gdlib 0.2.5

Rust library for editing Geometry Dash savefiles
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//! Here lies the decryption functions for GD savefiles
use std::{error::Error, fs, io::Read};

use base64::{Engine, engine::general_purpose};
use flate2::read::DeflateDecoder;

use crate::utils::get_local_levels_path;

/// Decompresses a `Vec<u8>` of a base64ed gzip-compressed payload.
///
/// # Arguments
/// * `data`: compressed input data
///
/// Returns decompressed base64ed gzip as a `Vec<u8>` if it sucessfully decoded, otherwise return Error
pub fn decompress(data: Vec<u8>) -> Result<Vec<u8>, Box<dyn Error>> {
    // convert from url-safe base64
    let replaced = data
        .iter()
        .filter_map(|c| match c {
            b'-' => Some(b'+'),
            b'_' => Some(b'/'),
            b'\0' => None,
            _ => Some(*c),
        })
        .collect::<Vec<u8>>();

    // dbg!(vec_as_str(&replaced[..100].to_vec()));

    // remove all trailing null chars
    let last_non_null = replaced.iter().rposition(|&c| c != 0).unwrap_or(0);
    // decode DEFLATE payload
    let decoded = general_purpose::STANDARD.decode(&replaced[..last_non_null + 1])?;
    let sliced = &decoded[10..];

    let mut decoder = DeflateDecoder::new(sliced);
    let mut decompressed_buf = Vec::new();

    decoder.read_to_end(&mut decompressed_buf)?;

    Ok(decompressed_buf)
}

/// Decrypts data by xoring with key 11 and decompressing it.
/// This is the algorithm used to decrypt GD savefiles.
///
/// # Arguments
/// * `data`: encrypted payload
///
/// Returns the raw file contents as a `Vec<u8>`
pub fn decrypt(data: Vec<u8>) -> Vec<u8> {
    decompress(data.iter().map(|c| *c ^ 11).collect()).unwrap()
}

/// Returns CCLocalLevels.dat decrypted if it exists
pub fn decode_levels_to_string() -> Result<String, Box<dyn Error>> {
    let savefile = fs::read(get_local_levels_path()?)?;
    let data = decrypt(savefile);

    Ok(String::from_utf8(data.to_vec()).unwrap())
}