Allow non UTF-8 time zones

Though it is unlikely that the time zone is stored in an encoding other
than UTF-8, it's not much work add to support for this edge case.

src/tz_macos.rs

@@ -1,22 +1,48 @@
-use core_foundation_sys::base::{CFRelease, CFTypeRef};
-use core_foundation_sys::string::{kCFStringEncodingUTF8, CFStringGetCStringPtr};
+use core_foundation_sys::base::{Boolean, CFRange, CFRelease, CFTypeRef};
+use core_foundation_sys::string::{kCFStringEncodingUTF8, CFStringGetBytes, CFStringGetLength};
 use core_foundation_sys::timezone::{CFTimeZoneCopySystem, CFTimeZoneGetName};
 
 pub(crate) fn get_timezone_inner() -> Result<String, crate::GetTimezoneError> {
-    unsafe {
-        if let Some(tz) = Dropping::new(CFTimeZoneCopySystem()) {
-            if let Some(name) = Dropping::new(CFTimeZoneGetName(tz.0)) {
-                let name = CFStringGetCStringPtr(name.0, kCFStringEncodingUTF8);
-                if !name.is_null() {
-                    let name = std::ffi::CStr::from_ptr(name);
-                    if let Ok(name) = name.to_str() {
-                        return Ok(name.to_owned());
-                    }
-                }
-            }
-        }
+    unsafe { get_timezone().ok_or(crate::GetTimezoneError::OsError) }
+}
+
+#[inline]
+unsafe fn get_timezone() -> Option<String> {
+    // The longest name in the IANA time zone database is 25 ASCII characters long.
+    const MAX_LEN: usize = 32;
+
+    // Get system time zone, and its name.
+    let tz = Dropping::new(CFTimeZoneCopySystem())?;
+    let name = Dropping::new(CFTimeZoneGetName(tz.0))?;
+
+    // Copy the name into the buffer.
+    let mut buf = [0; MAX_LEN];
+    let mut buf_bytes = 0;
+    let range = CFRange {
+        location: 0,
+        length: CFStringGetLength(name.0),
+    };
+    if CFStringGetBytes(
+        name.0,
+        range,
+        kCFStringEncodingUTF8,
+        b'\0',
+        false as Boolean,
+        buf.as_mut_ptr(),
+        buf.len() as isize,
+        &mut buf_bytes,
+    ) != range.length
+    {
+        // Could not convert the name.
+        None
+    } else if !(1..MAX_LEN as isize).contains(&buf_bytes) {
+        // The name should not be empty, or excessively long.
+        None
+    } else {
+        // Convert the name to a `String`.
+        let name = core::str::from_utf8(&buf[..buf_bytes as usize]).ok()?;
+        Some(name.to_owned())
     }
-    Err(crate::GetTimezoneError::OsError)
 }
 
 struct Dropping<T>(*const T);