crash if a socket is listed with --files-from

Summary

If the files to backup as read from a file using the --files-from option (see #151 (closed)) lists a file which is actually a unix domain socket duplicity will crash with TypeError and the message: Can't mix strings and bytes in path components.

The crash only occurs when using --files-from.

Environment

Gentoo Linux

duplicity 0.8.23, patched with !120 (closed) and !125 (closed) - not ideal for bug reports sorry, but 0.8.23 was the stable gentoo package at the time

Steps to reproduce

Bind a unix domain socket to the filesystem to be backed up, name it in a text file, pass file to duplicity using --files-from. **boom**

What is the current bug behaviour?

Crash in Selection.Iterate.error_handler() when calling os.path.join(), reporting the above TypeError. If the --files-from option is not used, duplicity just skips the socket and emits a message in the log (correct behaviour).

What is the expected correct behaviour?

Same behaviour as observed without --files-from option.

Relevant logs and/or screenshots

ERROR 30 TypeError
. Traceback (innermost last):
.   File "/usr/lib/python-exec/python3.10/duplicity", line 87, in <module>
.     with_tempdir(main)
.   File "/usr/lib/python-exec/python3.10/duplicity", line 70, in with_tempdir
.     fn()
.   File "/usr/lib/python3.10/site-packages/duplicity/dup_main.py", line 1580, in main
.     do_backup(action)
.   File "/usr/lib/python3.10/site-packages/duplicity/dup_main.py", line 1709, in do_backup
.     full_backup(col_stats)
.   File "/usr/lib/python3.10/site-packages/duplicity/dup_main.py", line 589, in full_backup
.     bytes_written = write_multivol(u"full", tarblock_iter,
.   File "/usr/lib/python3.10/site-packages/duplicity/dup_main.py", line 450, in write_multivol
.     at_end = gpg.GzipWriteFile(tarblock_iter, tdp.name, config.volsize)
.   File "/usr/lib/python3.10/site-packages/duplicity/gpg.py", line 451, in GzipWriteFile
.     new_block = next(block_iter)
.   File "/usr/lib/python3.10/site-packages/duplicity/diffdir.py", line 544, in __next__
.     result = self.process(next(self.input_iter))  # pylint: disable=assignment-from-no-return
.   File "/usr/lib/python3.10/site-packages/duplicity/diffdir.py", line 209, in get_delta_iter
.     for new_path, sig_path in collated:
.   File "/usr/lib/python3.10/site-packages/duplicity/diffdir.py", line 310, in collate2iters
.     for relem1 in riter1:
.   File "/usr/lib/python3.10/site-packages/duplicity/selection.py", line 93, in __next__
.     return next(self.iter)
.   File "/usr/lib/python3.10/site-packages/duplicity/selection.py", line 191, in Iterate
.     subpath, scan = next(dirs_to_scan[-1])
.   File "/usr/lib/python3.10/site-packages/duplicity/selection.py", line 155, in dir_scanner
.     new_path = robust.check_common_error(
.   File "/usr/lib/python3.10/site-packages/duplicity/robust.py", line 55, in check_common_error
.     return error_handler(exc, *args)
.   File "/usr/lib/python3.10/site-packages/duplicity/selection.py", line 113, in error_handler
.     fullpath = os.path.join(path.name, filename)
.   File "/usr/lib/python3.10/posixpath.py", line 90, in join
.     genericpath._check_arg_types('join', a, *p)
.   File "/usr/lib/python3.10/genericpath.py", line 155, in _check_arg_types
.     raise TypeError("Can't mix strings and bytes in path components") from None
.  TypeError: Can't mix strings and bytes in path components

Possible fixes

Duplicity crashes because the base path from the Path instance for the socket location is a bytestring (Path.name for the directory containing the socket) while the socket filename is a string (from the --files-from data structures). That the latter are strings otherwise works fine - when passed to Path.append() the constructor for that class helpfully encodes them as bytes.

The data structures used to implement the --files-from option should probably store encoded byte sequences instead of str instances, as this appears to be how the Path class deals with them.

Will post a patch shortly.