From: "YO4 (Yoshinao Muramatsu) via ruby-core" <ruby-core@...>
Date: 2025-12-04T11:38:19+00:00
Subject: [ruby-core:124026] [Ruby Bug#21763] Windows: output IO pipe ignores crlf newline conversion specified by set_encoding

Issue #21763 has been updated by YO4 (Yoshinao Muramatsu).


I made PR [#15405](https://github.com/ruby/ruby/pull/15405)


----------------------------------------
Bug #21763: Windows: output IO pipe ignores crlf newline conversion specified by set_encoding
https://bugs.ruby-lang.org/issues/21763#change-115457

* Author: YO4 (Yoshinao Muramatsu)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
On Windows, output pipes have no crlf conversion applied by default except for stdout/stderr, also it ignore set_encoding(crlf_newline: true).
```
> ruby -e "IO.pipe { |r,w| w.set_encoding('ascii-8bit', crlf_newline: true); w.puts ?a; w.close; p r.binmode.read }"
"a\n" # => "a\r\n" is expected
```

On other platforms, this is effective.
```
$ ruby -e "IO.pipe { |r,w| w.set_encoding('ascii-8bit', crlf_newline: true); w.puts ?a; w.close; p r.binmode.read }"
"a\r\n"
```

This occurs only when using the C runtime _write() for newline conversion. It works correctly when performing CRLF conversion using encoding conversion.
```
> ruby -e "IO.pipe { |r,w| w.set_encoding('us-ascii', crlf_newline: true); w.puts ?a; w.close; p r.binmode.read }"
"a\r\n"
```

This also affects an IO duped from stdout.
```
> ruby -e "STDOUT.puts ?a; STDOUT.dup.puts ?b" | ruby -e "p STDIN.binmode.read"
"a\r\nb\n" # => "b\n" seems to wrong
```




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