Minor changes to Ipv4Addr

* Impl IntoInner rather than AsInner for Ipv4Addr
* Add some comments
* Add test to show endiannes of Ipv4Addr display

Author: tesuji

library/std/src/net/addr.rs

@@ -268,7 +268,7 @@ impl SocketAddrV4 {
             inner: c::sockaddr_in {
                 sin_family: c::AF_INET as c::sa_family_t,
                 sin_port: htons(port),
-                sin_addr: *ip.as_inner(),
+                sin_addr: ip.into_inner(),
                 ..unsafe { mem::zeroed() }
             },
         }
@@ -286,6 +286,8 @@ impl SocketAddrV4 {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn ip(&self) -> &Ipv4Addr {
+        // SAFETY: `Ipv4Addr` is `#[repr(C)] struct { _: in_addr; }`.
+        // It is safe to cast from `&in_addr` to `&Ipv4Addr`.
         unsafe { &*(&self.inner.sin_addr as *const c::in_addr as *const Ipv4Addr) }
     }
 
@@ -302,7 +304,7 @@ impl SocketAddrV4 {
     /// ```
     #[stable(feature = "sockaddr_setters", since = "1.9.0")]
     pub fn set_ip(&mut self, new_ip: Ipv4Addr) {
-        self.inner.sin_addr = *new_ip.as_inner()
+        self.inner.sin_addr = new_ip.into_inner()
     }
 
     /// Returns the port number associated with this socket address.

library/std/src/net/ip.rs

@@ -12,7 +12,7 @@ use crate::hash;
 use crate::io::Write as IoWrite;
 use crate::mem::transmute;
 use crate::sys::net::netc as c;
-use crate::sys_common::{AsInner, FromInner};
+use crate::sys_common::{AsInner, FromInner, IntoInner};
 
 /// An IP address, either IPv4 or IPv6.
 ///
@@ -909,7 +909,10 @@ impl Eq for Ipv4Addr {}
 #[stable(feature = "rust1", since = "1.0.0")]
 impl hash::Hash for Ipv4Addr {
     fn hash<H: hash::Hasher>(&self, s: &mut H) {
-        // `inner` is #[repr(packed)], so we need to copy `s_addr`.
+        // NOTE:
+        // * hash in big endian order
+        // * in netbsd, `in_addr` has `repr(packed)`, we need to
+        //   copy `s_addr` to avoid unsafe borrowing
         { self.inner.s_addr }.hash(s)
     }
 }
@@ -944,13 +947,14 @@ impl PartialOrd<IpAddr> for Ipv4Addr {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Ord for Ipv4Addr {
     fn cmp(&self, other: &Ipv4Addr) -> Ordering {
+        // Compare as native endian
         u32::from_be(self.inner.s_addr).cmp(&u32::from_be(other.inner.s_addr))
     }
 }
 
-impl AsInner<c::in_addr> for Ipv4Addr {
-    fn as_inner(&self) -> &c::in_addr {
-        &self.inner
+impl IntoInner<c::in_addr> for Ipv4Addr {
+    fn into_inner(self) -> c::in_addr {
+        self.inner
     }
 }
 
@@ -2019,6 +2023,7 @@ mod tests {
 
     #[test]
     fn ipv4_addr_to_string() {
+        assert_eq!(Ipv4Addr::new(127, 0, 0, 1).to_string(), "127.0.0.1");
         // Short address
         assert_eq!(Ipv4Addr::new(1, 1, 1, 1).to_string(), "1.1.1.1");
         // Long address

library/std/src/sys_common/net.rs

@@ -585,8 +585,8 @@ impl UdpSocket {
 
     pub fn join_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr) -> io::Result<()> {
         let mreq = c::ip_mreq {
-            imr_multiaddr: *multiaddr.as_inner(),
-            imr_interface: *interface.as_inner(),
+            imr_multiaddr: multiaddr.into_inner(),
+            imr_interface: interface.into_inner(),
         };
         setsockopt(&self.inner, c::IPPROTO_IP, c::IP_ADD_MEMBERSHIP, mreq)
     }
@@ -601,8 +601,8 @@ impl UdpSocket {
 
     pub fn leave_multicast_v4(&self, multiaddr: &Ipv4Addr, interface: &Ipv4Addr) -> io::Result<()> {
         let mreq = c::ip_mreq {
-            imr_multiaddr: *multiaddr.as_inner(),
-            imr_interface: *interface.as_inner(),
+            imr_multiaddr: multiaddr.into_inner(),
+            imr_interface: interface.into_inner(),
         };
         setsockopt(&self.inner, c::IPPROTO_IP, c::IP_DROP_MEMBERSHIP, mreq)
     }