command_parser.rb

class CommandParser
  %%{
    machine wire_command_parser;
       
    action parse_error {
      @sess.parse_error
    }

    action command {
      command = data[0..p].pack("c*")
      @sess.dispatch(command)
    }
    
    action arg_command {
      command = data[0...p].pack("c*")
      json = data[p+1..eof].pack("c*")
      @sess.dispatch(command, json)
    }
        
    Command = ( 
      'LIST_STEP_DEFINITIONS' | 'OK' | 'FATAL' |
      'TABLE_DIFF_OK' | 'TABLE_DIFF_KO'
    );
   
    ArgCommand = (
      'STEP_DEFINITIONS' | 'INVOKE' | 'GROUPS_FOR_STEP_NAME' | 'GROUPS' |
      'DIFF' | 'FAIL' | 'EXCEPTION' 
    )':';
    
    main := ( Command @command | ArgCommand @arg_command ) @err(parse_error);        
  }%%
  
  def initialize(sess)
    @sess = sess
    %% write data;
  end

  def handle(data)
    data = data.unpack("c*")
    eof = data.length
    %% write init;
    %% write exec;
  end
end

class Session
  def parse_error
    puts "Parse Error!"
  end
  
  def dispatch(command, json=nil)
    puts "#{command}: #{json or "No data"}"
  end  
end

s = Session.new
p = CommandParser.new(s)
p.handle("LIST_STEP_DEFINITIONS")
p.handle('INVOKE:{ "command" : "INVOKE", "args" : { "id" : "some id", "args" : [ "foo", "bar" ] } }')
p.handle('GROUPS_FOR_STEP_NAME:{ "command" : "GROUPS_FOR_STEP_NAME", "id": "foo", "step_name": "My pet step" }')
p.handle('DIFF:{ "command" : "DIFF", "foo": "bar" }')
p.handle('FAIL:{ "command" : "FAIL", "msg": "Exception in foo step" }')
p.handle("BLARGLE")
p.handle("  LIST_STEP_DEFINITIONS")
p.handle("DIFF:") # This should throw a parse error, but currently it does not :-(
p.handle("TABLE_DIFF_O")