Merge nix-rust#2061

2061: For invalid IP address conversions with future Rust versions r=asomers a=asomers

Rust's standard library no longer guarantees that Ipv4Addr and Ipv6Addr are wrappers around the C types (though for now at least, they are identical on all platforms I'm aware of).  So do the conversions explicitly instead of transmuting.

Fixes nix-rust#2053

Co-authored-by: Alan Somers <asomers@gmail.com>

Cargo.toml

@@ -31,7 +31,6 @@ libc = { version = "0.2.137", features = [ "extra_traits" ] }
 bitflags = "1.1"
 cfg-if = "1.0"
 pin-utils = { version = "0.1.0", optional = true }
-static_assertions = "1"
 
 [target.'cfg(not(target_os = "redox"))'.dependencies]
 memoffset = { version = "0.7", optional = true }

src/sys/socket/addr.rs

@@ -41,21 +41,16 @@ use std::{fmt, mem, net, ptr, slice};
 /// Convert a std::net::Ipv4Addr into the libc form.
 #[cfg(feature = "net")]
 pub(crate) const fn ipv4addr_to_libc(addr: net::Ipv4Addr) -> libc::in_addr {
-    static_assertions::assert_eq_size!(net::Ipv4Addr, libc::in_addr);
-    // Safe because both types have the same memory layout, and no fancy Drop
-    // impls.
-    unsafe {
-        mem::transmute(addr)
+    libc::in_addr {
+        s_addr: u32::from_ne_bytes(addr.octets())
     }
 }
 
 /// Convert a std::net::Ipv6Addr into the libc form.
 #[cfg(feature = "net")]
 pub(crate) const fn ipv6addr_to_libc(addr: &net::Ipv6Addr) -> libc::in6_addr {
-    static_assertions::assert_eq_size!(net::Ipv6Addr, libc::in6_addr);
-    // Safe because both are Newtype wrappers around the same libc type
-    unsafe {
-        mem::transmute(*addr)
+    libc::in6_addr {
+        s6_addr: addr.octets()
     }
 }
 
@@ -1276,9 +1271,6 @@ impl SockaddrLike for () {
 }
 
 /// An IPv4 socket address
-// This is identical to net::SocketAddrV4.  But the standard library
-// doesn't allow direct access to the libc fields, which we need.  So we
-// reimplement it here.
 #[cfg(feature = "net")]
 #[repr(transparent)]
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]