sterror(3): added library for C-like error messages; Makefile: some efficiency changes

src/strerror.rs

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: FSFAP
+ *
+ * Copying and distribution of this file, with or without modification, are
+ * permitted in any medium without royalty provided the copyright notice and
+ * this notice are preserved.  This file is offered as-is, without any warranty.
+ */
+
+use std::ffi::{ c_int, c_char, CStr };
+
+/* binding to strerror(3p) */
+extern "C" { fn strerror(errnum: c_int) -> *mut c_char; }
+
+/* wrapper function for use in Rust */
+pub fn c_error(err: std::io::Error) -> String {
+	/* Get the raw OS error. If it’s None, what the hell is going on‽ */
+	let error = err.raw_os_error().unwrap_or_else(|| { panic!() }) as c_int;
+
+	/* Get a CStr from the error message so that it’s referenced and then
+	 * convert it to an owned value. If the string is not valid UTF-8, return
+	 * that error instead. */
+	match unsafe { CStr::from_ptr(strerror(error)) }.to_str() {
+		Ok(s) => s.to_owned(), // yay!! :D
+		Err(e) => e.to_string(), // awww :(
+	}
+}