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fix(traits): match RFC 9637 documentation /20 in is_public_ipv6 #917

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fix(traits): match RFC 9637 documentation /20 in is_public_ipv6 #917

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5 changes: 3 additions & 2 deletions crates/traits/src/app_components/host_safety.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -109,9 +109,10 @@ pub fn is_public_ipv6(addr: Ipv6Addr) -> bool {
if first == 0x2001 && second == 0x0db8 {
return false;
}
// Documentation 3fff::/20 (RFC 9637). It falls inside global-unicast
// Documentation 3fff::/20 (RFC 9637): first hextet 0x3fff with the top
// nibble of the second hextet zero. It falls inside global-unicast
// 2000::/3, so the terminal rule below would otherwise accept it.
if (first & 0xfff0) == 0x3ff0 {
if first == 0x3fff && (second & 0xf000) == 0 {
return false;
}
// Only global unicast 2000::/3 is routable today; reject anything else not
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2 changes: 1 addition & 1 deletion crates/traits/src/app_components/tests.rs
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Expand Up @@ -350,7 +350,7 @@ fn group_avatar_url_rejects_documentation_ipv6_ranges() {
"https://[2001:db8::1]/a.png",
"https://[2001:db8:abcd:12::1]/a.png",
"https://[3fff::1]/a.png",
"https://[3fff:ffff::1]/a.png",
"https://[3fff:0fff::1]/a.png",
] {
assert!(
validate_and_normalize_group_avatar_url(raw).is_err(),
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12 changes: 11 additions & 1 deletion crates/traits/tests/host_safety_public.rs
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Expand Up @@ -80,6 +80,15 @@ fn shared_host_safety_classifies_canonical_ipv6_ranges() {
assert!(is_public_ipv6("::ffff:93.184.216.34".parse().unwrap()));
assert!(is_public_ip(IpAddr::V6("2606:4700::1".parse().unwrap())));

// Only the actual RFC 9637 block 3fff:0000::/20 is documentation space.
// Neighbouring global-unicast hextets (3ff0:: to 3ffe::) and 3fff:: past the
// /20 boundary (second hextet >= 0x1000) are ordinary routable space.
for raw in ["3ff0::1", "3ffe::1", "3fff:1000::1", "3fff:ffff::1"] {
let addr: Ipv6Addr = raw.parse().expect("test IPv6 literal parses");
assert!(is_public_ipv6(addr), "{raw} should be accepted");
assert!(is_public_ip(IpAddr::V6(addr)), "{raw} should be accepted");
}

for raw in [
"::1", // loopback
"::", // unspecified
Expand All @@ -91,7 +100,8 @@ fn shared_host_safety_classifies_canonical_ipv6_ranges() {
"2002::1", // 6to4 transition prefix
"2001::1", // Teredo 2001:0000::/32
"2001:db8::1", // documentation
"3fff::1", // documentation 3fff::/20
"3fff::1", // documentation 3fff::/20 (lower edge)
"3fff:0fff::1", // documentation 3fff::/20 (upper edge)
"4000::1", // outside global-unicast 2000::/3
] {
let addr: Ipv6Addr = raw.parse().expect("test IPv6 literal parses");
Expand Down