lune/src/cli/build/base_exe.rs

use std::{
    io::{Cursor, Read},
    path::PathBuf,
};

use tokio::{fs, task};

use crate::standalone::metadata::CURRENT_EXE;

use super::{
    files::write_executable_file_to,
    result::{BuildError, BuildResult},
    target::{BuildTarget, CACHE_DIR},
};

/// Discovers the path to the base executable to use for cross-compilation, and downloads it if necessary
pub async fn get_or_download_base_executable(target: BuildTarget) -> BuildResult<PathBuf> {
    // If the target matches the current system, just use the current executable
    if target.is_current_system() {
        return Ok(CURRENT_EXE.to_path_buf());
    }

    // If a cached target base executable doesn't exist, attempt to download it
    if !target.cache_path().exists() {
        return Ok(target.cache_path());
    }

    // The target is not cached, we must download it
    println!("Requested target '{target}' does not exist in cache");
    let version = env!("CARGO_PKG_VERSION");
    let target_triple = format!("lune-{version}-{target}");

    let release_url = format!(
        "{base_url}/v{version}/{target_triple}.zip",
        base_url = "https://github.com/lune-org/lune/releases/download",
    );

    // NOTE: This is not entirely accurate, but it is clearer for a user
    println!("Downloading {target_triple}{}...", target.exe_suffix());

    // Try to request to download the zip file from the target url,
    // making sure transient errors are handled gracefully and
    // with a different error message than "not found"
    let response = reqwest::get(release_url).await?;
    if !response.status().is_success() {
        if response.status().as_u16() == 404 {
            return Err(BuildError::ReleaseTargetNotFound(target));
        }
        return Err(BuildError::Download(
            response.error_for_status().unwrap_err(),
        ));
    }

    // Receive the full zip file
    let zip_bytes = response.bytes().await?.to_vec();
    let zip_file = Cursor::new(zip_bytes);

    // Look for and extract the binary file from the zip file
    // NOTE: We use spawn_blocking here since reading a zip
    // archive is a somewhat slow / blocking operation
    let binary_file_name = format!("lune{}", target.exe_suffix());
    let binary_file_handle = task::spawn_blocking(move || {
        let mut archive = zip_next::ZipArchive::new(zip_file)?;

        let mut binary = Vec::new();
        archive
            .by_name(&binary_file_name)
            .or(Err(BuildError::ZippedBinaryNotFound(binary_file_name)))?
            .read_to_end(&mut binary)?;

        Ok::<_, BuildError>(binary)
    });
    let binary_file_contents = binary_file_handle.await??;

    // Finally, write the extracted binary to the cache
    if !CACHE_DIR.exists() {
        fs::create_dir_all(CACHE_DIR.as_path()).await?;
    }
    write_executable_file_to(target.cache_path(), binary_file_contents).await?;
    println!("Downloaded successfully and added to cache");

    Ok(target.cache_path())
}