Add Windows UWP support

build.rs

@@ -0,0 +1,17 @@
+#![deny(warnings)]
+
+use std::env;
+
+fn main() {
+    let target = env::var("TARGET").expect("TARGET was not set");
+    if target.contains("uwp") {
+        // for BCryptGenRandom
+        println!("cargo:rustc-link-lib=bcrypt");
+    } else if target.contains("windows") {
+        // for RtlGenRandom (aka SystemFunction036)
+        println!("cargo:rustc-link-lib=advapi32");
+    } else if target.contains("apple-ios") {
+        // for SecRandomCopyBytes and kSecRandomDefault
+        println!("cargo:rustc-link-lib=framework=Security");
+    }
+}

src/lib.rs

@@ -126,6 +126,14 @@ cfg_if! {
         macro_rules! error {
             ($($x:tt)*) => {};
         }
+        #[allow(unused)]
+        macro_rules! warn {
+            ($($x:tt)*) => {};
+        }
+        #[allow(unused)]
+        macro_rules! info {
+            ($($x:tt)*) => {};
+        }
     }
 }
 
@@ -216,6 +224,15 @@ cfg_if! {
         #[path = "solaris_illumos.rs"] mod imp;
     } else if #[cfg(target_os = "wasi")] {
         #[path = "wasi.rs"] mod imp;
+    } else if #[cfg(any(
+        // target_vendor was stabilized only in Rust 1.33
+        target = "i686-uwp-windows-gnu",
+        target = "x86_64-uwp-windows-gnu",
+        target = "aarch64-uwp-windows-msvc",
+        target = "x86_64-uwp-windows-msvc",
+        target = "i686-uwp-windows-msvc",
+    ))] {
+        #[path = "windows_uwp.rs"] mod imp;
     } else if #[cfg(windows)] {
         #[path = "windows.rs"] mod imp;
     } else if #[cfg(all(target_arch = "x86_64", any(

src/windows_uwp.rs

@@ -0,0 +1,55 @@
+// 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 superseed the `RtlGenRandom`-based implementation.
+use crate::Error;
+use core::{ffi::c_void, num::NonZeroU32, ptr, u32};
+
+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 codes
+        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 designated for OS codes.
+                let code = ret & (u32::MAX >> 1);
+                // 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(())
+}