wc: count_fast optimization using seek

src/uu/wc/src/count_fast.rs

@@ -10,7 +10,7 @@ use super::WordCountable;
 
 #[cfg(any(target_os = "linux", target_os = "android"))]
 use std::fs::OpenOptions;
-use std::io::{self, ErrorKind, Read};
+use std::io::{self, ErrorKind, Read, Seek, SeekFrom};
 
 #[cfg(unix)]
 use libc::{sysconf, S_IFREG, _SC_PAGESIZE};
@@ -100,7 +100,7 @@ pub(crate) fn count_bytes_fast<T: WordCountable>(handle: &mut T) -> (usize, Opti
             // would count up only to a couple of bytes.
             // This condition usually occurs for files in pseudo-filesystems like /proc, /sys
             // that report `st_size` in the multiples of system page size.
-            // In such cases - fall back on full read
+            // In such cases - attempt `seek()` for the end of file
             //
             // And finally a special case of input redirection in *nix shell:
             // `( wc -c ; wc -c ) < file` should return
@@ -126,6 +126,10 @@ pub(crate) fn count_bytes_fast<T: WordCountable>(handle: &mut T) -> (usize, Opti
                     // regular file or file from /proc, /sys and similar pseudo-filesystems
                     // with size that is NOT a multiple of system page size
                     return (stat.st_size as usize, None);
+                } else if let Some(file) = handle.inner_file() {
+                    if let Ok(n) = file.seek(SeekFrom::End(0)) {
+                        return (n as usize, None);
+                    }
                 }
             }
             #[cfg(any(target_os = "linux", target_os = "android"))]

src/uu/wc/src/countable.rs

@@ -17,12 +17,14 @@ use std::os::unix::io::AsRawFd;
 pub trait WordCountable: AsRawFd + Read {
     type Buffered: BufRead;
     fn buffered(self) -> Self::Buffered;
+    fn inner_file(&mut self) -> Option<&mut File>;
 }
 
 #[cfg(not(unix))]
 pub trait WordCountable: Read {
     type Buffered: BufRead;
     fn buffered(self) -> Self::Buffered;
+    fn inner_file(&mut self) -> Option<&mut File>;
 }
 
 impl WordCountable for StdinLock<'_> {
@@ -31,6 +33,9 @@ impl WordCountable for StdinLock<'_> {
     fn buffered(self) -> Self::Buffered {
         self
     }
+    fn inner_file(&mut self) -> Option<&mut File> {
+        None
+    }
 }
 
 impl WordCountable for File {
@@ -39,4 +44,8 @@ impl WordCountable for File {
     fn buffered(self) -> Self::Buffered {
         BufReader::new(self)
     }
+
+    fn inner_file(&mut self) -> Option<&mut File> {
+        Some(self)
+    }
 }