pipes.rs: don't mix raw write and buffered write

Author: oech3

src/uucore/Cargo.toml

@@ -170,7 +170,7 @@ parser-num = ["extendedbigdecimal", "num-traits"]
 parser-size = ["parser-num", "procfs"]
 parser-glob = ["glob"]
 parser = ["parser-num", "parser-size", "parser-glob"]
-pipes = []
+pipes = ["fs"]
 process = ["libc"]
 proc-info = ["tty", "walkdir"]
 quoting-style = ["i18n-common"]

src/uucore/src/lib/features/pipes.rs

@@ -139,12 +139,13 @@ where
                     // 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
+                    // intermediate pipe to stdout using raw read/write syscalls. Then
                     // we tell the caller to fall back.
                     debug_assert!(n <= MAX_ROOTLESS_PIPE_SIZE, "unexpected RAM usage");
-                    let mut drain = Vec::with_capacity(n);
-                    pipe_rd.take(n as u64).read_to_end(&mut drain)?;
-                    dest.write_all(&drain)?;
+                    let mut buf = Vec::with_capacity(n);
+                    let buf = buf.spare_capacity_mut();
+                    let (buf, _) = rustix::io::read(pipe_rd, &mut *buf)?;
+                    crate::io::write_all_raw(dest, buf)?;
                     return Ok(true);
                 }
             }
@@ -210,9 +211,11 @@ pub fn send_n_bytes(
                         }
                     } else {
                         debug_assert!(s <= MAX_ROOTLESS_PIPE_SIZE, "unexpected RAM usage");
-                        let mut drain = Vec::with_capacity(s);
-                        broker_r.take(s as u64).read_to_end(&mut drain)?;
-                        target.write_all(&drain)?;
+                        // drain pipe before fallback to raw write
+                        let mut buf = Vec::with_capacity(s);
+                        let buf = buf.spare_capacity_mut();
+                        let (buf, _) = rustix::io::read(broker_r, &mut *buf)?;
+                        crate::io::write_all_raw(&target, buf)?;
                         break true;
                     }
                 }