feat: works

__wasm/wit-bindgen-sample/engine/getrandom/src/use_file.rs

@@ -0,0 +1,139 @@
+// 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.
+
+//! Implementations that just need to read from a file
+use crate::{
+    util::LazyUsize,
+    util_libc::{open_readonly, sys_fill_exact},
+    Error,
+};
+use core::{
+    cell::UnsafeCell,
+    sync::atomic::{AtomicUsize, Ordering::Relaxed},
+};
+
+#[cfg(any(
+    target_os = "dragonfly",
+    target_os = "emscripten",
+    target_os = "haiku",
+    target_os = "macos",
+    target_os = "solaris",
+    target_os = "illumos"
+))]
+const FILE_PATH: &str = "/dev/random\0";
+#[cfg(any(target_os = "android", target_os = "linux", target_os = "redox"))]
+const FILE_PATH: &str = "/dev/urandom\0";
+
+pub fn getrandom_inner(dest: &mut [u8]) -> Result<(), Error> {
+    let fd = get_rng_fd()?;
+    let read = |buf: &mut [u8]| unsafe { libc::read(fd, buf.as_mut_ptr() as *mut _, buf.len()) };
+
+    if cfg!(target_os = "emscripten") {
+        // `Crypto.getRandomValues` documents `dest` should be at most 65536 bytes.
+        for chunk in dest.chunks_mut(65536) {
+            sys_fill_exact(chunk, read)?;
+        }
+    } else {
+        sys_fill_exact(dest, read)?;
+    }
+    Ok(())
+}
+
+// Returns the file descriptor for the device file used to retrieve random
+// bytes. The file will be opened exactly once. All subsequent calls will
+// return the same file descriptor. This file descriptor is never closed.
+fn get_rng_fd() -> Result<libc::c_int, Error> {
+    static FD: AtomicUsize = AtomicUsize::new(LazyUsize::UNINIT);
+    fn get_fd() -> Option<libc::c_int> {
+        match FD.load(Relaxed) {
+            LazyUsize::UNINIT => None,
+            val => Some(val as libc::c_int),
+        }
+    }
+
+    // Use double-checked locking to avoid acquiring the lock if possible.
+    if let Some(fd) = get_fd() {
+        return Ok(fd);
+    }
+
+    // SAFETY: We use the mutex only in this method, and we always unlock it
+    // before returning, making sure we don't violate the pthread_mutex_t API.
+    static MUTEX: Mutex = Mutex::new();
+    unsafe { MUTEX.lock() };
+    let _guard = DropGuard(|| unsafe { MUTEX.unlock() });
+
+    if let Some(fd) = get_fd() {
+        return Ok(fd);
+    }
+
+    // On Linux, /dev/urandom might return insecure values.
+    #[cfg(any(target_os = "android", target_os = "linux"))]
+    wait_until_rng_ready()?;
+
+    let fd = unsafe { open_readonly(FILE_PATH)? };
+    // The fd always fits in a usize without conflicting with UNINIT.
+    debug_assert!(fd >= 0 && (fd as usize) < LazyUsize::UNINIT);
+    FD.store(fd as usize, Relaxed);
+
+    Ok(fd)
+}
+
+// Succeeds once /dev/urandom is safe to read from
+#[cfg(any(target_os = "android", target_os = "linux"))]
+fn wait_until_rng_ready() -> Result<(), Error> {
+    // Poll /dev/random to make sure it is ok to read from /dev/urandom.
+    let fd = unsafe { open_readonly("/dev/random\0")? };
+    let mut pfd = libc::pollfd {
+        fd,
+        events: libc::POLLIN,
+        revents: 0,
+    };
+    let _guard = DropGuard(|| unsafe {
+        libc::close(fd);
+    });
+
+    loop {
+        // A negative timeout means an infinite timeout.
+        let res = unsafe { libc::poll(&mut pfd, 1, -1) };
+        if res >= 0 {
+            debug_assert_eq!(res, 1); // We only used one fd, and cannot timeout.
+            return Ok(());
+        }
+        let err = crate::util_libc::last_os_error();
+        match err.raw_os_error() {
+            Some(libc::EINTR) | Some(libc::EAGAIN) => continue,
+            _ => return Err(err),
+        }
+    }
+}
+
+struct Mutex(UnsafeCell<libc::pthread_mutex_t>);
+
+impl Mutex {
+    const fn new() -> Self {
+        Self(UnsafeCell::new(libc::PTHREAD_MUTEX_INITIALIZER))
+    }
+    unsafe fn lock(&self) {
+        let r = libc::pthread_mutex_lock(self.0.get());
+        debug_assert_eq!(r, 0);
+    }
+    unsafe fn unlock(&self) {
+        let r = libc::pthread_mutex_unlock(self.0.get());
+        debug_assert_eq!(r, 0);
+    }
+}
+
+unsafe impl Sync for Mutex {}
+
+struct DropGuard<F: FnMut()>(F);
+
+impl<F: FnMut()> Drop for DropGuard<F> {
+    fn drop(&mut self) {
+        self.0()
+    }
+}