Import errno 0.3.0upstream/0.3.0upstream

16 files changed, 910 insertions, 0 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
new file mode 100644
index 0000000..487400f
--- /dev/null
+++ b/.cargo_vcs_info.json
@@ -0,0 +1,6 @@
+{
+  "git": {
+    "sha1": "e1882701f6d21bd9f45c2941a85416c59fa019ac"
+  },
+  "path_in_vcs": ""
+}
\ No newline at end of file
diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 0000000..98e44ee
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "cargo"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000..9ee02b1
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,74 @@
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  schedule:
+    - cron: '5 21 * * 5'
+  workflow_dispatch:
+
+name: CI
+
+jobs:
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        rust: [stable, nightly, '1.48']
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Install toolchain
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.rust }}
+      # Workaround link failures if XCode 14 is combined with Rust <= 1.53
+      - name: Downgrade to XCode 13
+        if: ${{ matrix.os == 'macos-latest' && matrix.rust == '1.48' }}
+        uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: '13'
+      - name: Setup cache
+        uses: Swatinem/rust-cache@v2
+      - name: Test (no features)
+        run: cargo test --no-default-features
+      - name: Test (all features)
+        run: cargo test --all-features
+
+
+  wasi:
+    name: Test WASI
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Install toolchain
+        uses: dtolnay/rust-toolchain@nightly
+        with:
+          targets: wasm32-wasi
+      - name: Install wasmtime
+        run: |
+          curl https://wasmtime.dev/install.sh -sSf | bash
+          echo "$HOME/.wasmtime/bin" >> $GITHUB_PATH
+      - name: Test (no features)
+        run: CARGO_TARGET_WASM32_WASI_RUNNER=wasmtime cargo test --target wasm32-wasi --no-default-features
+      - name: Test (all features)
+        run: CARGO_TARGET_WASM32_WASI_RUNNER=wasmtime cargo test --target wasm32-wasi --all-features
+
+
+  lints:
+    name: Rustfmt & Clippy
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v3
+      - name: Install toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+      - name: Check formatting
+        run: cargo fmt --check
+      - name: Check clippy
+        run: cargo clippy -- -D warnings
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a9d37c5
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+target
+Cargo.lock
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..5f59319
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,30 @@
+# [Unreleased]
+
+# [0.3.0] - 2023-02-12
+
+- Add haiku support
+  [#42](https://github.com/lambda-fairy/rust-errno/pull/42)
+
+- Add AIX support
+  [#54](https://github.com/lambda-fairy/rust-errno/pull/54)
+
+- Add formatting with `#![no_std]`
+  [#44](https://github.com/lambda-fairy/rust-errno/pull/44)
+
+- Switch from `winapi` to `windows-sys` [#55](https://github.com/lambda-fairy/rust-errno/pull/55)
+
+- Update minimum Rust version to 1.48
+  [#48](https://github.com/lambda-fairy/rust-errno/pull/48) [#55](https://github.com/lambda-fairy/rust-errno/pull/55)
+
+- Upgrade to Rust 2018 edition [#59](https://github.com/lambda-fairy/rust-errno/pull/59)
+
+- wasm32-wasi: Use `__errno_location` instead of `feature(thread_local)`. [#66](https://github.com/lambda-fairy/rust-errno/pull/66)
+
+# [0.2.8] - 2021-10-27
+
+- Optionally support no_std
+  [#31](https://github.com/lambda-fairy/rust-errno/pull/31)
+
+[Unreleased]: https://github.com/lambda-fairy/rust-errno/compare/v0.3.0...HEAD
+[0.3.0]: https://github.com/lambda-fairy/rust-errno/compare/v0.2.8...v0.3.0
+[0.2.8]: https://github.com/lambda-fairy/rust-errno/compare/v0.2.7...v0.2.8
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..98668cb
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,49 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+rust-version = "1.48"
+name = "errno"
+version = "0.3.0"
+authors = ["Chris Wong <lambda.fairy@gmail.com>"]
+description = "Cross-platform interface to the `errno` variable."
+documentation = "https://docs.rs/errno"
+readme = "README.md"
+categories = [
+    "no-std",
+    "os",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/lambda-fairy/rust-errno"
+
+[features]
+default = ["std"]
+std = []
+
+[target."cfg(target_os=\"dragonfly\")".dependencies.errno-dragonfly]
+version = "0.1.1"
+
+[target."cfg(target_os=\"hermit\")".dependencies.libc]
+version = "0.2"
+
+[target."cfg(target_os=\"wasi\")".dependencies.libc]
+version = "0.2"
+
+[target."cfg(unix)".dependencies.libc]
+version = "0.2"
+
+[target."cfg(windows)".dependencies.windows-sys]
+version = "0.45"
+features = [
+    "Win32_Foundation",
+    "Win32_System_Diagnostics_Debug",
+]
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..bcae399
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,36 @@
+[package]
+
+name = "errno"
+version = "0.3.0"
+authors = ["Chris Wong <lambda.fairy@gmail.com>"]
+
+license = "MIT OR Apache-2.0"
+edition = "2018"
+documentation = "https://docs.rs/errno"
+repository = "https://github.com/lambda-fairy/rust-errno"
+description = "Cross-platform interface to the `errno` variable."
+categories = ["no-std", "os"]
+rust-version = "1.48"
+
+[target.'cfg(unix)'.dependencies]
+libc = "0.2"
+
+[target.'cfg(windows)'.dependencies.windows-sys]
+version = "0.45"
+features = [
+  "Win32_Foundation",
+  "Win32_System_Diagnostics_Debug",
+]
+
+[target.'cfg(target_os="dragonfly")'.dependencies]
+errno-dragonfly = "0.1.1"
+
+[target.'cfg(target_os="wasi")'.dependencies]
+libc = "0.2"
+
+[target.'cfg(target_os="hermit")'.dependencies]
+libc = "0.2"
+
+[features]
+default = ["std"]
+std = []
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..16fe87b
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,201 @@
+                              Apache License
+                        Version 2.0, January 2004
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+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
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+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
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+   liable to You for damages, including any direct, indirect, special,
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+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
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+Unless required by applicable law or agreed to in writing, software
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diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..66b6578
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,25 @@
+Copyright (c) 2014 Chris Wong
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..48def10
--- /dev/null
+++ b/README.md
@@ -0,0 +1,62 @@
+# errno [![CI](https://github.com/lambda-fairy/rust-errno/actions/workflows/main.yml/badge.svg)](https://github.com/lambda-fairy/rust-errno/actions/workflows/main.yml) [![Cargo](https://img.shields.io/crates/v/errno.svg)](https://crates.io/crates/errno)
+
+Cross-platform interface to the [`errno`][errno] variable. Works on Rust 1.48 or newer.
+
+Documentation is available at <https://docs.rs/errno>.
+
+[errno]: https://en.wikipedia.org/wiki/Errno.h
+
+
+## Dependency
+
+Add to your `Cargo.toml`:
+
+```toml
+[dependencies]
+errno = "*"
+```
+
+
+## Comparison with `std::io::Error`
+
+The standard library provides [`Error::last_os_error`][last_os_error] which fetches `errno` in the same way.
+
+This crate provides these extra features:
+
+- No heap allocations
+- Optional `#![no_std]` support
+- A `set_errno` function
+
+[last_os_error]: https://doc.rust-lang.org/std/io/struct.Error.html#method.last_os_error
+
+
+## Examples
+
+```rust
+extern crate errno;
+use errno::{Errno, errno, set_errno};
+
+// Get the current value of errno
+let e = errno();
+
+// Set the current value of errno
+set_errno(e);
+
+// Extract the error code as an i32
+let code = e.0;
+
+// Display a human-friendly error message
+println!("Error {}: {}", code, e);
+```
+
+
+## `#![no_std]`
+
+Enable `#![no_std]` support by disabling the default `std` feature:
+
+```toml
+[dependencies]
+errno = { version = "*", default-features = false }
+```
+
+The `Error` impl will be unavailable.
diff --git a/clippy.toml b/clippy.toml
new file mode 100644
index 0000000..f691ea3
--- /dev/null
+++ b/clippy.toml
@@ -0,0 +1 @@
+msrv = "1.48"
diff --git a/src/hermit.rs b/src/hermit.rs
new file mode 100644
index 0000000..99d4c32
--- /dev/null
+++ b/src/hermit.rs
@@ -0,0 +1,32 @@
+//! Implementation of `errno` functionality for RustyHermit.
+//!
+//! Currently, the error handling in RustyHermit isn't clearly
+//! defined. At the current stage of RustyHermit, only a placeholder
+//! is provided to be compatible to the classical errno interface.
+
+// Copyright 2015 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 Errno;
+
+pub fn with_description<F, T>(_err: Errno, callback: F) -> T
+where
+    F: FnOnce(Result<&str, Errno>) -> T,
+{
+    callback(Ok("unknown error"))
+}
+
+pub const STRERROR_NAME: &str = "strerror_r";
+
+pub fn errno() -> Errno {
+    Errno(0)
+}
+
+pub fn set_errno(_: Errno) {}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..20875b5
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,156 @@
+//! Cross-platform interface to the `errno` variable.
+//!
+//! # Examples
+//! ```
+//! use errno::{Errno, errno, set_errno};
+//!
+//! // Get the current value of errno
+//! let e = errno();
+//!
+//! // Set the current value of errno
+//! set_errno(e);
+//!
+//! // Extract the error code as an i32
+//! let code = e.0;
+//!
+//! // Display a human-friendly error message
+//! println!("Error {}: {}", code, e);
+//! ```
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[cfg_attr(unix, path = "unix.rs")]
+#[cfg_attr(windows, path = "windows.rs")]
+#[cfg_attr(target_os = "wasi", path = "wasi.rs")]
+#[cfg_attr(target_os = "hermit", path = "hermit.rs")]
+mod sys;
+
+use core::fmt;
+#[cfg(feature = "std")]
+use std::error::Error;
+#[cfg(feature = "std")]
+use std::io;
+
+/// Wraps a platform-specific error code.
+///
+/// The `Display` instance maps the code to a human-readable string. It
+/// calls [`strerror_r`][1] under POSIX, and [`FormatMessageW`][2] on
+/// Windows.
+///
+/// [1]: http://pubs.opengroup.org/onlinepubs/009695399/functions/strerror.html
+/// [2]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms679351%28v=vs.85%29.aspx
+#[derive(Copy, Clone, Eq, Ord, PartialEq, PartialOrd, Hash)]
+pub struct Errno(pub i32);
+
+impl fmt::Debug for Errno {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        sys::with_description(*self, |desc| {
+            fmt.debug_struct("Errno")
+                .field("code", &self.0)
+                .field("description", &desc.ok())
+                .finish()
+        })
+    }
+}
+
+impl fmt::Display for Errno {
+    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
+        sys::with_description(*self, |desc| match desc {
+            Ok(desc) => fmt.write_str(desc),
+            Err(fm_err) => write!(
+                fmt,
+                "OS error {} ({} returned error {})",
+                self.0,
+                sys::STRERROR_NAME,
+                fm_err.0
+            ),
+        })
+    }
+}
+
+impl From<Errno> for i32 {
+    fn from(e: Errno) -> Self {
+        e.0
+    }
+}
+
+#[cfg(feature = "std")]
+impl Error for Errno {
+    // TODO: Remove when MSRV >= 1.27
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        "system error"
+    }
+}
+
+#[cfg(feature = "std")]
+impl From<Errno> for io::Error {
+    fn from(errno: Errno) -> Self {
+        io::Error::from_raw_os_error(errno.0)
+    }
+}
+
+/// Returns the platform-specific value of `errno`.
+pub fn errno() -> Errno {
+    sys::errno()
+}
+
+/// Sets the platform-specific value of `errno`.
+pub fn set_errno(err: Errno) {
+    sys::set_errno(err)
+}
+
+#[test]
+fn it_works() {
+    let x = errno();
+    set_errno(x);
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn it_works_with_to_string() {
+    let x = errno();
+    let _ = x.to_string();
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn check_description() {
+    let expect = if cfg!(windows) {
+        "Incorrect function."
+    } else if cfg!(target_os = "illumos") {
+        "Not owner"
+    } else if cfg!(target_os = "wasi") {
+        "Argument list too long"
+    } else if cfg!(target_os = "haiku") {
+        "Operation not allowed"
+    } else {
+        "Operation not permitted"
+    };
+
+    let errno_code = if cfg!(target_os = "haiku") {
+        -2147483633
+    } else {
+        1
+    };
+    set_errno(Errno(errno_code));
+
+    assert_eq!(errno().to_string(), expect);
+    assert_eq!(
+        format!("{:?}", errno()),
+        format!(
+            "Errno {{ code: {}, description: Some({:?}) }}",
+            errno_code, expect
+        )
+    );
+}
+
+#[cfg(feature = "std")]
+#[test]
+fn check_error_into_errno() {
+    const ERROR_CODE: i32 = 1;
+
+    let error = io::Error::from_raw_os_error(ERROR_CODE);
+    let new_error: io::Error = Errno(ERROR_CODE).into();
+    assert_eq!(error.kind(), new_error.kind());
+}
diff --git a/src/unix.rs b/src/unix.rs
new file mode 100644
index 0000000..c22c587
--- /dev/null
+++ b/src/unix.rs
@@ -0,0 +1,85 @@
+//! Implementation of `errno` functionality for Unix systems.
+//!
+//! Adapted from `src/libstd/sys/unix/os.rs` in the Rust distribution.
+
+// Copyright 2015 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::str;
+#[cfg(target_os = "dragonfly")]
+use errno_dragonfly::errno_location;
+use libc::{self, c_char, c_int, size_t, strlen};
+
+use crate::Errno;
+
+fn from_utf8_lossy(input: &[u8]) -> &str {
+    match str::from_utf8(input) {
+        Ok(valid) => valid,
+        Err(error) => unsafe { str::from_utf8_unchecked(&input[..error.valid_up_to()]) },
+    }
+}
+
+pub fn with_description<F, T>(err: Errno, callback: F) -> T
+where
+    F: FnOnce(Result<&str, Errno>) -> T,
+{
+    let mut buf = [0u8; 1024];
+    let c_str = unsafe {
+        if strerror_r(err.0, buf.as_mut_ptr() as *mut _, buf.len() as size_t) < 0 {
+            let fm_err = errno();
+            if fm_err != Errno(libc::ERANGE) {
+                return callback(Err(fm_err));
+            }
+        }
+        let c_str_len = strlen(buf.as_ptr() as *const _);
+        &buf[..c_str_len]
+    };
+    callback(Ok(from_utf8_lossy(c_str)))
+}
+
+pub const STRERROR_NAME: &str = "strerror_r";
+
+pub fn errno() -> Errno {
+    unsafe { Errno(*errno_location()) }
+}
+
+pub fn set_errno(Errno(errno): Errno) {
+    unsafe {
+        *errno_location() = errno;
+    }
+}
+
+extern "C" {
+    #[cfg(not(target_os = "dragonfly"))]
+    #[cfg_attr(
+        any(target_os = "macos", target_os = "ios", target_os = "freebsd"),
+        link_name = "__error"
+    )]
+    #[cfg_attr(
+        any(
+            target_os = "openbsd",
+            target_os = "netbsd",
+            target_os = "bitrig",
+            target_os = "android"
+        ),
+        link_name = "__errno"
+    )]
+    #[cfg_attr(
+        any(target_os = "solaris", target_os = "illumos"),
+        link_name = "___errno"
+    )]
+    #[cfg_attr(target_os = "haiku", link_name = "_errnop")]
+    #[cfg_attr(target_os = "linux", link_name = "__errno_location")]
+    #[cfg_attr(target_os = "aix", link_name = "_Errno")]
+    fn errno_location() -> *mut c_int;
+
+    #[cfg_attr(target_os = "linux", link_name = "__xpg_strerror_r")]
+    fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t) -> c_int;
+}
diff --git a/src/wasi.rs b/src/wasi.rs
new file mode 100644
index 0000000..b18fa9b
--- /dev/null
+++ b/src/wasi.rs
@@ -0,0 +1,60 @@
+//! Implementation of `errno` functionality for WASI.
+//!
+//! Adapted from `unix.rs`.
+
+// Copyright 2015 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::str;
+use libc::{self, c_char, c_int, size_t, strlen};
+
+use crate::Errno;
+
+fn from_utf8_lossy(input: &[u8]) -> &str {
+    match str::from_utf8(input) {
+        Ok(valid) => valid,
+        Err(error) => unsafe { str::from_utf8_unchecked(&input[..error.valid_up_to()]) },
+    }
+}
+
+pub fn with_description<F, T>(err: Errno, callback: F) -> T
+where
+    F: FnOnce(Result<&str, Errno>) -> T,
+{
+    let mut buf = [0u8; 1024];
+    let c_str = unsafe {
+        if strerror_r(err.0, buf.as_mut_ptr() as *mut _, buf.len() as size_t) < 0 {
+            let fm_err = errno();
+            if fm_err != Errno(libc::ERANGE) {
+                return callback(Err(fm_err));
+            }
+        }
+        let c_str_len = strlen(buf.as_ptr() as *const _);
+        &buf[..c_str_len]
+    };
+    callback(Ok(from_utf8_lossy(c_str)))
+}
+
+pub const STRERROR_NAME: &str = "strerror_r";
+
+pub fn errno() -> Errno {
+    unsafe { Errno(*__errno_location()) }
+}
+
+pub fn set_errno(Errno(new_errno): Errno) {
+    unsafe {
+        *__errno_location() = new_errno;
+    }
+}
+
+extern "C" {
+    fn __errno_location() -> *mut c_int;
+    fn strerror_r(errnum: c_int, buf: *mut c_char, buflen: size_t) -> c_int;
+}
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) }
+}