toolkit: is_public, the addresses the egress proxy may reach

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)
2026-09-23 00:19:18 -07:00
parent adf6713866
commit 74da0c9d96
4 changed files with 212 additions and 0 deletions
@@ -0,0 +1,94 @@
+//! `is_public`: the egress proxy connects only to public addresses. Everything in the M3b spec,
+//! section 5, "Refused ranges" tables is not public; everything else is.
+
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr};
+
+/// True if `ip` is a public unicast address.
+pub fn is_public(ip: IpAddr) -> bool {
+    match ip {
+        IpAddr::V4(v4) => is_public_v4(v4),
+        IpAddr::V6(v6) => is_public_v6(v6),
+    }
+}
+
+fn is_public_v4(ip: Ipv4Addr) -> bool {
+    let [a, b, c, _] = ip.octets();
+    if a == 0 {
+        return false;
+    }
+    if a == 10 {
+        return false;
+    }
+    if a == 100 && (64..=127).contains(&b) {
+        return false;
+    }
+    if a == 127 {
+        return false;
+    }
+    if a == 169 && b == 254 {
+        return false;
+    }
+    if a == 172 && (16..=31).contains(&b) {
+        return false;
+    }
+    if a == 192 && b == 0 && c == 0 {
+        return false;
+    }
+    if a == 192 && b == 0 && c == 2 {
+        return false;
+    }
+    if a == 192 && b == 168 {
+        return false;
+    }
+    if a == 198 && (b == 18 || b == 19) {
+        return false;
+    }
+    if a == 198 && b == 51 && c == 100 {
+        return false;
+    }
+    if a == 203 && b == 0 && c == 113 {
+        return false;
+    }
+    if a >= 224 {
+        return false;
+    }
+    true
+}
+
+fn is_public_v6(ip: Ipv6Addr) -> bool {
+    let s = ip.segments();
+    if is_ipv4_mapped(s) {
+        let last32 = (u32::from(s[6]) << 16) | u32::from(s[7]);
+        return is_public_v4(Ipv4Addr::from(last32));
+    }
+    if is_nat64(s) {
+        let last32 = (u32::from(s[6]) << 16) | u32::from(s[7]);
+        return is_public_v4(Ipv4Addr::from(last32));
+    }
+    if s[0..6].iter().all(|&x| x == 0) {
+        return false;
+    }
+    if s[0] & 0xfe00 == 0xfc00 {
+        return false;
+    }
+    if s[0] & 0xffc0 == 0xfe80 {
+        return false;
+    }
+    if s[0] & 0xff00 == 0xff00 {
+        return false;
+    }
+    if s[0] == 0x2001 && s[1] == 0x0db8 {
+        return false;
+    }
+    true
+}
+
+/// `::ffff:0:0/96`: the high 80 bits are zero, then the `ffff` marker.
+fn is_ipv4_mapped(s: [u16; 8]) -> bool {
+    s[0..5].iter().all(|&x| x == 0) && s[5] == 0xffff
+}
+
+/// `64:ff9b::/96`: the NAT64 prefix, then 32 zero bits, then the embedded IPv4 address.
+fn is_nat64(s: [u16; 8]) -> bool {
+    s[0] == 0x64 && s[1] == 0xff9b && s[2] == 0 && s[3] == 0 && s[4] == 0 && s[5] == 0
+}
@@ -2,6 +2,7 @@

 use proto::tools::{HttpFetchArgs, ReadFileArgs, ShellArgs, WriteFileArgs};

+pub mod addr;
 pub mod fetch;
 pub mod files;
 pub mod input;
@@ -0,0 +1,116 @@
+//! `is_public`: the egress proxy connects only to public addresses. Every range in the M3b spec,
+//! section 5, has a case at each end, and a public neighbour just outside it. Do not edit.
+
+use std::net::IpAddr;
+
+use toolkit::addr::is_public;
+
+fn ip(s: &str) -> IpAddr {
+    s.parse().unwrap()
+}
+
+#[test]
+fn refused_ipv4() {
+    for s in [
+        "0.0.0.0",
+        "0.255.255.255",
+        "10.0.0.0",
+        "10.255.255.255",
+        "100.64.0.0",
+        "100.100.100.100",
+        "100.127.255.255",
+        "127.0.0.1",
+        "127.255.255.255",
+        "169.254.0.1",
+        "169.254.255.255",
+        "172.16.0.0",
+        "172.31.255.255",
+        "192.0.0.0",
+        "192.0.0.255",
+        "192.0.2.1",
+        "192.168.0.1",
+        "192.168.255.255",
+        "198.18.0.0",
+        "198.19.255.255",
+        "198.51.100.7",
+        "203.0.113.9",
+        "224.0.0.1",
+        "239.255.255.255",
+        "240.0.0.0",
+        "255.255.255.255",
+    ] {
+        assert!(!is_public(ip(s)), "{s} must be refused");
+    }
+}
+
+#[test]
+fn public_ipv4() {
+    for s in [
+        "1.1.1.1",
+        "8.8.8.8",
+        "9.255.255.255",
+        "11.0.0.0",
+        "100.63.255.255",
+        "100.128.0.0",
+        "126.255.255.255",
+        "128.0.0.0",
+        "169.253.255.255",
+        "172.15.255.255",
+        "172.32.0.0",
+        "192.0.1.0",
+        "192.0.3.0",
+        "192.167.255.255",
+        "192.169.0.0",
+        "198.17.255.255",
+        "198.20.0.0",
+        "198.51.99.255",
+        "203.0.112.255",
+        "223.255.255.255",
+        "93.184.216.34",
+    ] {
+        assert!(is_public(ip(s)), "{s} is public");
+    }
+}
+
+#[test]
+fn refused_ipv6() {
+    for s in [
+        "::",
+        "::1",
+        "fc00::1",
+        "fdff:ffff::1",
+        "fd7a:115c:a1e0::1",
+        "fe80::1",
+        "febf::1",
+        "ff02::1",
+        "ff00::",
+        "2001:db8::1",
+        "2001:db8:ffff::1",
+        "::ffff:127.0.0.1",
+        "::ffff:10.1.2.3",
+        "::ffff:100.100.100.100",
+        "64:ff9b::7f00:1",
+        "64:ff9b::a01:203",
+        "::ffff:0.0.0.0",
+        "::127.0.0.1",
+        "::1.1.1.1",
+        "::ffff",
+    ] {
+        assert!(!is_public(ip(s)), "{s} must be refused");
+    }
+}
+
+#[test]
+fn public_ipv6() {
+    for s in [
+        "2606:4700:4700::1111",
+        "2a00:1450::1",
+        "fbff::1",
+        "fec0::1",
+        "2001:db9::1",
+        "::ffff:1.1.1.1",
+        "64:ff9b::101:101",
+    ] {
+        assert!(is_public(ip(s)), "{s} is public");
+    }
+}