The blog of dlaa.me

Not romantically binding [promise-ring wraps Node.js callbacks with native ES6 Promises]

JavaScript Promises are a powerful way of working with asynchronous code. They make sequencing operations easy and offer a clear, predictable way to handle errors that might occur along the way. Much has been written about the benefits of Promises and I won't try to repeat it here.

What I do hope to do is make Promises a slightly more natural part of the Node.js development experience. In version 0.12.* (as well as in io.js), ES6 Promises are natively available. But the standard set of modules (such as File System) still use their original callback-based design and there's a bit of a disconnect between how you might want to write something and how you're able to. Fortunately, most of the Promise libraries that are already available include wrappers to convert callback-based functions into ones that return a Promise. However, most of those libraries assume you'll be using their custom implementation of Promise (from the "olden days" when that was the only option). And while different Promises/A+ implementations are meant to be interoperable, it seems silly to pull in a second Promise implementation when a perfectly good one is already available.

That's where promise-ring comes in: it's a tiny npm package that provides functions to convert typical callback-based APIs into their Promise-based counterparts using the V8 JavaScript engine's native Promise implementation. Briefly:

promise-ring is small, simple library with no dependencies that eases the use of native JavaScript Promises in projects without a Promise library.

Documentation is available in the README along with runnable samples demonstrating the use of each API. It's all quite simple and exactly what you'd expect. A bonus feature is the wrapAll function which makes it easier to work with modules that expose many different callback-based functions (such as the File System module; see below).

For an example of using promise-ring and Promises to simplify code, here is a typical callback-based snippet to copy a file onto itself:

var fs = require("fs");

// Copy a file onto itself using callbacks
fs.stat(file, function(err) {
  if (err) {
    console.error(err);
  } else {
    fs.readFile(file, encoding, function(errr, content) {
      if (errr) {
        console.error(errr);
      } else {
        fs.writeFile(file, content, encoding, function(errrr) {
          if (errrr) {
            console.error(errrr);
          } else {
            console.log("Copied " + file);
          }
        });
      }
    });
  }
});

And here's the same code converted to use Promises via promise-ring:

var pr = require("promise-ring");
var fsp = pr.wrapAll(require("fs"));

// Copy a file onto itself using Promises
fsp.stat(file)
  .then(function() {
    return fsp.readFile(file, encoding);
  })
  .then(function(content) {
    return fsp.writeFile(file, content, encoding);
  })
  .then(function() {
    console.log("Copied " + file);
  })
  .catch(console.error);

The second implementation is more concise, easier to follow, and DRY-er. That's the power of Promises! :)

Find out more by visiting promise-ring on GitHub or promise-ring in the npm gallery.

Lint-free documentation [markdownlint is a Node.js style checker and lint tool for Markdown files]

I'm a strong believer in using static analysis tools to identify problems and catch mistakes. The Node.js/io.js community has some great options for linting JavaScript code (ex: JSHint and ESLint), and I use them regularly. But code isn't the only important asset - documentation can be just as important to a project's success.

The open-source community has pretty much standardized on Markdown for documentation which is a great choice because it's easy to read, write, and understand. That said, Markdown has a syntax, so there are "right" and "wrong" ways to do things - and not all parsers handle nuances the same way (though the CommonMark effort is trying to standardize). In particular, there are constructs that can lead to missing/broken text in some parsers but which are not obviously wrong in the original Markdown.

To show what I mean, I created a Gist of common Markdown mistakes. If you're not a Markdown expert, you might learn something by comparing the source and output. :)

Aside: The Markdown parser used by GitHub is quite good - but many issues are user error and it can't (yet) read your mind.

 

You shouldn't need to be a Markdown expert to avoid silly mistakes - that's what we have computers for. When I looked around for a Node-based linter, I didn't see anything - but I did find a very nice implementation for Ruby by Mark Harrison. I don't tend to have Ruby available in my development environment, but I had an itch to scratch, so I installed it and added a couple of rules to Mark's tool for the checks I wanted. Mark kindly accepted the corresponding pull requests, and all was well.

Except that once I'd tasted of the fruit of Markdown linting, I wanted to integrate it into other workflows - many of which are exclusively Node-based. I briefly entertained the idea of creating a Node package to install Ruby then use it to install and run a Ruby gem - but that made my head hurt...

 

So I prototyped a Node version of markdownlint by porting a few rules over and then ran the idea by Mark. He was supportive (and raised some great points!), so I gradually ported the rest of the rules to JavaScript with the same numbering/naming system to make it easy for people to migrate between the two tools. Mark already had a fantastic test infrastructure and great documentation for rules, so I shamelessly reused both in the Node version. Configuration for JavaScript tools is typically JSON, so the Node version uses a slightly different format than Ruby (though both are simple/obvious). I started with a fully asynchronous API for efficiency, but ended up adding a synchronous version for scenarios where that's more convenient. I strived to achieve functional parity with the Ruby implementation (and continue to do so as Mark makes updates!), but duplicating the CLI was a non-goal (please have a look at the mdl gem if that's what you need).

If this sounds interesting, please have a look at markdownlint on GitHub. As of this writing, it supports the same set of ~40 rules that the Ruby implementation does - you can read all about them in Mark's fantastic Rules.md. markdownlint exposes a single API which can be called in an asynchronous or synchronous manner and accepts an options object to identify the files/strings to lint and the set of rules to apply. It returns a simple object that lists the items that were checked along with the line numbers for any violations. The documentation shows of all of this and includes examples of calling markdownlint from both gulp and Grunt.

 

To make sure markdownlint works well, I've integrated it into some of my own projects, including this blog which I wrote specifically to allow authoring in Markdown. That's a nice start, but it doesn't prove markdownlint can handle larger projects with significant documentation written by different people at different times. For that you'd need to integrate with a project like ESLint which has extensive documentation that's entirely Markdown-based.

So I did. :) Supporting ESLint was one of the motivating factors behind porting markdownlint to Node in the first place: I love the tool and use it in all my projects. The documentation is excellent, but every now and then I'd come across weird or broken text. After submitting a couple of pull requests with fixes, I decided adding a Markdown linter to their test script would be a better way to keep typos out of the documentation. It turns out this was on the team's radar as well, and they - especially project owner Nicholas - were very helpful and accommodating as I introduced markdownlint and tweaked things to satisfy some of the rules.

 

At this point, maybe I've convinced you markdownlint works for my own purposes and that it works for some other purposes, but it's likely you have special requirements or would like to "try before you buy". (Which seems an ironic thing to say about free software, but there's a cost to everything, so maybe it's not that unreasonable after all.) Well, I have just the thing for you:

An interactive markdownlint demo that runs in the browser!

Although browser support was not (is not!) a goal, the relevant code is all JavaScript with just one dependency (that itself offers browser support) and only two methods that need polyfills (trimLeft/trimRight). So it was actually fairly straightforward (with some help from Browserify) to create a standalone, offline-enabled web page that lets anyone use a (modern) browser to experiment with markdownlint and validate arbitrary content. To make it super easy to get started, I made some deliberate mistakes in the sample content for the demo - feel free to fix them for me. :)

 

In summary:

  • Markdown is great
  • It's easy to read and write
  • Sometimes it doesn't do what you think
  • There are tools to help
  • markdownlint is one of them
  • Get it for Ruby or Node
  • Or try it in the browser

Extensibility is a wonderful thing [A set of Visual Studio Code tasks for common npm functionality in Node.js and io.js]

Yesterday at its Build conference, Microsoft released the Visual Studio Code editor which is a lightweight, cross-platform tool for building web and cloud applications. I've been using internal releases for a while and highly recommend trying it out!

One thing I didn't know about until yesterday was support for Tasks to automate common steps like build and testing. As the documentation shows, there's already knowledge of common build frameworks, including gulp for Node.js and io.js. But for simple Node projects I like to automate via npm's scripts because they're simple and make it easy to integrate with CI systems like Travis. So I whipped up a simple tasks.json for Code that handles build, test, and lint for typical npm configurations. I've included it below for anyone who's interested.

Note: Thanks to metadata, the build and test tasks are recognized as such by Code and easily run with the default hotkeys Ctrl+Shift+B and Ctrl+Shift+T.

Enjoy!

 

{
  "version": "0.1.0",
  "command": "npm",
  "isShellCommand": true,
  "suppressTaskName": true,
  "tasks": [
    {
      // Build task, Ctrl+Shift+B
      // "npm install --loglevel info"
      "taskName": "install",
      "isBuildCommand": true,
      "args": ["install", "--loglevel", "info"]
    },
    {
      // Test task, Ctrl+Shift+T
      // "npm test"
      "taskName": "test",
      "isTestCommand": true,
      "args": ["test"]
    },
    {
      // "npm run lint"
      "taskName": "lint",
      "args": ["run", "lint"]
    }
  ]
}

Updated 2015-05-02: Added --loglevel info to npm install for better progress reporting

Updated 2016-02-27: Added isShellCommand, suppressTaskName, and updated args to work with newer versions of VS Code

Solving puzzles at 30,000 feet [An iterative solution for the "Is this a binary search tree?" programming problem]

Sitting on a plane recently looking for a distraction, I recalled a programming challenge by James Michael Hare: Little Puzzlers-Is Tree a Binary Search Tree?. All I had to work with was a web browser, so I used JavaScript to come up with a solution. James subsequently blogged a recursive implementation in C# which is quite elegant. Wikipedia's Binary search tree page uses the same approach and C++ for its verification sample.

Because I did things a little differently, I thought I'd share - along with a few thoughts:

/**
 * Determines if a tree of {value, left, right} nodes is a binary search tree.
 * @param {Object} root Root of the tree to examine.
 * @returns {Boolean} True iff root is a binary search tree.
 */
function isBinarySearchTree(root) {
  var wrapper, node, stack = [{ node: root }];
  while (wrapper = stack.pop()) {
    if (node = wrapper.node) {
      if ((node.value <= wrapper.min) || (wrapper.max <= node.value)) {
        return false;
      }
      stack.push({ node: node.left, min: wrapper.min, max: node.value },
                 { node: node.right, min: node.value, max: wrapper.max });
    }
  }
  return true;
}

Notes:

  • Tree nodes are assumed to have a numeric value and references to their left and right nodes (both possibly null).
    • I used the name value (vs. data) because it is slightly more specific.
  • I decided on an iterative algorithm because it has two notable advantages over recursion:
    • In the worst case for a tree with N nodes, an iterative solution has bookkeeping for N/2 nodes (when starting to process the leaf nodes of a balanced tree assuming nodes were queued) whereas a recursive solution has bookkeeping for all N nodes (when processing the deepest node of a completely unbalanced tree).
      • Because there are two recursive calls, I don't think tail recursion can be counted on to fix the worst-case behavior.
    • The memory used for bookkeeping by an iterative solution comes from the heap which is generally much larger than the thread stack.
    • To be fair, neither advantage is likely to be significant in practice - but they make good discussion points during an interview. :)
  • The iterative algorithm has a disadvantage:
    • Bookkeeping requires an additional object type (wrapper in the code above) which associates the relevant min and max bounds with pending node instances.
      • ... unless you avoid the wrapper by augmenting the node elements themselves.
        • ... which is quite easy in JavaScript thanks to its dynamic type system.
      • The creation/destruction of wrapper objects creates additional memory pressure.
        • Although these objects are short-lived and therefore low-impact for typical garbage collection algorithms.
  • I intended the code to be concise, so I made use of assignments in conditional expressions.
  • The code uses a stack (vs. a queue) because stacks tend to be simpler than queues - especially when implemented with an array.
  • I made use of the fact that comparing a number to undefined evaluates to false so I could avoid specifying explicit minimum/maximum values (as in the Wikipedia example) or making HasValue checks (as in James's example).
  • If you have a different approach or a suggestion to simplify this one, please share!
    • And note: I'm interested in algorithmic changes, not tweaks like removing extra parenthesis. :)

Supporting both sides of the Grunt vs. Gulp debate [check-pages is a Gulp-friendly task to check various aspects of a web page for correctness]

A few months ago, I wrote about grunt-check-pages, a Grunt task to check various aspects of a web page for correctness. I use grunt-check-pages when developing my blog and have found it very handy for preventing mistakes and maintaining consistency.

Two things have changed since then:

  1. I released multiple enhancements to grunt-check-pages that make it more powerful
  2. I extracted its core functionality into the check-pages package which works well with Gulp

 

First, an overview of the improvements; here's the change log for grunt-check-pages:

  • 0.1.0 - Initial release, support for checkLinks and checkXhtml.
  • 0.1.1 - Tweak README for better formatting.
  • 0.1.2 - Support page-only mode (no link or XHTML checks), show response time for requests.
  • 0.1.3 - Support maxResponseTime option, buffer all page responses, add "no-cache" header to requests.
  • 0.1.4 - Support checkCaching and checkCompression options, improve error handling, use gruntMock.
  • 0.1.5 - Support userAgent option, weak entity tags, update nock dependency.
  • 0.2.0 - Support noLocalLinks option, rename disallowRedirect option to noRedirects, switch to ESLint, update superagent and nock dependencies.
  • 0.3.0 - Support queryHashes option for CRC-32/MD5/SHA-1, update superagent dependency.
  • 0.4.0 - Rename onlySameDomainLinks option to onlySameDomain, fix handling of redirected page links, use page order for links, update all dependencies.
  • 0.5.0 - Show location of redirected links with noRedirects option, switch to crc-hash dependency.
  • 0.6.0 - Support summary option, update crc-hash, grunt-eslint, nock dependencies.
  • 0.6.1 - Add badges for automated build and coverage info to README (along with npm, GitHub, and license).
  • 0.6.2 - Switch from superagent to request, update grunt-eslint and nock dependencies.
  • 0.7.0 - Move task implementation into reusable check-pages package.
  • 0.7.1 - Fix misreporting of "Bad link" for redirected links when noRedirects enabled.

There are now more things you can validate and better diagnostics during validation. For information about the various options, visit the grunt-check-pages package in the npm repository.

 

Secondly, I started looking into Gulp as an alternative to Grunt. My blog's Gruntfile.js is the most complicated I have, so I tried converting it to a gulpfile.js. Conveniently, existing packages supported everything I already do (test, LESS, lint) - though not what I use grunt-check-pages for (no surprise).

Clearly, the next step was to create a version of the task for Gulp - but it turns out that's not necessary! Gulp's task structure is simple enough that invoking standard asynchronous helpers is easy to do inline. So all I really needed was to factor out the core functionality into a reusable method.

Here's how that looks:

/**
 * Checks various aspects of a web page for correctness.
 *
 * @param {object} host Specifies the environment.
 * @param {object} options Configures the task.
 * @param {function} done Callback function.
 * @returns {void}
 */
module.exports = function(host, options, done) { ... }

With that in place, it's easy to invoke check-pages - whether from a Gulp task or something else entirely. The host parameter handles log/error messages (pass console for convenience), options configures things in the usual fashion, and the done callback gets called at the end (with an Error parameter if anything went wrong).

Like so:

var gulp = require("gulp");
var checkPages = require("check-pages");

gulp.task("checkDev", [ "start-development-server" ], function(callback) {
  var options = {
    pageUrls: [
      'http://localhost:8080/',
      'http://localhost:8080/blog',
      'http://localhost:8080/about.html'
    ],
    checkLinks: true,
    onlySameDomain: true,
    queryHashes: true,
    noRedirects: true,
    noLocalLinks: true,
    linksToIgnore: [
      'http://localhost:8080/broken.html'
    ],
    checkXhtml: true,
    checkCaching: true,
    checkCompression: true,
    maxResponseTime: 200,
    userAgent: 'custom-user-agent/1.2.3',
    summary: true
  };
  checkPages(console, options, callback);
});

gulp.task("checkProd", function(callback) {
  var options = {
    pageUrls: [
      'http://example.com/',
      'http://example.com/blog',
      'http://example.com/about.html'
    ],
    checkLinks: true,
    maxResponseTime: 500
  };
  checkPages(console, options, callback);
});

As a result, grunt-check-pages has become a thin wrapper over check-pages and there's no duplication between the two packages (though each has a complete set of tests just to be safe). For information about the options above, visit the check-pages package in the npm repository.

 

The combined effect is that I'm able to do a better job validating web site updates and I can use whichever of Grunt or Gulp feels more appropriate for a given scenario. That's good for peace of mind - and a great way to become more familiar with both tools!

Everything old is new again [crc-hash is a Node.js Crypto Hash implementation for the CRC algorithm]

Yep, another post about hash functions... True, I could have stopped when I implemented CRC-32 for .NET or when I implemented MD5 for Silverlight. Certainly, sharing the code for four versions of ComputeFileHashes could have been a good laurel upon which to rest.

But then I started using Node.js, and found one more hash-oriented itch to scratch. :)

From the project page:

Node.js's Crypto module implements the Hash class which offers a simple Stream-based interface for creating hash digests of data. The createHash function supports many popular algorithms like SHA and MD5, but does not include older/simpler CRC algorithms like CRC-32. Fortunately, the crc package in npm provides comprehensive CRC support and offers an API that can be conveniently used by a Hash subclass.

crc-hash is a Crypto Hash wrapper for the crc package that makes it easy for Node.js programs to use the CRC family of hash algorithms via a standard interface.

With just one (transitive!) dependency, crc-hash is lightweight. Because it exposes a common interface, it's easy to integrate with existing scenarios. Thanks to crc, it offers support for all the popular CRC algorithms. You can learn more on the crc-hash npm page or the crc-hash GitHub page.

Notes:

  • One of the great things about the Node community is the breadth of packages available. In this case, I was able to leverage the comprehensive crc package by alexgorbatchev for all the algorithmic bits.
  • After being indifferent on the topic of badges, I discovered shields.io and its elegance won me over. You can see the five badges I picked near the top of README.md on the npm/GitHub pages above.

Out of hibernation [A new home and a bunch of updates for TextAnalysisTool.NET]

TextAnalysisTool.NET is one of the first side projects I did at Microsoft, and one of the most popular. (Click here for relevant blog posts by tag.) Many people inside and outside the company have written me with questions, feature requests, or sometimes just to say "thank you". It's always great to hear from users, and they've provided a long list of suggestions and ideas for ways to make TextAnalysisTool.NET better.

By virtue of changing teams and roles various times over the years, I don't find myself using TextAnalysisTool.NET as much as I once did. My time and interests are spread more thinly, and I haven't been updating the tool as aggressively. (Understatement of the year?)

Various coworkers have asked for access to the code, but nothing much came of that - until recently, when a small group showed up with the interest, expertise, and motivation to drive TextAnalysisTool.NET forward! They inspired me to simplify the contribution process and they have been making a steady stream of enhancements for a while now. It's time to take things to the next level, and today marks the first public update to TextAnalysisTool.NET in a long time!

 

The new source for all things TextAnalysisTool is: the TextAnalysisTool.NET home page

That's where you'll find an overview, download link, release notes, and other resources. The page is owned by the new TextAnalysisTool GitHub organization, so all of us are able to make changes and publish new releases. There's also an issue tracker, so users can report bugs, comment on issues, update TODOs, make suggestions, etc..

The new 2015-01-07 release can be downloaded from there, and includes the following changes since the 2013-05-07 release:

2015-01-07 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Added a tooltip to the loaded file indicator in the status bar
* Fixed a bug where setting a marker used in an active filter causes the
  current selection of lines to be changed

2015-01-07 by David Anson (http://dlaa.me/)
----------
* Improve HTML representation of clipboard text when copying for more
  consistent paste behavior

2015-01-01 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Fixed a bug where TAB characters are omitted in the display
* Fixed a bug where lines saved to file include an extra white space at the
  start

2014-12-21 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Changed compilation to target .NET Framework 4.0

2014-12-11 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Redesigned the status bar indications to be consistent with Visual Studio and
  added the number of currently selected lines

2014-12-04 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Added the ability to append an existing filters file to the current filters
  list

2014-12-01 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Added recent file/filter menus for easy access to commonly-used files
* Added a new settings registry key to set the
  maximum number of recent files or filter files allowed in the
  corresponding file menus
* Fixed bug where pressing SPACE with no matching lines from filters
  crashed the application
* Fixed a bug where copy-pasting lines from the application to Lync
  resulted in one long line without carriage returns

2014-11-11 by Uriel Cohen (http://github.com/cohen-uriel)
----------
* Added support for selection of background color in the filters
  (different selection of colors than the foreground colors)
* The background color can be saved and loaded with the filters
* Filters from previous versions that lack a background color will have the
  default background color
* Saving foreground color field in filters to 'foreColor' attribute.
  Old 'color' attribute is still being loaded for backward compatibility
  purposes.
* Changed control alignment in Find dialog and Filter dialog

2014-10-21 by Mike Morante (http://github.com/mike-mo)
----------
* Fix localization issue with the build string generation

2014-04-22 by Mike Morante (http://github.com/mike-mo)
----------
* Line metadata is now visually separate from line text contents
* Markers can be shown always/never/when in use to have more room for line text
  and the chosen setting persists across sessions
* Added statusbar panel funnel icon to reflect the current status of the Show
  Only Filtered Lines setting

2014-02-27 by Mike Morante (http://github.com/mike-mo)
----------
* Added zoom controls to quickly increase/decrease the font size
* Zoom level persists across sessions
* Added status bar panel to show current zoom level

 

These improvements were all possible thanks to the time and dedication of the new contributors (and organization members):

Please join me in thanking these generous souls for taking time out of their busy schedule to contribute to TextAnalysisTool.NET! They've been a pleasure to work with, and a great source of ideas and suggestions. I've been really pleased with their changes and hope you find the new TextAnalysisTool.NET more useful than ever!

Casting a Spell✔ [A simple app that makes it easy to spell-check with a browser]

I pay attention to spelling. Maybe it's because I'm not a very good speller. Maybe it's because I have perfectionist tendencies. Maybe it's just a personality flaw.

Whatever the reason, I'm always looking for ways to avoid mistakes.

Some time ago, I wrote a code analysis rule for .NET/FxCop. More recently I shared two command-line programs to extract strings and comments from C#/JavaScript and followed up with a similar extractor for HTML/XML.

Those tools work well, but I also wanted something GUI for a more natural fit with UI-centric workflows. I prototyped a simple WPF app that worked okay, but it wasn't as ubiquitously available as I wanted. Surprisingly often, I'd find myself on a machine without latest version of the tool. (Classic first world problem, I know...) So I decided to go with a web app instead.

The key observation was that modern browsers already integrate with the host operating system's spell-checker via the spellcheck HTML attribute. By leveraging that, my app would automatically get a comprehensive dictionary, support for multiple languages, native-code performance, and support for the user's custom dictionary. #winning!

Aside: The (very related) forceSpellCheck API isn't supported by any browser I've tried. Fortunately, it's not needed for Firefox, its absence can be coded around for Chrome, and there's a simple manual workaround for Internet Explorer. Click the "Help / About" link in the app for more information.

 

Inspired by web browsers' native support for spell-checking, I've created Spell✔ (a.k.a. SpellV), a simple app that makes it easy to spell-check with a browser. Click the link to try it out now - it's offline-enabled, so you can use it again later even without a network connection!

To import content, Spell✔ supports pasting text from the clipboard, drag-dropping a file, or browsing the folder structure. For a customized experience, you can switch among multiple views of the data, including:

  • Original text (duh...)
  • Unique words, sorted alphabetically and displayed compactly for easy scanning
  • HTML/XML content (including text, comments, and attributes)
  • JSON content (string values only)
  • JavaScript code comments and string literals

Read more about how Spell✔ works, how it was built, or check out the code on the GitHub page for SpellV!

A quick programming challenge with money [Counting and enumerating the ways to break a $1 bill]

Sunday evening I happened across a blog post by Josh Smith about finding all the ways to break a $1 bill. Specifically, the goal is to:

Count the number of ways to combine coins worth 100, 50, 25, 10, 5, and 1 cent for a total value of 100 cents

As Josh says, it's a fun challenge and I encourage you to stop reading now and solve it!

Seriously: Stop now. Spoilers ahead...

I took his advice and sat down with pen, paper, and a self-imposed 30 minute time limit. I came up with the C# solution below just before time ran out. As I note in the code, I forgot one line (though I caught it when typing up the solution). Less embarrassingly, this implementation worked correctly the first time I ran it. What's more, it's flexible with regard to the target amount and number/value of the coins (both of which are passed as parameters to the constructor). For bonus points, it outputs all the combinations it finds along the way.

I've added some comments to the code to outline the general algorithm. There are some opportunities to refactor for clarity and an implicit assumption values are passed in decreasing order, but otherwise I'm pretty happy with how it turned out.

If you take on the challenge and come up with something interesting, please leave a note - I'd love to see other approaches!

 

using System;

// Problem: Count (and output) all ways to make $1 with U.S. coins (100, 50, 25, 10, 5, 1 cents).
// Inspiration: http://ijoshsmith.com/2014/11/30/getting-into-functional-programming-with-swift/

class BreakADollar
{
    public static void Main()
    {
        // Entry point/test harness
        Console.WriteLine("Total possibilities: {0}",
            new BreakADollar(
                100,
                new[] { 100, 50, 25, 10, 5, 1 })
            .Invoke());
    }

    // Input
    private readonly int _target;
    private readonly int[] _values;
    // State
    private readonly int[] _counts;
    private int _ways;

    public BreakADollar(int target, int[] values)
    {
        // Initialize
        _target = target;
        _values = values;
        _counts = new int[values.Length];
        _ways = 0;
    }

    public int Invoke()
    {
        // Start the recursive process and return the result
        Recurse(0, 0);
        return _ways;
    }

    private bool Recurse(int i, int sum)
    {
        if (_target == sum)
        {
            // Met the target, done here
            ShowCounts();
            _ways++;
            return false;
        }
        else if (i == _counts.Length)
        {
            // Out of values, keep looking
            return true;
        }
        else if (sum < _target)
        {
            // Search, using increasing counts of current value
            while (Recurse(i + 1, sum))
            {
                _counts[i]++; // Note: Missed this line at first
                sum += _values[i];
            }
            // Reset and continue
            _counts[i] = 0;
            return true;
        }
        else
        {
            // Exceeded the target, done here
            return false;
        }
    }

    private void ShowCounts()
    {
        // Show the count for each value
        for (var i = 0; i < _counts.Length; i++)
        {
            Console.Write("{0}:{1} ", _values[i], _counts[i]);
        }
        Console.WriteLine();
    }
}

Not another POODLE pun [Batch script to disable SSL 3.0 on Windows servers - including virtual machines and Azure cloud services]

Much has been penned (and punned) recently about POODLE, the "Padding Oracle On Downgraded Legacy Encryption" security vulnerability. If you're not familiar with it, the Wikipedia entry for POODLE is a good start and Troy Hunt's POODLE treatise provides more detail.

Assuming you've made the decision to disable SSL 3.0 to mitigate POODLE attacks, this Azure Blog post includes a two-part batch/PowerShell script to do that. Based on the information in KB245030, that script can be run on a bare OS, a VM, or as part of an Azure cloud service.

It's a fine script as scripts go [ :) ], but maybe you're not a PowerShell fanatic or maybe you'd prefer a single file and/or less code to audit. If so, I present the following batch-only script for your consideration:

@echo off
setlocal
set REBOOT=N
set LOG=%~d0\DisableSslv3.log
set SSLKEY=HKLM\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\SSL 3.0

call :MAIN >> %LOG% 2>&1

goto :EOF


:MAIN

REM Show current SSL 3.0 configuration
reg.exe query "%SSLKEY%" /s

REM Check current SSL 3.0 configuration
for /f "tokens=3" %%v in ('reg.exe query "%SSLKEY%\Server" /v Enabled') do (
    if NOT "0x0"=="%%v" set REBOOT=Y
)
if ERRORLEVEL 1 set REBOOT=Y
for /f "tokens=3" %%v in ('reg.exe query "%SSLKEY%\Client" /v DisabledByDefault') do (
    if NOT "0x1"=="%%v" set REBOOT=Y
)
if ERRORLEVEL 1 set REBOOT=Y

REM Update and reboot if necessary
if "%REBOOT%"=="Y" (
    echo Update needed to disable SSL 3.0.
    reg.exe add "%SSLKEY%\Server" /v Enabled /t REG_DWORD /d 0 /f
    reg.exe add "%SSLKEY%\Client" /v DisabledByDefault /t REG_DWORD /d 1 /f
    echo Rebooting to apply changes...
    shutdown.exe /r /c "Rebooting to disable SSL 3.0" /f /d p:2:4
) else (
    echo SSL 3.0 already disabled.
)

goto :EOF

Notes:

  • This is a riff on the aforementioned script, meant to serve as a jumping-off point and alternate approach.
  • Like the original script, this one is idempotent and can be safely run multiple times (for example, every startup) on a bare OS, VM, or cloud service. The log file is additive, so you can see if it ever made changes.
  • Security Advisory 3009008 only mentions disabling SSL 3.0 for server scenarios; this script also disables it for client scenarios to protect outgoing connections to machines that have not been secured.
  • I work almost exclusively with recent OS releases on Azure; SSL 2.0 is already disabled there, so this script leaves those settings alone. André Klingsheim's post on hardening Windows Server provides more context.
  • An immediate reboot is performed whenever changes are made - consider commenting that line out during testing. :)
  • While reviewing this post, I found a discussion of related techniques on Server Fault which may also be of interest.

Whatever you do to address the POODLE vulnerability, be sure to check your work, perhaps with one of the following oft-recommended resources: