Use degit to download a template in your CLI tool.

#javascript #opensource #git #tarball

I found a file named "degit" in the Remotion source code.
Remotion helps you make videos programatically.

In this article, we will look at the following concepts:

What is Degit?
Build a simple degit function inspired by Remotion's degit file

What is Degit?

I do remember seeing "degit" mentioned in one of the Readmes in the open source, but I could not recall which repository it was so I googled what a degit means and found this degit npm package.

In simple terms, You can use degit to quickly make a copy of a Github repository by only downloading the latest commit
instead of the entire git history.

Visit the official npm package for degit to read more about this package.

You can use this degit package to download repos from Gitlab or Bitbucket as well so its not just limited to Github repositories.

# download from GitLab
degit gitlab:user/repo

# download from BitBucket
degit bitbucket:user/repo

degit user/repo
# these commands are equivalent
degit github:user/repo

Here's a sample usage in Javascript:

const degit = require('degit');

const emitter = degit('user/repo', {
    cache: true,
    force: true,
    verbose: true,
});

emitter.on('info', info => {
    console.log(info.message);
});

emitter.clone('path/to/dest').then(() => {
    console.log('done');
});

Build a simple degit function inspired by Remotion's degit file

To understand how to build a simple degit function, let’s break down the code from Remotion’s degit.ts file. This file implements a basic version of what the degit npm package does: fetching a GitHub repository’s latest state without downloading the full history.

1. Imports used

import https from 'https';
import fs from 'node:fs';
import {tmpdir} from 'node:os';
import path from 'node:path';
import tar from 'tar';
import {mkdirp} from './mkdirp';

https: Used to make a network request to fetch the repository.
fs: Interacts with the file system, such as writing the downloaded files.
tmpdir: Provides the system's temporary directory path.
path: Handles and transforms file paths.
tar: Extracts the contents of the tarball (compressed file).
mkdirp: A helper function to create directories recursively, provided in a separate file.

2: Fetching the Repository

export function fetch(url: string, dest: string) {
    return new Promise<void>((resolve, reject) => {
        https.get(url, (response) => {
            const code = response.statusCode as number;
            if (code >= 400) {
                reject(
                    new Error(
                        `Network request to ${url} failed with code ${code} (${response.statusMessage})`,
                    ),
                );
            } else if (code >= 300) {
                fetch(response.headers.location as string, dest)
                    .then(resolve)
                    .catch(reject);
            } else {
                response
                    .pipe(fs.createWriteStream(dest))
                    .on('finish', () => resolve())
                    .on('error', reject);
            }
        }).on('error', reject);
    });
}

URL Handling: The function checks if the request is successful (status codes below 300). If it’s a redirect (codes between 300 and 399), it follows the new URL. If it’s an error (codes 400+), it rejects the promise.
File Saving: The repository is downloaded and saved to the dest path using fs.createWriteStream.

3: Extracting the Repository

After downloading the repository, it’s necessary to extract the contents of the tarball:

function untar(file: string, dest: string) {
    return tar.extract(
        {
            file,
            strip: 1,
            C: dest,
        },
        [],
    );
}

Tar Extraction: This function extracts the contents of the .tar.gz file into the specified destination directory.

4: Putting It All Together

The main degit function ties everything together, handling directory creation, fetching, and extracting the repository:

export const degit = async ({
    repoOrg,
    repoName,
    dest,
}: {
    repoOrg: string;
    repoName: string;
    dest: string;
}) => {
    const base = path.join(tmpdir(), '.degit');
    const dir = path.join(base, repoOrg, repoName);
    const file = `${dir}/HEAD.tar.gz`;
    const url = `https://github.com/${repoOrg}/${repoName}/archive/HEAD.tar.gz`;

    mkdirp(path.dirname(file));
    await fetch(url, file);

    mkdirp(dest);
    await untar(file, dest);
    fs.unlinkSync(file);
};