codech.rs

use std::fs;
use std::io;
use std::path::PathBuf;
use structopt::{clap::ArgGroup, StructOpt};

#[derive(Clone, StructOpt, Debug)]
#[structopt(group = ArgGroup::with_name("action").required(true))]
struct Arguments {
    /// File containing a G4C key
    key_file: PathBuf,
    /// File to encode or decode
    source: PathBuf,
    /// Output file
    dest: PathBuf,
    /// Action to execute on the source file
    #[structopt(short, long, group = "action")]
    encode: bool,
    /// Action to execute on the source file
    #[structopt(short, long, group = "action")]
    decode: bool,
}

fn main() -> io::Result<()> {
    let args = Arguments::from_args();
    let key = fs::read_to_string(args.key_file)?;
    let key: Vec<u8> = key[5..40]
        .split_ascii_whitespace()
        .filter_map(|s| u8::from_str_radix(&s, 2).ok())
        .collect();
    let encode_lookup = [
        key[0] ^ key[1] ^ key[2] ^ key[3],
        key[3],
        key[2],
        key[2] ^ key[3],
        key[1],
        key[1] ^ key[3],
        key[1] ^ key[2],
        key[1] ^ key[2] ^ key[3],
        key[0],
        key[0] ^ key[3],
        key[0] ^ key[2],
        key[0] ^ key[2] ^ key[3],
        key[0] ^ key[1],
        key[0] ^ key[1] ^ key[3],
        key[0] ^ key[1] ^ key[2],
        0,
    ];

    let source = fs::read(args.source)?;
    const SHIFT: u8 = 4;
    let result = if args.encode {
        let mut encoded = Vec::with_capacity(source.len() * 2);
        const MASK: u8 = 0x0f;
        for byte in source {
            encoded.push(encode_lookup[(byte & MASK) as usize]);
            encoded.push(encode_lookup[(byte >> SHIFT) as usize]);
        }
        encoded
    } else {
        let mut decoded = Vec::with_capacity(source.len() / 2);
        let mut lookup = [0; 256];
        for (i, val) in encode_lookup.iter().enumerate() {
            lookup[*val as usize] = i as u8;
        }
        let decode_lookup = lookup;
        for bytes in source.chunks(2) {
            decoded.push(
                decode_lookup[bytes[0] as usize] | (decode_lookup[bytes[1] as usize] << SHIFT),
            );
        }
        decoded
    };
    fs::write(args.dest, &result)
}