Not Modified response, otherwise, it returns the resource representation with a 200 OK response.

so according to the HTTP specification you can control caching using "Expires" and/or "Cache-Control" headers together with a "Last-Modified" header. This will cause the browser cache to perform what's called a "conditional GET" request as it includes the "If-Modified-Since" header.

Upvotes: 1

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