Load librpm on demand for IPAVersion

ctypes.util.find_library() is costly and slows down startup of ipa CLI.
ipaplatform.redhat.tasks now defers loading of librpm until its needed.
CFFI has been replaced with ctypes, too.

See: https://pagure.io/freeipa/issue/6851
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>

ipaplatform/redhat/tasks.py

@@ -25,6 +25,7 @@ system tasks.
 '''
 from __future__ import print_function
 
+import ctypes
 import logging
 import os
 import socket
@@ -36,7 +37,6 @@ from ctypes.util import find_library
 from functools import total_ordering
 from subprocess import CalledProcessError
 
-from cffi import FFI
 from pyasn1.error import PyAsn1Error
 from six.moves import urllib
 
@@ -50,15 +50,6 @@ from ipaplatform.base.tasks import BaseTaskNamespace
 
 logger = logging.getLogger(__name__)
 
-_ffi = FFI()
-_ffi.cdef("""
-int rpmvercmp (const char *a, const char *b);
-""")
-
-# use ctypes loader to get correct librpm.so library version according to
-# https://cffi.readthedocs.org/en/latest/overview.html#id8
-_librpm = _ffi.dlopen(find_library("rpm"))
-
 
 def selinux_enabled():
     """
@@ -78,6 +69,21 @@ def selinux_enabled():
 
 @total_ordering
 class IPAVersion(object):
+    _rpmvercmp_func = None
+
+    @classmethod
+    def _rpmvercmp(cls, a, b):
+        """Lazy load and call librpm's rpmvercmp
+        """
+        rpmvercmp_func = cls._rpmvercmp_func
+        if rpmvercmp_func is None:
+            librpm = ctypes.CDLL(find_library('rpm'))
+            rpmvercmp_func = librpm.rpmvercmp
+            # int rpmvercmp(const char *a, const char *b)
+            rpmvercmp_func.argtypes = [ctypes.c_char_p, ctypes.c_char_p]
+            rpmvercmp_func.restype = ctypes.c_int
+            cls._rpmvercmp_func = rpmvercmp_func
+        return rpmvercmp_func(a, b)
 
     def __init__(self, version):
         self._version = version
@@ -90,12 +96,12 @@ class IPAVersion(object):
     def __eq__(self, other):
         if not isinstance(other, IPAVersion):
             return NotImplemented
-        return _librpm.rpmvercmp(self._bytes, other._bytes) == 0
+        return self._rpmvercmp(self._bytes, other._bytes) == 0
 
     def __lt__(self, other):
         if not isinstance(other, IPAVersion):
             return NotImplemented
-        return _librpm.rpmvercmp(self._bytes, other._bytes) < 0
+        return self._rpmvercmp(self._bytes, other._bytes) < 0
 
     def __hash__(self):
         return hash(self._version)

ipatests/test_ipaplatform/test_tasks.py

@@ -0,0 +1,28 @@
+#
+# Copyright (C) 2017  FreeIPA Contributors see COPYING for license
+#
+
+from ipaplatform.tasks import tasks
+
+
+def test_ipa_version():
+    v3 = tasks.parse_ipa_version('3.0')
+    assert v3.version == u'3.0'
+    if hasattr(v3, '_rpmvercmp'):
+        assert v3._rpmvercmp_func is None
+        v3._rpmvercmp(b'1', b'2')
+        assert v3._rpmvercmp_func is not None
+
+    v4 = tasks.parse_ipa_version('4.0')
+    assert v4.version == u'4.0'
+    if hasattr(v4, '_rpmvercmp'):
+        assert v4._rpmvercmp_func is not None
+
+    assert v3 < v4
+    assert v3 <= v4
+    assert v3 <= v3
+    assert v3 != v4
+    assert v3 == v3
+    assert not v3 == v4
+    assert v4 > v3
+    assert v4 >= v3