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Firefox and Chrome resolve any localhost domain (*.localhost) to loopback address
I was reading this reddit's thread and this comment caught my interest:-
Chrome and Firefox also consider "*.localhost" as secure so you can develop multiple websites with different service workers. They automatically resolve to "localhost" so it's very handy.
I didn't know this and after trying myself on Firefox, that's turn out to be true. I checked my /etc/hosts
to make sure I didn't have the name defined that and also checked via host
command and dig
as well. Both returned domain not found result.
host web01.localhostHost web01.localhost not found: 3(NXDOMAIN)
So it pretty sure coming from Firefox itself. Firefox also has this pretty handy dns lookup tools (accessible via about:networking#dns
):-
I can't find much information about this so why not just look directly in the source code? After some googling, I guess the networking portion for Firefox is under the directory called netwerk
and made my educated guess that the code could be in nsHostResolver.cpp
. Then using browser's Find on page for "localhost", voila! The code looks like this:-
// Check if we have a localhost domain, if so hardcode to loopback if (IS_ADDR_TYPE(type) && IsLoopbackHostname(host)) { nsresult rv; RefPtr<nsHostRecord> result = InitLoopbackRecord(key, &rv); if (NS_WARN_IF(NS_FAILED(rv))) { return rv; } MOZ_ASSERT(result); aCallback->OnResolveHostComplete(this, result, NS_OK); return NS_OK; }
https://github.com/mozilla/gecko-dev/blob/master/netwerk/dns/nsHostResolver.cpp#L1031
Original Link: https://dev.to/k4ml/firefox-and-chrome-resolve-any-localhost-domain-localhost-to-loopback-address-26d9
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