Ban lists: where Guard and fail2ban ban addresses

A program bans an address (every port, or a protocol's ports) for a
time; the ban list says what it is kept from: the firewall, some hosts
behind it, or everything. Bans drop ahead of every rule, close the
address's connections, group IPv6 by /64, are kept in the database
across restarts and audited. Never banned: the inside, the firewall's
own addresses, the caller, the list's never. bans grant (bans:write:LIST),
hc banlist/bans/ban/unban, Traffic -> Bans, a fail2ban action in contrib/,
and failed logins and refused tokens logged for Guard and fail2ban.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/model/addr.go

@@ -32,6 +32,34 @@ func (a Address) String() string {
 	return a.Prefix.String()
 }
 
+// Contains reports whether the entry holds an address.
+func (a Address) Contains(x netip.Addr) bool {
+	x = x.Unmap()
+	if a.First.IsValid() {
+		return x.Is4() == a.First.Is4() && !x.Less(a.First) && !a.End.Less(x)
+	}
+	return a.Prefix.Contains(x)
+}
+
+// Overlaps reports whether the entry and a prefix share an address.
+func (a Address) Overlaps(p netip.Prefix) bool {
+	if !a.First.IsValid() {
+		return a.Prefix.Overlaps(p)
+	}
+	if a.First.Is4() != p.Addr().Is4() {
+		return false
+	}
+	// The prefix's first and last addresses against the range.
+	first := p.Masked().Addr()
+	last := first
+	b := last.AsSlice()
+	for i := p.Bits(); i < len(b)*8; i++ {
+		b[i/8] |= 0x80 >> (i % 8)
+	}
+	last, _ = netip.AddrFromSlice(b)
+	return !last.Less(a.First) && !a.End.Less(first)
+}
+
 // ParseAddress reads an address, a prefix (host bits must be zero) or a
 // range, IPv4 or IPv6.
 func ParseAddress(s string) (Address, error) {