Correctly ignore all values in rpmdiff

Related: https://pagure.io/koji/issue/994

koji/rpmdiff.py

@@ -86,7 +86,7 @@ class Rpmdiff:
             for entry in FILEIDX:
                 if tag == entry[0]:
                     # store marked position for erasing data
-                    entry[1] = -entry[1]
+                    entry[1] = -entry[1] - 100
                     break
 
         old = self.__load_pkg(old)
@@ -140,8 +140,8 @@ class Rpmdiff:
                         diff = 1
                     elif entry[1] < 0:
                         # erase fields which are ignored
-                        old_file[-entry[1]] = None
-                        new_file[-entry[1]] = None
+                        old_file[-entry[1] - 100] = None
+                        new_file[-entry[1] - 100] = None
                         format = format + '.'
                     else:
                         format = format + '.'

tests/test_hub/test_rpmdiff.py

@@ -62,6 +62,27 @@ class TestRPMDiff(unittest.TestCase):
             d = koji.rpmdiff.Rpmdiff(rpm1, rpm2, ignore='S5TN')
             self.assertEqual(d.textdiff(), '')
 
+    def test_rpmdiff_size(self):
+        data_path = os.path.abspath("tests/test_hub/data/rpms")
+
+        # the only differences between rpm1 and rpm2 are 1) create time 2) file name
+        rpm1 = os.path.join(data_path, 'different_size_a.noarch.rpm')
+        rpm2 = os.path.join(data_path, 'different_size_b.noarch.rpm')
+
+        diff_output = "S.5.......T /bin/test"
+
+        # case 1. no ignore option, timestamp is different
+        # perform twice check to verify issue: #994
+        for _ in range(0, 2):
+            d = koji.rpmdiff.Rpmdiff(rpm1, rpm2)
+            self.assertEqual(d.textdiff(), diff_output)
+
+        # case 2. ignore timestamp, two rpms should be the same
+        # perform twice check to verify issue: #994
+        for r in range(0, 2):
+            d = koji.rpmdiff.Rpmdiff(rpm1, rpm2, ignore='S5TN')
+            self.assertEqual(d.textdiff(), '')
+
 class TestCheckNoarchRpms(unittest.TestCase):
     @mock.patch('kojihub.rpmdiff')
     def test_check_noarch_rpms_empty_invocation(self, rpmdiff):