before page 2 - Dave's Blog

I'm done playing Fez. The style is atmospheric retro nastalgia and on the surface the gameplay is standard 2D platformer with one interesting Flatland style game mechanic but dig deeper to find Myst style puzzles. Despite the following I thoroughly enjoyed the game and would recommend it to anyone intrigued by the previous. Five eighths through the game I ran into one of the game's infamous Fez save game breaking issues, but I enjoyed the game enough that I started over before any patches were released and had no further issues.

While playing the game I created some tools to help keep track of my Fez notes (spoilers) including a Pixelated Image Creator that makes it easy to generate data URIs for large, black and white pixelated images, and (spoilers) a Fez Transliteration Tool to help me translate the in-game writing system.

The goal of this experiment was to combine the flipping tables emoticons with the Threw It On The Ground video using shiny new HTML5-ish features and the end result is the table flipper flipping the Threw It On the Ground video.

The table flipper emoticon is CSS before content that changes on hover. Additionally on hover a CSS transform is applied to flip the video upside down several times and move it to the right and there's a CSS transition to animate the flipping. The only issue I ran into is that (at least on Windows) Flash doesn't like to have CSS transform rotations applied to it. So to get the most out of the flip experiment you must opt-in to HTML5 video on YouTube. And of course you must use a browser that supports the various things I just mentioned, like the latest Chrome (or not yet released IE10).

Elaborating on a previous brief post on the topic of Web Worker initialization race conditions, there's two important points to avoid a race condition when setting up a Worker:

1. The parent starts the communication posting to the worker.
2. The worker sets up its message handler in its first synchronous block of execution.

For example the following has no race becaues the spec guarentees that messages posted to a worker during its first synchronous block of execution will be queued and handled after that block. So the worker gets a chance to setup its onmessage handler. No race:

'parent.js':
   var worker = new Worker();
   worker.postMessage("initialize");

'worker.js':
   onmessage = function(e) {
      // ...
   }

The following has a race because there's no guarentee that the parent's onmessage handler is setup before the worker executes postMessage. Race (violates 1):

'parent.js':
   var worker = new Worker();
   worker.onmessage = function(e) {
      // ...
   };

'worker.js':
   postMessage("initialize");

The following has a race because the worker has no onmessage handler set in its first synchronous execution block and so the parent's postMessage may be sent before the worker sets its onmessage handler. Race (violates 2):

'parent.js':
   var worker = new Worker();
   worker.postMessage("initialize");

'worker.js':
   setTimeout(
      function() {
         onmessage = function(e) {
            // ...
         }
      },
      0);

As a professional URI aficionado I deal with various levels of ignorance on URI percent-encoding (aka URI encoding, or URL escaping).

Getting into the more subtle levels of URI percent-encoding ignorance, folks try to apply their knowledge of percent-encoding to URIs as a whole producing the concepts escaped URIs and unescaped URIs. However there are no such things - URIs themselves aren't percent-encoded or decoded but rather contain characters that are percent-encoded or decoded. Applying percent-encoding or decoding to a URI as a whole produces a new and non-equivalent URI.

Instead of lingering on the incorrect concepts we'll just cover the correct ones: there's raw unencoded data, non-normal form URIs and normal form URIs. For example:

1. http://example.com/%74%68%65%3F%70%61%74%68?query
2. http://example.com/the%3Fpath?query
3. "http", "example.com", "the?path", "query"

In the above (A) is not an 'encoded URI' but rather a non-normal form URI. The characters of 'the' and 'path' are percent-encoded but as unreserved characters specific in the RFC should not be encoded. In the normal form of the URI (B) the characters are decoded. But (B) is not a 'decoded URI' -- it still has an encoded '?' in it because that's a reserved character which by the RFC holds different meaning when appearing decoded versus encoded. Specifically in this case, it appears encoded which means it is data -- a literal '?' that appears as part of the path segment. This is as opposed to the decoded '?' that appears in the URI which is not part of the path but rather the delimiter to the query.

Usually when developers talk about decoding the URI what they really want is the raw data from the URI. The raw decoded data is (C) above. The only thing to note beyond what's covered already is that to obtain the decoded data one must parse the URI before percent decoding all percent-encoded octets.

Of course the exception here is when a URI is the raw data. In this case you must percent-encode the URI to have it appear in another URI. More on percent-encoding while constructing URIs later.

As a professional URI aficionado I deal with various levels of ignorance on URI percent-encoding (aka URI encoding, or URL escaping).

Worse than the lame blog comments hating on percent-encoding is the shipping code which can do actual damage. In one very large project I won't name, I've fixed code that decodes all percent-encoded octets in a URI in order to get rid of pesky percents before calling ShellExecute. An unnamed developer with similar intent but clearly much craftier did the same thing in a loop until the string's length stopped changing. As it turns out percent-encoding serves a purpose and can't just be removed arbitrarily.

Percent-encoding exists so that one can represent data in a URI that would otherwise not be allowed or would be interpretted as a delimiter instead of data. For example, the space character (U+0020) is not allowed in a URI and so must be percent-encoded in order to appear in a URI:

1. http://example.com/the%20path/
2. http://example.com/the path/

In the above the first is a valid URI while the second is not valid since a space appears directly in the URI. Depending on the context and the code through which the wannabe URI is run one may get unexpected failure.

For an additional example, the question mark delimits the path from the query. If one wanted the question mark to appear as part of the path rather than delimit the path from the query, it must be percent-encoded:

1. http://example.com/foo%3Fbar
2. http://example.com/foo?bar

In the second, the question mark appears plainly and so delimits the path "/foo" from the query "bar". And in the first, the querstion mark is percent-encoded and so the path is "/foo%3Fbar".

Most existing DRM attempts to only allow the user to access the DRM'ed content with particular applications or with particular credentials so that if the file is shared it won't be useful to others. A better solution is to encode any of the user's horrible secrets into unique versions of the DRM'ed content so that the user won't want to share it. Entangle the users and the content provider's secrets together in one document and accordingly their interests. I call this Blackmail DRM. For an implementation it is important to point out that the user's horrible secret doesn't need to be verified as accurate, but merely verified as believable.

Apparently I need to get these blog posts written faster because only recently I read about Social DRM which is a light weight version of my idea but with a misleading name. Instead of horrible secrets, they say they'll use personal information like the user's name in the DRM'ed content. More of my thoughts stolen and before I even had a chance to think of it first!

Shortly after joining the Internet Explorer team I got a bug from a PM on a popular Microsoft web server product that I'll leave unnamed (from now on UWS). The bug said that IE was handling empty path segments incorrectly by not removing them before resolving dotted path segments. For example UWS would do the following:

A.1. http://example.com/a/b//../
A.2. http://example.com/a/b/../
A.3. http://example.com/a/

In step 1 they are given a URI with dotted path segment and an empty path segment. In step 2 they remove the empty path segment, and in step 3 they resolve the dotted path segment. Whereas, given the same initial URI, IE would do the following:

B.1. http://example.com/a/b//../
B.2. http://example.com/a/b/

IE simply resolves the dotted path segment against the empty path segment and removes them both. So, how did I resolve this bug? As "By Design" of course!

The URI RFC allows path segments of zero length and does not assign them any special meaning. So generic user agents that intend to work on the web must not treat an empty path segment any different from a path segment with some text in it. In the case above IE is doing the correct thing.

That's the case for generic user agents, however servers may decide that a URI with an empty path segment returns the same resource as a the same URI without that empty path segment. Essentially they can decide to ignore empty path segments. Both IIS and Apache work this way and thus return the same resource for the following URIs:

http://exmaple.com/foo//bar///baz
http://example.com/foo/bar/baz

The issue for UWS is that it removes empty path segments before resolving dotted path segments. It must follow normal URI procedure before applying its own additional rules for empty path segments. Not doing that means they end up violating URI equivalency rules: URIs (A.1) and (B.2) are equivalent but UWS will not return the same resource for them.

A bug came up the other day involving markup containing <input type="image" src="http://example.com/.... I knew that "image" was a valid input type but it wasn't until that moment that I realized I didn't know what it did. Looking it up I found that it displays the specified image and when the user clicks on the image, the form is submitted with an additional two name value pairs: the x and y positions of the point at which the user clicked the image.

Take for example the following HTML:

<form action="http://example.com/">
<input type="image" name="foo" src="http://deletethis.net/dave/images/davebefore.jpg">
</form>

If the user clicks on the image, the browser will submit the form with a URI like the following:http://example.com/?foo.x=145&foo.y=124.

This seemed like an incredibly specific feature to be built directly into the language when this could instead be done with javascript. I looked a bit further and saw that its been in HTML since at least HTML2, which of course makes much more sense. Javascript barely existed at that point and sending off the user's click location in a form may have been the only way to do something interesting with that action.

I had previously replaced my use of Delicious with Google Reader. Delicious had a number of issues during their switch over from Yahoo to the new owners and I was eventually fed up enough to remove it from daily use. I used Delicious to do the following things:

• Create a list of things to read later
• Save things to read again in the future
• Search through things I read and enjoyed (esp via tags)
• Annotate and share things on my blog

I realized that since I did most of my web browsing in Google Reader now anyway I may as well make use of its features. I star things to note I want to read it later or save to read again later. I can annotate with notes in Google Reader and I can share items to my web site by way of the shared items feed. Additionally for when I'm not in Google Reader there's a bookmarklet to add an arbitrary web site as a shared item in Google Reader.

Of course I wrote this and switched over about 1 week before Google removed the sharing feature from Google Reader. I'm irritated but in practice it forced me to find a different option which has worked out mostly better. New blog post coming soon about that...

The following code works fine. I have a ccomptr named resolvedUri and I want to update its hostname so I do the following:

        CreateIUriBuilder(resolvedUri, 0, 0, &builder);
        builder->SetHost(host);
        builder->CreateUri(0xFFFFFFFF, 0, 0, &resolvedUri);

But the following similar looking code has a bug:

    ResolveHost(resolvedUri, &resolvedUri);

The issue is that doing &resolvedUri gets the address of the pointer but also clears out the pointer due to the definition of my smart pointer class:

    operator T**()  
    {  
        T *ptrValue = mPtrValue;
        mPtrValue->Release();
        mPtrValue = NULL;
        return &ptrValue;
    }

In C++ there’s no guarantee about the order in which parameters for a function or method are evaluated. In the case above, &resolvedUri clears out the ccomptr before evaluating resolvedUri.Get() and so ResolveHostAlias gets a nullptr.

An interesting and related thread on stack overflow on undefined behavior in C++.

I used FiddlerCore in GeolocMock to edit HTTPS responses and ran into two stumbling blocks that I'll document here. The first is that I didn't check if the Fiddler root cert existed or was installed, which of course is necessary to edit HTTPS traffic. The following is my code where I check for the certs.

    if (!Fiddler.CertMaker.rootCertExists())
    {
        if (!Fiddler.CertMaker.createRootCert())
        {
            throw new Exception("Unable to create cert for FiddlerCore.");
        }
    }

    if (!Fiddler.CertMaker.rootCertIsTrusted())
    {
        if (!Fiddler.CertMaker.trustRootCert())
        {
            throw new Exception("Unable to install FiddlerCore's cert.");
        }
    }

The second problem I had (which would have been solved had I read all the sample code first) was that my changes weren't being applied. In my app I only need the BeforeResponse but in order to modify the response I must also sign up for the BeforeRequest event and mark the bBufferResponse flag on the session before the response comes back. For example:

    Fiddler.FiddlerApplication.BeforeRequest += new SessionStateHandler(FiddlerApplication_BeforeRequest);
    Fiddler.FiddlerApplication.BeforeResponse += new SessionStateHandler(FiddlerApplication_BeforeResponse);
...
    private void FiddlerApplication_BeforeRequest(Session oSession)
    {
        if (IsInterestingSession(oSession))
        {
            oSession.bBufferResponse = true;
        }
    }

I just found out that I like the group Ratatat. I'd first heard them way back when the Zune was first released as the backing for Los Corazones on the zune-arts.net website.




But I didn't know who they were until today when I watched this Filmography 2010 video (via Kottke)



Until about 1:16 in, the music is Ratatat's Nostrand. On the first viewing it drove me crazy because I could only vaguely recall hearing something like that music before. I tracked it down via the zune-arts thing above and eventually found my way to the Nostrand video. Funny, all the recent comments on that one are from people who also just watched the Filmography video.