[Haskell-cafe] ANN: HTTPbis / HTTP-4000.x package available

Duncan Coutts duncan.coutts at worc.ox.ac.uk
Sun Jan 18 09:42:10 EST 2009

On Sat, 2009-01-17 at 20:34 -1000, Tim Newsham wrote:
> > Speaking of proxies, I've been looking into how to find the right proxy
> > to use on Windows systems. Turns out that to do it properly you need a
> > JavaScript interpreter! Yes, really.
> Uhh.. What!?  That's not right.

I think you mean it should not be right! :-) Of course it's possible to
specify a list of proxies in Windows and that info is kept in the
registry. It's also common in corporate networks to use proxy
auto-configuration. The client gets told the URL of the these (.pac)
files and the client downloads it to work out what proxy to use. You'll
notice a space to specify an auto-configuration URL (.pac file) in the
proxy setting dialog of any web browser.

Proxy auto-configuration files are JavaScript. It uses more or less the
full JavaScript language (ECMA these days), though with a small subset
of the standard library.

Web browsers are ok because they've got a JavaScript interpreter. The MS
WinHTTP library uses the Windows scripting host service. The open source
pacparser C library links to the Mozilla SpiderMonkey JavaScript engine.
Apparently we have Netscape to thank for this mess.


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