Eliminate some more `transmute()` (#8879)

* eliminate some more transmute()

* Address `review comments`

* Make unsafe block smaller
* Use different byte-order than `std`, read words as big endian instead
of little endian!

* Fix IpAddresses nits

* Use `from_be` to work both for big and little endian
* Ipv6 addresses were incorrectly `transmuted`

* remove needless lifetime annotation

ethash/src/compute.rs

@@ -137,11 +137,11 @@ fn hash_compute(light: &Light, full_size: usize, header_hash: &H256, nonce: u64)
 		($n:expr, $value:expr) => {{
 			// We use explicit lifetimes to ensure that val's borrow is invalidated until the
 			// transmuted val dies.
-			unsafe fn make_const_array<'a, T, U>(val: &'a mut [T]) -> &'a mut [U; $n] {
+			unsafe fn make_const_array<T, U>(val: &mut [T]) -> &mut [U; $n] {
 				use ::std::mem;
 
 				debug_assert_eq!(val.len() * mem::size_of::<T>(), $n * mem::size_of::<U>());
-				mem::transmute(val.as_mut_ptr())
+ 				&mut *(val.as_mut_ptr() as *mut [U; $n])
 			}
 
 			make_const_array($value)
@@ -177,7 +177,7 @@ fn hash_compute(light: &Light, full_size: usize, header_hash: &H256, nonce: u64)
 
 			ptr::copy_nonoverlapping(header_hash.as_ptr(), out.as_mut_ptr(), header_hash.len());
 			ptr::copy_nonoverlapping(
-				mem::transmute(&nonce),
+				&nonce as *const u64 as *const u8,
 				out[header_hash.len()..].as_mut_ptr(),
 				mem::size_of::<u64>(),
 			);
@@ -266,18 +266,20 @@ fn hash_compute(light: &Light, full_size: usize, header_hash: &H256, nonce: u64)
 
 	let mix_hash = buf.compress_bytes;
 
-	let value: H256 = unsafe {
+	let value: H256 = {
 		// We can interpret the buffer as an array of `u8`s, since it's `repr(C)`.
-		let read_ptr: *const u8 = mem::transmute(&buf);
+		let read_ptr: *const u8 = &buf as *const MixBuf as *const u8;
 		// We overwrite the second half since `keccak_256` has an internal buffer and so allows
 		// overlapping arrays as input.
-		let write_ptr: *mut u8 = mem::transmute(&mut buf.compress_bytes);
-		keccak_256::unchecked(
-			write_ptr,
-			buf.compress_bytes.len(),
-			read_ptr,
-			buf.half_mix.bytes.len() + buf.compress_bytes.len(),
-		);
+		let write_ptr: *mut u8 = &mut buf.compress_bytes as *mut [u8; 32] as *mut u8;
+		unsafe { 
+			keccak_256::unchecked(
+				write_ptr,
+				buf.compress_bytes.len(),
+				read_ptr,
+				buf.half_mix.bytes.len() + buf.compress_bytes.len(),
+			);
+		}
 		buf.compress_bytes
 	};
 

util/network-devp2p/src/ip_utils.rs

@@ -20,8 +20,8 @@ use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV
 use std::io;
 use igd::{PortMappingProtocol, search_gateway_from_timeout};
 use std::time::Duration;
-use node_table::{NodeEndpoint};
-use ipnetwork::{IpNetwork};
+use node_table::NodeEndpoint;
+use ipnetwork::IpNetwork;
 
 /// Socket address extension for rustc beta. To be replaces with now unstable API
 pub trait SocketAddrExt {
@@ -225,28 +225,17 @@ mod getinterfaces {
 				let sa: *const sockaddr_in = sa as *const sockaddr_in;
 				let sa = unsafe { &*sa };
 				let (addr, port) = (sa.sin_addr.s_addr, sa.sin_port);
-				(IpAddr::V4(Ipv4Addr::new(
-					(addr & 0x0000_00FF) as u8,
-					((addr & 0x0000_FF00) >>  8) as u8,
-					((addr & 0x00FF_0000) >> 16) as u8,
-					((addr & 0xFF00_0000) >> 24) as u8)),
-					port)
+				// convert u32 to an `Ipv4 address`, but the u32 must be converted to `host-order`
+				// that's why `from_be` is used!
+				(IpAddr::V4(Ipv4Addr::from(<u32>::from_be(addr))), port)
 			},
 			AF_INET6 => {
 				let sa: *const sockaddr_in6 = sa as *const sockaddr_in6;
 				let sa = & unsafe { *sa };
 				let (addr, port) = (sa.sin6_addr.s6_addr, sa.sin6_port);
-				let addr: [u16; 8] = unsafe { mem::transmute(addr) };
-				(IpAddr::V6(Ipv6Addr::new(
-					addr[0],
-					addr[1],
-					addr[2],
-					addr[3],
-					addr[4],
-					addr[5],
-					addr[6],
-					addr[7])),
-					port)
+				let ip_addr = Ipv6Addr::from(addr);
+				debug_assert!(addr == ip_addr.octets());
+				(IpAddr::V6(ip_addr), port)
 			},
 			_ => return None,
 		};