Solaris: Replace cast with TryFrom.

Author: briansmith

src/solaris.rs

@@ -13,7 +13,7 @@
 //! https://blogs.oracle.com/solaris/post/solaris-new-system-calls-getentropy2-and-getrandom2
 //! which also explains why this crate should not use getentropy(2).
 use crate::{util_libc::last_os_error, Error};
-use core::{ffi::c_void, mem::MaybeUninit};
+use core::{ffi::c_void, mem::MaybeUninit, num::NonZeroUsize};
 
 const MAX_BYTES: usize = 1024;
 
@@ -22,12 +22,11 @@ pub fn getrandom_inner(dest: &mut [MaybeUninit<u8>]) -> Result<(), Error> {
         let ptr = chunk.as_mut_ptr().cast::<c_void>();
         let ret = unsafe { libc::getrandom(ptr, chunk.len(), libc::GRND_RANDOM) };
         // In case the man page has a typo, we also check for negative ret.
-        if ret <= 0 {
-            return Err(last_os_error());
-        }
         // If getrandom(2) succeeds, it should have completely filled chunk.
-        if (ret as usize) != chunk.len() {
-            return Err(Error::UNEXPECTED);
+        match usize::try_from(ret) {
+            Ok(ret) if ret == chunk.len() => {} // Good. Keep going
+            Ok(0) => return Err(last_os_error()),
+            _ => return Err(Error::UNEXPECTED),
         }
     }
     Ok(())