saslauthd_yaml/src/main.rs

use std::fs::{metadata, set_permissions};
use std::io::{Error, ErrorKind, Read, Write};
use std::net::Shutdown;
use std::os::unix::fs::PermissionsExt;
use std::os::unix::net::{UnixListener, UnixStream};
use std::path::PathBuf;
use std::thread;

extern crate yaml_rust;

use yaml_rust::{YamlEmitter, YamlLoader};

const RESPONSE_NO: [u8; 4] = [0x0, 0x2, b'N', b'O'];
const RESPONSE_OK: [u8; 4] = [0x0, 0x2, b'O', b'K'];

struct SaslSock {
    name: PathBuf,
    listener: UnixListener,
}

impl SaslSock {
    pub fn new(name: &str) -> Result<SaslSock, Error> {
        let path = PathBuf::from(&name);
        if path.exists() {
            std::fs::remove_file(&path)?;
        }

        let listener = UnixListener::bind(&name)?;

        let mut perms = metadata(&path)?.permissions();
        perms.set_mode(0o0777);
        set_permissions(&path, perms)?;

        Ok(SaslSock {
            name: PathBuf::from(&name),
            listener,
        })
    }
}

impl Drop for SaslSock {
    fn drop(&mut self) {
        let _result = std::fs::remove_file(&self.name);
        println!("Shutting down");
    }
}

/// The saslauthd protocol transmits strings as
/// 16-bit unsigned network-byte-order lengths followed
/// by the string itself.
///
fn read_string(stream: &mut UnixStream) -> Result<String, Error> {
    let mut length_buffer = [0u8, 0u8];

    stream.read_exact(&mut length_buffer)?;
    let length = u16::from_be_bytes(length_buffer);

    let mut string_buffer = vec![0u8; length as usize];

    stream.read_exact(&mut string_buffer)?;

    match String::from_utf8(string_buffer) {
        Ok(str) => Ok(str),
        Err(_err) => Err(Error::new(ErrorKind::Other, "Invalid UTF-8 sent")),
    }
}

fn write_string(s: &str, stream: &mut UnixStream) -> Result<(), Error> {
    let length = s.len();

    if length > 0xffff {
        return Err(Error::new(ErrorKind::Other, "String too long to write"));
    }

    let length_buffer = [(length >> 8) as u8, (length & 0xff) as u8];

    stream.write_all(&length_buffer)?;
    stream.write_all(s.as_bytes())?;

    Ok(())
}

fn check_auth(mut stream: UnixStream) -> Result<(), Error> {
    let userid = read_string(&mut stream)?;
    let password = read_string(&mut stream)?;
    let service = read_string(&mut stream)?;
    let _realm = read_string(&mut stream)?;

    stream.write_all(&RESPONSE_NO)?;
    stream.shutdown(Shutdown::Both)?;

    Ok(())
}

fn handle_client(stream: UnixStream) {
    if let Err(error) = check_auth(stream) {
        eprint!("{}", error);
    }
}

fn main() -> std::io::Result<()> {
    let sock = SaslSock::new("/tmp/saslauthd.sock")?;

    // accept connections and process them, spawning a new thread for each one
    for stream in sock.listener.incoming() {
        match stream {
            Ok(stream) => {
                /* connection succeeded */
                thread::spawn(|| handle_client(stream));
            }
            Err(_err) => {
                /* connection failed */
                break;
            }
        }
    }
    Ok(())
}