lssh/src/main.rs

//! Evaluates [ssh_config(5)] files to find all **Host** declarations.
//!
//! **Include** directives will be resolved and evaluated. Pathnames will be expanded in the same
//! ways as in [ssh(1)], with the notable exception of runtime tokens (see "TOKENS" section in
//! [ssh_config(5)].
//!
//! Patterns given to any **Host** directive will be ignored (see "PATTERNS" section in
//! [ssh_config(5)]).
//!
//! [glob(7)]: <https://manpages.debian.org/buster/manpages/glob.7.en.html>
//! [ssh(1)]: <https://manpages.debian.org/testing/manpages-de/ssh.1.de.html>
//! [ssh_config(5)]: <https://manpages.debian.org/bullseye/openssh-client/ssh_config.5.en.html>

mod logger;
mod ssh;

use std::{
    collections::HashSet,
    env::{self},
    fs::File,
    io::{self, BufRead, BufReader, Read},
    path::{Path, PathBuf},
    process,
};

use clap::Parser;
use glob::glob;
use log::LevelFilter;

use crate::ssh::{SSH_SYSTEM_CONFIG, SSH_USER_CONFIG, Words, expand_inlude_args, is_host_pattern};

/// List host names in ssh_config(5) files
#[derive(Debug, Parser)]
struct Cli {
    /// This emulates the behaviour of the ssh(1) -F option
    #[arg(short = 'F')]
    file: Option<PathBuf>,
    /// Increase logging verbosity
    #[arg(short = 'v', action = clap::ArgAction::Count)]
    verbose: u8,
}

macro_rules! continue_if_error {
    ($l:tt: $e:expr) => {
        match $e {
            Ok(v) => v,
            Err(e) => {
                log::$l!("{e}");
                continue;
            }
        }
    };
}

macro_rules! io_error {
    ($kind:ident) => {
        Err(std::io::Error::new(
            std::io::ErrorKind::$kind,
            format!("{}", std::io::ErrorKind::$kind),
        ))
    };
    ($kind:ident, $prefix:expr) => {
        Err(io::Error::new(
            std::io::ErrorKind::$kind,
            format!("{}: {}", $prefix, std::io::ErrorKind::$kind),
        ))
    };
}

fn main() {
    let cli = Cli::parse();

    logger::init(match cli.verbose {
        0 => LevelFilter::Error,
        1 => LevelFilter::Info,
        2 => LevelFilter::Debug,
        3.. => LevelFilter::Trace,
    });

    let filenames = match &cli.file {
        Some(path) if path == "none" => vec![],
        Some(path) => vec![path.clone()],
        None => match env::home_dir() {
            Some(home) => vec![SSH_SYSTEM_CONFIG.into(), home.join(SSH_USER_CONFIG)],
            None => vec![SSH_SYSTEM_CONFIG.into()],
        },
    };

    let hosts = {
        let mut hosts = HashSet::new();
        for filename in filenames {
            match find_hosts(&filename) {
                Ok(h) => hosts.extend(h),
                Err(err) => {
                    eprintln!("{err}");
                    process::exit(1);
                }
            };
        }

        let mut hosts = Vec::from_iter(hosts);
        hosts.sort();
        hosts
    };

    for host in hosts {
        println!("{host}");
    }
}

fn find_hosts(filename: &Path) -> io::Result<HashSet<String>> {
    log::info!("reading config file: {}", filename.display());

    if !filename.exists() {
        return io_error!(NotFound, filename.display());
    }

    if filename.is_dir() {
        return io_error!(IsADirectory, filename.display());
    }

    let mut reader = {
        let file = File::open(filename)?;
        BufReader::new(file)
    };

    let mut hosts = HashSet::new();
    let mut buf = String::new();

    loop {
        buf.clear();
        let n = (&mut reader).take(1024 * 16).read_line(&mut buf)?;

        if n == 0 {
            return Ok(hosts);
        }

        let line = buf[..n].trim();

        let mut words: Words<'_> = line.into();
        let Some(Ok(keyword)) = words.next() else {
            continue;
        };

        match keyword {
            k if k.starts_with('#') => {}
            k if k.eq_ignore_ascii_case("include") => {
                find_hosts_in_include_directive(&mut hosts, words);
            }
            k if k.eq_ignore_ascii_case("host") => {
                find_hosts_in_host_directive(&mut hosts, words);
            }
            k => {
                log::trace!("skip unrelated keyword: '{k}'");
            }
        }
    }
}

fn find_hosts_in_include_directive(hosts: &mut HashSet<String>, words: Words<'_>) {
    for arg in words {
        let arg = continue_if_error!(warn: arg);

        // Expanding env vars before globbing is what ssh does as well.
        let pattern = continue_if_error!(warn: expand_inlude_args(arg));

        if arg != pattern {
            log::debug!("expanded include '{arg}' -> '{pattern}'");
        }

        let paths = continue_if_error!(warn: glob(&pattern));

        let mut matches = 0;
        for path in paths {
            matches += 1;

            let path = continue_if_error!(error: path);
            let ihosts = continue_if_error!(error: find_hosts(&path));

            hosts.extend(ihosts);
        }

        if matches < 1 {
            log::warn!("include {pattern} matched no files");
        }
    }
}

fn find_hosts_in_host_directive(hosts: &mut HashSet<String>, words: Words<'_>) {
    for word in words {
        let word = continue_if_error!(warn: word);

        if is_host_pattern(word) {
            log::debug!("skip host pattern: '{word}'");
            continue;
        }

        hosts.insert(word.to_string());
    }
}

#[cfg(test)]
mod tests {
    use clap::CommandFactory;

    use super::*;

    #[test]
    fn cli() {
        Cli::command().debug_assert();
    }

    #[test]
    fn find_hosts() {
        let mut hosts = HashSet::new();
        find_hosts_in_host_directive(&mut hosts, "foo.test".into());
        assert!(hosts.contains("foo.test"));

        find_hosts_in_host_directive(&mut hosts, "*".into());
        assert!(!hosts.contains("*"));

        find_hosts_in_host_directive(&mut hosts, "bar.test *.test".into());
        assert!(hosts.contains("bar.test"));
        assert!(!hosts.contains("*.test"));
    }
}