Node.js: Unzip Async Await

March 14, 2021 · 2 min read

#javascript #nodejs #webdev #programming

Photo by Florian Steciuk on Unsplash


I am developing a new feature of DeckDeckGo for which I have to unzip a data in Firebase Functions.

It took more time than expected to code such a Node.js function, that’s why I am sharing this solution, hoping it might help you some day too 😇.


Unzipper

Node.js provides a compression module Zlib but, it does not support ZIP files. Luckily, we can use the library unzipper to handle these.

npm i unzipper --save

Unzip With Async Await

My new feature reads and writes data uploaded in Firebase Storage through streams. I also develop my code with a promises (async / await) approach. Therefore, both have to coexist.

To narrow down the following example, I replaced the cloud storage with local files handled with file system streams (fs ).

The function unzip instantiates a stream on the zip data which is piped with unzipper . Each entry are iterated and piped themselves to writable outputs. Summarized: the zip is opened and each files it contains are extracted.

unzip is called in a retro compatible top await function and, that’s basically it 🥳.

const {Parse} = require('unzipper'); const {createWriteStream, createReadStream} = require('fs'); const unzip = () => { const stream = createReadStream('/Users/david/data.zip').pipe(Parse()); return new Promise((resolve, reject) => { stream.on('entry', (entry) => { const writeStream = createWriteStream(`/Users/david/${entry.path}`); return entry.pipe(writeStream); }); stream.on('finish', () => resolve()); stream.on('error', (error) => reject(error)); }); }; (async () => { try { await unzip(); } catch (err) { console.error(err); } })();

Read To String With Async Await

I had to read files with streams too. Consequently and cherry on top, here is how I integrated these in my code.

const {createReadStream} = require('fs'); const read = () => { const stream = createReadStream('/Users/david/meta.json'); return new Promise((resolve, reject) => { let data = ''; stream.on('data', (chunk) => (data += chunk)); stream.on('end', () => resolve(data)); stream.on('error', (error) => reject(error)); }); }; (async () => { try { const meta = await read(); console.log({meta}); } catch (err) { console.error(err); } })();

It follows the same approach as previously and read the file content to an in memory string.


Summary

Coding is like a box of chocolates. You never know what you’re gonna get. Sometimes it should be quick, it takes time. Sometimes it should take so much time but, it goes fast — For-dev-rest Gump

To infinity and beyond!

David

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