support building against mingw headers

[totaam]

Building on MSYS2 requires some minor changes, please consider merging them:

• only include gss.h as the other header files don't exist - this can easily be IFDEFed (I just hacked it)
• gss_mech_krb5 is not defined in those header files, I used python struct.pack to generate the value
• I provided environment variables to skip detection, alternatively the detection can be enhanced to detect the mingw paths
• skip running krb5-config gssapi which is not installed - it would error out

To test, just install msys2, then install gss: pacman -S mingw-w64-x86_64-gss and then try to build python-gssapi.

To see the exact changes that I made to get it to build, please see:
xpra ticket 1691 - comment 7

[DirectXMan12]

Awesome, can you submit a PR with your chances? Some initial feedback based on the linked bug:

• only include gss.h as the other header files don't exist - this can easily be IFDEFed (I just hacked it)

Yep, the three header files are already designed to conditionalize logic like that (they currently do it for OSX strangeness). You'd just need to modify setup.py to populate a constant to indicate that we need gss.h if gssapi.h, etc are missing on Windows.

• gss_mech_krb5 is not defined in those header files, I used python struct.pack to generate the value.

There's a method on the OID class itself that should do that for you (from_int_seq if you have numbers, or use the elements argument to the constructor if you have bytes).

However, those constants shouldn't strictly be necessary to compile, and the compilation of that file can be disabled by setting the GSSAPI_MECHS environment variable to an empty string at build time:

python-gssapi/setup.py

Lines 195 to 203 in 7018e58

	MECHS_SUPPORTED = os.environ.get('GSSAPI_MECHS', 'krb5').split(',')
	for mech in MECHS_SUPPORTED:
	res.append(Extension('gssapi.raw.mech_%s' % mech,
	extra_link_args=link_args,
	extra_compile_args=compile_args,
	library_dirs=library_dirs,
	sources=['gssapi/raw/mech_%s.%s' % (mech,
	SOURCE_EXT)]))

• I provided environment variables to skip detection, alternatively the detection can be enhanced to detect the mingw paths

I'd prefer to see if we can detect mingw, but an environment variable is fine for a first pass if you don't have time.

[totaam]

Here's the pull request for the first part:
#149

I'm a little bit nervous about the gss_mech_krb5 change: do you mean using gb.MechType.kerberos or using gb.OID(elements=kerberos_bytes) and getting the list of bytes from somewhere?
This part could potentially break python-gssapi so I've not included in the pull request.

For the record, here's the build error due to the missing definition for gss_mech_krb5 on a 32-bit system:

running build_ext
building 'gssapi.raw.mech_krb5' extension
C:\msys32\mingw32\bin/i686-w64-mingw32-gcc.exe -fno-strict-aliasing -march=i686 -mtune=generic -O2 -pipe -fwrapv -D__USE_MINGW_ANSI_STDIO=1 -DNDEBUG -DNDEBUG -Igssapi/raw -I./gssapi/raw -IC:/msys32/mingw32/include/python2.7 -c gssapi/raw/mech_krb5.c -o build/temp.mingw-2.7/gssapi/raw/mech_krb5.o -fPIC
gssapi/raw/mech_krb5.c: In function 'initmech_krb5':
gssapi/raw/mech_krb5.c:1557:80: error: 'gss_mech_krb5' undeclared (first use in this function); did you mean 'initmech_krb5'?
   __pyx_t_4 = ((PyObject *)__pyx_f_6gssapi_3raw_17cython_converters_c_make_oid(gss_mech_krb5)); if (unlikely(!__pyx_t_4)) __PYX_ERR(1, 21, __pyx_L1_error)
                                                                                ^~~~~~~~~~~~~
                                                                                initmech_krb5
gssapi/raw/mech_krb5.c:1557:80: note: each undeclared identifier is reported only once for each function it appears in
Building from Cython files...
error: command 'C:\\msys32\\mingw32\\bin/i686-w64-mingw32-gcc.exe' failed with exit status 1

[totaam]

Fix for the pedantic python syntax checkers which didn't like the "bare except" statement:
a9c3c44

[frozencemetery]

I believe this was addressed in #149.