Making Of ruby-stocks Plasma DataEngine

Hello Planet KDE, hello RubyCorner

Since I wrote my last Blog post much time has past. After my last exam last Friday I just started to do some hacking on KDE. As it should be something simple for the beginning and something useful, too, I decided to provide a new plasma dataengine for retrieving stocks information.

I used ruby, because plasma hacking with ruby is freaking awesome and totally easy. Let’s prove it!

How To Use It

Simple Plasmoid made with Ruby Before diving into the development process, you probably want to test the final result yourself. First you have to download the plasma package. Then you can install it easily with the plasma package manager.

plasmapkg -t dataengine -i

You won’t need to be root for that. You should get a success response afterwards.

As there is by now no plasmoid to display the provided data, you have to use the plasmaengineexplorer to test the engine. Call this program on your shell and look for ruby-stocks. You have to type in a stocks symbol like GOOG (Google) or NOK (Nokia) to get the information. Is is also possible to just call:

plasmaengineexplorer --engine ruby-stocks --source NOK

You can remove the engine with this short command:

plasmapkg -t dataengine -r ruby-stocks

How To Create It

I started with a look on the plasma ruby examples and copied the inital construct from the given time data engine example. There was also an attempt to create a stocks engine with C++. The code is available in the playground.

The most time took the clean implementation of the cvs data parsing.

If you want to start yourself with a ruby based dataengine, I recommend to start with the time engine example, too. Do not change the given file structure, which should be:

├── contents
│   └── code
│       ├── main.rb
│       └── …
└── metadata.desktop

The top directory gets packaged into a zip for distribution.

Let’s take a look on the main.rb. There a some important things you have to be aware of, when you want to use ruby for plasma dataengines:

  • when you name your engine “ruby-stocks” (see metadata.desktop), you have to name the top module RubyStocks. Otherwise your engine will fail.
  • Plasma looks for a class called Main in that module, which have to inherit from PlasmaScripting::DataEngine
  • make sure, that you implement the member methods: sourceRequestEvent and updateSourceEvent

As both methods should do the same in my example, I used an method alias. If you ever did a plasma dataengine using C++ you have noticed, that it is a straight forward port from C++ to ruby. There is hardly something different.

# file: 'main.rb'
# kate: remove-trailing-space on; replace-trailing-space-save on; indent-width 2; indent-mode ruby; syntax ruby; replace-tabs on; replace-tabs-save on; space-indent on;
require 'plasma_applet'

# the dictonary replaces the ruby hash as we need an ordered hash. only ruby 1.9 uses ordered one.
# when ruby1.9 is the default version, we can switch back to native ruby hash
require 'dictionary'

module RubyStocks
  class Main < PlasmaScripting::DataEngine

    # the url needs to be extended by the stock ID at the end of the string
    # format code:
    DATA = Dictionary[
      "j1" => ["market capitalization", Float],
      "p2" => ["percent change", String],
      "s0" => ["symbol",String],
      "d1" => ["last trade date", Qt::Date],
      "t1" => ["last trade time", Qt::Time],
      "c1" => ["change", Float],
      "o0" => ["open", Float],
      "h0" => ["days high", Float],
      "g0" => ["days low", Float],
      "v0" => ["volume", Float],
      "a2" => ["average daily volume", Float],
      "l1" => ["last trade", Float],
      "c4" => ["currency", String]

    SOURCE_URL = "{DATA.keys.join}&e=.csv&s="

    def initialize parent, args = nil
      super parent

      # don't update faster than once a minute
      setMinimumPollingInterval 60000
      # dafault update rate is 10 minutes
      setPollingInterval 600000


    def updateSourceEvent source
      request_url = SOURCE_URL + Qt::Url::toPercentEncoding(source).data.strip
      job = KIO::storedGet, KIO::NoReload, KIO::HideProgressInfo
      job.connect( SIGNAL( 'result( KJob* )' ) ) do |aJob|
        parseCSVLine source,

      return false

    def parseCSVLine source, dataByteArray
      $stderr.puts "ruby-stocks plasma dataengine: retrieved data: " +
      dataArray = ","
      if dataArray.size >= DATA.size
        DATA.values.each do |aValue|
          data =  dataArray.shift
          unless data =~ %r{N/A}
            if aValue[1] == Float
                data.gsub! /B$/, "E6"
                data.gsub! /M$/, "E3"
                setData source, aValue[0], data.to_f unless data == "N/A"
            elsif aValue[1] == String
              data = data[1..-2]
              setData source, aValue[0], data unless data.empty?
            elsif aValue[1] == Qt::Time
              setData source, aValue[0], Qt::Time.fromString(data, '"h:mmap"')
            elsif aValue[1] == Qt::Date
              setData source, aValue[0], Qt::Date.fromString(data, '"M/d/yyyy"')

    alias sourceRequestEvent updateSourceEvent



The second file you need is the metadata.desktop.

# file: 'metadata.desktop'
[Desktop Entry]
Name=Stocks Data Engine
Comment=Stocks Data Engine powered by Yahoo! Finance (real time delayed by around 15 minutes


X-KDE-PluginInfo-Author=Robert Riemann
X-KDE-PluginInfo-Category=Online Services

# Icon=alarmclock

What Comes Next?

The engine should be quite usable by now. I plan to create a plasmoid which lets you search for a company name to get the stocks symbol and then shows some important numbers (like the weather widget, but without these nice graphics).

After that I want to create a second plasmoid which just shows a chart from Yahoo! Finance. The most work will probably be to create a settings dialog similar to the one you find here below the chart.

What do you think? Would you use a stocks plasmoid? What do you expect it to display? Why didn’t you have already used ruby to create a dataengine? :wink: And after all, how do I get this engine into KDE trunk?