From: "YO4 (Yoshinao Muramatsu) via ruby-core" <ruby-core@...>
Date: 2025-11-17T13:20:42+00:00
Subject: [ruby-core:123829] [Ruby Bug#21691] On Windows some of binary read functions of IO are not functional

Issue #21691 has been reported by YO4 (Yoshinao Muramatsu).

----------------------------------------
Bug #21691: On Windows some of binary read functions of IO are not functional
https://bugs.ruby-lang.org/issues/21691

* Author: YO4 (Yoshinao Muramatsu)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
When using the binary read method of IO on a file containing ���\r\n���, it should read ���\r���, but some methods do not function correctly on Windows.
```ruby
File.binwrite("crlf.txt", "\r\n")

methods = {
  readn: proc { |f| f.read(1) },
  getbyte: proc { |f| f.getbyte.chr },
  readbyte: proc { |f| f.readbyte.chr },
  readpartial: proc { |f| f.readpartial(1) },
  read_nonblock: proc { |f| f.read_nonblock(1) },
  sysread: proc { |f| f.sysread(1) },
  pread: proc { |f| f.pread(1, 0) },
}

def test(mode, name, method)
  open("crlf.txt", "r") do |f|
    p [mode, name, method.call(f)]
  end
end

methods.each { |k, v| test("r", k, v) }
methods.each { |k, v| test("rt", k, v) }
```
results:
```ruby
["r", :readn, "\r"]
["r", :getbyte, "\n"] # => shold be "\r"
["r", :readbyte, "\n"] # => shold be "\r"
["r", :readpartial, "\n"] # => shold be "\r"
["r", :read_nonblock, "\n"] # => shold be "\r"
["r", :sysread, "\n"] # => shold be "\r"
["r", :pread, "\r"]
["rt", :readn, "\r"]
["rt", :getbyte, "\n"] # => shold be "\r"
["rt", :readbyte, "\n"] # => shold be "\r"
["rt", :readpartial, "\n"] # => shold be "\r"
["rt", :read_nonblock, "\n"] # => shold be "\r"
["rt", :sysread, "\n"] # => shold be "\r"
["rt", :pread, "\r"]
```
On Ubuntu in WSL, all returns are ���\r���.



-- 
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