Remove unnecessary unsafety

1 files changed, 31 insertions, 3 deletions

diff --git a/talpid-core/src/firewall/windows/mod.rs b/talpid-core/src/firewall/windows/mod.rs
index d4b0b883d4..fa59611132 100644
--- a/talpid-core/src/firewall/windows/mod.rs
+++ b/talpid-core/src/firewall/windows/mod.rs
@@ -455,11 +455,13 @@ pub extern "system" fn log_sink(
     }
 }
 
+/// Convert `mb_string`, with the given character encoding `codepage`, to a UTF-16 string.
 fn multibyte_to_wide(mb_string: &CStr, codepage: u32) -> Result<Vec<u16>, io::Error> {
-    if unsafe { *mb_string.as_ptr() } == 0 {
+    if mb_string.is_empty() {
         return Ok(vec![]);
     }
 
+    // SAFETY: `mb_string` is null-terminated and valid.
     let wc_size = unsafe {
         MultiByteToWideChar(
             codepage,
@@ -475,8 +477,10 @@ fn multibyte_to_wide(mb_string: &CStr, codepage: u32) -> Result<Vec<u16>, io::Er
         return Err(io::Error::last_os_error());
     }
 
-    let mut wc_buffer = Vec::with_capacity(wc_size as usize);
+    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,
@@ -492,11 +496,35 @@ fn multibyte_to_wide(mb_string: &CStr, codepage: u32) -> Result<Vec<u16>, io::Er
         return Err(io::Error::last_os_error());
     }
 
-    unsafe { wc_buffer.set_len((chars_written - 1) as usize) };
+    wc_buffer.truncate(usize::try_from(chars_written - 1).unwrap());
 
     Ok(wc_buffer)
 }
 
+#[cfg(test)]
+mod test {
+    use super::multibyte_to_wide;
+    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:?}"
+        );
+    }
+}
+
 // Convert `result` into an option and log the error, if any.
 fn consume_and_log_hyperv_err<T>(
     action: &'static str,