rework lookup_account_name to use LocalBox<Sid>

src/wrappers/lookup_account_name.rs

@@ -9,16 +9,9 @@ use windows_sys::Win32::Security::{LookupAccountNameW, SID_NAME_USE};
 use crate::{
     constants::SidNameUse,
     utilities::{buf_from_os, os_from_buf},
-    Sid,
+    LocalBox, Sid,
 };
 
-// Initial buffer size to use
-// If this isn't big enough, we'll try again
-const BUFFER_SIZE: usize = 256;
-
-// If we have to retry more than this many times, panic
-const MAX_RETRIES: usize = 5;
-
 /// Wraps [`LookupAccountNameW`](https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-lookupaccountnamew)
 ///
 /// Returns SID, referenced domain name, and use in that order.
@@ -42,85 +35,70 @@ const MAX_RETRIES: usize = 5;
 pub fn LookupAccountName(
     system_name: Option<impl AsRef<OsStr>>,
     account_name: impl AsRef<OsStr>,
-) -> io::Result<(Box<Sid>, OsString, SidNameUse)> {
-    // Buffers to hold the SID itself, the DOM name, and the SID name use
-    let mut sid_buf: Vec<u8> = vec![0; BUFFER_SIZE];
-    let mut ref_dom_name_buf: Vec<u16> = vec![0; BUFFER_SIZE];
-    let mut sid_name_use: SID_NAME_USE = 0;
-
+) -> io::Result<(LocalBox<Sid>, OsString, SidNameUse)> {
     // Convert the system name and account name into buffers
     let system_name = system_name.map(|s| buf_from_os(s.as_ref()));
     let account_name = buf_from_os(account_name.as_ref());
 
-    let mut retry_counter = 0;
-
-    loop {
-        // Increment the retry counter
-        retry_counter += 1;
-
-        // If the retry counter passes its threshold, we panic
-        assert!(
-            retry_counter <= MAX_RETRIES,
-            "LookupAccountName retried too many times"
-        );
-
-        // Get the current length
-        let mut sid_len: u32 = sid_buf.len() as u32;
-        let mut ref_dom_name_len: u32 = ref_dom_name_buf.len() as u32;
-
-        // Convert the system name to a pointer, defaulting to null
-        let system_name_ptr = match system_name {
-            Some(ref b) => b.as_ptr(),
-            None => null(),
-        };
-
-        // Save the original values
-        // If the call fails
-        let orig_sid_len = sid_len;
-        let orig_ref_dom_name_len = ref_dom_name_len;
+    // Convert the system name to a pointer, defaulting to null
+    let system_name_ptr = match system_name {
+        Some(ref b) => b.as_ptr(),
+        None => null(),
+    };
+    let mut sid_len: u32 = 0;
+    let mut ref_dom_name_len: u32 = 0;
+    let mut sid_name_use: SID_NAME_USE = 0;
 
-        let result = unsafe {
-            LookupAccountNameW(
-                system_name_ptr,
-                account_name.as_ptr(),
-                sid_buf.as_mut_ptr() as *mut _,
-                &mut sid_len,
-                ref_dom_name_buf.as_mut_ptr(),
-                &mut ref_dom_name_len,
-                &mut sid_name_use,
+    unsafe {
+        LookupAccountNameW(
+            system_name_ptr,
+            account_name.as_ptr(),
+            std::ptr::null_mut(),
+            &mut sid_len,
+            std::ptr::null_mut(),
+            &mut ref_dom_name_len,
+            &mut sid_name_use,
+        )
+    };
+
+    let (sid, mut ref_dom_name_buf) = if sid_len != 0 || ref_dom_name_len != 0 {
+        (
+            unsafe { LocalBox::<Sid>::try_allocate(true, sid_len as usize)? },
+            vec![0u16; ref_dom_name_len as usize],
+        )
+    } else {
+        return Err(io::Error::last_os_error());
+    };
+
+    let result = unsafe {
+        LookupAccountNameW(
+            system_name_ptr,
+            account_name.as_ptr(),
+            sid.as_ptr() as *mut _,
+            &mut sid_len,
+            ref_dom_name_buf.as_mut_ptr(),
+            &mut ref_dom_name_len,
+            &mut sid_name_use,
+        )
+    };
+
+    if result != 0 {
+        // Success! Return the appropriate values, converting as necessary
+
+        // Convert the referenced domain name into an OsString
+        let ref_dom_name = os_from_buf(&ref_dom_name_buf);
+
+        // Figure out SidNameUse
+        let sid_name_use = SidNameUse::from_raw(sid_name_use).unwrap_or_else(|| {
+            panic!(
+                "LookupAccountNameW returned unrecognized SidNameUse variant {:?}",
+                sid_name_use
             )
-        };
-
-        if result != 0 {
-            // Success! Return the appropriate values, converting as necessary
-
-            // Resize the SID buffer based on the SID length and convert to a Box
-            sid_buf.truncate(sid_len as usize);
-            let sid_box = sid_buf.into_boxed_slice();
-            let sid = unsafe { Box::from_raw(Box::into_raw(sid_box) as *mut Sid) };
-
-            // Convert the referenced domain name into an OsString
-            let ref_dom_name = os_from_buf(&ref_dom_name_buf);
-
-            // Figure out SidNameUse
-            let sid_name_use = SidNameUse::from_raw(sid_name_use).unwrap_or_else(|| {
-                panic!(
-                    "LookupAccountNameW returned unrecognized SidNameUse variant {:?}",
-                    sid_name_use
-                )
-            });
-
-            break Ok((sid, ref_dom_name, sid_name_use));
-        } else if sid_len != orig_sid_len || ref_dom_name_len != orig_ref_dom_name_len {
-            // Failure! They indicated a reallocation requirement
+        });
 
-            // Resize both the SID buffer and the referenced domain name buffer based
-            // on the indicated correct sizes
-            sid_buf.resize(sid_len as usize, 0);
-            ref_dom_name_buf.resize(ref_dom_name_len as usize, 0);
-        } else {
-            // Failure! We're not recovering
-            break Err(io::Error::last_os_error());
-        }
+        Ok((sid, ref_dom_name, sid_name_use))
+    } else {
+        // Failure! We're not recovering
+        Err(io::Error::last_os_error())
     }
 }