add Multiaddr::ip_addr

src/lib.rs

@@ -222,6 +222,20 @@ impl Multiaddr {
     pub fn protocol_stack(&self) -> ProtoStackIter<'_> {
         ProtoStackIter { parts: self.iter() }
     }
+
+    // Returns the IP address of this multiaddress, if it has one.
+    ///
+    /// Iterates the components of this multiaddress and returns the first
+    /// [`Protocol::Ip4`] or [`Protocol::Ip6`] found. Multiaddresses without an
+    /// IP component, hostname-based (`/dns4/...`) or non-IP transport
+    /// addresses (`/memory/`), return `None`. Hostnames are not resolved.
+    pub fn ip_addr(&self) -> Option<IpAddr> {
+        self.iter().find_map(|p| match p {
+            Protocol::Ip4(addr) => Some(IpAddr::V4(addr)),
+            Protocol::Ip6(addr) => Some(IpAddr::V6(addr)),
+            _ => None,
+        })
+    }
 }
 
 impl fmt::Debug for Multiaddr {

tests/lib.rs

@@ -809,6 +809,8 @@ fn arbitrary_impl_for_all_proto_variants() {
 }
 
 mod multiaddr_with_p2p {
+    use std::net::{IpAddr, Ipv4Addr};
+
     use multiaddr::{Multiaddr, PeerId};
 
     fn test_multiaddr_with_p2p(
@@ -868,4 +870,39 @@ mod multiaddr_with_p2p {
             Err("/ip4/127.0.0.1/p2p/QmNnooDu7bfjPFoTZYxMNLWUQJyrVwtbZg5gBMjTezGAJN"),
         )
     }
+    #[test]
+    fn ip_addr_of_ip_addresses() {
+        let v4: Multiaddr = "/ip4/127.0.0.1/udp/4001/quic-v1".parse().unwrap();
+        assert_eq!(v4.ip_addr(), Some(IpAddr::V4(Ipv4Addr::LOCALHOST)));
+
+        let v6: Multiaddr = "/ip6/2001:db8::1/tcp/443".parse().unwrap();
+        assert_eq!(
+            v6.ip_addr(),
+            Some(IpAddr::V6("2001:db8::1".parse().unwrap()))
+        );
+    }
+
+    #[test]
+    fn ip_addr_absent_without_ip_component() {
+        // Hostname-based addresses are not resolved.
+        let hostname: Multiaddr = "/dns4/example.com/tcp/443".parse().unwrap();
+        assert_eq!(hostname.ip_addr(), None);
+
+        let memory: Multiaddr = "/memory/1234".parse().unwrap();
+        assert_eq!(memory.ip_addr(), None);
+
+        assert_eq!(Multiaddr::empty().ip_addr(), None);
+    }
+
+    #[test]
+    fn ip_addr_tracks_components() {
+        let mut address: Multiaddr = "/ip4/127.0.0.1/tcp/80".parse().unwrap();
+        assert_eq!(address.ip_addr(), Some(IpAddr::V4(Ipv4Addr::LOCALHOST)));
+
+        address.pop(); // `tcp`
+        assert_eq!(address.ip_addr(), Some(IpAddr::V4(Ipv4Addr::LOCALHOST)));
+
+        address.pop(); // `ip4` — nothing left
+        assert_eq!(address.ip_addr(), None);
+    }
 }