How to download and unzip a zip file in memory in NodeJs?

You need a library that can handle buffers. The latest version of adm-zip will do:

npm install adm-zip

My solution uses the http.get method, since it returns Buffer chunks.

Code:

var file_url="http://notepad-plus-plus.org/repository/7.x/7.6/npp.7.6.bin.x64.zip";

var AdmZip = require('adm-zip');
var http = require('http');

http.get(file_url, function(res) {
  var data = [], dataLen = 0; 

  res.on('data', function(chunk) {
    data.push(chunk);
    dataLen += chunk.length;

  }).on('end', function() {
    var buf = Buffer.alloc(dataLen);

    for (var i = 0, len = data.length, pos = 0; i < len; i++) { 
      data[i].copy(buf, pos); 
      pos += data[i].length; 
    } 

    var zip = new AdmZip(buf);
    var zipEntries = zip.getEntries();
    console.log(zipEntries.length)

    for (var i = 0; i < zipEntries.length; i++) {
      if (zipEntries[i].entryName.match(/readme/))
        console.log(zip.readAsText(zipEntries[i]));
    }
  });
});

The idea is to create an array of buffers and concatenate them into a new one at the end. This is due to the fact that buffers cannot be resized.

Update

This is a simpler solution that uses the request module to obtain the response in a buffer, by setting encoding: null in the options. It also follows redirects and resolves http/https automatically.

var file_url="https://github.com/mihaifm/linq/releases/download/3.1.1/linq.js-3.1.1.zip";

var AdmZip = require('adm-zip');
var request = require('request');

request.get({url: file_url, encoding: null}, (err, res, body) => {
  var zip = new AdmZip(body);
  var zipEntries = zip.getEntries();
  console.log(zipEntries.length);

  zipEntries.forEach((entry) => {
    if (entry.entryName.match(/readme/i))
      console.log(zip.readAsText(entry));
  });
});

The body of the response is a buffer that can be passed directly to AdmZip, simplifying the whole process.