HTTP Proxy Cache
Saturday, July 5th, 2008 What is HTTP Proxy Cache?
There are three reasons for using a HTTP proxy server:
- Because you are behind a firewall (for security) and you have to.
- Because using a cache speeds up Web browsing significantly, for you and everyone else.
- Because you don’t have enough ‘real’ IP addresses for your machines.
If you are behind a firewall you are probably using one already. If not, you might consider installing one.
Configuring a browser for HTTP proxy
Some browsers may accept only one value, for instance (on Unix) by using setenv http_proxy http://somewhere.org:80/. Certain domains may be excluded, typically ones own domain, by using setenv no_proxy some.org,some.other.org. Other browsers, such as Netscape, have a more sophisticated scheme for supporting multiple proxies. Netscape has a scheme for automated proxy handling using Javascript. Mosaic-2.7 also allows a list of proxies.
Bypassing cache in Proxy
If an http request has the Pragma: no-cache header set, then the cache is directed to get a new copy. It may, however, save the new copy itself. Using Reload on Netscape, Mosaic and Lynx (possibly all browsers) sends a request with this header.
Cacheable and uncacheable documents and Proxy
Regular HTML files are usually cacheable. Cacheing agents may require a valid Last-Modified header , and may not cache objects greater than a certain size or subject to other restrictions. HTML documents generated by CGI scripts can be made cacheable or not by generating an Expires header, though some agents may not cache URLs with “cgi-bin” or a query string. Documents requiring authorisation should not normally be cached. Netscape has an option to cache documents obtained from an SSL (Secure) server locally. If you turn this on, someone who gains access to your computer (perhaps by stealing it) can read all your recent secure transactions. Note that different cache servers may interpret the http specification in slightly different ways, so that a document cached by one may not be cached by another.