Nonsense errors reported by msilib.FCICreate for bad argument

[JeffreyArmstrong]

BPO	21931
Nosy	@loewis, @tjguk, @ezio-melotti, @bitdancer, @zware, @zooba
Files	_msi.3.4.0.patch: patch for Python 3.4.0

^{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 2015-05-18.05:57:32.221>
created_at = <Date 2014-07-07.12:53:10.675>
labels = ['extension-modules', 'type-bug', 'OS-windows']
title = 'Nonsense errors reported by msilib.FCICreate for bad argument'
updated_at = <Date 2015-05-18.05:57:32.220>
user = 'https://bugs.python.org/JeffreyArmstrong'

bugs.python.org fields:

activity = <Date 2015-05-18.05:57:32.220>
actor = 'zach.ware'
assignee = 'none'
closed = True
closed_date = <Date 2015-05-18.05:57:32.221>
closer = 'zach.ware'
components = ['Extension Modules', 'Windows']
creation = <Date 2014-07-07.12:53:10.675>
creator = 'Jeffrey.Armstrong'
dependencies = []
files = ['35935']
hgrepos = []
issue_num = 21931
keywords = ['patch']
message_count = 12.0
messages = ['222458', '222853', '222883', '223206', '226597', '230583', '230616', '230656', '243405', '243415', '243457', '243459']
nosy_count = 8.0
nosy_names = ['loewis', 'tim.golden', 'ezio.melotti', 'r.david.murray', 'python-dev', 'zach.ware', 'steve.dower', 'Jeffrey.Armstrong']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21931'
versions = ['Python 3.4', 'Python 3.5']

[JeffreyArmstrong]

The function fcicreate in PC/_msi.c can return nonsense if the list of files passed to msilib.FCICreate does not contains tuples as expected. To replicate,

import msilib
msilib.FCICreate("test.cab", ["entry.txt"])

The above code will return a ValueError of the format:

ValueError: FCI error 11260524

The error code is meaningless. If one were to examine the code, you can see in PC/_msi.c:246 (in "current"):

    if (!PyArg_ParseTuple(item, "ss", &filename, &cabname))
        goto err;

If we look at the error handler at PC/_msi.c:262, it assumes that one of the Windows MSI API calls had failed, and will print the contents of the ERF error structure:

err:
PyErr_Format(PyExc_ValueError, "FCI error %d", erf.erfOper); /* XXX better error type */

In the case where the list does not contain tuples, the value of erf.erfOper was never initialized or set because the error being raised is not due to the Windows MSI API. The error is highly misleading as it is simply an argument error.

[ezio-melotti]

Do you want to propose a patch?

[JeffreyArmstrong]

Attached a patch. The dangers of using goto...

[bitdancer]

mslib doesn't have many tests, but it looks like it would be easy enough to add one for this?

[JeffreyArmstrong]

Is this patch going to be accepted? It fixes actual incorrect code in msilib, and it seems to have stagnated

[loewis]

I haven't had any time to work on Python in the last year, so it may take some more time for me to look into this.

[JeffreyArmstrong]

There's not much to look into. If the Python function encounters an argument error, it returns an uninitialized integer as an "error code." This patch fixes incorrect C code, nothing more.

[loewis]

Right, the entire patch might be processed in 30 minutes. I won't have these 30 minutes any time soon.

[JeffreyArmstrong]

I thought, while I'm here reporting another bug, I'd bump this once more.

There is a patch here, and it corrects clearly broken code. Should I mark this as "won't fix?"

[zware]

I'll try to have a look at this later today, but unfortunately can't
guarantee anything (I don't know C, MSI, or _msi very well).

[python-dev]

New changeset 41281737d71a by Zachary Ware in branch '3.4':
Issue bpo-21931: Fix error handling in msilib.FCICreate().
https://hg.python.org/cpython/rev/41281737d71a

New changeset cb0d1d86215e by Zachary Ware in branch 'default':
Closes bpo-21931: Merge with 3.4
https://hg.python.org/cpython/rev/cb0d1d86215e