Thursday, August 23, 2018

Release Management and my release tool for full and differential releases

In this post I'll discuss some of the common tasks I perform for release management, and a tool I created to help with it, release.exe. You can find release.exe's source code here on github.

Release Management : Your Mileage May Vary

If you're responsible for software release management, source control is a given--but what else does release management entail? That really depends... it depends on what you hold important, on what constraints come with your target environment(s), and on what customer requirements you have to contend with. Release management might mean nothing more than deploying the latest code from source control to a public cloud; or, it might be a very complex multi-step process involving release packaging, electronic or media transfer to a customer, security scans, patching, approval(s), and network transfers by client IT departments--where some of the process is out of your hands. Whether simple or complex, good release management requires discipline and careful tracking. A well-thought-out procedure, supported with some tools, makes all the difference.

In the release management I regularly perform, common tasks are these:

1. Packaging up a full release to ship to a location, where it will be delivered to the client, go through multiple security processing steps, and eventually end-up on-site, ready for deployment.
2. On-site deployment of an approved release to new or existing servers.

The most interesting new development in all of this has been being able to generate differential releases, where only files that have been changed are delivered. This adds several more common tasks:

3. Packaging up a partial release (just what's changed) to ship to a location, and go through the same processing and approval steps.
4. On-site deployment of an approved partial release to new or existing servers.

Differential releases are massively valuable, especially when your full release might be tens of thousands of files (perhaps spanning multiple DVDs), whereas an update might have only changed a handful of files that take up 1/10th of a DVD. However, getting differential releases to work smoothly and seamlessly requires some careful attention to detail. Most importantly, you need a means to verify what you end up with is a complete, intact release.

To help with release packaging and on-site release verification, I created the release.exe command for Windows. Let's take a look at what it can do.

Hashing: a way to verify that a file has the expected contents

My release.exe command borrows an idea from my Alpha Micro minicomputer days: file hashes and hashed directory files. Back then, our DIR command had a very useful /HASH switch which would give us a hash code for a file, such as 156-078-940-021. Changing even a single byte of a file would yield a dramatically different hash.

When we would ship releases to customers, we would include a directory file of every file with its hash code. On the receiving end, a client could use a verify command which would read the hashed directory file and compare it against the computed hash of each file on the local system--displaying any discrepencies found. This process worked beautifully, and I've always missed having it on Windows. Now I have a version of the same concept in a tool I can use on Windows.

The release command can generate a file hash, with the command release hash:

Command form: release hash file

The hash is a partial MD5 hash. Why partial? Well, the entire hash is really long (20 segments), which is rather onerous if you need to send a hash code to someone or discuss it with someone else. So, I've shortened it to the the first two and last two segements of the full MD5 hash. Since the hash will change dramatically if even one byte changes, this is perfectly adequate for our puposes.

Here's a sample output:

path> release hash readme.txt
05B-8E8-D57-E7C readme.txt

path> release hash release.exe
BB9-AFA-F22-32A release.exe

File hashes will form the basis for packaging up releases with a manifest of files and their hashes; and for verifying those manifests on the receiving side.

Creating A Full Release Manifest

To generate a complete release, we first get the files intended for the release in a folder with the name of the release. For example, if our application's latest changeset in source control was 3105, we might create a 3105_release folder. Within that we copy all of our release files, which will likely include many files and many subfolders.

With the release files copied, we can now use the release create command to create a release manifest:

Command form: release create release-name.txt

3105_release> release create 3105.txt
Creating manifest for c:\3105_release
F7C-2C3-AE1-4BC C:\3105_release\readme.txt
63A-EE0-17F-2D4 C:\3105_release\bin\appmain.dll
9AB-6F4-RE3-007 C:\3105_release\bin\security.dll
3B2-B16-5Ac-007 C:\3105_release\bin\service.dll
47C-08D-A42-FD5 C:\3105_release\bin\en-US\resources.dll
98D-1E1-399-A7A C:\3105_release\Content\css\site.css
652-8A0-52A-ED0 C:\3105_release\Views\Login\login.cshtml
179-488-E60-E22 C:\3105_release\Views\App\main.cshtml
77c-874-963-791 C:\3105_release\Views\App\add.cshtml
6E5-3B0-68C-349 C:\3105_release\Views\Admin\customize.cshtml
E02-C9C-A53-37C C:\3105_release\Views\Admin\settings.cshtml
F01-a37-eed-629 C:\3105_release\Views\Report\monthlysales.cshtml

The result of all this is simply to add one file to the release, 3105.txt in this case, which contains every file in the release and its hash. We also add release.exe itself to the release folder. This will give us what we need on the receiving end to verify the release is correct.

Verifying a Release

Once your release has gone through all of the permutations that get it to where it needs to go, and you have deployed it, you'll want to verify that it is complete and intact. Because the release shipped with release.exe and the manifest .txt file, you can easily verify your release by opening a command window, CDing to the root of where the release was deployed to, and using the release verify command.

Command form: release verify release-name.txt

If every file in the manifest is present and has the expected hash, you'll see Verified Release in green.

c:\InetPub\wwwroot> release verify 3105.txt
8713 files checked
Release Verified

If on the other hand there are differences, you will see one or more errrors listed in yellow or red. Yellow indicates a file is present but doesn't have the expected hash. Red indicates a missing file.

c:\InetPub\wwwroot> release verify 3105.txt
FILE NOT FOUND   c:\3105_release\Views\Report\summary.cshtml
A41-BBC-B4B-125  c:\3105_release\Content\css\site.css - ERROR: file is different
782-661-022-411  c:\3105_release\web.config - ERROR: file is different
8713 files checked
3 error(s)

In reviewing the results, note that it may well be normal for a file or two to be different. For example, an ASP.NET web application might have a different web.config file, with settings specific to the target environment.

This simple procedure, which generally takes under a minute even for large releases, is a huge confidence builder that your release is right. If you're in a position where processing steps sometimes lose files, mangle files, or rename files, using release.exe can detect and warn you about all of that.

Creating A Differential Release

At the start of this article I mentioned differential releases, where only changed files are provided. You can generate a differential release (and its manifest .txt file) with the release diff command.

Command form: release diff release-name.txt prior-release-name.txt

Up until now, we have seen variations of the release command that create manifest .txt files or verify them. The release diff command is different: it will not only generate a manifest .txt file, it will also compare it to the prior full release's manfest .txt file--and then delete files from the release folder that have not changed. For this reason, a prominent warning is displayed. The operator must press Y to continue, after confirming they are in the directory they want to be and wish to proceed. Be careful you only run this command from a folder where you intend files to be removed.

Let's say some time has passed since your last full release (3105) and you now wish to issue release 3148--but only a dozen or so files that have changed.

1. You start by creating a 3148_release folder and publishing all of your release files to that folder. So far, this is identical to the process used for full releases.
2. You copy into the folder release.exe and the manifest from the last full release, 3105.txt.
3. Next, you use the release diff command to create a differential release:

3148_release> release diff 3148.txt 3105.txt
Differential release:
    New release manifest file ............ 3148.txt
    Prior release manifest file .......... 3105.txt
    Files common to prior release and this reease will be DELETED from this folder, leaving only new/changed files.

WARNING: This command will DELETE FILES from c:\3148_release\
Are you sure? Type Y to proceed 

3. After confirming this is what you want to do, you press Y and release.exe goes to work.
4. When release.exe is finished, you will see a summary of what it did:

Differential release created:
    Release manifest file .................. 3148.txt
    Files in Full Release .................. 8713
    Files in Differential Release .......... 12
    Files removed from this directory ...... 8701

Only 12 files were left in the directory, because the other 8701 files were identical to the last full release--so they don't need to be in the update. Your folder contains only the handful of files that have changed since last release, making for a smaller, simpler release package.

However, the 3148.txt manifest will list every file in the cumulative release and its hash. This is important, because on-site you will be overlaying this partial 3148 release on top of a prior 3105 full release. You want to be able to perform a release verify 3148.txt command which will verify the entire release, not just the changed files.

c:\InetPub\wwwroot> release verify 3148.txt
8713 files checked
Release Verified


The release.exe command has already made my life a lot easier, as someone who has to regularly generate releases--sometimes in a hurry. It is also making deployment a lot less problematic on the customer delivery side: the completeness and correctness of deployments can be immediately ascertained, and if there are problems the specific files are clearly identified.

Download source code

Saturday, August 4, 2018

My First Chrome Extension: Airgap Scan

Today I wrote my first Chrome Extension, and it was fun. I want to share what the experience was like. The code for this post may be found here:

Chrome has become a favorite browser to many, and if you do web development at all you have no doubt seen how important Chrome Extensions have become. Some of the ones I use frequently are WhatFont (tells me what font I am looking at when I hover over text in a page) and ng-inspector (AngularJS variable inspector), among many others.

It's always best to learn something new when you have a firm project idea in mind, something that needs to be created. Fortunately, I had a project in mind.

AirgapScan: An Extension That Scans Pages for Disallowed Internet URLs

Today I decided I was in need of a Chrome Extension to help verify whether my web site pages were air-gapped. What is air-gapping? Air-gapping is when your software has to be able to run in a location that allows no Internet access; for various reasons, there are security-minded customers with that requirement. Honoring this requirement is harder than you might think: as a modern developer, we tend to take Internet availability for granted. And, we frequently rely on open source libraries, many of which also take Internet availability for granted.

And so, having made changes to support air-gapping, it's important to test that we haven't missed an Internet reference somewhere. That's why I wanted this Chrome extension: when our testers visit one of our solution's web pages, I want the extension to report if there are airgap violations (that is, Internet access outside of the approved network).

The way I'd like this to work is as follows: you browse to a page in your application. If you want to check your air-gapping, you right-click the AirgapScan icon and select Scan Page. You'll either get a happy green message box telling you all is well, or a red alert box listing the HREF(s) found in the page that are disallowed.

Hello, World

But you have to walk before you can run, so next up was to take a basic tutorial and create a simple "Hello, World!" extension in order to get familiar with the basics. I stumbled across an excellent getting started tutorial by Jake Prins, How to Create and Publish a Chrome Extension in 20 Minutes which walked me through the basics.

I was surprised and pleased to learn just how easy it is to write a Chrome Extension. In a nutshell, here are the basics:

  1. Web Technologies. Your extension is written in familiar HTML, CSS, and JavaScript.
  2. Developer Mode. While developing, you can easily load and re-load your extension in Chrome as you make changes, making for a great interactive experience as you work. This is done by visiting chrome://extensions and switching on Developer Mode. When you want to load your extension, click LOAD UNPACKED and browse to the folder where your files are. It's a very simple process.
  3. Manifest. Your extension starts with a manifest.json file, in which you declare a number of things about your extension--including name, version, icon, permissions needed, and which css / script files it uses.
  4. Scripts. You'll write some JavaScript code to do your magic. Depending on what you do, you may have to create more than one based on Google's rules. Again, tutorials and documentation are your friend.
  5. You Can Use Your Favorite Libraries. Used to using jQuery? Or one of the many other popular libraries out there? It's fine to include those in your extension--just copy the .js/.css files to your extension folder and declare them in your manifest.
  6. Your Extension Can Do A Lot Of Things. In the tutorial I took, I learned I could control the page that is created when a new browser tab is opened. Later on, I learned how to scan the current page's DOM. You can also do things like add context menus to a selection on the page. It's a really powerful platform.
Creating the AirgapScan Extension

1. The Manifest

The first element of any Chrome Extension is the manifest, manifest.json.

  "manifest_version": 2,
  "name": "Airgap Scan",
  "author": "David Pallmann",
  "version": "1.0",
  "description": "Scans the page for Internet references. Useful for testing software meant for air-gapped environments (without public Internet access).",
  "background": {
"scripts": [ "background.js" ]
  "icons": {
"128": "icon-128.png"
  "browser_action": {
   "default_icon": "tab-icon.png",
   "default_title": "Airgap Scanner"
  "content_scripts": [
      "matches": [
  "css": ["jquery-confirm.min.css"],
      "js": ["jquery-2.2.4.min.js", "jquery-confirm.min.js", "content.js"]
  "permissions" : [

Key things to note about the manifest:

  • It lists required permissions, similar to what you do in a phone app. When the user installs, they'll be asked to confirm they are okay with the extension's required permissions. In my case, I had to list adding context menus as a a permission, since I want to use a context menu item to perform scans on-demand.
  • The background property, scripts property specifies one of my script files, background.js.
  • The content_scripts object declares some important things. 
    • The matches property indicates which URLs the extension is active for (all URLs, in my case). 
    • The css property lists CSS files we're including (jquery-confirm.min.css). 
    • The js property lists JavaScript files we're including: my own source file content.js, plus libraries jquery.js and jquery-confirm.js.

Why is my JavaScript code in two places (background.js and content.js)? Well, with Chrome extensions there are content scripts which run in the context of page (content.js). But you may also need a global script or page that is running for the lifetime of your extension (background.js).

2. Content.js

Content.js is my page-level JavaScript code. This includes the following important elements:

  • A message listener, whose purpose is to listen for the context menu's Scan Page command being clicked. When that happens, the listener invokes the airgapScan function.
  • The airgapScan function, which is the heart of the extension. It uses jQuery to find all the HREFs on the page. It discounts some of them, such as mailto: and javascript: links. The rest, it compares against the array of allowableNetworks. If the href partially matches any of the allowable networks, all is well. If not, an error is counted and the URL is added to a list of in-violation URLs. After scanning the HREFs on the page, a green message box (if no errors) or red alert box (displaying the problem URLs) is displayed.

// content.js

// This routes a message from background.js (context menu action selected) to the airgapScan function in this file.

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {

// airgapScan: scan the page, examine each href. Collect a list of non-allowable hrefs and display an alert.

function airgapScan() {

console.log('--- Airgap Scan ---');

var allowableNetworks = [ '://10.',       // allowed: [http|https]://10.x.x.x 
  '://'  // allowed: [http|https]://
var urlCount = 0;
var errorCount = 0;
var url;
var urls = [];
var errList = '';
var listAll = false;

$("a").each(function() {
if (this.href != undefined) {
url = this.href;
if (url!=null && url!='' && url.indexOf('javascript:')==-1 && url.indexOf('mailto:')==-1) {
var error = true;
for (var p = 0; p < allowableNetworks.length; p++) {
if (url.indexOf(allowableNetworks[p])!=-1) {
error = false;
if (error) {
console.error('URL outside of network detected: ' + url);
errList = errList + '
' + url;


if (listAll && urls.length > 0) {
for (var i = 0; i < urls.length; i++) {
console.log(i.toString() + ': ' + urls[i]);

console.log('--- end Airgap Scan - URLs: ' + urlCount.toString() + ', Errors: ' + errorCount.toString() + ' ---');

if (errorCount > 0) {
if (errorCount==1) {
//icon: 'fa fa-warning',
type: 'red',
title: 'Airgap Alert',
content: 'Warning: Airgrap scan found 1 url that violates airgap rules:
' + errList,

useBootstrap: false
else {
//icon: 'fa fa-warning',
type: 'red',
title: 'Airgap Alert',
content: 'Warning: Airgrap scan found ' + errorCount.toString() + ' urls that violate airgap rules:
' + errList,

useBootstrap: false
else {
title: 'Airgap OK',
type: 'green',
content: 'All good: No airgap errors found',
useBootstrap: false

// Default state is that the user initiates a scan from the context menu. Uncomment the line below if you want the scan to automatically run when a page loads. 

3. Background.js

Background.js is the lifetime-of-the-extension JavaScript file. It contains
  • A call to Chrome.contextMenus.create, which adds a context menu item to the extension, available to the user by right-clicking it's icon.
  • A listener to respond to the menu item being clicked. This in turns sends a message to content.js to please invoke the airgapScan method.

// Add "Scan page" action to extension context menu.

"id": "AG_ScanPage",
    title: "Scan Page",
    contexts: ["browser_action"],
    onclick: function() {

// When context menu item is selected, send a message to context.js to run an airgap Scan.

chrome.contextMenus.onClicked.addListener(function(info, tab) {
  if (tab && info.menuItemId=="AG_ScanPage")
    chrome.tabs.sendMessage(, {args: null }, function(response) {

4. Library Files

As mentioned earlier, we are using a few libraries: jquery and jquery-confirm. The .js and .css files for them are included in the folder, and are referenced in the manifest.

5. Icons

Lastly, we have some icons in different sizes. The icon for AirgapScan is shown below.

And that's it. Time from first-time-hello-world-extension to AirgapScan was just a few hours on a Saturday. 

AirgapScan in Action

As I developed AirgapScan, I continually tested in chrome://extensions. When I had an update, I would REMOVE and then LOAD UNPACKED to get the latest changes applied, then visit a fresh page to test it out.

After visiting a page to be tested, the AG icon is visible. Hovering over it shows its name in a tooltip. Right-clicking it shows the Scan Page context menu that the extension code added.

Clicking Scan Page quickly comes back with a message box with the results of the scan. If one or more in-violation HREFs are found, a red alert box itemizes them.

If no violations are found, a green Airgap OK message appears.

You can download this extension here:

This was a lot of fun, plus I created something that my team needs. Chrome Extensions are surprisingly easy to create and the platform is well thought through which makes it a pleasure to use. I am highly motivated now to create other extensions.