[ruby-core:116194] [Ruby master Bug#19542] Operations on zero-sized IO::Buffer are raising

Issue #19542 has been updated by ioquatix (Samuel Williams).


See https://github.com/ruby/ruby/pull/9532 for the proposed changes.

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Bug #19542: Operations on zero-sized IO::Buffer are raising
https://bugs.ruby-lang.org/issues/19542#change-106210

* Author: hanazuki (Kasumi Hanazuki)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-linux]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
I found that IO::Buffer of zero length is not cloneable.

```
% ruby -v
ruby 3.2.1 (2023-02-08 revision 31819e82c8) [x86_64-linux]

% ruby -e 'p IO::Buffer.for("").dup'
-e:1:in `initialize_copy': The buffer is not allocated! (IO::Buffer::AllocationError)
        from -e:1:in `initialize_dup'
        from -e:1:in `dup'
        from -e:1:in `<main>'

% ruby -e 'p IO::Buffer.new(0).dup'
-e:1: warning: IO::Buffer is experimental and both the Ruby and C interface may change in the future!
-e:1:in `initialize_copy': The buffer is not allocated! (IO::Buffer::AllocationError)
        from -e:1:in `initialize_dup'
        from -e:1:in `dup'
        from -e:1:in `<main>'
```

It seems `IO::Buffer.new(0)` allocates no memory for buffer on object creation and thus prohibits reading from or writing to it. So `#dup` method copying zero bytes into the new IO::Buffer raises the exception.
Empty buffers, however, often appear in corner cases of usual operations (encrypting an empty string, encoding an empty list of items into binary, etc.) and it would be easy if such cases could be handled consistently.

Other operations on NULL IO::Buffers are also useful but currently raising.

```
IO::Buffer.new(0) <=> IO::Buffer.new(1)
IO::Buffer.new(0).each(:U8).to_a
IO::Buffer.new(0).get_values([], 0)
IO::Buffer.new(0).set_values([], 0, [])
```

I'm not sure this is a bug or by design, but at least I don't want cloning and comparison to raise.



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