Infinite loop when "input file is output file"

[TheHardew]

What version of bat are you using?
[paste the output of bat --version here]
bat 0.15.4
Describe the bug you encountered:
When input file is also an output file, an infinite loop can be created, where shell writes to a file, bat reads the file, the shell redirects it to the same file and bat has to read than again, ad infinitum.
To reproduce:

echo a > a
bat a b > b

Describe what you expected to happen?
bat should behave as cat; cat prints cat: b: input file is output file to stderr. While this behaviour could be useful, it has the potential to use up all the disk space and reduce nand lifespan.

How did you install bat?
pacman, Arch Linux

---

[paste the output of info.sh here]
system

$ uname -srm
Linux 5.8.9-zen2-1-zen x86_64

bat

$ bat --version
bat 0.15.4

$ env
ALACRITTY_LOG=/tmp/Alacritty-59883.log
COLORTERM=truecolor
DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/1000/bus
DISPLAY=:0
HOME=/home/lizzie
I3SOCK=/run/user/1000/sway-ipc.1000.720.sock
LANG=en_US.UTF-8
LANGUAGE=en_US:en
LC_ADDRESS=pl_PL.UTF-8
LC_COLLATE=pl_PL.UTF-8
LC_CTYPE=pl_PL.UTF-8
LC_MEASUREMENT=pl_PL.UTF-8
LC_MESSAGES=en_US.UTF-8
LC_MONETARY=pl_PL.UTF-8
LC_NAME=pl_PL.UTF-8
LC_NUMERIC=pl_PL.UTF-8
LC_PAPER=pl_PL.UTF-8
LC_TELEPHONE=pl_PL.UTF-8
LC_TIME=pl_PL.UTF-8
LOGNAME=lizzie
MAIL=/var/spool/mail/lizzie
OMF_CONFIG=/home/lizzie/.config/omf
OMF_PATH=/home/lizzie/.local/share/omf
PATH=/usr/local/sbin:/usr/local/bin:/usr/bin:/usr/bin/site_perl:/usr/bin/vendor_perl:/usr/bin/core_perl
PWD=/home/lizzie
QT_QPA_PLATFORM=wayland
SHELL=/usr/bin/fish
SHLVL=2
SWAYSOCK=/run/user/1000/sway-ipc.1000.720.sock
TERM=alacritty
USER=lizzie
WAYLAND_DISPLAY=wayland-0
XCURSOR_SIZE=24
XDG_RUNTIME_DIR=/run/user/1000
XDG_SEAT=seat0
XDG_SESSION_CLASS=user
XDG_SESSION_ID=1
XDG_SESSION_TYPE=tty
XDG_VTNR=1

bat_config

bat_wrapper

No wrapper script for 'bat'.

bat_wrapper_function

No wrapper function for 'bat'.

No wrapper function for 'cat'.

tool

$ less --version
less 551 (PCRE regular expressions)

[sharkdp]

Thank you very much for reporting this!

This should be fixed. I wonder how cat implements this feature? Apparently, it detects that file/inode behind the stdout file descriptor is the same as one of the input files.

[sharkdp]

yes. it's comparing inodes:

      if (out_isreg
          && stat_buf.st_dev == out_dev && stat_buf.st_ino == out_ino
          && lseek (input_desc, 0, SEEK_CUR) < stat_buf.st_size)
        {
          error (0, 0, _("%s: input file is output file"), quotef (infile));
          ok = false;
          goto contin;
        }

[sharkdp]

Here is a short demo program that shows how this can be solved on Unix systems:

//! 'cat'-like program that detects if the output is piped
//! to one of the input files, e.g.: cat a b c > b

use std::fs::File;
use std::io::{self, prelude::*, BufReader};
use std::os::unix::io::AsRawFd;

use nix::sys::stat::fstat;

fn main() {
    let stdout = io::stdout();
    let stat = fstat(stdout.as_raw_fd()).unwrap();
    let output_dev = stat.st_dev;
    let output_ino = stat.st_ino;

    for path in std::env::args().skip(1) {
        let file = File::open(path).unwrap();

        let file_stat = fstat(file.as_raw_fd()).unwrap();
        let file_dev = file_stat.st_dev;
        let file_ino = file_stat.st_ino;

        if file_dev == output_dev && file_ino == output_ino {
            eprintln!("input file is output file!");
            std::process::exit(1);
        }

        let buf_reader = BufReader::new(file);
        for line in buf_reader.lines() {
            println!("{}", line.unwrap());
        }
    }
}

[sharkdp]

Fixed in bat v0.17 (by @niklasmohrin).

[sharkdp]

Re-opening for now, see #1396