Increase limit of open files / IO in ruby

Get [current, maximum] value pair:

Process.getrlimit(:NOFILE)[1]

Set limit:

number = 1000
Process.setrlimit(:NOFILE, number)

The operation can’t be completed because one or more required items can’t be found. (Error code -43)

In my case this error appear after some operations with File Vault when I tried to delete any file/folder using finder. Go to Disk utility. Select main drive (or wherever the error appear). There should be 2 active buttons. Use 'Verify Disk' and 'Repair disk'.

Unpack .dz file. read *.dict.dz, *.dict

.dz is just .bz file. It is Stardict dictionary data file. And inside it is XML file (looks like). To unpack run:

gunzip filename.dict.dz -S .dz

For ruby You could read it using GZip reader and process as xml using nokogiri.

require 'nokogiri'
require 'zlib'
include Zlib
data = GzipReader.open("dict.dict.dz"){|f|f.read}
doc = Nokogiri::XML(data)
p doc.xpath("k")[0].content

Chrome extension download file example

Some example of generating file from chrome extension.

logError: function(error) { console.log(error); }
downloadFile: function(format, file_name, data){
    if(!format){
      format = 'txt';
    }
    if(!file_name){
      file_name = 'default';
    }
    file_name = file_name + '.' + format;
    if(data.length == 0){
      return; // stupid stub
    }
    window.requestFileSystem = window.requestFileSystem || window.webkitRequestFileSystem;
    window.requestFileSystem(window.TEMPORARY, 1024*1024, function(fs) {
      fs.root.getFile(file_name, {create: true}, function(fileEntry) {
        fileEntry.createWriter(function(fileWriter) {
          var blob = new Blob([data]);
          fileWriter.addEventListener("writeend", function() {
            chrome.tabs.create({ url: fileEntry.toURL() });
          }, false);
          fileWriter.write(blob);
        }, logError);
      }, logError);
    }, logError);
  },

Download Youtube video/audio

Download tool for grabbing data:

brew install youtube-dl

Update it:

sudo youtube-dl -U

If You want to have just mp3 files. Install tools for converting files from http://ffmpegmac.net/ Move all files to bin folder:

cd path_to_unpacked_zip_tools
sudo mv * /urs/local/bin

Get video file:

youtube-dl https://www.youtube.com/xyz

Get audio file:

youtube-dl https://www.youtube.com/xyz -x --audio-format=mp3

Command pattern ruby

class Command
  attr_reader :name
  def initialize(name)
    @name = name
  end
  def run
    raise "Implement me"
  end
end

class MakeBold < Command
  def initialize(text)
    super("Make bold text: #{text}")
    @text = text
  end
  
  def run; puts "<b>#{@text}</b>"; end
end

class MakeItalic < Command
  def initialize(text)
    super("Make italic text: #{text}")
    @text = text
  end
  
  def run; puts "<i>#{@text}</i>"; end
end

class MakeSized < Command
  def initialize(text, size=14)
    super("Make text: #{text} to be size: #{size}")
    @text = text
    @size = size
  end
  
  def run; puts "<span style='font-size:#{@size}px;'>#{@text}</span>"; end
end

commands = []
commands << MakeBold.new("to be bold")
commands << MakeItalic.new("to be italic")
commands << MakeSized.new("to be sized", 20)
commands << MakeBold.new("other to be bold")

# show description for each command prior to execution
commands.each {|command| command.name }
# execute commands
commands.each {|command| command.run }

Output:

$ ruby command.rb 
<b>to be bold</b>
<i>to be italic</i>
<span style='font-size:20px;'>to be sized</span>
<b>other to be bold</b>

Iterator pattern ruby

Iterator is too obvious in ruby, so assume some theoretical example.

class Iterator
  def first; end
  def last; end
  def next; end
  def current; end
  def has_next?; end
end

class InfiniteNumbers < Iterator
  def initialize
    @current = 0
  end
  
  def first
    1
  end
  
  def last
    raise "Infinite number"
  end
  
  def next
    @current += 1
  end
  
  def current
    @current
  end
  
  def has_next?
    true
  end  
end

iterator = InfiniteNumbers.new
puts 100.times.collect { iterator.next }.join(',')

Composite pattern ruby

Class ItemsGroup could be called Composite in current example.

class Component
  attr_reader :data
  
  def initialize(data)
    @data = data
  end
  
  def display
    raise "Implement me"
  end
end

class ItemsGroup < Component
  def initialize
    @children = []
  end
  
  def add_child(child)
    @children << child
  end
  
  def remove_child(child)
    @children.delete(child)
  end
  
  def display
    @children.each do |child|
      child.display
    end
  end
end

class Item < Component
  def display
    puts data.inspect
  end
end

group = ItemsGroup.new
group1 = ItemsGroup.new
group2 = ItemsGroup.new

group1.add_child(Item.new('label'))
group1.add_child(Item.new('input text'))
group2.add_child(Item.new('label'))
group2.add_child(Item.new('input password'))

group.add_child(Item.new("header"))
group.add_child(group1)
group.add_child(group2)
group.add_child(Item.new("submit button"))

group.display

Observer pattern ruby

Current implementation dont have base class for Observers. Observer methods moved to module. This is a basic solution without any checkings.

module ObserverMethods
  def initialize
    @observers = []
  end
  def add_observer(observer)
    @observers << observer
  end
  def delete_observer(observer)
    @observers.delete(observer)
  end
  def notify_observers
    @observers.each do |observer|
      observer.update(self)
    end
  end
end


class Entity
  include ObserverMethods
  
  attr_reader :name, :description
  
  def name=(value)
    @name = value
    notify_observers
  end
  def description=(value)
    @description = value
    notify_observers
  end
end

class TxtObserver
  def update(entity)
    puts "txt: #{entity.name}, #{entity.description}"
  end
end
class TxtConsoleObserver
  def update(entity)
    puts ">> #{entity.name}, #{entity.description}"
  end
end


entity = Entity.new
entity.add_observer(TxtConsoleObserver.new)
entity.add_observer(TxtObserver.new)

entity.name = "Name"
entity.description = "Description"

$ ruby observer.rb 
>> Name, 
txt: Name, 
>> Name, Description
txt: Name, Description

Strategy pattern ruby

In Ruby implementation base class Strategy could be removed.

class Strategy
  def output(data)
    raise "Implement me"
  end
end

class TxtOutput < Strategy
  def output(data)
    puts data.inspect
  end
end

class ConsoleTxtOutput < Strategy
  def output(data)
    puts ">> #{data.inspect}"
  end
end

class SomeLogic
  attr_accessor :output_formatter
  
  def initialize(output_formatter)
    @output_formatter = output_formatter
  end
  
  def do_some_job
    @data = { "some" => "data", "here" => 10 }
  end
  
  def print_somewhere
    @output_formatter.output(@data)
  end
end

txt_output = TxtOutput.new
console_txt_outut = ConsoleTxtOutput.new

# Specify formatter dynamically
logic = SomeLogic.new(txt_output)
logic.do_some_job
logic.print_somewhere
# Specify formatter dynamically
logic.output_formatter = console_txt_outut
logic.print_somewhere

Template method pattern ruby

class ReportGenerator
  
  def initialize
    @report = ""
  end
  
  def output
    prepare_header
    prepare_body
    prepare_footer
    @report
  end
  
  def prepare_header
    raise "Prepare header should be implemented"
  end
  def prepare_body
    raise "Prepare body should be implemented"
  end
  def prepare_footer
    raise "Prepare footer should be implemented"
  end
end

class TxtReportGenerator < ReportGenerator
  def prepare_header
    @report << "Txt Report header \n"
  end
  def prepare_body
    @report << "body \n"
  end
  def prepare_footer
    @report << "footer \n"
  end
end

class PdfReportGenerator < ReportGenerator
  def prepare_header
    @report << "Pdf Report header \n"
  end
  def prepare_body
    @report << "some encoded body \n"
  end
  def prepare_footer
    @report << "encoded footer \n"
  end
end

txt = TxtReportGenerator.new
pdf = PdfReportGenerator.new

puts txt.output
puts pdf.output

Mac OS Vagrant interfaces failure

If You see this:

....
There was an error while executing `VBoxManage`, a CLI used by Vagrant
for controlling VirtualBox. The command and stderr is shown below.

Command: ["hostonlyif", "create"]

Stderr: 0%...
Progress state: NS_ERROR_FAILURE
VBoxManage: error: Failed to create the host-only adapter

Just do this:

$ sudo /Library/StartupItems/VirtualBox/VirtualBox restart

It will re-create virtual adapters for VB installation.