[ruby-core:56518] [ruby-trunk - Bug #8767][Open] IO.copy_stream should write in binary mode.

Issue #8767 has been reported by godfat (Lin Jen-Shin).

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Bug #8767: IO.copy_stream should write in binary mode.
https://bugs.ruby-lang.org/issues/8767

Author: godfat (Lin Jen-Shin)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: current: 2.1.0
ruby -v: ruby 2.1.0dev (2013-08-11 trunk 42495) [x86_64-darwin12.2.1]
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


This patch makes `IO.copy_stream' always copy in binary mode,
fixing the following scenario:

    require 'tempfile'
    require 'stringio'
    Encoding.default_internal = 'UTF-8'
    out = Tempfile.new('out')
    out.binmode
    # before this patch it raises:
    # in `write': "\xDE" from ASCII-8BIT to UTF-8 (Encoding::UndefinedConversionError)
    IO.copy_stream(StringIO.new("\xDE\xAD\xBE\xEF"), out)

The other way to fix this would be trying to preserve the file mode
from Tempfile instead of always writing in binary mode. However,
this won't be the case for other objects responding to `to_path'.

I think as we're treating destination as streams, we would always
want writing in binary. So I guess this is ok.

Thank you for reviewing.
This is discovered by using rubyzip, which is using Tempfile for
buffering input/output stream.

Commit on Github:
https://github.com/godfat/ruby/commit/94d9f3dd733fd19f5ade7b6e6f5bdf0c904e06c1


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