list page 7 - Dave's Blog

The 'Is It UTF-8?' Quick and Dirty Test

I've found while debugging networking in IE its often useful to quickly tell if a string is encoded in UTF-8. You can check for the Byte Order Mark (EF BB BF in UTF-8) but, I rarely see the BOM on UTF-8 strings. Instead I apply a quick and dirty UTF-8 test that takes advantage of the well-formed UTF-8 restrictions.

Unlike other multibyte character encoding forms (see Windows supported character sets or IANA's list of character sets), for example Big5, where sticking together any two bytes is more likely than not to give a valid byte sequence, UTF-8 is more restrictive. And unlike other multibyte character encodings, UTF-8 bytes may be taken out of context and one can still know that its a single byte character, the starting byte of a three byte sequence, etc.

The full rules for well-formed UTF-8 are a little too complicated for me to commit to memory. Instead I've got my own simpler (this is the quick part) set of rules that will be mostly correct (this is the dirty part). For as many bytes in the string as you care to examine, check the most significant digit of the byte:

F:

This is byte 1 of a 4 byte encoded codepoint and must be followed by 3 trail bytes.

E:

This is byte 1 of a 3 byte encoded codepoint and must be followed by 2 trail bytes.

C..D:

This is byte 1 of a 2 byte encoded codepoint and must be followed by 1 trail byte.

8..B:

This is a trail byte.

0..7:

This is a single byte encoded codepoint.

Tab Expansion in PowerShell

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;
         }
    }
}

G1 Android Phone

I finally replaced my old regular cell-phone which was literally being held together by a rubber band with a fancy new G1, my first Internet accessible phone.

I had to call the T-Mobile support line to get data added to my plan and the person helping me was disconcertingly friendly. She asked about my weekend plans and so I felt compelled to ask her the same. Her plans involved replacing her video card so she could get back to World of Warcraft and do I enjoy computer gaming? I couldn't tell if she was genuine or if she was signing me up for magazines.

I was with Sarah in her new car, trying out the phone's GPS functionality via Google Maps while she drove. I switched to Street View and happened to find my car. It was a weird feeling, kind of like those Google conspiracy videos.

The phone runs Google's open source OS and I really enjoy the application API. Its all in Java and URIs and mime-types are sort of basics. Rather than invoking the builtin item picker control directly you invoke an 'intent' specifying the URI of your list of items, a mime-type describing the type of items in the list, and an action 'PICK' and whatever is registered as the picker on the system pops up and lets the user pick from that list. The same goes if you want to 'EDIT' an image, or 'VIEW' an mp3.

I wanted to replace the Google search box gadget that appears on the home screen with my own search box widget that uses OpenSearch descriptors but apparently in the current API you can't make home screen gadgets without changing parts of the OS. My other desired application is something to replace this GPS photo tracker device by recording my location to a file and an additional program on my computer to apply those locations to photos.

Investigation of a Few Application Protocols (Updated)

Windows allows for application protocols in which, through the registry, you specify a URL scheme and a command line to have that URL passed to your application. Its an easy way to hook a webbrowser up to your application. Anyone can read the doc above and then walk through the registry and pick out the application protocols but just from that info you can't tell what the application expects these URLs to look like. I did a bit of research on some of the application protocols I've seen which is listed below. Good places to look for information on URI schemes: Wikipedia URI scheme, and ESW Wiki UriSchemes.

Failing Electronics

Electronic devices shouldn't fail, they should just sit wherever I place them and work forever. A while back my home web server started failing so I moved over to a real web hosting service. And this was the home web server I built from pieces Eric gave me after my previous one died during the big power failure the year before. The power socket on my old laptop has come undone from the motherboard so that it can no longer be powered. Just a week or two ago my Xbox 360 stopped displaying video. The CPU fan on my media center died. I also want to put my camera and GPS in this list, but the camera died due to accidentally turning on in my pocket and the GPS was stolen so those aren't the devices just arbitrarily failing.

Party Movies Recommended by Netflix

Netflix has recommended three party movies over my time with Netflix and if you're OK with movies featuring sex, drugs, rock&roll (or techno) as almost the main character then I can recommend at least The Boys and Girls Guide to Getting Down.

24 Hour Party People is based on the true story of Tony Wilson, journalist, band manager, and club owner (not all at once) around the rise of punk and new wave in England. Like many true-story based movies it starts off strong and very interesting but gets very slow at the end like the writers got bored and just started copying the actual events. Unless you have some interest in the history of music in the 80s in Manchester I don't recommend this movie.

Human Traffic is fun and funny following a group of friends going out for a night of clubbing and partying. I had to get over seeing John Simm as not The Master from Doctor Who but rather as a partying youth. It felt like it was geared towards viewers who were on something like the totally odd techno musical interludes with the characters dancing for no apparent reason. Otherwise the movie was good.

The Boys and Girls Guide to Getting Down is done in the style of an old educational movie on the topic of clubbing and partying. It sounds like a premise that would get old but they do a good job. While demonstrating drinking and driving they have scientists push a mouse around in a toy convertible. Enough said. It was funny and I recommend it.

Xbox Achievements for Everyday Life

I just upgraded to the Zune 3.0 software which includes games and purchasing music on the Zune via WiFi and once again I'm thrilled that the new firmware is available for old Zunes like mine. Rooting around looking at the new features I noticed Zune Badges for the first time. They're like Xbox Achievements, for example I have a Pixies Silver Artist Power Listener award for listening to the Pixies over 1000 times. I know its ridiculous but I like it, and now I want achievements for everything.

Achievements everywhere would require more developments in self-tracking. Self-trackers, folks who keep statistics on exactly when and what they eat, when and how much they exercise, anything one may track about one's self, were the topic of a Kevin Kelly Quantified Self blog post (also check out Cory Doctorow's SF short story The Things that Make Me Weak and Strange Get Engineered Away featuring a colony of self-trackers). For someone like me with a medium length attention span the data collection needs to be completely automatic or I will lose interest and stop collecting within a week. For instance, Nike iPod shoes that keep track of how many steps the wearer takes. I'll also need software to analyze, display, and share this data on a website like Mycrocosm. I don't want to have to spend extreme amounts of time to create something as wonderful as the Feltron Report (check out his statistic on how many daily measurements he takes for the report). Once we have the data we can give out achievements for everything!

Achievements for Everyday Life

	Carnivore Eat at least ten different kinds of animals.
	Make Friends Meet at least 10% of the residents in your home town.
	Globetrotter Visit a city in every country.
	You're Old Survive at least 80 years of life.

Of course none of the above is practical yet, but how about Delicious achievements based on the public Delicious feeds? That should be doable...