[New-bugs-announce] [issue40049] tarfile cannot extract from stdin

[Danijel]

New submission from Danijel <danijel.tasov at consol.de>:

Hi,

I have the following code:

```
import tarfile
import sys

tar = tarfile.open(fileobj=sys.stdin.buffer, mode='r|*')
tar.extractall("tarout")
tar.close()
```

then doing the following on a debian 10 system:

```
$ python -m tarfile -c git.tar /usr/share/doc/git
$ python -V
Python 3.8.1
$ cat git.tar | python foo.py
$ cat git.tar | python foo.py
Traceback (most recent call last):
  File "foo.py", line 5, in <module>
    tar.extractall("tarout")
  File "/home/danielt/miniconda3/lib/python3.8/tarfile.py", line 2026, in extractall
    self.extract(tarinfo, path, set_attrs=not tarinfo.isdir(),
  File "/home/danielt/miniconda3/lib/python3.8/tarfile.py", line 2067, in extract
    self._extract_member(tarinfo, os.path.join(path, tarinfo.name),
  File "/home/danielt/miniconda3/lib/python3.8/tarfile.py", line 2139, in _extract_member
    self.makefile(tarinfo, targetpath)
  File "/home/danielt/miniconda3/lib/python3.8/tarfile.py", line 2178, in makefile
    source.seek(tarinfo.offset_data)
  File "/home/danielt/miniconda3/lib/python3.8/tarfile.py", line 513, in seek
    raise StreamError("seeking backwards is not allowed")
tarfile.StreamError: seeking backwards is not allowed
```

The second extraction trys to seek, although the mode is 'r|*'.


For reference if I remove ".buffer" from the code above, I can run
it with python2 without problems:

```
$ cat foo2.py
import tarfile
import sys

tar = tarfile.open(fileobj=sys.stdin, mode='r|*')
tar.extractall("tarout")
tar.close()

$ cat git.tar | python2 foo2.py
$ cat git.tar | python2 foo2.py
$ cat git.tar | python2 foo2.py
$ cat git.tar | python2 foo2.py
$ cat git.tar | python2 foo2.py
```

----------
components: Library (Lib)
messages: 364860
nosy: dtamuc
priority: normal
severity: normal
status: open
title: tarfile cannot extract from stdin
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40049>
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