I want to write a program that can monitor all system HTTP/HTTPS protocols used to open the default browser, and block certain ones, automatically changing certain requested URL into another. The process of changing a URL is simple, but the monitoring and blocking part is quite puzzling.
e.g. When clicking on the URL 'https://example.com/asdf.htm', the request will be blocked by the program and the the Windows system will receive the command of 'http://www.example2.org/asdf.htm' instead and the latter instead of the former URL will be opened by the default browser.
I am an amateur developer and student who do not have much experience in solving such problems.
I searched the web and found someone asked a similar question years ago:
https://superuser.com/questions/554668/block-specific-http-request-from-windows
However, I didn't find any useful advice on coding in the page. Maybe I can use an antivirus program to block certain URLs or change the hosts file to block certain URLs but the URL replacement cannot be done. Certainly, changing the hosts to a certain server which redirects certain requests might work but that's too complex. I wish someone can help me solve the problem by giving a simple method on monitoring the Windows system itself. Thanks!
To summarize our conversation in the comments, in order to redirect or restrict traffic, either to sites, either to ports (protocols are actually "mapped" via ports) the main solutions usually are:
a software firewall - keep in mind that SWFW don't usually redirect, they just permit or allow traffic via ports
a hardware firewall (or advanced router, not the commercial ones, but enterprise grade) - they do what you want, but they are very expensive and not worth for a home experiment
a proxy server - this can do what you want
Other alternatives that might or might not work would include editing the hosts file, as you said, but as stated earlier I don't recommend it, it's a system file and if you forget about it, then it can be a hindrance (also keep in mind that normally you should not use a Windows user with admin rights even at home, but that is another story) and a browser extension (which I would guess only changes content on pages, not the way a browser works (such as changing URLs).
I think a proxy server is the best pick here. Try it and let me know.
Keep in mind I still recommend you read about networking in order to get a better idea of what you can and can't do in each setup.