(Attn. @bradfitz)

I'm fine moving that special case rule down further pass the explicit match/no-match checks, but let's not add a new environment variable.

@bradfitz Not sure I’m following you. The function returns true (use proxy) only if none of the NO_PROXY rules match the request. So if you just move the check past all those rules, it will still fire unavoidably for all localhost requests.

FWIW, I have found this easy to work around for my use cases (I add tsohlacol to my /etc/hosts and put it in my URLs instead of localhost), so I’d be OK with closing this issue.

👋 Hi all, just wasted about half an hour trying to figure out why requests to localhost weren't respecting my http_proxy. Can this be documented somewhere if this is a permanent feature of the http.DefaultClient

Honestly I don't remember why the localhost exception exists. If somebody could dig through the history to figure that out, that'd be great. Hopefully we could just remove it. But we need to understand why first.

@bradfitz we need this so we can proxy to localhost locations. I am running web server instances in docker on my local machine for testing. I am trying to sniff the traffic using a go proxy, but it just does not work because of this localhost exception issue.

Just for reference #1589

Change https://golang.org/cl/239164 mentions this issue: http/httpproxy: Allow localhost to be proxied

What do other http clients do in this case? It might be beneficial to at least check curl and some of the popular browsers.

Please keep in mind that a major use case for proxies are corporate settings where the settings are often not changeable by end users and the proxy exceptions contain usually some internal services already. In those settings Go tests and Go applications spawning a browser might suddenly stop working. One important application in that area is redirecting an OAuth flow to the browser from the cli or the go trace viewer.

MY examination of a few applications and runtimes show that the user must be explicit, i.e., if you don't want localhost proxied add it to the NO_PROXY list.

Related #33695

Bitten by this myself today while trying to insert a proxy between my program and a locally running service it was connecting to. Editing /etc/hosts to add a non localhost name works, but is far from ideal.

Ignoring localhost by default is fine, but there really needs to be someway to disable that behaviour - Changeset https://golang.org/cl/239164 seemed reasonable - would be nice to see it merged