adding IPV6_RECVHOPLIMIT socket option

src/socket.rs

@@ -1972,9 +1972,9 @@ impl Socket {
 
     /// Set the value of the `IPV6_RECVTCLASS` option for this socket.
     ///
-    /// If enabled, the `IPV6_TCLASS` ancillary message is passed with incoming
-    /// packets. It contains a byte which specifies the traffic class field of
-    /// the packet header.
+    /// The received hop limit is returned as ancillary data by recvmsg()
+    /// only if the application has enabled the IPV6_RECVHOPLIMIT socket
+    /// option:
     #[cfg(not(any(
         target_os = "dragonfly",
         target_os = "fuchsia",
@@ -1998,6 +1998,35 @@ impl Socket {
             )
         }
     }
+
+    /// Set the value of the `IPV6_RECVHOPLIMIT` option for this socket.
+    ///
+    /// If enabled, the `IPV6_TCLASS` ancillary message is passed with incoming
+    /// packets. It contains a byte which specifies the traffic class field of
+    /// the packet header.
+    #[cfg(not(any(
+        target_os = "dragonfly",
+        target_os = "fuchsia",
+        target_os = "illumos",
+        target_os = "netbsd",
+        target_os = "openbsd",
+        target_os = "redox",
+        target_os = "solaris",
+        target_os = "haiku",
+        target_os = "hurd",
+        target_os = "espidf",
+        target_os = "vita",
+    )))]
+    pub fn set_recv_hoplimit_v6(&self, recv_hoplimit: bool) -> io::Result<()> {
+        unsafe {
+            setsockopt(
+                self.as_raw(),
+                sys::IPPROTO_IPV6,
+                sys::IPV6_RECVHOPLIMIT,
+                recv_hoplimit as c_int,
+            )
+        }
+    }
 }
 
 /// Socket options for TCP sockets, get/set using `IPPROTO_TCP`.

src/sys/unix.rs

@@ -135,6 +135,20 @@ pub(crate) use libc::ipv6_mreq as Ipv6Mreq;
     target_os = "espidf",
     target_os = "vita",
 )))]
+pub(crate) use libc::IPV6_RECVHOPLIMIT;
+#[cfg(not(any(
+    target_os = "dragonfly",
+    target_os = "fuchsia",
+    target_os = "hurd",
+    target_os = "illumos",
+    target_os = "netbsd",
+    target_os = "openbsd",
+    target_os = "redox",
+    target_os = "solaris",
+    target_os = "haiku",
+    target_os = "espidf",
+    target_os = "vita",
+)))]
 pub(crate) use libc::IPV6_RECVTCLASS;
 #[cfg(all(feature = "all", not(any(target_os = "redox", target_os = "espidf"))))]
 pub(crate) use libc::IP_HDRINCL;