1 files changed, 156 insertions, 0 deletions
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());
+}