base64.a85decode adobe flag incorrectly utilizes <~ as a marker causing error

[SorenSolari]

BPO	25913
Nosy	@terryjreedy, @pitrou, @serhiy-storchaka
Files	iss_25913.patch: Fix on the basis of comments. iss_25913_2.patch iss_25913_3.patch: Corrects the test.

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2016-02-24.10:13:00.441>
created_at = <Date 2015-12-19.23:31:52.977>
labels = ['type-bug', 'library']
title = 'base64.a85decode adobe flag incorrectly utilizes <~ as a marker causing error'
updated_at = <Date 2016-02-24.10:13:00.439>
user = 'https://bugs.python.org/SorenSolari'

bugs.python.org fields:

activity = <Date 2016-02-24.10:13:00.439>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2016-02-24.10:13:00.441>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2015-12-19.23:31:52.977>
creator = 'Soren Solari'
dependencies = []
files = ['41377', '41393', '41621']
hgrepos = []
issue_num = 25913
keywords = ['patch']
message_count = 9.0
messages = ['256745', '256842', '258080', '258268', '259767', '259802', '260570', '260781', '260782']
nosy_count = 7.0
nosy_names = ['terry.reedy', 'pitrou', 'python-dev', 'serhiy.storchaka', 'isoschiz', 'curioswati', 'Soren Solari']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue25913'
versions = ['Python 3.5', 'Python 3.6']

[SorenSolari]

According to the PDF Spec http://www.adobe.com/devnet/pdf/pdf_reference.html section 7.4.3,
The ascii85decode function only utilizes ~> as an EOD 2byte character, there is no mention of leading <. Therefore using the base64.a85decode(data, adobe=True) does not work on valid data coming from a pdf because that data may not have a leading <.

Solution: do not require leading <~ for adobe=True.

[isoschiz]

The proposed patch does stop requiring the leading <~, but still trims the first two characters off the data set. This will no doubt fail in cases where there is no leading marker.

I think it will need to explicitly handle the case where the leading marker is there vs. not.

[terryjreedy]

Soren, for me, the page you link to is impossible to read as it blinks every second or so, something I have never seen before. Perhaps it is trying to forward to the actual reference. As near as I can tell, it just lists about 3 other documents and is not a reference in itself, and for me has no sections. Can you provide a better link, perhaps one that is more direct?

[curioswati]

Modified according to Serhiy's last comment.

[curioswati]

Is there any requirement for further modification or it can be accepted?

[serhiy-storchaka]

Martin, Antoine, what would you say about this?

[isoschiz]

3.patch looks good to me.

[python-dev]

New changeset ce5bf3290621 by Serhiy Storchaka in branch '3.5':
Issue bpo-25913: Leading <~ is optional now in base64.a85decode() with adobe=True.
https://hg.python.org/cpython/rev/ce5bf3290621

New changeset 90d5473b8673 by Serhiy Storchaka in branch 'default':
Issue bpo-25913: Leading <~ is optional now in base64.a85decode() with adobe=True.
https://hg.python.org/cpython/rev/90d5473b8673

[serhiy-storchaka]

Thank you Soren for your report, thank you Swati for your patch, and thank you Martin for your review.