buf_copy: remove unnecessary flush

src/uucore/src/lib/features/buf_copy/linux.rs

@@ -13,6 +13,18 @@ use std::{
     os::fd::AsFd,
 };
 
+/// A readable file descriptor.
+pub trait FdReadable: Read + AsFd {}
+
+impl FdReadable for std::fs::File {}
+impl FdReadable for std::io::PipeReader {}
+
+/// A writable file descriptor.
+pub trait FdWritable: Write + AsFd {}
+
+impl FdWritable for std::fs::File {}
+impl FdWritable for std::io::PipeWriter {}
+
 /// Copy data from `Read` implementor `source` into a `Write` implementor
 /// `dest`. This works by reading a chunk of data from `source` and writing the
 /// data to `dest` in a loop.
@@ -24,10 +36,10 @@ use std::{
 /// # Arguments
 /// * `source` - `Read` implementor to copy data from.
 /// * `dest` - `Write` implementor to copy data to.
-pub fn copy_stream<R, S>(src: &mut R, dest: &mut S) -> UResult<()>
+pub fn copy_stream<R, W>(src: &mut R, dest: &mut W) -> UResult<()>
 where
-    R: Read + AsFd,
-    S: Write + AsFd,
+    R: FdReadable,
+    W: FdWritable,
 {
     // If we're on Linux or Android, try to use the splice() system call
     // for faster writing. If it works, we're done.
@@ -38,12 +50,5 @@ where
 
     // If the splice() call failed, fall back on slower writing.
     std::io::copy(src, dest)?;
-
-    // If the splice() call failed and there has been some data written to
-    // stdout via while loop above AND there will be second splice() call
-    // that will succeed, data pushed through splice will be output before
-    // the data buffered in stdout.lock. Therefore additional explicit flush
-    // is required here.
-    dest.flush()?;
     Ok(())
 }