nanoforge 0.1.0

//! Defines the actions around unpacking compressed Docker files from the manifest.
use std::fs::File;
use std::io::Read;
use std::path::Path;
use serde_json::Value;
use tar::Archive;
use flate2::read::GzDecoder;


/// Reads a JSON file.
///
/// # Notes
/// This function is mainly used for reading the manifest.json file in the unpacked Docker image
/// directory so we can extract the layers.
///
/// # Arguments
/// * `path` - Path to the JSON file being read.
fn read_json_file<P: AsRef<Path>>(path: P) -> serde_json::Result<Value> {
    let mut file = File::open(path).unwrap();
    let mut contents = String::new();
    file.read_to_string(&mut contents).unwrap();
    serde_json::from_str(&contents)
}


/// Decompresses the layers from the Docker image and extracts them to a directory.
///
/// # Arguments
/// * `main_path` - The path to the compressed extracted layers from the Docker image.
/// * `unpack_path` - The path to where the layers will be extracted.
///
/// # Returns
/// The path to where the layers are extracted.
pub fn extract_layers(main_path: &str, unpack_path: &str) -> std::io::Result<String> {

    let manifest_path = std::path::Path::new(main_path).join("manifest.json");
    let blobs_dir = std::path::Path::new(main_path);
    let unpack_path = std::path::Path::new(unpack_path);

    if !unpack_path.exists() {
        std::fs::create_dir_all(&unpack_path)?;
    }

    let manifest = read_json_file(manifest_path).expect("Failed to read manifest.json");

    if let Some(layers) = manifest[0]["Layers"].as_array() {
        println!("Found {} layers in manifest", layers.len());
        for layer in layers {
            println!("Extracting layer: {}", layer);
            let base_path = blobs_dir;
            let layer_path = base_path.join(layer.as_str().unwrap());

            // Extract the layer's tarball to a directory
            let tar_file = File::open(layer_path)?;
            // Create a GzDecoder to handle the gzip decompression
            let decompressed = GzDecoder::new(tar_file);
            let mut archive = Archive::new(decompressed);
            archive.unpack(unpack_path).unwrap();
        }
    }
    else {
        println!("No layers found in manifest");
    }

    Ok(unpack_path.to_str().unwrap().to_string())
}