Bug #20067: IO.pipe `int_enc` and `ext_enc` not working as documented?

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN

[byroot (Jean Boussier)]

From the documentation:

pipe(ext_enc, int_enc, **opts)

If argument int_enc is given, it must be an Encoding object or encoding name string that specifies the internal encoding to be used; if argument ext_enc is also given, it must be an Encoding object or encoding name string that specifies the external encoding to be used.

Test script:

ios = IO.pipe(Encoding::BINARY, Encoding::BINARY)

p [:internal, *ios.map(&:internal_encoding)]
p [:external, *ios.map(&:external_encoding)]

Encoding.default_internal = Encoding::UTF_8
Encoding.default_external = Encoding::UTF_8

ios = IO.pipe(Encoding::BINARY, Encoding::BINARY)

p [:internal, *ios.map(&:internal_encoding)]
p [:external, *ios.map(&:external_encoding)]

Actual output:

[:internal, nil, nil]
[:external, #<Encoding:ASCII-8BIT>, nil]
[:internal, nil, nil]
[:external, #<Encoding:ASCII-8BIT>, #<Encoding:UTF-8>]

Expected output:

[:internal, #<Encoding:ASCII-8BIT>, #<Encoding:ASCII-8BIT>]
[:external, #<Encoding:ASCII-8BIT>, #<Encoding:ASCII-8BIT>]
[:internal, #<Encoding:ASCII-8BIT>, #<Encoding:ASCII-8BIT>]
[:external, #<Encoding:ASCII-8BIT>, #<Encoding:ASCII-8BIT>]

Am I reading the documentation incorrectly, or is it just not working as claimed?

I tried on older versions, and it seems to have been like that all the way down to Ruby 1.9.

The only reliable way I found to have a "binary" pipe is to call IO#binmode.

[nobu (Nobuyoshi Nakada)]

If the same encoding is specified for the internal and external encodings, it means that no encoding conversion will occur.
That's what the internal encoding nil means.

$ ruby -e 'File.open(IO::NULL, "r:ASCII-8BIT:ASCII-8BIT") {|f| p [f.internal_encoding, f.external_encoding]}'
[nil, #<Encoding:ASCII-8BIT>]

Regarding the external encoding of write-io, it feels something wrong a little.