fix(iroh-net): Fix in detecting globally routable IPv6 addresses

iroh-net/src/net/interfaces.rs

@@ -282,10 +282,10 @@ impl State {
     }
 }
 
-/// Reports whether ip is a usable IPv4 address which could
-/// conceivably be used to get Internet connectivity. Globally routable and
-/// private IPv4 addresses are always Usable, and link local 169.254.x.x
-/// addresses are in some environments.
+/// Reports whether ip is a usable IPv4 address which should have Internet connectivity.
+///
+/// Globally routable and private IPv4 addresses are always Usable, and link local
+/// 169.254.x.x addresses are in some environments.
 fn is_usable_v4(ip: &IpAddr) -> bool {
     if !ip.is_ipv4() || ip.is_loopback() {
         return false;
@@ -294,15 +294,25 @@ fn is_usable_v4(ip: &IpAddr) -> bool {
     true
 }
 
-/// Reports whether ip is a usable IPv6 address which could
-/// conceivably be used to get Internet connectivity. Globally routable
-/// IPv6 addresses are always Usable, and Unique Local Addresses
+/// Reports whether ip is a usable IPv6 address which should have Internet connectivity.
+///
+/// Globally routable IPv6 addresses are always Usable, and Unique Local Addresses
 /// (fc00::/7) are in some environments used with address translation.
+///
+/// We consider all 2000::/3 addresses to be routable, which is the interpretation of
+/// <https://www.iana.org/assignments/ipv6-unicast-address-assignments/ipv6-unicast-address-assignments.xhtml>
+/// as well.  However this probably includes some addresses which should not be routed,
+/// e.g. documentation addresses.  See also
+/// <https://doc.rust-lang.org/std/net/struct.Ipv6Addr.html#method.is_global> for an
+/// alternative implementation which is both stricter and laxer in some regards.
 fn is_usable_v6(ip: &IpAddr) -> bool {
     match ip {
         IpAddr::V6(ip) => {
             // V6 Global1 2000::/3
-            if matches!(ip.segments(), [0x2000, _, _, _, _, _, _, _]) {
+            let mask: u16 = 0b1110_0000_0000_0000;
+            let base: u16 = 0x2000;
+            let segment1 = ip.segments()[0];
+            if (base & mask) == (segment1 & mask) {
                 return true;
             }
 
@@ -383,6 +393,8 @@ impl HomeRouter {
 
 #[cfg(test)]
 mod tests {
+    use std::net::Ipv6Addr;
+
     use super::*;
 
     #[tokio::test]
@@ -398,4 +410,19 @@ mod tests {
         let home_router = HomeRouter::new().expect("missing home router");
         println!("home router: {:#?}", home_router);
     }
+
+    #[test]
+    fn test_is_usable_v6() {
+        let loopback = Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0x1);
+        assert!(!is_usable_v6(&loopback.into()));
+
+        let link_local = Ipv6Addr::new(0xfe80, 0, 0, 0, 0xcbc9, 0x6aff, 0x5b07, 0x4a9e);
+        assert!(!is_usable_v6(&link_local.into()));
+
+        let derp_use1 = Ipv6Addr::new(0x2a01, 0x4ff, 0xf0, 0xc4a1, 0, 0, 0, 0x1);
+        assert!(is_usable_v6(&derp_use1.into()));
+
+        let random_2603 = Ipv6Addr::new(0x2603, 0x3ff, 0xf1, 0xc3aa, 0x1, 0x2, 0x3, 0x1);
+        assert!(is_usable_v6(&random_2603.into()));
+    }
 }

iroh-net/src/netcheck.rs

@@ -847,7 +847,10 @@ mod tests {
                     "expected key 1 in DERPLatency; got {:?}",
                     r.derp_latency
                 );
-                assert!(r.global_v4.is_some(), "expected globalV4 set");
+                assert!(
+                    r.global_v4.is_some() || r.global_v6.is_some(),
+                    "expected at least one of global_v4 or global_v6"
+                );
                 assert!(r.preferred_derp.is_some());
             } else {
                 eprintln!("missing UDP, probe not returned by network");

iroh-net/src/netcheck/reportgen.rs

@@ -581,6 +581,7 @@ impl Actor {
     ///     aborted.  That is, the main actor loop stops polling them.
     async fn spawn_probes_task(&mut self) -> Result<JoinSet<Result<ProbeReport>>> {
         let if_state = interfaces::State::new().await;
+        debug!(?if_state, "Local interfaces");
         let plan = match self.last_report {
             Some(ref report) => ProbePlan::with_last_report(&self.derp_map, &if_state, report),
             None => ProbePlan::initial(&self.derp_map, &if_state),