Merge pull request #2643 from jhscheer/tail_fix_for_gnutestsuite

tail: add fixes to pass "tail-2/tail-c.sh" from GNU's test suite

src/uu/tail/src/tail.rs

@@ -22,7 +22,7 @@ use chunks::ReverseChunks;
 use clap::{App, Arg};
 use std::collections::VecDeque;
 use std::fmt;
-use std::fs::File;
+use std::fs::{File, Metadata};
 use std::io::{stdin, stdout, BufRead, BufReader, Read, Seek, SeekFrom, Write};
 use std::path::Path;
 use std::thread::sleep;
@@ -32,6 +32,8 @@ use uucore::ringbuffer::RingBuffer;
 
 #[cfg(unix)]
 use crate::platform::stdin_is_pipe_or_fifo;
+#[cfg(unix)]
+use std::os::unix::fs::MetadataExt;
 
 pub mod options {
     pub mod verbosity {
@@ -189,7 +191,8 @@ pub fn uumain(args: impl uucore::Args) -> i32 {
                 continue;
             }
             let mut file = File::open(&path).unwrap();
-            if is_seekable(&mut file) {
+            let md = file.metadata().unwrap();
+            if is_seekable(&mut file) && get_block_size(&md) > 0 {
                 bounded_tail(&mut file, &settings);
                 if settings.follow {
                     let reader = BufReader::new(file);
@@ -437,6 +440,8 @@ fn unbounded_tail<T: Read>(reader: &mut BufReader<T>, settings: &Settings) {
 
 fn is_seekable<T: Seek>(file: &mut T) -> bool {
     file.seek(SeekFrom::Current(0)).is_ok()
+        && file.seek(SeekFrom::End(0)).is_ok()
+        && file.seek(SeekFrom::Start(0)).is_ok()
 }
 
 #[inline]
@@ -464,3 +469,14 @@ fn parse_num(src: &str) -> Result<(usize, bool), ParseSizeError> {
 
     parse_size(size_string).map(|n| (n, starting_with))
 }
+
+fn get_block_size(md: &Metadata) -> u64 {
+    #[cfg(unix)]
+    {
+        md.blocks()
+    }
+    #[cfg(not(unix))]
+    {
+        md.len()
+    }
+}

tests/by-util/test_tail.rs

@@ -425,3 +425,23 @@ fn test_tail_num_with_undocumented_sign_bytes() {
         .succeeds()
         .stdout_is("efghijklmnopqrstuvwxyz");
 }
+
+#[test]
+#[cfg(unix)]
+fn test_tail_bytes_for_funny_files() {
+    // gnu/tests/tail-2/tail-c.sh
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+    for &file in &["/proc/version", "/sys/kernel/profiling"] {
+        if !at.file_exists(file) {
+            continue;
+        }
+        let args = ["--bytes", "1", file];
+        let result = ts.ucmd().args(&args).run();
+        let exp_result = unwrap_or_return!(expected_result(&ts, &args));
+        result
+            .stdout_is(exp_result.stdout_str())
+            .stderr_is(exp_result.stderr_str())
+            .code_is(exp_result.code());
+    }
+}