Use File::metadata to get file size and not libc methods

src/unix.rs

@@ -1,7 +1,8 @@
 extern crate libc;
 
-use std::mem::MaybeUninit;
-use std::os::unix::io::RawFd;
+use std::fs::File;
+use std::mem::ManuallyDrop;
+use std::os::unix::io::{FromRawFd, RawFd};
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::{io, ptr};
 
@@ -304,19 +305,10 @@ fn page_size() -> usize {
 }
 
 pub fn file_len(file: RawFd) -> io::Result<u64> {
-    #[cfg(not(any(target_os = "linux", target_os = "emscripten", target_os = "l4re")))]
-    use libc::{fstat, stat};
-    #[cfg(any(target_os = "linux", target_os = "emscripten", target_os = "l4re"))]
-    use libc::{fstat64 as fstat, stat64 as stat};
-
+    // SAFETY: We must not close the passed-in fd by dropping the File we create,
+    // we ensure this by immediately wrapping it in a ManuallyDrop.
     unsafe {
-        let mut stat = MaybeUninit::<stat>::uninit();
-
-        let result = fstat(file, stat.as_mut_ptr());
-        if result == 0 {
-            Ok(stat.assume_init().st_size as u64)
-        } else {
-            Err(io::Error::last_os_error())
-        }
+        let file = ManuallyDrop::new(File::from_raw_fd(file));
+        Ok(file.metadata()?.len())
     }
 }

src/windows.rs

@@ -1,8 +1,10 @@
 #![allow(non_camel_case_types)]
 #![allow(non_snake_case)]
 
+use std::fs::File;
+use std::mem::ManuallyDrop;
 use std::os::raw::c_void;
-use std::os::windows::io::RawHandle;
+use std::os::windows::io::{FromRawHandle, RawHandle};
 use std::{io, mem, ptr};
 
 type BOOL = i32;
@@ -82,22 +84,6 @@ pub struct FILETIME {
     pub dwHighDateTime: DWORD,
 }
 
-#[repr(C)]
-struct BY_HANDLE_FILE_INFORMATION {
-    dwFileAttributes: DWORD,
-    ftCreationTime: FILETIME,
-    ftLastAccessTime: FILETIME,
-    ftLastWriteTime: FILETIME,
-    dwVolumeSerialNumber: DWORD,
-    nFileSizeHigh: DWORD,
-    nFileSizeLow: DWORD,
-    nNumberOfLinks: DWORD,
-    nFileIndexHigh: DWORD,
-    nFileIndexLow: DWORD,
-}
-
-type LPBY_HANDLE_FILE_INFORMATION = *mut BY_HANDLE_FILE_INFORMATION;
-
 extern "system" {
     fn GetCurrentProcess() -> HANDLE;
 
@@ -124,11 +110,6 @@ extern "system" {
 
     fn FlushFileBuffers(hFile: HANDLE) -> BOOL;
 
-    fn GetFileInformationByHandle(
-        hFile: HANDLE,
-        lpFileInformation: LPBY_HANDLE_FILE_INFORMATION,
-    ) -> BOOL;
-
     fn FlushViewOfFile(lpBaseAddress: LPCVOID, dwNumberOfBytesToFlush: SIZE_T) -> BOOL;
 
     fn UnmapViewOfFile(lpBaseAddress: LPCVOID) -> BOOL;
@@ -526,16 +507,10 @@ fn allocation_granularity() -> usize {
 }
 
 pub fn file_len(handle: RawHandle) -> io::Result<u64> {
-    let info = unsafe {
-        let mut info = mem::MaybeUninit::<BY_HANDLE_FILE_INFORMATION>::uninit();
-
-        let ok = GetFileInformationByHandle(handle, info.as_mut_ptr());
-        if ok == 0 {
-            return Err(io::Error::last_os_error());
-        }
-
-        info.assume_init()
-    };
-
-    Ok((info.nFileSizeHigh as u64) << 32 | info.nFileSizeLow as u64)
+    // SAFETY: We must not close the passed-in fd by dropping the File we create,
+    // we ensure this by immediately wrapping it in a ManuallyDrop.
+    unsafe {
+        let file = ManuallyDrop::new(File::from_raw_handle(handle));
+        Ok(file.metadata()?.len())
+    }
 }