cat: avoid pipe() if stdout is pipe

Author: oech3

src/uu/cat/src/splice.rs

@@ -24,32 +24,43 @@ pub(super) fn write_fast_using_splice<R: FdReadable, S: AsRawFd + AsFd>(
     write_fd: &S,
 ) -> CatResult<bool> {
     use nix::fcntl::{FcntlArg, fcntl};
-    let (pipe_rd, pipe_wr) = pipe()?;
     // improve performance
-    let _ = fcntl(
+    if fcntl(
         write_fd,
         FcntlArg::F_SETPIPE_SZ(MAX_ROOTLESS_PIPE_SIZE as i32),
-    );
-
-    loop {
-        match splice(&handle.reader, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
-            Ok(n) => {
-                if n == 0 {
-                    return Ok(false);
+    )
+    .is_ok()
+    {
+        loop {
+            match splice(&handle.reader, &write_fd, MAX_ROOTLESS_PIPE_SIZE) {
+                Ok(0) => return Ok(false),
+                Ok(_) => {}
+                Err(_) => return Ok(true),
+            }
+        }
+    } else {
+        // output is not pipe. Needs hihi cost pipe as broker to use splice()
+        let (pipe_rd, pipe_wr) = pipe()?;
+        loop {
+            match splice(&handle.reader, &pipe_wr, MAX_ROOTLESS_PIPE_SIZE) {
+                Ok(n) => {
+                    if n == 0 {
+                        return Ok(false);
+                    }
+                    if splice_exact(&pipe_rd, write_fd, n).is_err() {
+                        // If the first splice manages to copy to the intermediate
+                        // pipe, but the second splice to stdout fails for some reason
+                        // we can recover by copying the data that we have from the
+                        // intermediate pipe to stdout using normal read/write. Then
+                        // we tell the caller to fall back.
+                        copy_exact(&pipe_rd, write_fd, n)?;
+                        return Ok(true);
+                    }
                 }
-                if splice_exact(&pipe_rd, write_fd, n).is_err() {
-                    // If the first splice manages to copy to the intermediate
-                    // pipe, but the second splice to stdout fails for some reason
-                    // we can recover by copying the data that we have from the
-                    // intermediate pipe to stdout using normal read/write. Then
-                    // we tell the caller to fall back.
-                    copy_exact(&pipe_rd, write_fd, n)?;
+                Err(_) => {
                     return Ok(true);
                 }
             }
-            Err(_) => {
-                return Ok(true);
-            }
         }
     }
 }