Restore conversions from ip v4/6 Sockaddr types to std::net equivalents.

Fixes #1710

CHANGELOG.md

@@ -5,6 +5,11 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ## [Unreleased] - ReleaseDate
 ### Added
+
+- impl From<SockaddrIn> for std::net::SocketAddrV4 and
+  impl From<SockaddrIn6> for std::net::SocketAddrV6.
+  (#[1711](https://github.com/nix-rust/nix/pull/1711))
+
 ### Changed
 ### Fixed
 ### Removed

src/sys/socket/addr.rs

@@ -1233,6 +1233,16 @@ impl From<net::SocketAddrV4> for SockaddrIn {
     }
 }
 
+#[cfg(feature = "net")]
+impl From<SockaddrIn> for net::SocketAddrV4 {
+    fn from(addr: SockaddrIn) -> Self {
+        net::SocketAddrV4::new(
+            net::Ipv4Addr::from(addr.0.sin_addr.s_addr.to_ne_bytes()),
+            u16::from_be(addr.0.sin_port)
+        )
+    }
+}
+
 #[cfg(feature = "net")]
 impl std::str::FromStr for SockaddrIn {
     type Err = net::AddrParseError;
@@ -1329,6 +1339,18 @@ impl From<net::SocketAddrV6> for SockaddrIn6 {
     }
 }
 
+#[cfg(feature = "net")]
+impl From<SockaddrIn6> for net::SocketAddrV6 {
+    fn from(addr: SockaddrIn6) -> Self {
+        net::SocketAddrV6::new(
+            net::Ipv6Addr::from(addr.0.sin6_addr.s6_addr),
+            u16::from_be(addr.0.sin6_port),
+            u32::from_be(addr.0.sin6_flowinfo),
+            u32::from_be(addr.0.sin6_scope_id)
+        )
+    }
+}
+
 #[cfg(feature = "net")]
 impl std::str::FromStr for SockaddrIn6 {
     type Err = net::AddrParseError;

test/sys/test_socket.rs

@@ -257,6 +257,19 @@ pub fn test_socketpair() {
     assert_eq!(&buf[..], b"hello");
 }
 
+#[test]
+pub fn test_std_conversions() {
+    use nix::sys::socket::*;
+
+    let std_sa = SocketAddrV4::from_str("127.0.0.1:6789").unwrap();
+    let sock_addr = SockaddrIn::from(std_sa);
+    assert_eq!(std_sa, sock_addr.into());
+
+    let std_sa = SocketAddrV6::from_str("[::1]:6000").unwrap();
+    let sock_addr: SockaddrIn6 = SockaddrIn6::from(std_sa);
+    assert_eq!(std_sa, sock_addr.into());
+}
+
 mod recvfrom {
     use nix::Result;
     use nix::sys::socket::*;