KST: Fix too small input file for expr_io_ternary test

[Mingun]

The test requires 1 + 4 + 8 = 13 bytes, but term_strz.bin used as input contains only 12 bytes. Strange, but Ruby test was successfully passed -- it seems Ruby runtime has a bug in substream implementation. According to that test:
https://github.com/kaitai-io/kaitai_struct_ruby_runtime/blob/ecf67519a990296bb1e095363ef2dc414e600502/spec/subio_spec.rb#L70-L76
is it normal for Ruby to be able to read from a stream more that it contains successfully?

This commit replaces too small term_strz.bin file with if_struct.bin which size is 13 bytes.

The test was introduced in https://github.com/kaitai-io/kaitai_struct_tests/commits/dceaee2ebf9eb05177e6f5d0effd1b1b907be9ac

cc @GreyCat

[generalmimon]

Strange, but Ruby test was successfully passed -- it seems Ruby runtime has a bug in substream implementation.

Looks like it, that's why I added the {Eof,Eos}ExceptionSized tests in 99f9229.

[generalmimon]

@Mingun:

According to that test:
https://github.com/kaitai-io/kaitai_struct_ruby_runtime/blob/ecf67519a990296bb1e095363ef2dc414e600502/spec/subio_spec.rb#L70-L76
is it normal for Ruby to be able to read from a stream more that it contains successfully?

Well, it is, just as it is for StringIO or any other IO from the Ruby stdlib. If you look closely at the test you're linking to, it asserts that Kaitai::Struct::SubIO behaves the same as the Ruby built-in class StringIO in various cases.

Note that Kaitai::Struct::SubIO is not a class that any code outside the runtime library should directly interact with. It is only used internally in the substream method lib/kaitai/struct/struct.rb:529-533:

  def substream(n)
    sub = Stream.new(SubIO.new(@_io, @_io.pos, n))
    @_io.seek(@_io.pos + n)
    sub
  end

The problem is not with the internal Kaitai::Struct::SubIO#read method (as long it works the same as the native read methods would, it's fine), but that the substream method or the Kaitai::Struct::SubIO constructor lack any checks that we're not creating a substream that exceeds the parent stream size.

[Mingun]

@GreyCat , @generalmimon, what the status?

[generalmimon]

@Mingun LGTM, thanks!