[issue40049] tarfile cannot extract from stdin

[Tal Einat]

Tal Einat  added the comment:

This is actually a duplicate of issue12800, which itself describe precisely the 
same issue as in issue10761, which was fixed but then the fix was lost in a bad 
merge.

I'm closing this, as discussion should happen on the original issues.

--
resolution:  -> duplicate
stage: patch review -> resolved
status: open -> closed

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[issue40049] tarfile cannot extract from stdin

[Tal Einat]

Tal Einat  added the comment:

GNU tar (v1.30, Ubuntu 20.04) does indeed overwrite files with symlinks upon 
extracting, while both `ln -s` and `os.symlink` do not. Therefore I agree that 
the appropriate behavior would seem to be to overwrite this way, as in the 
attached PR.

--
nosy: +taleinat

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[issue40049] tarfile cannot extract from stdin

[Danijel]

Danijel  added the comment:

For me, this patch solves my problems. Thank you.

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[issue40049] tarfile cannot extract from stdin

[Jonathan Hsu]

Jonathan Hsu  added the comment:

This is caused when tarfile tries to write a symlink that already exists. Any 
exceptions to os.symlink() as handled as if the platform doesn't support 
symlinks, so it scans the entire tar to try and find the linked files. When it 
resumes extraction, it needs to do a negative seek to pick up where it left 
off, which causes the exception.

I've reproduced the error on both Windows 10 and Ubuntu running on WSL. Python 
2.7 handled this situation by checking if the symlink exists, but it looks like 
the entire tarfile library was replaced with an alternate implementation that 
doesn't check if the symlink exists. I've created a pull request to address 
this issue.

--
nosy: +Jonathan Hsu

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[issue40049] tarfile cannot extract from stdin

[Roundup Robot]

Change by Roundup Robot :


--
keywords: +patch
nosy: +python-dev
nosy_count: 2.0 -> 3.0
pull_requests: +18546
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/19187

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[issue40049] tarfile cannot extract from stdin

[Danijel]

Danijel  added the comment:

Hi,

well, it says entity too large. I've attached a smaller one, that throws a 
similar but slightly different error. (Note: only on the _second_ extraction, 
it looks like problems with symlinks)

You can find larger ones here:

https://data.rbfh.de/issue40049/

The typescript*.txt are showing a shell session with two different python 
versions. (3.4.2 and 3.8.2)

--
Added file: https://bugs.python.org/file49003/test.tar

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[issue40049] tarfile cannot extract from stdin

[Manjusaka]

Manjusaka  added the comment:

Hello
 
I can't reproduce this issue on my Laptop from 3.8.1 to 3.9.0a4

I think maybe it depends on the file you use

would you mind to upload the file with the problem?

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nosy: +Manjusaka

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[issue40049] tarfile cannot extract from stdin

[Danijel]

Change by Danijel :


--
type:  -> crash

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[issue40049] tarfile cannot extract from stdin

[Danijel]

New submission from Danijel :

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 
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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