Py_GetVersion() is broken when using mqueue and a long patch name

[ericsnowcurrently]

BPO	21313
Nosy	@ericsnowcurrently, @vadmium
Files	parse-version.patch

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

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GitHub fields:

assignee = None
closed_at = <Date 2016-06-08.12:16:20.554>
created_at = <Date 2014-04-19.22:17:18.809>
labels = ['interpreter-core', 'type-bug']
title = 'Py_GetVersion() is broken when using mqueue and a long patch name'
updated_at = <Date 2016-06-08.12:16:20.552>
user = 'https://github.com/ericsnowcurrently'

bugs.python.org fields:

activity = <Date 2016-06-08.12:16:20.552>
actor = 'martin.panter'
assignee = 'none'
closed = True
closed_date = <Date 2016-06-08.12:16:20.554>
closer = 'martin.panter'
components = ['Interpreter Core']
creation = <Date 2014-04-19.22:17:18.809>
creator = 'eric.snow'
dependencies = []
files = ['42836']
hgrepos = []
issue_num = 21313
keywords = ['patch']
message_count = 6.0
messages = ['216883', '238905', '265443', '265444', '267827', '267842']
nosy_count = 3.0
nosy_names = ['python-dev', 'eric.snow', 'martin.panter']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21313'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

[ericsnowcurrently]

Py_GetVersion() (in Python/getversion.c) builds the version string returned by sys.version:

PyOS_snprintf(version, sizeof(version), "%.80s (%.80s) %.80s",
PY_VERSION, Py_GetBuildInfo(), Py_GetCompiler());

In turn, Py_GetBuildInfo() (in Modules/getbuildinfo.c) returns the "build" portion of Python's version string. When available, the tag returned by "hg id -t" constitutes part of that build string.

The problem is that when using mqueue the result of "hg id -t" can be pretty long. For example:

bpo-21226-fix-PyImport_ExecCodeModuleObject.diff qbase qtip tip

That's 74 characters for just part of a build string that may be well over 100 characters. However, Py_GetVersion() truncates it to 80 characters.

The consequence is that this value of sys.version causes platform._sys_version() to fail since the version string does not match the expected pattern.

So either Py_GetVersion() should relax (-1) or Py_GetBuildInfo() should restrict the length of the resulting build string (+1). Would it work to truncate just the hgid part so that the whole string returned by Py_GetBuildInfo() is no more than length 80? E.g.

-    PyOS_snprintf(buildinfo, sizeof(buildinfo),
-                  "%s%s%s, %.20s, %.9s", hgid, sep, revision, DATE, TIME);
+    PyOS_snprintf(buildinfo, 80,
+                  "%.43s%.1s%.13s, %.20s, %.9s", hgid, sep, revision, DATE, TIME);

[BreamoreBoy]

Any comments on the proposal to restrict the length of the returned string from Py_GetBuildInfo() to 80 characters?

[vadmium]

Currently Py_GetBuildInfo() just returns a long untruncated string. Perhaps it would be safer to leave that as it is, and just make the parsing in the “platform” module more tolerant. What do you think?

I never really cared about the details in Py_GetBuildInfo(), but it would be nice if the test suite would run :)

[vadmium]

>>> Py_GetBuildInfo = pythonapi.Py_GetBuildInfo
>>> Py_GetBuildInfo.restype = c_char_p
>>> Py_GetBuildInfo()  # Not truncated
'qbase qtip subprocess-stderr_redirect_with_no_stdout_redirect-2.diff tip:0b641285389d+, May 13 2016, 02:10:26'

Demo of my problem with the test suite:

$ ./python -m test.regrtest
Traceback (most recent call last):
  [. . .]
  File "/media/disk/home/proj/python/cpython/Lib/test/test_support.py", line 1423, in check_impl_detail
    return guards.get(platform.python_implementation().lower(), default)
  File "/media/disk/home/proj/python/cpython/Lib/platform.py", line 1451, in python_implementation
    return _sys_version()[0]
  File "/media/disk/home/proj/python/cpython/Lib/platform.py", line 1416, in _sys_version
    repr(sys_version))
ValueError: failed to parse CPython sys.version: '2.7.11+ (qbase qtip subprocess-stderr_redirect_with_no_stdout_redirect-2.diff tip:0b64128) \n[GCC 5.3.0]'

[python-dev]

New changeset b86e259271b3 by Martin Panter in branch '2.7':
Issue bpo-21313: Tolerate truncated buildinfo in sys.version
https://hg.python.org/cpython/rev/b86e259271b3

New changeset 4deec876db0d by Martin Panter in branch '3.5':
Issue bpo-21313: Tolerate truncated buildinfo in sys.version
https://hg.python.org/cpython/rev/4deec876db0d

New changeset aec5a3fc4890 by Martin Panter in branch 'default':
Issue bpo-21313: Merge version parsing from 3.5
https://hg.python.org/cpython/rev/aec5a3fc4890

[vadmium]

Closing now that platform._sys_version() can tolerate the truncated version info.