While caching build artifact: "Cannot extract [path to socket file] into staging-area. Unsupported type."

Summary

Socket files in build directory fail to be stored in build artifact.

Steps to reproduce

Create a socket file in build directory. Probably pipe would also fail.

What is the current bug behavior?

You get an error like:

    [00:00:41] FAILURE base/gpgme.bst: Cannot extract /home/valentin/.cache/buildstream/build/base-gpgme-_z05id4i/root/buildstream/base-sdk/base/gpgme.bst/bst_build_dir/tests/gpg/S.gpg-agent into staging-area. Unsupported type.

What is the expected correct behavior?

Socket file is just ignored.

Relevant logs and/or screenshots

Possible fixes

Ignore special files in build artifacts.

Other relevant information

Edited by Valentin David