gh-75203: Add support for custom compressor in tarfile

[insomniacslk]

Exposed interface to specify a custom compressor for tarfile.
To achieve this, a new compression type, "custom", and a new keyword argument compressor have been added. The compressor has to be a callable with the interface as explained below.

This change just exposes the internal interface. Ideally the interface should be simpler, and just require an input and an output streams to compress/decompress and some modifiers. Additionally the classmethod is not necessary and any callable with the below interface should work. This could be done iteratively in a subsequent commit.

The compressor has to be a class method that takes as input cls, name, mode, fileobj, compresslevel and **kwargs. This is exactly the same interface as the open methods referenced by OPEN_METH in tarfile.py, e.g. TarFile.gzipopen or TarFile.bz2open.

The stream interface via the internal _Stream class is not exposed. As a consequence it is not possible to specify a compressor that uses such interface.

https://bugs.python.org/issue31020

• Issue: Add support for custom compressor in tarfile #75203

[the-knights-who-say-ni]

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[insomniacslk]

Update my account on BPO to include my github handle, should be ok now

[insomniacslk]

Any chance this could get a look?

[Mariatta]

Thanks for the PR. The changes proposed aren't considered trivial, and requires an issue to be created in https://bugs.python.org

Can you first create the issue? Thanks.

[insomniacslk]

Sure! Just created http://bugs.python.org/issue31020

[insomniacslk]

What are the next steps here? I created the bug on BPO, not sure if now it's just matter of waiting until someone looks at the issue or if there's something to be done on my side. Thanks!

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[encukou]

To use a custom compressor, pass a file-like object like LZMAFile as fileobj.
Adding dedicated support, as in this PR, would complicate the API and test matrix too much.
See the issue for discussion.

Sorry for the delay in responding. Hopefully, it's better late than never.