Move part of libbase to Rust

native/src/base/misc.rs

@@ -1,4 +1,5 @@
 use std::cmp::min;
+use std::ffi::CStr;
 use std::fmt;
 use std::fmt::Arguments;
 
@@ -39,3 +40,77 @@ pub fn fmt_to_buf(buf: &mut [u8], args: Arguments) -> usize {
         0
     }
 }
+
+// The cstr! macro is inspired by https://github.com/Nugine/const-str
+
+macro_rules! const_assert {
+    ($s: expr) => {
+        assert!($s)
+    };
+}
+
+pub struct ToCStr<'a>(pub &'a str);
+
+impl ToCStr<'_> {
+    const fn assert_no_nul(&self) {
+        let bytes = self.0.as_bytes();
+        let mut i = 0;
+        while i < bytes.len() {
+            const_assert!(bytes[i] != 0);
+            i += 1;
+        }
+    }
+
+    pub const fn eval_len(&self) -> usize {
+        self.assert_no_nul();
+        self.0.as_bytes().len() + 1
+    }
+
+    pub const fn eval_bytes<const N: usize>(&self) -> [u8; N] {
+        let mut buf = [0; N];
+        let mut pos = 0;
+        let bytes = self.0.as_bytes();
+        let mut i = 0;
+        while i < bytes.len() {
+            const_assert!(bytes[i] != 0);
+            buf[pos] = bytes[i];
+            pos += 1;
+            i += 1;
+        }
+        pos += 1;
+        const_assert!(pos == N);
+        buf
+    }
+}
+
+#[macro_export]
+macro_rules! cstr {
+    ($s:literal) => {{
+        const LEN: usize = $crate::ToCStr($s).eval_len();
+        const BUF: [u8; LEN] = $crate::ToCStr($s).eval_bytes();
+        unsafe { CStr::from_bytes_with_nul_unchecked(&BUF) }
+    }};
+}
+
+#[macro_export]
+macro_rules! r_cstr {
+    ($s:literal) => {
+        cstr!($s).as_ptr()
+    };
+}
+
+pub unsafe fn ptr_to_str<'a, T>(ptr: *const T) -> &'a str {
+    CStr::from_ptr(ptr.cast()).to_str().unwrap_or("")
+}
+
+pub fn errno() -> &'static mut i32 {
+    // On Android, errno is obtained through the __errno function for thread local storage
+    extern "C" {
+        fn __errno() -> *mut i32;
+    }
+    unsafe { &mut *__errno() }
+}
+
+pub fn error_str() -> &'static str {
+    unsafe { ptr_to_str(libc::strerror(*errno())) }
+}