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use std::ffi::CStr;
use std::io;
use std::ptr;
use windows_sys::Win32::Globalization::MultiByteToWideChar;
/// Convert `mb_string`, with the given character encoding `codepage`, to a UTF-16 string.
pub fn multibyte_to_wide(mb_string: &CStr, codepage: u32) -> Result<Vec<u16>, io::Error> {
if mb_string.is_empty() {
return Ok(vec![]);
}
// SAFETY: `mb_string` is null-terminated and valid.
let wc_size = unsafe {
MultiByteToWideChar(
codepage,
0,
mb_string.as_ptr() as *const u8,
-1,
ptr::null_mut(),
0,
)
};
if wc_size == 0 {
return Err(io::Error::last_os_error());
}
let mut wc_buffer = vec![0u16; usize::try_from(wc_size).unwrap()];
// SAFETY: `wc_buffer` can contain up to `wc_size` characters, including a null
// terminator.
let chars_written = unsafe {
MultiByteToWideChar(
codepage,
0,
mb_string.as_ptr() as *const u8,
-1,
wc_buffer.as_mut_ptr(),
wc_size,
)
};
if chars_written == 0 {
return Err(io::Error::last_os_error());
}
wc_buffer.truncate(usize::try_from(chars_written - 1).unwrap());
Ok(wc_buffer)
}
#[cfg(test)]
mod test {
use super::*;
use windows_sys::Win32::Globalization::CP_UTF8;
#[test]
fn test_multibyte_to_wide() {
// € = 0x20AC in UTF-16
let converted = multibyte_to_wide(c"€€", CP_UTF8);
const EXPECTED: &[u16] = &[0x20AC, 0x20AC];
assert!(
matches!(converted.as_deref(), Ok(EXPECTED)),
"expected Ok({EXPECTED:?}), got {converted:?}",
);
// boundary case
let converted = multibyte_to_wide(c"", CP_UTF8);
assert!(
matches!(converted.as_deref(), Ok([])),
"unexpected result {converted:?}"
);
}
}
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