1 files changed, 59 insertions, 0 deletions
diff --git a/getrandom/src/windows_uwp.rs b/getrandom/src/windows_uwp.rs
new file mode 100644
index 0000000..586c6f6
--- /dev/null
+++ b/getrandom/src/windows_uwp.rs
@@ -0,0 +1,59 @@
+// Copyright 2018 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Implementation for Windows UWP targets. After deprecation of Windows XP
+//! and Vista, this can supersede the `RtlGenRandom`-based implementation.
+use crate::Error;
+use core::{ffi::c_void, num::NonZeroU32, ptr};
+
+const BCRYPT_USE_SYSTEM_PREFERRED_RNG: u32 = 0x00000002;
+
+extern "system" {
+    fn BCryptGenRandom(
+        hAlgorithm: *mut c_void,
+        pBuffer: *mut u8,
+        cbBuffer: u32,
+        dwFlags: u32,
+    ) -> u32;
+}
+
+pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
+    // Prevent overflow of u32
+    for chunk in dest.chunks_mut(u32::max_value() as usize) {
+        let ret = unsafe {
+            BCryptGenRandom(
+                ptr::null_mut(),
+                chunk.as_mut_ptr(),
+                chunk.len() as u32,
+                BCRYPT_USE_SYSTEM_PREFERRED_RNG,
+            )
+        };
+        // NTSTATUS codes use two highest bits for severity status
+        match ret >> 30 {
+            0b01 => {
+                info!("BCryptGenRandom: information code 0x{:08X}", ret);
+            }
+            0b10 => {
+                warn!("BCryptGenRandom: warning code 0x{:08X}", ret);
+            }
+            0b11 => {
+                error!("BCryptGenRandom: failed with 0x{:08X}", ret);
+                // We zeroize the highest bit, so the error code will reside
+                // inside the range of designated for OS codes.
+                let code = ret ^ (1 << 31);
+                // SAFETY: the second highest bit is always equal to one,
+                // so it's impossible to get zero. Unfortunately compiler
+                // is not smart enough to figure out it yet.
+                let code = unsafe { NonZeroU32::new_unchecked(code) };
+                return Err(Error::from(code));
+            }
+            _ => (),
+        }
+    }
+    Ok(())
+}