Sending a hash using eventmachine

Question

I want to send a hash populated with data from a EventMachine client to a server. The problem is that the server receive_date method just prints a string.

The server:

  def receive_data(data)
    send_data("Ready")
    puts data[:total]
  end

The client:

def receive_data(data)
  send_data( get_memory() )
end

def get_memory
  sigar = Sigar.new
  mem = sigar.mem
  swap = sigar.swap
  memory = { :total => (mem.total / 1024), :cat => "kwiki", :mouse => "squeaky" }
end

This line: puts data[:total]

prints only nil

Answer 1

Why don't you convert the Hash to a JSON string before sending it, and convert it back to a Hash when the server receive it?

Answer 2

You need to serialize the data that you send over the wire. In other words, normally everything is outputted as plain ascii. In your case you could use YAML for serialization, since you memory hash only contains ascii chars.

client:

require 'yaml'

def receive_data(data)
  send_data(get_memory().to_yaml)
end

server:

require 'yaml'

def receive_data(data)
  puts YAML.load(data)
end

Of course there are other serialization methods like JSON, or something.

Answer 3

Hey rtaconni, You have to do things a little different if you want to send the data from a custom object. There is the DRbUndumped module you can include in your class to have your class become Marshalable.

You can build the module and include it with your class. http://www.ruby-doc.org/stdlib/libdoc/drb/rdoc/classes/DRb/DRbUndumped.html

ex.

require 'drb'
include DRbUndumped


class Sigar
  def initialize(*args)
  end

def ect
  end

end

Now you can use Marshal.dump(object), and Marshal.load(object), and as long as the recipient file / process also shared (eg. require 'sigar') then it will be able to work with your Ruby object without having to do costly transformations to the Object just to send it back and forth.

Marshal.load(), Marshal.dump() work with almost all Objects, there are some special cases with Sockets where Marshaling runs into exceptions.

Happy Hacking.