closed - Dave's Blog

Search

Debugging anecdote - the color transparent black breaks accessibility

2014 May 22, 10:36

Some time back while I was working on getting the Javascript Windows Store app platform running on Windows Phone (now available on the last Windows Phone release!) I had an interesting bug that in retrospect is amusing.

I had just finished a work item to get accessibility working for JS WinPhone apps when I got a new bug: With some set of JS apps, accessibility appeared to be totally broken. At that time in development the only mechanism we had to test accessibility was a test tool that runs on the PC, connects to the phone, and dumps out the accessibility tree of whatever app is running on the phone. In this bug, the tool would spin for a while and then timeout with an error and no accessibility information.

My first thought was this was an issue in my new accessibility code. However, debugging with breakpoints on my code I could see none of my code was run nor the code that should call it. The code that called that code was a more generic messaging system that hit my breakpoints constantly.

Rather than trying to work backward from the failure point, I decided to try and narrow down the repro and work forwards from there. One thing all the apps with the bug had in common was their usage of WinJS, but not all WinJS apps demonstrated the issue. Using a binary search approach on one such app I removed unrelated app code until all that was left was the app's usage of the WinJS AppBar and the bug still occurred. I replaced the WinJS AppBar usage with direct usage of the underlying AppBar WinRT APIs and continued.

Only some calls to the AppBar WinRT object produced the issue:

        var appBar = Windows.UI.WebUI.Core.WebUICommandBar.getForCurrentView(); 
// appBar.opacity = 1;
// appBar.closeDisplayMode = Windows.UI.WebUI.Core.WebUICommandBarClosedDisplayMode.default;
appBar.backgroundColor = Windows.UI.Colors.white; // Bug!
Just setting the background color appeared to cause the issue and I didn't even have to display the AppBar. Through additional trial and error I was blown away to discover that some colors I would set caused the issue and other colors did not. Black wouldn't cause the issue but transparent black would. So would aqua but not white.

I eventually realized that predefined WinRT color values like Windows.UI.Colors.aqua would cause the issue while JS literal based colors didn't cause the issue (Windows.UI.Color is a WinRT struct which projects in JS as a JS literal object with the struct members as JS object properties so its easy to write something like {r: 0, g: 0, b: 0, a: 0} to make a color) and I had been mixing both in my tests without realizing there would be a difference. I debugged into the backgroundColor property setter that consumed the WinRT color struct to see what was different between Windows.UI.Colors.black and {a: 1, r: 0, g: 0, b: 0} and found the two structs to be byte wise exactly the same.

On a hunch I tried my test app with only a reference to the color and otherwise no interaction with the AppBar and not doing anything with the actual reference to the color: Windows.UI.Colors.black;. This too caused the issue. I knew that the implementation for these WinRT const values live in a DLL and guessed that something in the code to create these predefined colors was causing the issue. I debugged in and no luck. Now I also have experienced crusty code that would do exciting things in its DllMain, the function that's called when a DLL is loaded into the process so I tried modifying my C++ code to simply LoadLibrary the DLL containing the WinRT color definition, windows.ui.xaml.dll and found the bug still occurred! A short lived moment of relief as the world seemed to make sense again.

Debugging into DllMain nothing interesting happened. There were interesting calls in there to be sure, but all of them behind conditions that were false. I was again stumped. On another hunch I tried renaming the DLL and only LoadLibrary'ing it and the bug went away. I took a different DLL renamed it windows.ui.xaml.dll and tried LoadLibrary'ing that and the bug came back. Just the name of the DLL was causing the issue.

I searched for the DLL name in our source code index and found hits in the accessibility tool. Grinning I opened the source to find that the accessibility tool's phone side service was trying to determine if a process belonged to a XAML app or not because XAML apps had a different accessibility contract. It did this by checking to see if windows.ui.xaml.dll was loaded in the target process.

At this point I got to fix my main issue and open several new bugs for the variety of problems I had just run into. This is a how to on writing software that is difficult to debug.

PermalinkCommentsbug debug javascript JS technical windows winrt

“House Hunters:” What It Was Like to Be On the Show

2012 Jun 11, 6:48

Apparently they cast folks who have already closed on a house.  Well… at least the folks on the show are non-actors who were actually recently looking for a new house…

PermalinkCommentshumor tv house-hunters

Prime HTTP Status Codes

2012 Feb 22, 4:00
These are the prime HTTP status codes:
PermalinkCommentshttp prime technical useless

Tab Expansion in PowerShell

2008 Nov 18, 6:38

PowerShell gives us a real CLI for Windows based around .Net stuff. I don't like the creation of a new shell language but I suppose it makes sense given that they want something C# like but not C# exactly since that's much to verbose and strict for a CLI. One of the functions you can override is the TabExpansion function which is used when you tab complete commands. I really like this and so I've added on to the standard implementation to support replacing a variable name with its value, tab completion of available commands, previous command history, and drive names (there not restricted to just one letter in PS).

Learning the new language was a bit of a chore but MSDN helped. A couple of things to note, a statement that has a return value that you don't do anything with is implicitly the return value for the current function. That's why there's no explicit return's in my TabExpansion function. Also, if you're TabExpansion function fails or returns nothing then the builtin TabExpansion function runs which does just filenames. This is why you can see that the standard TabExpansion function doesn't handle normal filenames: it does extra stuff (like method and property completion on variables that represent .Net objects) but if there's no fancy extra stuff to be done it lets the builtin one take a crack.

Here's my TabExpansion function. Probably has bugs, so watch out!

function EscapePath([string] $path, [string] $original)
{
    if ($path.Contains(' ') -and !$original.Contains(' '))
    {
        '"'   $path   '"';
    }
    else
    {
        $path;
    }
}

function PathRelativeTo($pathDest, $pathCurrent)
{
    if ($pathDest.PSParentPath.ToString().EndsWith($pathCurrent.Path))
    {
        '.\'   $pathDest.name;
    }
    else
    {
        $pathDest.FullName;
    }
}

#  This is the default function to use for tab expansion. It handles simple
# member expansion on variables, variable name expansion and parameter completion
# on commands. It doesn't understand strings so strings containing ; | ( or { may
# cause expansion to fail.

function TabExpansion($line, $lastWord)
{
    switch -regex ($lastWord)
    {
         # Handle property and method expansion...
         '(^.*)(\$(\w|\.) )\.(\w*)$' {
             $method = [Management.Automation.PSMemberTypes] `
                 'Method,CodeMethod,ScriptMethod,ParameterizedProperty'
             $base = $matches[1]
             $expression = $matches[2]
             Invoke-Expression ('$val='   $expression)
             $pat = $matches[4]   '*'
             Get-Member -inputobject $val $pat | sort membertype,name |
                 where { $_.name -notmatch '^[gs]et_'} |
                 foreach {
                     if ($_.MemberType -band $method)
                     {
                         # Return a method...
                         $base   $expression   '.'   $_.name   '('
                     }
                     else {
                         # Return a property...
                         $base   $expression   '.'   $_.name
                     }
                 }
             break;
          }

         # Handle variable name expansion...
         '(^.*\$)([\w\:]*)$' {
             $prefix = $matches[1]
             $varName = $matches[2]
             foreach ($v in Get-Childitem ('variable:'   $varName   '*'))
             {
                 if ($v.name -eq $varName)
                 {
                     $v.value
                 }
                 else
                 {
                    $prefix   $v.name
                 }
             }
             break;
         }

         # Do completion on parameters...
         '^-([\w0-9]*)' {
             $pat = $matches[1]   '*'

             # extract the command name from the string
             # first split the string into statements and pipeline elements
             # This doesn't handle strings however.
             $cmdlet = [regex]::Split($line, '[|;]')[-1]

             #  Extract the trailing unclosed block e.g. ls | foreach { cp
             if ($cmdlet -match '\{([^\{\}]*)$')
             {
                 $cmdlet = $matches[1]
             }

             # Extract the longest unclosed parenthetical expression...
             if ($cmdlet -match '\(([^()]*)$')
             {
                 $cmdlet = $matches[1]
             }

             # take the first space separated token of the remaining string
             # as the command to look up. Trim any leading or trailing spaces
             # so you don't get leading empty elements.
             $cmdlet = $cmdlet.Trim().Split()[0]

             # now get the info object for it...
             $cmdlet = @(Get-Command -type 'cmdlet,alias' $cmdlet)[0]

             # loop resolving aliases...
             while ($cmdlet.CommandType -eq 'alias') {
                 $cmdlet = @(Get-Command -type 'cmdlet,alias' $cmdlet.Definition)[0]
             }

             # expand the parameter sets and emit the matching elements
             foreach ($n in $cmdlet.ParameterSets | Select-Object -expand parameters)
             {
                 $n = $n.name
                 if ($n -like $pat) { '-'   $n }
             }
             break;
         }

         default {
             $varNameStar = $lastWord   '*';

             foreach ($n in @(Get-Childitem $varNameStar))
             {
                 $name = PathRelativeTo ($n) ($PWD);

                 if ($n.PSIsContainer)
                 {
                     EscapePath ($name   '\') ($lastWord);
                 }
                 else
                 {
                     EscapePath ($name) ($lastWord);
                 }
             }

             if (!$varNameStar.Contains('\'))
             {
                foreach ($n in @(Get-Command $varNameStar))
                {
                    if ($n.CommandType.ToString().Equals('Application'))
                    {
                       foreach ($ext in @((cat Env:PathExt).Split(';')))
                       {
                          if ($n.Path.ToString().ToLower().EndsWith(($ext).ToString().ToLower()))
                          {
                              EscapePath($n.Path) ($lastWord);
                          }
                       }
                    }
                    else
                    {
                        EscapePath($n.Name) ($lastWord);
                    }
                }

                foreach ($n in @(Get-psdrive $varNameStar))
                {
                    EscapePath($n.name   ":") ($lastWord);
                }
             }

             foreach ($n in @(Get-History))
             {
                 if ($n.CommandLine.StartsWith($line) -and $n.CommandLine -ne $line)
                 {
                     $lastWord   $n.CommandLine.Substring($line.Length);
                 }
             }

             # Add the original string to the end of the expansion list.
             $lastWord;

             break;
         }
    }
}


PermalinkCommentscli technical tabexpansion powershell

TileStack - Your Creative Playground

2008 Jun 9, 5:10"Remember that great application that used to come with all Macs called HyperCard?" I do! Closed beta now but looks fun.PermalinkCommentshypercard programming web apple mac

Crossing Four Way Stops Fast and Searching Closed Caption MCE Videos: More Stolen Thoughts

2008 Jan 22, 9:56

More ideas stolen from me in the same vein as my stolen OpenID thoughts.

Fast Pedestrian Crossing on Four Way Stops. In college I didn't have a car and every weekend I had weekly poker with friends who lived nearby so I would end up waiting to cross from one corner of a traffic lit four way stop to the opposite corner. Waiting there in the cold gave me plenty of time to consider the fastest method of getting to the opposite corner of a four-way stop. My plan was to hit the pedestrian crossing button for both directions and travel on the first one available. This only seems like a bad choice if the pedestrian crossing signal travels clockwise or counter clockwise around the four way stop. In those two cases its better to take the later of the two pedestrian signal crossings, but I have yet to see those two patterns on a real life traffic stop. I decided recently to see if my plan was actually sound and looked up info on traffic signals. But the info didn't say much other than "its complicated" and "it depends" (I'm paraphrasing). Then I found some guy's analysis of this problem. So I'm done with this and I'll continue pressing both buttons and crossing on the first pedestrian signal. Incidentally on one such night when I was waiting to cross this intersection I heard a loud multi-click sound and realized that the woman in the SUV waiting to cross the intersection next to me had just locked her doors. I guess my thinking-about-crossing-the-street face is intimidating.

Windows Searching Windows Media Center Recorded TV's Closed Captions. An Ars-Technica article on a fancy DVR described one of the DVRs features: full text search over the subtitles of the recorded TV shows. I thought implementing this for Windows Media Center recorded TV shows and Windows Search would be an interesting project to learn about video files, and extending Windows Search. As it turns out though some guy, Stephen Toub implemented Windows Search over MCE closed captions already. Stephen Toub's article is very long and describes some other very interesting related projects including 'summarizing video files' which you may want to read.

PermalinkCommentsstolen-thoughts windows search mce windows traffic closed captions four-way-stop windows-media-center

Stephen Toub : DVR-MS: Adventures in Closed Captioning

2008 Jan 14, 10:16Stephen Toub implements closed captioning searching of videos recorded with Windows Media Center through Windows Desktop Search as an IFilter. I wanted to do the same thing after reading the related Ars Technica article. Other interesting things in thePermalinkComments.net mce programming reference video caption dvr-ms howto ifilter development com software microsoft msdn blog article

IPv6 Roundup: Address Syntax on Windows

2008 Jan 9, 11:34

IPv6 address syntax consists of 8 groupings of colon delimited 16-bit hex values making up the 128-bit address. An optional double colon can replace any consecutive sequence of 0 valued hex values. For example the following is a valid IPv6 address: fe80::2c02:db79

Some IPv6 addresses aren't global and in those cases need a scope ID to describe their context. These get a '%' followed by the scope ID. For example the previous example with a scope ID of '8' would be: fe80::2c02:db79%8

IPv6 addresses in URIs may appear in the host section of a URI as long as they're enclosed by square brackets. For example: http://[fe80::2c02:db79]/. The RFC explicitly notes that there isn't a way to add a scope ID to the IPv6 address in a URI. However a draft document describes adding scope IDs to IPv6 addresses in URIs. The draft document uses the IPvFuture production from the URI RFC with a 'v1' to add a new hostname syntax and a '+' instead of a '%' for delimiting the scope id. For example: http://[v1.fe80::2c02:db79+8]/. However, this is still a draft document, not a final standard, and I don't know of any system that works this way.

In Windows XPSP2 the IPv6 stack is available but disabled by default. To enable the IPv6 stack, at a command prompt run 'netsh interface ipv6 install'. In Vista IPv6 is the on by default and cannot be turned off, while the IPv4 stack is optional and may be turned off by a command similar to the previous.

Once you have IPv6 on in your OS you can turn on IPv6 for IIS6 or just use IIS7. The address ::1 refers to the local machine.

In some places in Windows like UNC paths, IPv6 addresses aren't allowed. In those cases you can use a Vista DNS IPv6 hack that lives in the OS name resolution stack that transforms particularly crafted names into IPv6 addresses. Take your IPv6 address, replace the ':'s with '-'s and the '%' with an 's' and then append '.ipv6-literal.net' to the end. For example: fe80--2c02-db79s8.ipv6-literal.net. That name will resolve to the same example I've been using in Vista. This transformation occurs inside the system's local name resolution stack so no DNS servers are involved, although Microsoft does own the ipv6-literal.net domain name.

MSDN describes IPv6 addresses in URIs in Windows and I've described IPv6 addresses in URIs in IE7. File URIs in IE7 don't support IPv6 addresses. If you want to put a scope ID in a URI in IE7 you use a '%25' to delimit the scope ID and due to a bug you must have at least two digits in your scope ID. So, to take the previous example: http://[fe80::2c02:db79%2508]/. Note that its 08 rather than just 8.

PermalinkCommentsroundup ip windows ipv6 technical microsoft boring syntax

California Trip

2007 Dec 23, 11:18Other Jelly FishSarah and I went down to California at the end of last month for a Thanksgiving visit with my parents. We visited the famous Monterey Bay Aquarium (fun fact: the aquarium scenes in Star Trek IV were filmed here) and saw many jelly fish. We wandered around Capitola where we visited many local shops and ate on the wharf. We shopped in Carmel and ate at the Forge in the Forest (fun fact: Clint Eastwood was the mayor of this city in the late 80s). We visited the Santa Cruz Beach Boardwalk which was very cold and closed.
Silly Party HatsMy parents took us out to dinner on the first night and the rest of the nights we ate dinner at their house. They had the Shelton's over and I got to see Chris and Alison. It was fun to talk with them and catch up since its been quite a while since I'd seen them.
Beach House LivingroomWe stayed in the lovely beach house of our family friend's the Goodwins. My parents have been helping them fix it up and decorate it and it looks great. It was quite a treat staying in a house right on the ocean. Also of note, this was the first trip on which I was old enough to rent the car and accordingly I did all of the driving. This trip was very fun and relaxing.PermalinkCommentsaquarium friends parents personal beach california vacation

Sculpture Garden

2007 May 15, 8:38Tall SculptureLast Saturday Sarah and I went to the Sculpture Garden in Seattle. Its laid out with exhibits all outside running down to the water.

Sarah in the ValleySarah and I followed the trail of sculptures down to the shore and took some more photos on the sand and rocks on the mini beach. There's also a green house but it was closed the day we were there. The glass of the green house is tinted green and the long walls of the house slope down in the back giving a forced perspective to the viewer on one end.

Black Winding ArtThe sculptures aren't roped off rather they mingle with the normal urban artifacts. There are little signs around that politely ask viewers not to touch the art for fear of damage that reminded me of the show Arrested Development.PermalinkCommentssculpture washington personal art seattle nontechnical

Aquanaut adventure

2007 Apr 23, 1:07An Australian biologist lives in a "bio-regenerative microcosm" an enclosed box underwater for weeks. In that time he writes a song...PermalinkCommentsscience article weird biodome biosub

Plane Wackiness

2004 Apr 22, 6:44My interview was scheduled for Monday starting at 8am, so when I signed up for the trip and MS suggested a departure time of 4:30pm on Monday I thought that'd be good. Unfortunately the entire process ended at 4:15pm and it takes a little more than 15 minutes to get from Redmond to Seattle and then through the whole airport deal. So after the taxi ride to the airport and waiting in line for like 20 minutes its 5:30pm and I'm at the front of the line asking this woman for a new ticket.

Woman: *typing* Well I can get you to LA... Me: Yeah well that's the right state. Woman: *still typing* Oh... Hmm... Uhoh... *other non-words* Me: *waiting patiently* ... Woman: Are you ready to run? Here's your ticket. Gate C11.

I look at the ticket and the plane's boarding at, what do you know?, 5:30pm. So yeah I start running. I hit the security check point line and I know all about this. I take off my belt and shoes and empty my pockets into my backpack, my only luggage. I am Mr. Prepared, or maybe Prepared-ness is my middle name, whatever. I get through the line with no problem, put on my backpack and holding my shoes and belt in one hand I notice a big old clock just to my left. While I'm staring at it, it changes from 5:42 to 5:43. "Oh shit!" I think, so I start running again. I finally get to the appropriate gate and get on the plane all out of breath. I'm walking down the aisle with shoes and belt in hand, and I guess I look a bit out of sorts. I sit in my seat and I'm telling the guy next to me about my whole deal: "Ha. Yeah. I was late and with the running and the security checkpoint..." into incoherent mumbling and gesturing. So it turns out the pilot and copilot's incoming flight was way late and I ended up sitting in my seat for another 15 minutes before we could take off. All that wasted running. What a shame. Coming into LA we've been "landing" for like 20 minutes. We finally get on the ground and its 30 minutes passed the boarding time of my connecting flight. I start thinking about anyone I know who lives in LA. All the other passengers stand up and block the aisle. Then, an announcement "Will Daniel Riesney please come to the front of the plane." OK I can tell that's supposed to be my name, but how the hell am I supposed to get to the front of the plane? The people near me who have heard me talking to the guy next to me about this let me past easily enough. But now I have to explain this to each person out of ear shot to further my progress. "Hi. Excuse me. They called me to the front of the plane. Pardon me. Can I get by." And so on. Its getting more hostile the closer I get to first class. Up to this one guy. He's trying to talk on his cell phone but its not working because everybody is trying to talk on their cell phone now that we've landed. His phone connection has failed. I can't guess at what else has happened to him today but he's decided to make his Custerian last stand here between me and the rest of the plane.

Me: *continuing from previous passengers* Excuse me. Pardon me. Guy: *spinning around* WHAT!? Me: Can I please get by? Guy: What? Why? Were not going anywhere! This whole time I've been forcing my way past him. Guy: There OK your past me now! Your several feet ahead of me! Congratulations! Me: Dude, I'm sorry they called me to the front of the plane. Guy: I find that highly unlikely!

Whatever. I keep walking and like 7 people past the asshole I guess the flight attendants give up on me and start letting people off the plane. Now who feels like an asshole? Its me. I get off the plane and some airport guy has a new schedule for me. Oh good I'm thinking, I've got an hour until the next flight's boarding time at 10:30pm. So I get on a tram to travel to the other side of LAX. I wait for oncoming traffic to stop so I can climb up a stopped escalator (Incidentally right next to it is another escalator which has been closed off. Why would they do that? Escalators cannot break they just become stairs.) I get up there and wait in line for an extreeeeme amount of time and finally get up to claim my ticket. Its 10:20. I get my ticket and, yeah, the departure time is 10:30, the boarding time is 10:10. So I start running again. More security check fun. I finally find my boarding gate. I rush up...

Me: *breathing heavy* Here's my ticket Lady: Oh good your finally here. Just go right out that door, *points* down the stairs, *more pointing* and wait for the tram.

WHAT? Isn't there supposed to be a PLANE somewhere? This is what I'm thinking not what I'm saying. So I walk outside and down these steps. And I'm waiting. The lady from inside joins me.

*awkward silence* Lady: The bus should be here pretty soon. Me: So... I'm going to miss my plane huh? Lady: Oh no, see here? *points at my ticket* Your ticket is confirmed so they can't leave without you. Me: Oh good... I hope they didn't tell the other passengers that.

Lets see how many passengers I can piss off in one night. Eventually this bus shows up. I get in and the guy starts driving. "Do you know where I'm going?" I ask. "Yeah" the guy says. Great. Fine. Whatever. I don't care anymore. So we drive back around to the OTHER SIDE of the airport. You know, the side I started on. Yeah that side. So I get off the bus and walk into the small building set aside for smaller airlines. I see the frantic looking ladies manning another of these gates. They see me, check my ID and ticket, and one of them ushers me out the door next to the gate. Out the door and into a small gated area outside. So me and this new lady are just standing here. Even had I the energy to ask her what was going on its very loud what with all the planes. So we just stand here at this gate facing the planes for a while. I look at her trying to make eye contact and get some sort of acknowledgment that we are in fact waiting for SOMETHING. Eventually one of the day-glow guys appears from between some planes and saunters up. The lady hands him a paper and walks away. At the time I was kind of offended but looking back on it, maybe the lady was a deaf mute and I'm the one being insensitive. So now I follow this guy through a bunch of planes. I'm yelling "San Luis Obispo?" trying to be heard over all the ambient noise and this guy is somehow responding to me with an even tone no yelling required. I don't know how he did that. We finally get to the plane and its 10:40. So I delayed the flight ten minutes. I'm thinking its going to be really awkward when I sit down and we immediately leave. Its going to be suspicious even. But, not to worry, we wait while the flight attendant argues with the guy who brought me to the plane for another ten minutes about how many people are supposed to be on the plane. Whatever.PermalinkComments
Older Entries Creative Commons License Some rights reserved.