Safely convert SocketAddr into raw SOCKADDR

Do not rely on the memory layout of std::net::SocketAddrV*

Author: faern

src/net.rs

@@ -13,6 +13,8 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 
 use winapi::ctypes::*;
 use winapi::shared::guiddef::*;
+use winapi::shared::in6addr::{in6_addr_u, IN6_ADDR};
+use winapi::shared::inaddr::{in_addr_S_un, IN_ADDR};
 use winapi::shared::minwindef::*;
 use winapi::shared::minwindef::{FALSE, TRUE};
 use winapi::shared::ntdef::*;
@@ -456,16 +458,64 @@ fn cvt(i: c_int, size: DWORD) -> io::Result<Option<usize>> {
     }
 }
 
-fn socket_addr_to_ptrs(addr: &SocketAddr) -> (*const SOCKADDR, c_int) {
+/// A type with the same memory layout as `SOCKADDR`. Used in converting Rust level
+/// SocketAddr* types into their system representation. The benefit of this specific
+/// type over using `SOCKADDR_STORAGE` is that this type is exactly as large as it
+/// needs to be and not a lot larger. And it can be initialized cleaner from Rust.
+#[repr(C)]
+pub(crate) union SocketAddrCRepr {
+    v4: SOCKADDR_IN,
+    v6: SOCKADDR_IN6_LH,
+}
+
+impl SocketAddrCRepr {
+    pub(crate) fn as_ptr(&self) -> *const SOCKADDR {
+        self as *const _ as *const SOCKADDR
+    }
+}
+
+fn socket_addr_to_ptrs(addr: &SocketAddr) -> (SocketAddrCRepr, c_int) {
     match *addr {
-        SocketAddr::V4(ref a) => (
-            a as *const _ as *const _,
-            mem::size_of::<SOCKADDR_IN>() as c_int,
-        ),
-        SocketAddr::V6(ref a) => (
-            a as *const _ as *const _,
-            mem::size_of::<SOCKADDR_IN6_LH>() as c_int,
-        ),
+        SocketAddr::V4(ref a) => {
+            let sin_addr = unsafe {
+                let mut s_un = mem::zeroed::<in_addr_S_un>();
+                *s_un.S_addr_mut() = u32::from_ne_bytes(a.ip().octets());
+                IN_ADDR { S_un: s_un }
+            };
+
+            let sockaddr_in = SOCKADDR_IN {
+                sin_family: AF_INET as ADDRESS_FAMILY,
+                sin_port: a.port().to_be(),
+                sin_addr,
+                sin_zero: [0; 8],
+            };
+
+            let sockaddr = SocketAddrCRepr { v4: sockaddr_in };
+            (sockaddr, mem::size_of::<SOCKADDR_IN>() as c_int)
+        }
+        SocketAddr::V6(ref a) => {
+            let sin6_addr = unsafe {
+                let mut u = mem::zeroed::<in6_addr_u>();
+                *u.Byte_mut() = a.ip().octets();
+                IN6_ADDR { u }
+            };
+            let u = unsafe {
+                let mut u = mem::zeroed::<SOCKADDR_IN6_LH_u>();
+                *u.sin6_scope_id_mut() = a.scope_id();
+                u
+            };
+
+            let sockaddr_in6 = SOCKADDR_IN6_LH {
+                sin6_family: AF_INET6 as ADDRESS_FAMILY,
+                sin6_port: a.port().to_be(),
+                sin6_addr,
+                sin6_flowinfo: a.flowinfo(),
+                u,
+            };
+
+            let sockaddr = SocketAddrCRepr { v6: sockaddr_in6 };
+            (sockaddr, mem::size_of::<SOCKADDR_IN6_LH>() as c_int)
+        }
     }
 }
 
@@ -650,7 +700,7 @@ unsafe fn connect_overlapped(
     let mut bytes_sent: DWORD = 0;
     let r = connect_ex(
         socket,
-        addr_buf,
+        addr_buf.as_ptr(),
         addr_len,
         buf.as_ptr() as *mut _,
         buf.len() as u32,
@@ -723,7 +773,7 @@ impl UdpSocketExt for UdpSocket {
             1,
             &mut sent_bytes,
             0,
-            addr_buf as *const _,
+            addr_buf.as_ptr() as *const _,
             addr_len,
             overlapped,
             None,