A small Windows console program that detects the current HTTP proxy (if any) and display settings needed for various programs to work with that proxy.
If you're in a corporate environment and the browsers work fine but you can't run curl, httpie, NPM, pip etc from a console, then this program should get you running.
In technical terms, this program uses the Windows API to process the proxy auto-config (PAC) on the internal network, then display settings on the console.
In a bash-like shell (e.g. cygwin, git-bash or msys2):
$ ./proxyhelper --help
usage: proxyhelper.exe [flags]
Options:
-c --cmd set env for CMD (DOS) shell
-b --bash set env for Bash shell (Cygwin, Git Bash, msys)
-x --setx setx style
-n --npm settings for NPM
In an environment with a proxy server, you'll get a result like:
$ ./proxyhelper.exe --bash
export http_proxy=10.20.30.40:8080
export https_proxy=10.20.30.40:8080
export ftp_proxy=10.20.30.40:8080
export rsync_proxy=10.20.30.40:8080
It is possible there are two or more proxies, separated by ';', e.g. "10.20.30.40:8080;22.33.44.55:9090".
If that happens, the current version just picks the first one.
In an environment with no proxy server, the command-line will unset the proxies, like this:
$ ./proxyhelper --bash --npm
unset http_proxy
unset https_proxy
unset ftp_proxy
unset rsync_proxy
npm config delete proxy
npm config delete https-proxy
This is for people who are in a corporate environment but change between networks. For example, when you're docked, the ethernet has a proxy, but on wifi you don't.
Run with --cmd to get settings appropriate for a CMD window:
C:\> proxyhelper --cmd
set http_proxy=
set https_proxy=
set ftp_proxy=
set rsync_proxy=
C:\>
This implementation uses the Windows API to retrieve and process the proxy. Read about the [winhttp autoproxy API on MSDN].
The underlying implementation is a different beast. Basically, a corporate environment hosts a JavaScript file on the network somewhere. The file contains a JavaScript function that yields the proxy server address (or addresses) based on input like which site you want to load.
Read about proxy auto-config on Wikipedia
I don't fully understand how the system knows where the file is, but maybe DNS? In any case, you can see the result in Chrome by loading this URL: chrome://net-internals/#proxy
Parsing the PAC file without a browser or the built-in system API can be done by using any JavaScript engine. @manugarg did it years ago using Mozilla's then JavaScript engine, spider monkey: pacparser.
For msys2, may also be relevant: https://stackoverflow.com/a/47335314
For NPM on windows, see: https://stackoverflow.com/a/21241320