Applying Plug-in Concepts

A personal hobby of mine is collecting CDs and whenever I acquire a new CD, there is an entire workflow that happens:  The CD gets ripped, the cover art is acquired or created, then the files are processed to embed the cover art, lyrics, and ReplayGain values.  These last three bits are something for which there is no decent tooling.  So, I wrote a tool myself.

The most volatile part is finding and downloading lyrics for the songs.  There is a gray area with regard to lyrics as they are usually included in the booklet “by permission” and are prone to litigation when published.  As such, the availability of lyrics and the websites that host them are unpredictable.

Legality concerns aside, the utility I wrote has to cope with these disparate websites that come and go and also the differences between them.  The original version of the lyric utility had a different class for each website, with specific logic as to how to download and parse the lyrics when given an artist and song title.  Pretty general architecture.  I had radio buttons in the application where you could select which site to attempt to download the lyrics from.

Over time, things got a little annoying.  A site would vanish and I’d have to swap it out for another.  Write a new class and edit the form to change the radio buttons, then change the code to instantiate the right class to process the lyrics.  I should point out that early on, I implemented an interface so I only had to manage the instantiation of the right class.  More typical architecture, growing as the the application’s requirements grow.

Finally, I was down to one working website and was ready to add a bunch more, but I was irritated at the thought of having to modify my UI code to support these new classes.  I decided to make the classes external to the application using a plug-in type design.  The interfaces and generic classes I was already using, I made them public, then created additional projects that referenced the main application and those classes.  In the UI, I changed the radio buttons to a dropdown and loaded it up with instances of classes loaded from DLLs in the bin folder (I’m speaking very generally, here).  Then I moved all my website-specific code into these other class projects and had the post-build action copy the DLL to the main application’s bin folder.  The conversion only took an hour or so.  The rest of the time was creating new parsers for new websites.

The meat of the code is simply looping through the DLLs (which are named consistently) and looping through the classes in each DLL looking for the classes that implement the interface.

lyricProviders = New Dictionary(Of String, ILyricProvider)


For Each path As String In IO.Directory.GetFiles(My.Application.Info.DirectoryPath, “*lyricprovider.dll”)
     a = System.Reflection.Assembly.LoadFile(path)
     For Each t As Type In a.GetTypes
         If t.GetInterfaces.Contains(GetType(ILyricProvider)) Then
             p = CType(a.CreateInstance(t.FullName), ILyricProvider)
             lyricProviders.Add(p.ProviderName, p)
         End If
     Next


Next

So this Dictionary has a list of websites and an instance of the class that downloads the information.  I look up a dictionary entry based on the name that was chosen the drop down list.  I get an instance to execute to get the lyrics.  Plug-ins utilizing interfaces are not as difficult as they may appear.

Maybe you’re thinking I’ve created more work for myself because if I want to add support for a new website, I have to create a whole new project to add it to the application.  But now, I don’t have to touch any of the code in the main application ever again.  I code to the interfaces and that’s it.  If a website dies and I need to no longer support it, I delete its respective DLL from the bin folder and I’m done.  No code changes at all.

Make Your API User Friendly

So, an API is by definition an application interface, meaning it should be usable by applications.  But you know who really has to use them?  People.  Developers.  And if you’re going to write an API, you should make it usable for the interfacing applications, but simple and friendly for the developers.  I don’t think I’m going to hear any argument about this.

I’m writing here to bitch and bitch and bitch about a project that is breaking me.  I expect it will be the last project I do with this company.  This API I have been tasked to consume and integrate with our own system is so difficult to work with and so brittle it is mind-numbing.

When you read their documentation, which is perpetually out of date, and see the data you are working with, the initial conclusion you get is that you literally have to write a UI as defined by their specs.  And that would be the easiest solution, but the dumbest one because then they should just write it themselves and host it for everyone instead of making an API.

The project involves forms.  We fill them out and send them the results.  However, we already have our own forms, so the integration should be as easy as taking our values and translating them to their values.  As part of the integration, they will send us a JSON file with a form definition.  This JSON file contains EVERYTHING needed to construct a UI.  It has the field names, the form control types, the validations, groups (with potentially infinite nesting), rules on groups, required attachments per field, permissions… you get the point here.  It’s not just a simple form definition.

Ok, so I parse out the groups and fields, then add mappings and translation code.  The translation code is off the rails because a “No” in our form must be converted to a “No” in their form.  And a “No” in their form is a GUID.  A GUID nested under the potential response values for a specific question.  So yeah, not just mapping questions, but mapping answers.  On a form with 200+ questions.

Then on top of this, they implement versioning.  So a form can be updated and we’ll get a new definition.  They may (and have done so) rename groups or fields or answers, which just causes the translation code to blow up.  Call me a lame programmer all you want, but I’d like to see someone effectively handle a value they’ve never seen before.  I’ll take the hit for not wrapping everything in an IF to see if the field was removed or renamed.  The timeline demanded does not permit that level of attention.

That’s only part of the troubles.  For each form we complete, we have to make multiple service calls.  Four, actually.  And today, they told me I’m supposed to be making a fifth call, even though things have been working for the 15+ test cases I’ve successfully completed so far.  Ok, that little gripe is not really about a specific API, but more about how the company itself has really created a monster in sum.

So back to the meat of the topic, the simplicity of an API.  So when you want someone to use your API, you want to make it easy.  If you are updating a child record, you shouldn’t have to specify the ID of the parent unless you are allowing that ID to be changed.  You can get everything you need from the ID of the child.  So why in this API must I provide so much data about so many related pieces when all I should have to provide is the ID of the data I am updating??  And another point: the values I’m returning aren’t updatable values anyway.  All that’s happening is the message is being fat and heavy and data is being thrown away.  Or maybe, the data is being saved and my work is saving them the effort of looking it up for themselves.  If that’s the case, then its unvalidated data and subject to exploit.  There is no good answer here.

So lets talk about the responses we have to send to this API.  It’s a JSON body with a dynamically constructed object with properties representing the fields of the form.  And although the field property has a name of UniqueID, it has to be returned in a fully-qualified manner, prepending each containing group’s UniqueID.  So if a group name changes, all fields under it change in the response.  It could have been easier to just send the UniqueID (since it is supposed to be unique, right?).  And the structure of the object, what the fuck.  Why not just have a simple array of key/value pairs.  Instead, you have some mystery object where a property may or may not exist.  It’s the same shit, iterate over properties or iterate over an array.  One can be handled in code with a class and a generic List, the other has to be done through a complex library like Newtonsoft and still results in an object that can’t really be navigated.  I get that JavaScript is taking over the goddamn world, but JS makes everything harder for no real benefit.

That’s as much ranting as I want to do right now.  Although it feels good to get it out, it doesn’t give me any improved perspective of the project or its viability.

First Step Into A.I. using ML.NET

I have this side project which, on Reddit, would be considered DataHoarding and altruistically would be called digital archival preservation.  In brief, it is downloading images from online catalogs to preserve them in the event the online store goes out of business, which would result in those images being lost forever.  Pre-Internet, it would the equivalent of saving and preserving print catalogs from stores, but no one prints catalogs anymore.

With that explanation made, this is a project I have invested years of time into and over those years, I have developed software that assists me in my tasks.  Initially, the software was a way to stitch large images together from partial tiles when a website wouldn’t allow you download the full resolution image.  Then it expanded to automating downloading, with subsequent performance improvements along the way, then the tools for selection improved.   But through all this, the process was still manual.  I actually viewed every single image that was downloaded and made the determination as to whether to keep it or not.  To give you an idea of how many images I have viewed, I download images in batches, usually a sequence 100,000 large.  That yields maybe 80,000 images.  After filtering and selection, I have maybe 25,000 images.  In my collection, I have over 1.6 million images.  That’s 1.6M images after a 30% keep ratio.  Math that out to figure out how many images I have seen.

To be fair, I’ve gotten extremely fast at selecting images.  More accurately, I have gotten very fast at spotting images that need to be filtered out.  I can view a page of 60 images and within a couple of seconds determine if the whole page can be downloaded or if it needs filtered.  This comes from years of seeing the same images over and over and when something looks out of place, it fires a stop response.

But how fast could this process go if I could just take the identification skill I have built up over years and turn it into code?  Well, that day has arrived with ML.NET.  I am attempting to implement AI into my utility to do some of the easy selection for me and also do some of the easy weeding for me.  The middle ground I’ll still have to process myself, but having any help is welcome.  After all, this is only a one man operation.

To begin, I modified my download utility to save the images I was filtering in two folders: Keep and Discard.  After a short run, I ended up with about 12k images totaling 386MB, containing about twice as many discards as keeps. (I did say I was fast.)  I used VisiPics to remove any duplicates and near-duplicates so hopefully the AI will have more unique imagery to work with.  Then I used the Model Builder tool to train the AI as to what was a good image and what was not.  I trained on my local machine, which is reported as an “AMD Ryzen 5 1600 Six-core processor” with 16GB of RAM.  The tool ran through all the images, did some processing, then ran through them again and did another computation, then a third time, and a fourth, a fifth, sixth, seventh, eighth.  Each pass takes a little over half an hour.  The process is using about 75% of my CPU consistently.  After the 3rd pass, I saw mentions that it had a 99% accuracy rate.  If so, that’s amazing.  I’m trying to make sense of the results each time and there’s one number that seems to be decrementing each pass.  I hope that can’t be considered a countdown to zero because it’s at 116 after the 7th pass and that suggests I have two more full days of training.

As this process is in its 4th hour, I’ve been reading all the stuff I should have read before starting.  First, you should have an equal number of images in each category, where I have more Discards than Keeps.  Second, it seems that 1000 images per category should be sufficient.  Having 12k total images is definitely working against me here.  But, my model should be pretty broad to capture all the different images I could come across.  Next time, I will use VisiPics to narrow down the similar items even further.

It finished in 5 hours with an accuracy of 99.63%.  The model ended up being a 93MB ZIP file.  Now to test it out.  After a small struggle as to what references I had to apply to my test application, I set it up to run through my previously downloaded queue of images, copying the “Keeps” to one folder and the “Discards” to another.  Then I opened both folders to see the results and let it rip.  How are the results?  So far, perfection.  Not a single miscategorized image.  I’m not taking the confidence level into account, only the Keep/Discard determination.

Now, while its accuracy is astounding, its speed is quite underwhelming.  This is cutting-edge tech so maybe I’m asking too much, but it’s taking 4 seconds to process one image.  Also, the dependencies are a little heavy.  My little test app is over 100MB in libraries, plus the 90MB model.  222MB in total.  CPU usage is 10-15% while processing an image.  RAM usage is a bit more obscene, using up to 2GB of RAM when processing an image.  Granted, the memory is released right away, but that’s quite a bite for each image.  4 seconds per image is simply not doable.

I examined the generated code and found that I was calling a method that would load the model every call and create the prediction algorithm each time.  So I moved that code into my main program and organized it so it would only load the model once.  Holy crap, what a speed difference.  It’s about 160ms to process an image once the model is loaded and ready to go.  This is now absolutely doable.

With the higher volume, I began to see more inaccuracy, so it was time to take the confidence level into account.  If the result had less than a 90% confidence, I moved it to a third folder called “Maybe”.  In the final implementation, these would be ones that were neither selected nor deleted.  I would manually review them.

After seeing the >90% keeps and discards, I had the confidence myself to run it on my download queue for real.  And I sat back and watched as it selected and discarded all by itself.  Absolutely amazing.  Am I faster?  Sure, but I do need to stop every once in a while for rest or food or just from burnout.  The AI doesn’t have to.

The last major enhancement a had added to this utility was a “lasso” feature for selecting or discarding images and my throughput increased by an insane amount.  Afterwards, I wondered why I ever waited so long to implement that feature – it was a game-changer.  This new AI feature is going to be another game-changer on a whole new level.

VS Extensions – Writing Code To Write Code

It’s a phrase I’ve used many times:  Writing code to write code.  This time it was done to save my sanity.  As is pretty evident in my blog, I am a VB.NET developer.  Despite that, I can understand the shrinking usage of the language.  Many of the newer technologies are simply not supporting VB.NET.  And I guess to a certain degree, that’s fine.  VB.NET will continue in the arena it is well suited for, and it won’t for newer application designs and models.  So be it.

At my workplace, they’ve been a VB shop forever.  And I was the longest holdout on that technology, but I’ve finally caved in to the reality that we’re going to have to convert to C#.  It’s an ideal time as everything is kind of in a paused state.  So I’ve been evaluating code converters and one that I tried ran for over 30 hours on our primary desktop application, then crashed with a useless error.  in discussing this result with another developer, it was mentioned that C# is Option Strict always, which gave me an idea that the conversion was taking so long and maybe the crash was because the converter was attempting to resolve all the implicit conversions in the code.  That’s something we should clean up first on our own.

I had a grand idea many years ago to get the project Option Strict compliant and I remember when I turned the option on, I was floored by the number of errors that needed resolved.  You have to understand, this code is 15 years old, with a variety of developers at varying skill levels, and type safety has never been enforced.  Further, all the state was held in datatables (in which everything is an object) and there are a plethora of ComboBoxes and DataGridViews, where everything is an object, too.  So while bad coding practices were allowed, the architecture of the application worked against us as well.

When I committed to the fix and turned Option Strict on, I wasn’t prepared for the number of errors I had to fix.  It was over 10,000.  That’s 10k cases of implicit type conversion that need to be explicitly corrected.  And that’s the easy route.  Refactoring the code to actually use strong typing is essentially a rewrite.  That’s not possible.  I’m barely sure the refactoring is possible.  But, I can turn Option Strict back off and return at a later time if absolutely needed.,

After about 1500 instances of typing CInt and CStr and CBool, I finally had enough.  The difficult part was Ctrl-Shift-arrowing to get to the end of the element to be wrapped in the cast.  Sometimes it was easy, and I got quite quick at hitting End and a closing parens, but it wasn’t quick enough.  I needed to write an extension that would take whatever was highlighted and wrap it in a cast with a hotkey.  And so that’s what I wrote.

Now, with my mouse, I can double-click and drag to select full words, then with Shift-Alt and a key, I can wrap that code.  S for CStr, D for CDbl, B for CBool, etc.  My productivity grew exponentially.  Still though, I have about 8700 more fixes to get through.  A few full days of that and I should be good to go.

403 XMLRPC Error In WordPress Hosted On Windows IIS (Remember Your Security Changes)

This is more of a note for myself.  Hopefully it will end up in a search engine and I’ll be able to find my own solution when this happens again.

Yesterday, I went to post something to one of my blogs that I self-host on a Windows server.  You’re on one of those blogs right now, go figure.  And when I did, I got a very common error: 403 Forbidden when accessing the xmlrpc.php file.  But, I had just successfully posted two days ago!  What could have changed?

I connected to the server and updated the permissions on the folder, since that is usually what 403 means.  That didn’t fix it.  I did an IISRESET.  That didn’t fix it.  I did a full reboot.  That didn’t fix it.  I kept searching for information.

When you search for WordPress and xmlrpc, you get a crap-ton of results that warn of the dangers of leaving this file exposed.  It’s a gateway for hackers!!!!!!  It’s so hackable!!!!!  Turn it off!!!!  Disable any remote capabilities to WordPress!!!!  These warning are geared toward users who use and reuse weak passwords.  Of course there is authentication on anything xmlrpc does, so if you’re getting hacked, it’s your fault.  Granted, there’s no protection from a hacker brute-forcing your xmlrpc URL until it finally hits something, but again, strong, unique passwords, people!

With that little rant out of the way, I do recognize the high sensitivity of this file.  It would not be unlike me to take some extra precautions on it.  And that’s exactly what I had done, and what I had forgotten I’d done.

I set up an IP address restriction on just that file, so only my home PC could access it.  That makes sense since I only post using Live Writer from home.  However, my IP address from my ISP changed in the last couple days and I didn’t notice.  This is how I fixed it.  If you instead want to use this info to secure your own WP site (and forget about it until your IP changes), go ahead.

In IIS, I navigated to the xmlrpc.php file in the content view

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After highlighting the file, I right-clicked and chose Switch to Features View.  You can see the specific file name is in the title.  I chose IP Address Restrictions

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And in here is where I added/changed my home IP address.  You can find yours at https://www.whatismyip.com.

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And as you would expect, I am able to post to blogs again, as evidenced by this post right here.

Web Request Always Redirects, While Web Browser Does Not

Today I had a breakthrough on an issue that has stewing for many months.  Every once in a while, I would pick the project back up again and see if I could approach it differently and maybe come up with a solution.  Today is the day.

The problem was in one of my homebrew personal utility programs, used to download images from the Internet.  One day, when I went to run the utility, it suddenly started failing and I could not get it to resume.  When I would request the same URL in a web browser, the download worked without any problem, but trying to download using code was a no-go.

Clearly, there is a difference between handmade code and a web browser, the task was to determine what the difference was in order to make the code better emulate the browser.  I added many http headers, trying to find out what was the missing piece.  I tried capturing cookies, but that had no effect either.  I even used a network monitor to capture the network traffic and couldn’t see any significant difference between my code and a browser.

Today, starting from scratch in a new project, I tried again.  To get the basic browser header that I needed, I visited a web site, like I had done in previous attempts.  This particular web site returned a number of headers I had never seen before, which I found very curious.  When I duplicated all those headers in my code, my requests worked.  Eliminating the headers one by one identified the one that I needed: X-Forwarded-Proto.

This header has been around for nearly a decade, although I’ve never heard of it, nor seen it implemented anywhere.  It seems to be specific to load balancers, which is actually relevant since the image host I am calling runs through a load balancer.  I was able to add the header to a standard WebClient and didn’t actually need to go to the HttpWebRequest level of code and my requests started working again.

I am not sure if the obscurity of this header was a browser-sniffing check by the load balancer to weed out bots and automated download tools (of which my utility would be classified), or whether it was just part of a new, stricter set of w3c standards that got included in a software update.  Realistically, it didn’t break anything for their users since their primary traffic is web browsers.

Utility: HardLinker

Many years ago, I used to use ACDSee for image viewing and have since switched to Faststone Image Viewer.  Not all that long ago, I had sent an email to their “comment box” with praise and a suggestion (the praise was to hopefully get my suggestion implemented).  Despite not hearing back from them, it didn’t stop me from brainstorming solutions to my problem.  I have found a way to address my needs, by writing a utility.

To summarize my request, I was looking for some sort of photo management like “albums” or “collections”.  For a pure image viewing application like Faststone, I can understand the trepidation the developers would have in implementing that feature.  It would be sure to divide their userbase as to whether it was done properly and whether it should have been done at all.

You can organize photos into folders on your hard drive, sure, but what if you want a photo in two or more albums?  You have duplicate files wasting space and possibly getting out of sync.  So my suggestion was that the file browser in FastStone have the capability to parse windows shortcuts, which are just LNK text files with pointers to the original file.  That way, you could put shortcuts into album folders and keep the originals where they are.

Recently, I stumbled on the concept of symbolic links, which are like shortcuts, but operate at a lower level.  A symbolic link looks just like a file to an application.  It doesn’t know any different.  By using symbolic links, I could get the functionality I needed with no application changes to Faststone.  I tested this concept and it was completely successful.  So I set about trying to figure out how to build something that I could use with Faststone.

Faststone has a way to call external applications for editing photos.  I could use this same feature to call a utility to generate symbolic links in a selected folder.  My first version of the utility was very simple.  It simply opened a FolderBrowserDialog and wrote links for the files specified on the command line.  However, FastStone had a limitation.  It would not send multiple filenames on a command line.  Instead it would call the external application over and over, once per selected file.

The second version of the utility would capture the multiple calls and write the links in one pass, as long as you left the dialog open until Faststone was done calling the external application.  This was ok, but I couldn’t get any visual feedback on how many files were queued up while the dialog was open.  So I had to create my own folder browser and use my own form which would not be open modally.

As with any attempt to recreate a standard windows control. the results are less than perfect, although serviceable.  The result is a utility called HardLinker.  HardLinker will remember the last folder you used as well as the size of the window.  The files queued will climb as the utility is called multiple times.

image

Under normal usage, you need to be an administrator to create a symbolic link, so HardLinker needs to be run as an administrator.  However, in Windows 10, now you can enable developer mode and create links without being in admin mode.  See: https://blogs.windows.com/windowsdeveloper/2016/12/02/symlinks-windows-10/ for more information.

So, in addition to calling HardLinker from Faststone, I also added a shortcut to the utility in my SendTo folder, so I can use it with Windows Explorer.  Calling it from Explorer is very fast since all the files are on the command line and you don’t have to wait for the multiple instances to keep spinning up.

If you are interested in this utility, you can download it from here.

CUERipper CUE Only Modification

In another hobby of mine, CD collecting, I utilize a few different tools in my collecting and cataloging process.  One of which is Exact Audio Copy (EAC), which I use to rip the CD audio to my computer.  When you collect early-edition CDs as I do, you might run into some CDs that had a special equalization called pre-emphasis, which requires you to apply an inverse equalization to the files after ripping.  Additionally, some early CDs had track subindexes, where you could jump to defined sections within a long track.

EAC, while being a good ripping program, is not able to identify either of these special features, which is why I also use CUERipper.  CUERipper is a part of the CUETools suite, which is an open-source program for ripping, authoring, and modifying CUE files.  CUE files are the true index of a CD’s tracks.  They include information such as indexes, track gaps, and pre-emphasis flags.

However, one of the drawbacks to CUERipper is that you have to rip the entire CD to get the CUE file.  Well, you can cancel the rip early, or you can specify an invalid compressor causing it to error out after the CUE generation.  Neither is an efficient workflow.  So, I downloaded the source code and made some changes specific to what I wanted.

Since I was going to run through a large number of CDs to get the pre-emphasis and index info, I wanted a way to only generate a CUE file.  To make the process even quicker, I wanted CUERipper to start the rip as soon as it had the album metadata to use, and I wanted it to eject the CD as soon as it was done with the CUE file.

image

I added three new options to CUERipper, with obvious meanings:

  • Eject after extraction
  • Start immediately
  • Create CUE file only

The options are useful even if you are doing a full CD rip, but for my needs, the CUE file generation was reduced to inserting a CD, waiting about 30 seconds while the disc indexes are read, then switching CDs after the tray ejects.

If you are interested in using this modified version of CUERipper, you can download it from here.

Youtube-dl Bookmarklet

One of my favorite things is custom protocol handlers.  The idea you can launch an application with a URL is awesome to me.  I implemented it at my current company for their internal application and it is far and away the most progressive feature the business users love.

One of my side hobbies is digital archiving, which is simply downloading stuff and saving it.  Aside from the archivist mentality of it, I do like to have local copies of items just because you can’t trust the Internet for anything.  Content comes and goes at will, and even with that, connectivity comes and goes, and one thing that keeps coming and never goes is advertising.  So, local copies win out every time in every case.

I’ve written utilities to assist in my image archiving, but when it comes to video archiving, I’ve usually used FreeDownloadManager. but sometimes it doesn’t do the job.  I had recently learned of an open-source tool called YouTube-dl, which is a command-line tool to download videos from a wide variety of websites.

I downloaded it and tried it out on a few concert videos and the utility worked quite well, so it’s been added into my toolkit.  But, being a command-line tool, it’s a little cumbersome.  What I wanted to do was launch the downloader passing the URL of the page I was currently viewing, which was hosting the video I wanted to download.  This is something I do with my image downloading utilities, too, so it’s a concept not too foreign to me.  It involves custom protocol handlers and bookmarklets.

First thing we need to do is create a custom protocol handler.  For this, ytdl:// is the protocol I chose to use.  I created a registry file (protocol.reg) with the following contents.

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\ytdl]
"URL Protocol"=""
@="URL:Youtube-DL Application"

[HKEY_CLASSES_ROOT\ytdl\shell]
[HKEY_CLASSES_ROOT\ytdl\shell\open]
[HKEY_CLASSES_ROOT\ytdl\shell\open\command]

@="\"wscript \"y:\\videos\\youtube-dlWrapper.vbs\" \"%1"\""

Notice the execution path command.  This will obviously be different paths for different people, but there is a VBScript file that needs to be created at that location to execute.  The contents of that script are as follows.

dim shell
set shell=createobject(“wscript.shell”)

cmdline=”””y:\videos\youtube-dl.exe”” “”” & replace(wscript.arguments(0),”ytdl://”,””) & “”””
ret=shell.run(cmdline,8,true)

set shell=nothing

The cmdline is generated to execute the actual youtube-dl utility, passing the URL of the video.  However, the URL in arguments(0) has the custom protocol handler ytdl:// prefixing it, so that is stripped out.

The last part is the bookmarklet itself.  In your web browser, create a new bookmark for whatever page you’re on, then edit the bookmark to give it a better title and to have the following URL:

javascript:location.href='ytdl://'+location.href;

This is how the VBScript ends up with ytdl:// in the address.  To summarize the entire process:

  1. You click the bookmarklet on a page with a video
  2. The URL of the page is prepended with ytdl:// and is navigated to
  3. Your browser recognizes it as a custom protocol and executes the URL on the local system (after appropriate security warnings)
  4. Windows looks up the protocol in the registry and determines it is to launch youtube-dlWrapper.vbs passing the URL as an argument.  The URL still has ytdl:// in front of it at this time.
  5. The wrapper VBScript strips out the leading protocol and passes the remaining URL to the youtube-dl.exe for download.
  6. A command window opens with youtube-dl running and closes when the download is complete.

System.Net.Http Error After Visual Studio 15.8.1 (2017) Update

Today we started getting an error from three web applications.  Two were web services and one was an ASP.NET MVC website.  The error was:

Could not load file or assembly ‘System.Net.Http, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a’ or one of its dependencies. The located assembly’s manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

The error was occurring on this standard line in the global.asax file:

WebApiConfig.Register(GlobalConfiguration.Configuration)

Looking at the trace statements on the error page, there was a mention of a binding redirect, which I recall seeing in the web.config of the site.  That section in the web config looked like:

<runtime>
    <assemblybinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentassembly>
        <assemblyidentity culture="neutral" publickeytoken="b03f5f7f11d50a3a" name="System.Net.Http">
          <bindingredirect newversion="2.2.29.0" oldversion="0.0.0.0-2.2.29.0">
          </bindingredirect>
        </assemblyidentity>
      </dependentassembly>
    </assemblybinding>
</runtime>

This config block had been in place since December, 2015.  The block seems to have been added by a NuGet package at the same time, possibly with a Framework version upgrade.

However it originally ended up there, removing the config block allowed the sites to launch again.  It’s unknown why this started happening after a Visual Studio upgrade.