Bug #20416: IO#read doesn't preserve buffer encoding if `maxlen = nil`

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: 3.3.0
• Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN

[andrykonchin (Andrew Konchin)]

IO#read(nil, buffer) doesn't change buffer's encoding, but it does when maxlen parameter is specified:

buffer = "".encode(Encoding::ISO_8859_1)
p File.open("test.rb").read(1000, buffer).encoding # => #<Encoding:ISO-8859-1>

buffer = "".encode(Encoding::ISO_8859_1)
p File.open("test.rb").read(nil, buffer).encoding  # => #<Encoding:UTF-8>

I would expect changing buffer encoding in all the cases.

[byroot (Jean Boussier)]

Related: https://github.com/ruby/spec/pull/1145

[Eregon (Benoit Daloze)]

• Description updated (diff)

[byroot (Jean Boussier)]

I git blamed this behavior all the way down to 2007, by @matz (Yukihiro Matsumoto): https://github.com/ruby/ruby/commit/0ca7036682dad1caea4e7a4fe8fd908d94c878e8 and it seems deliberate

* io.c (read_all): should associate default external encoding.
* io.c (io_read): should NOT associate default external encoding.