1 files changed, 81 insertions, 0 deletions
diff --git a/src/windows.rs b/src/windows.rs
new file mode 100644
index 0000000..9c7c0e4
--- /dev/null
+++ b/src/windows.rs
@@ -0,0 +1,81 @@
+//! Implementation of `errno` functionality for Windows.
+//!
+//! Adapted from `src/libstd/sys/windows/os.rs` in the Rust distribution.
+
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use core::char::{self, REPLACEMENT_CHARACTER};
+use core::ptr;
+use core::str;
+use windows_sys::Win32::Foundation::{GetLastError, SetLastError, WIN32_ERROR};
+use windows_sys::Win32::System::Diagnostics::Debug::{
+    FormatMessageW, FORMAT_MESSAGE_FROM_SYSTEM, FORMAT_MESSAGE_IGNORE_INSERTS,
+};
+
+use crate::Errno;
+
+fn from_utf16_lossy<'a>(input: &[u16], output: &'a mut [u8]) -> &'a str {
+    let mut output_len = 0;
+    for c in char::decode_utf16(input.iter().copied().take_while(|&x| x != 0))
+        .map(|x| x.unwrap_or(REPLACEMENT_CHARACTER))
+    {
+        let c_len = c.len_utf8();
+        if c_len > output.len() - output_len {
+            break;
+        }
+        c.encode_utf8(&mut output[output_len..]);
+        output_len += c_len;
+    }
+    unsafe { str::from_utf8_unchecked(&output[..output_len]) }
+}
+
+pub fn with_description<F, T>(err: Errno, callback: F) -> T
+where
+    F: FnOnce(Result<&str, Errno>) -> T,
+{
+    // This value is calculated from the macro
+    // MAKELANGID(LANG_SYSTEM_DEFAULT, SUBLANG_SYS_DEFAULT)
+    let lang_id = 0x0800_u32;
+
+    let mut buf = [0u16; 2048];
+
+    unsafe {
+        let res = FormatMessageW(
+            FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
+            ptr::null_mut(),
+            err.0 as u32,
+            lang_id,
+            buf.as_mut_ptr(),
+            buf.len() as u32,
+            ptr::null_mut(),
+        );
+        if res == 0 {
+            // Sometimes FormatMessageW can fail e.g. system doesn't like lang_id
+            let fm_err = errno();
+            return callback(Err(fm_err));
+        }
+
+        let mut msg = [0u8; 2048];
+        let msg = from_utf16_lossy(&buf[..res as usize], &mut msg[..]);
+        // Trim trailing CRLF inserted by FormatMessageW
+        callback(Ok(msg.trim_end()))
+    }
+}
+
+pub const STRERROR_NAME: &str = "FormatMessageW";
+
+pub fn errno() -> Errno {
+    unsafe { Errno(GetLastError() as i32) }
+}
+
+pub fn set_errno(Errno(errno): Errno) {
+    unsafe { SetLastError(errno as WIN32_ERROR) }
+}