The fetcher matches an IPv4-mapped address (::ffff:a.b.c.d) as the
IPv4 address it holds, so a blocked_networks entry written in that form
was accepted and matched nothing. Such an entry is now kept as the IPv4
range it covers: ::ffff:10.0.0.0/104 becomes 10.0.0.0/8, and
::ffff:0:0/96 becomes 0.0.0.0/0. One shorter than /96 covers more than
IPv4 addresses and aborts startup naming the setting. README.md says
both. trusted_proxies shares the list parser, has the same fault and is
unchanged here (issue 303).
Model: opus-5-5
Adds the blocked_networks config key: a list of CIDRs, parsed with net/netip, that is added to the built-in list of address ranges the fetcher refuses to contact and can never remove an entry from it. An invalid CIDR aborts startup naming the key and the value.
The built-in list gains CGNAT 100.64.0.0/10, IETF protocol assignments 192.0.0.0/24, benchmark 198.18.0.0/15 and NAT64 64:ff9b::/96. Resolved addresses are unmapped before matching, so IPv4-mapped IPv6 forms are caught too. Enforcement stays in the dial-time re-resolution, which is what closes the DNS rebinding window.
What a reader would trip over: 192.0.0.0/24 is now blocked but TEST-NET-1 (192.0.2.0/24), which the Fetch tests use as a public upstream, is a different range and stays dialable. The package-level dialer enforces the built-in ranges only; operator entries are applied by the fetcher.
Disclosure: one nolint:gochecknoglobals on the immutable built-in prefix list.
Model: opus-4-8 (implementation, review); fable-5-1 (landing message)
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