Psych

Description

Psych is a YAML parser and emitter. Psych leverages libyaml for it’s YAML parsing and emitting capabilities. In addition to wrapping libyaml, Psych also knows how to serialize and de-serialize most Ruby objects to and from the YAML format.

Install

You need Ruby 1.9.2-p0 or higher. Also install libyaml fx in one of the following ways…

$ brew install libyaml $ port install libyaml +universal $ yum install libyaml-devel

Examples

# Load YAML in to a Ruby object
Psych.load('--- foo') # => 'foo'

# Emit YAML from a Ruby object
Psych.dump("foo")     # => "--- foo\n...\n"

Documentation

tenderlovemaking.com/2010/04/17/event-based-json-and-yaml-parsing/

Our event listener is only going to listen for scalar events, meaning that when Psych parses a string, it will send that string to our listener. There are many different events that can happen, so Psych ships with a handler from which you can inherit. If you check out the source for the base class handler, you can see what types of events your handler can intercept.

require 'psych'

class Listener < Psych::Handler
  def scalar(value, anchor, tag, plain, quoted, style)
    puts value
  end
end

listener = Listener.new
parser   = Psych::Parser.new listener
parser.parse DATA

__END__

In this example, our handler simply prints out every scalar value encountered. We created a new instance of the listener, pass that listener to a new instance of the parser, and tell the parser to parse DATA. We can hand the parser an IO object or a String object. This is important because we’d like to hand the parser our socket connection, that way the parser can deal with reading from the socket for us.

require 'socket'
require 'psych'

class StreamClient
  def initialize user, pass
    @ba = ["#{user}:#{pass}"].pack('m').chomp
  end

  def listen listener
    socket = TCPSocket.new 'stream.twitter.com', 80
    # .. (authentication) ...

    # Read the headers
    while((line = socket.readline) != "\r\n"); puts line if $DEBUG; end

    reader, writer = IO.pipe
    producer = Thread.new(socket, writer) do |s, io|
      loop do
        io.write "---\n"
        io.write s.read s.readline.strip.to_i 16
        io.write "...\n"
        s.read 2 # strip the blank line
      end
    end

    parser = Psych::Parser.new listener
    parser.parse reader

    producer.join
  end
end

class Listener < Psych::Handler
  def initialize
    @was_text = false
  end

  def scalar value, anchor, tag, plain, quoted, style
    puts value if @was_text
    @was_text = value == 'text'
  end
end

StreamClient.new(ARGV[0], ARGV[1]).listen Listener.new

We configure the “listen” method in our client to munge the feed to a pipe, and hand that off to our YAML processor. I only care about the text of people’s tweets, so let’s modify our listener too.

Dependencies

  • libyaml

Installation

  • sudo port install libyaml +universal

  • sudo gem install psych

License

Copyright 2009 Aaron Patterson, et al.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ‘Software’), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED ‘AS IS’, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.