Allow creating Kaitai::Struct::Stream from StringIO (not just String)

[Petr Pučil]

This code:

require 'stringio'
require_relative 'lib/kaitai/struct/struct'

io = Kaitai::Struct::Stream.new(StringIO.new("PK\x03\x04"))

currently fails with

$ ruby t.rb
C:/temp/kaitai_struct/runtime/ruby/lib/kaitai/struct/struct.rb:104:in `initialize': can be initialized with IO, SubIO or String only (TypeError)
        from t.rb:4:in `new'
        from t.rb:4:in `<main>'

because the Stream.new implementation expects to receive a plain String instead:

io = Kaitai::Struct::Stream.new("PK\x03\x04")

and it will create a StringIO itself:

kaitai_struct_ruby_runtime/lib/kaitai/struct/struct.rb

Lines 97 to 104 in 515d34d

 def initialize(arg) 
   if arg.is_a?(String) 
     @_io = StringIO.new(arg) 
   elsif arg.is_a?(IO) or arg.is_a?(SubIO) 
     @_io = arg 
   else 
     raise TypeError.new('can be initialized with IO, SubIO or String only') 
   end 

I think rejecting the accepted StringIO and insisting on creating it "automatically" is an unnecessary restriction, and initialization with StringIO should be allowed as well to make it foolproof.

[Mikhail Yakshin]

Interesting... I've never realized that StringIO is not derived from IO in Ruby. I've tried to fix it.