Added functionality to extract .pack.xz files. The npm modules available to do this were a mess, being either outdated or refusing to build on windows. In order to achieve this, I wrote up a small java library which will extract these files. We simply pass the files we want to extract to the command line using a corresponding argument and it does the rest. This should be no issue as we will always have a JRE present on this launcher, whether that be bundled or already installed.

app/assets/js/assetguard.js

@@ -29,7 +29,8 @@ const mkpath = require('mkdirp');
 const async = require('async')
 const crypto = require('crypto')
 const AdmZip = require('adm-zip')
-const EventEmitter = require('events');
+const child_process = require('child_process')
+const EventEmitter = require('events')
 const {remote} = require('electron')
 
 // Classes
@@ -269,6 +270,21 @@ function _validateForgeJar(buf, checksums){
     return true
 }
 
+function _extractPackXZ(filePath){
+    const libPath = path.join(__dirname, '..', 'libraries', 'java', 'PackXZExtract.jar')
+    console.log(libPath)
+    const child = child_process.spawn('C:\\Program Files\\Java\\jre1.8.0_131\\bin\\javaw.exe', ['-jar', libPath, '-packxz', filePath])
+    child.stdout.on('data', (data) => {
+        console.log('minecraft:', data.toString('utf8'))
+    })
+    child.stderr.on('data', (data) => {
+        console.log('minecraft:', data.toString('utf8'))
+    })
+    child.on('close', (code, signal) => {
+        console.log('exited with code', code)
+    })
+}
+
 /**
  * Initiate an async download process for an AssetGuard DLTracker.
  * 
@@ -594,5 +610,6 @@ module.exports = {
     processDlQueues,
     instance,
     Asset,
-    Library
+    Library,
+    _extractPackXZ
 }