Add IP_TTL/IPV6_UNICAST_HOPS SockOpts

Test: `cargo test --test test test_ttl_opts`

CHANGELOG.md

@@ -36,6 +36,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
   (#[1511](https://github.com/nix-rust/nix/pull/1511))
 - Added `Ipv4RecvErr` and `Ipv6RecvErr` sockopts and associated control messages.
   (#[1514](https://github.com/nix-rust/nix/pull/1514))
+- Added `Ipv4Ttl` and `Ipv6Ttl` sockopts.
+  (#[1515](https://github.com/nix-rust/nix/pull/1515))
 
 ### Changed
 

src/sys/socket/sockopt.rs

@@ -349,6 +349,10 @@ sockopt_impl!(Both, Ipv6V6Only, libc::IPPROTO_IPV6, libc::IPV6_V6ONLY, bool);
 sockopt_impl!(Both, Ipv4RecvErr, libc::IPPROTO_IP, libc::IP_RECVERR, bool);
 #[cfg(any(target_os = "android", target_os = "linux"))]
 sockopt_impl!(Both, Ipv6RecvErr, libc::IPPROTO_IPV6, libc::IPV6_RECVERR, bool);
+#[cfg(any(target_os = "android", target_os = "freebsd", target_os = "linux"))]
+sockopt_impl!(Both, Ipv4Ttl, libc::IPPROTO_IP, libc::IP_TTL, libc::c_int);
+#[cfg(any(target_os = "android", target_os = "freebsd", target_os = "linux"))]
+sockopt_impl!(Both, Ipv6Ttl, libc::IPPROTO_IPV6, libc::IPV6_UNICAST_HOPS, libc::c_int);
 
 #[cfg(any(target_os = "android", target_os = "linux"))]
 #[derive(Copy, Clone, Debug)]

test/sys/test_sockopt.rs

@@ -135,3 +135,13 @@ fn test_so_tcp_keepalive() {
         assert_eq!(getsockopt(fd, sockopt::TcpKeepInterval).unwrap(), x + 1);
     }
 }
+
+#[test]
+fn test_ttl_opts() {
+    let fd4 = socket(AddressFamily::Inet, SockType::Datagram, SockFlag::empty(), None).unwrap();
+    setsockopt(fd4, sockopt::Ipv4Ttl, &1)
+        .expect("setting ipv4ttl on an inet socket should succeed");
+    let fd6 = socket(AddressFamily::Inet6, SockType::Datagram, SockFlag::empty(), None).unwrap();
+    setsockopt(fd6, sockopt::Ipv6Ttl, &1)
+        .expect("setting ipv6ttl on an inet6 socket should succeed");
+}