Maybe I can use the GPC header as a way to let advertisers track and target me with exciting offers. Perhaps they can create a "fingerprint" from the three headers I send: Host+Connection+GPC, as I request web pages with netcat or tcpclient through a localhost-bound TLS forward proxy. I use these clients on a daily basis for making HTTP requests. I read HTML with a text-only browser. I do not use DNS when requesting www pages. The needed IP addresses are stored in the proxy's memory. For some reason I never see any ads.

Unfortunately, the sec-gpc header does not seem to be working as I have not received any advertisements after I started using it. Perhaps I have to manually request the ads and send the telemetry since I am not using browser that auto-loads resources or runs Javascript. Maybe I need to put the IP addresses for the tracking and ad servers into the proxy's memory.

Meanwhile, I am missing out on whatever products, services and campaign drivel the advertisers might show to people who use netcat/tcpclient and send only three HTTP headers. No doubt all the online merchants using text-only e-commerce platforms must target some amazing offers to all the online shoppers using netcat/tcpclient.^1 Someday maybe I too can receive them.

1. IIRC, funnily enough, there is a commandline "e-commerce solution", i.e., online store, that has been shared on HN before, perhaps as joke.