RGBCube/uutils-coreutils
1
Fork 0
mirror of https://github.com/RGBCube/uutils-coreutils synced 2025-07-28 11:37:44 +00:00
Code Issues Activity

Merge pull request #2885 from jfinkels/head-find-nth-line-from-end

Browse source 
head: refactor helper function find_nth_line_from_end()
This commit is contained in:
Sylvestre Ledru 2022-01-20 21:53:47 +01:00 • committed by GitHub
commit d64b32d121
No known key found for this signature in database
GPG key ID: 4AEE18F83AFDEB23
1 changed files with 98 additions and 38 deletions
Download patch file Download diff file Expand all files Collapse all files

136
src/uu/head/src/head.rs
View file

@ -3,10 +3,10 @@
// * For the full copyright and license information, please view the LICENSE
// * file that was distributed with this source code.
// spell-checker:ignore (vars) zlines BUFWRITER
// spell-checker:ignore (vars) zlines BUFWRITER seekable
use clap::{crate_version, App, Arg};
use std::convert::TryFrom;
use std::convert::{TryFrom, TryInto};
use std::ffi::OsString;
use std::io::{self, BufWriter, ErrorKind, Read, Seek, SeekFrom, Write};
use uucore::display::Quotable;
@ -291,16 +291,95 @@ fn read_but_last_n_lines(
Ok(())
}
fn head_backwards_file(input: &mut std::fs::File, options: &HeadOptions) -> std::io::Result<()> {
assert!(options.all_but_last);
/// Return the index in `input` just after the `n`th line from the end.
///
/// If `n` exceeds the number of lines in this file, then return 0.
///
/// The cursor must be at the start of the seekable input before
/// calling this function. This function rewinds the cursor to the
/// beginning of the input just before returning unless there is an
/// I/O error.
///
/// If `zeroed` is `false`, interpret the newline character `b'\n'` as
/// a line ending. If `zeroed` is `true`, interpret the null character
/// `b'\0'` as a line ending instead.
///
/// # Errors
///
/// This function returns an error if there is a problem seeking
/// through or reading the input.
///
/// # Examples
///
/// The function returns the index of the byte immediately following
/// the line ending character of the `n`th line from the end of the
/// input:
///
/// ```rust,ignore
/// let mut input = Cursor::new("x\ny\nz\n");
/// assert_eq!(find_nth_line_from_end(&mut input, 0, false).unwrap(), 6);
/// assert_eq!(find_nth_line_from_end(&mut input, 1, false).unwrap(), 4);
/// assert_eq!(find_nth_line_from_end(&mut input, 2, false).unwrap(), 2);
/// ```
///
/// If `n` exceeds the number of lines in the file, always return 0:
///
/// ```rust,ignore
/// let mut input = Cursor::new("x\ny\nz\n");
/// assert_eq!(find_nth_line_from_end(&mut input, 3, false).unwrap(), 0);
/// assert_eq!(find_nth_line_from_end(&mut input, 4, false).unwrap(), 0);
/// assert_eq!(find_nth_line_from_end(&mut input, 1000, false).unwrap(), 0);
/// ```
fn find_nth_line_from_end<R>(input: &mut R, n: usize, zeroed: bool) -> std::io::Result<usize>
where
R: Read + Seek,
{
let size = input.seek(SeekFrom::End(0))?;
let size = usize::try_from(size).unwrap();
let mut buffer = [0u8; BUF_SIZE];
let buffer = &mut buffer[..BUF_SIZE.min(size)];
let mut i = 0usize;
let mut lines = 0usize;
loop {
// the casts here are ok, `buffer.len()` should never be above a few k
input.seek(SeekFrom::Current(
-((buffer.len() as i64).min((size - i) as i64)),
))?;
input.read_exact(buffer)?;
for byte in buffer.iter().rev() {
match byte {
b'\n' if !zeroed => {
lines += 1;
}
0u8 if zeroed => {
lines += 1;
}
_ => {}
}
// if it were just `n`,
if lines == n + 1 {
input.seek(SeekFrom::Start(0))?;
return Ok(size - i);
}
i += 1;
}
if size - i == 0 {
input.seek(SeekFrom::Start(0))?;
return Ok(0);
}
}
}
fn head_backwards_file(input: &mut std::fs::File, options: &HeadOptions) -> std::io::Result<()> {
assert!(options.all_but_last);
match options.mode {
Modes::Bytes(n) => {
let size = input.metadata()?.len().try_into().unwrap();
if n >= size {
return Ok(());
} else {
input.seek(SeekFrom::Start(0))?;
read_n_bytes(
&mut std::io::BufReader::with_capacity(BUF_SIZE, input),
size - n,
@ -308,41 +387,10 @@ fn head_backwards_file(input: &mut std::fs::File, options: &HeadOptions) -> std:
}
}
Modes::Lines(n) => {
let mut buffer = [0u8; BUF_SIZE];
let buffer = &mut buffer[..BUF_SIZE.min(size)];
let mut i = 0usize;
let mut lines = 0usize;
let found = 'o: loop {
// the casts here are ok, `buffer.len()` should never be above a few k
input.seek(SeekFrom::Current(
-((buffer.len() as i64).min((size - i) as i64)),
))?;
input.read_exact(buffer)?;
for byte in buffer.iter().rev() {
match byte {
b'\n' if !options.zeroed => {
lines += 1;
}
0u8 if options.zeroed => {
lines += 1;
}
_ => {}
}
// if it were just `n`,
if lines == n + 1 {
break 'o i;
}
i += 1;
}
if size - i == 0 {
return Ok(());
}
};
input.seek(SeekFrom::Start(0))?;
let found = find_nth_line_from_end(input, n, options.zeroed)?;
read_n_bytes(
&mut std::io::BufReader::with_capacity(BUF_SIZE, input),
size - found,
found,
)?;
}
}
@ -459,6 +507,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
#[cfg(test)]
mod tests {
use std::ffi::OsString;
use std::io::Cursor;
use super::*;
fn options(args: &str) -> Result<HeadOptions, String> {
@ -580,4 +629,15 @@ mod tests {
assert!(read_n_bytes(&mut empty, 0).is_ok());
assert!(read_n_lines(&mut empty, 0, false).is_ok());
}
#[test]
fn test_find_nth_line_from_end() {
let mut input = Cursor::new("x\ny\nz\n");
assert_eq!(find_nth_line_from_end(&mut input, 0, false).unwrap(), 6);
assert_eq!(find_nth_line_from_end(&mut input, 1, false).unwrap(), 4);
assert_eq!(find_nth_line_from_end(&mut input, 2, false).unwrap(), 2);
assert_eq!(find_nth_line_from_end(&mut input, 3, false).unwrap(), 0);
assert_eq!(find_nth_line_from_end(&mut input, 4, false).unwrap(), 0);
assert_eq!(find_nth_line_from_end(&mut input, 1000, false).unwrap(), 0);
}
}