Do not rewind unrewindable IOs

[ixti]

Reported by @mikker:

---

We're using IO.pipe for chunked POST requests in @elastic's APM Agent and I'm stubbing away rewind on my reader objects because of this.

# HTTP.rb calls #rewind the body stream which IO.pipes don't support
class ModdedIO < IO
  def self.pipe(ext_enc = nil)
    super(ext_enc).tap do |rw|
      rw[0].define_singleton_method(:rewind) { nil }
    end
  end
end

Just wanted to provide an actual use of IO.pipe.

[janko]

@ixti The issue is that IO.pipe objects still respond to #rewind, but calling #rewind will fail.

I personally don't think that http.rb shouldn't attempt to do any rewinding, precisely because some IO objects are not rewindable. But I'd like to hear what others think.

[ixti]

Oh. Right. Because IO.pipe returns 2 IO objects in fact... So, probably we should do something like:

def ignorant_rewind(io)
  io.rewind if io.respond_to? :rewind
rescue Errno::ESPIPE
  nil
end

[janko]

Yes, that would be a good fix for pipes.

[ixti]

I think the same should be implemented for http/form_data as well.

[mikker]

Solves my case perfectly ❤️