error type

cowslice/src/error.rs

@@ -0,0 +1,41 @@
+use super::*;
+use std::{error, fmt};
+use std::ffi::CStr;
+
+/// A `libcow` error object.
+#[derive(Debug, Clone, PartialEq, Eq, Hash, PartialOrd, Ord)]
+#[repr(transparent)]
+pub struct Error(i32);
+
+impl Error
+{
+    /// The last error in `libcow`.
+    #[inline(always)] pub fn last() -> Self
+    {
+	Self(unsafe {ffi::cow_err()})
+    }
+}
+
+impl error::Error for Error{}
+impl fmt::Display for Error
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	const DEFAULT: &'static [u8] = b"unknown\0"; // must be `nul`'d
+	let cstr = unsafe {
+	    let ptr = ffi::cow_err_msg(self.0);
+	    if ptr.is_null() {
+		CStr::from_bytes_with_nul_unchecked(DEFAULT)
+	    } else {
+		let ptr = *ptr;
+		if ptr.is_null() {
+		    CStr::from_bytes_with_nul_unchecked(DEFAULT)
+		} else {
+		    CStr::from_ptr(ptr as *const i8)
+		}
+	    }
+	};
+	write!(f, "{}", cstr.to_string_lossy())
+    }
+}
+

cowslice/src/lib.rs

@@ -3,15 +3,13 @@
 
 mod ffi;
 
+pub mod error;
+pub use error::Error;
+
 #[cfg(test)]
 mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
     #[test]
     fn link_works() {
-	
 	unsafe {
 	    let raw_h = super::ffi::cow_create(100);
 	    assert_ne!(raw_h as usize, 0);