Support constructing OIDs from integers

This commit introduces support for constructing OIDs using integers
(instead of having to pass the BER-encoded bytes to the constructor).

Author: sigmaris

gssapi/raw/oids.pyx

@@ -1,5 +1,7 @@
 GSSAPI="BASE"  # This ensures that a full module is generated by Cython
 
+import six
+
 from libc.string cimport memcmp, memcpy
 from libc.stdlib cimport free, malloc
 
@@ -61,6 +63,54 @@ cdef class OID:
         memcpy(self.raw_oid.elements, byte_str, self.raw_oid.length)
         return 0
 
+    @classmethod
+    def from_int_seq(cls, integer_sequence):
+        """Create a OID from a sequence of integers
+
+        This method creates an OID from a sequence of integers.
+        The sequence can either be in dotted form as a string,
+        or in list form.
+
+        This method is not for BER-encoded byte strings, which
+        can be passed directly to the OID constructor.
+
+        Args:
+            integer_sequence: either a list of integers or
+                a string in dotted form
+
+        Returns:
+            OID: the OID represented by the given integer sequence
+
+        Raises:
+            ValueError: the sequence is less than two elements long
+        """
+
+        if isinstance(integer_sequence, six.string_types):
+            integer_sequence = integer_sequence.split('.')
+
+        oid_seq = [int(x) for x in integer_sequence]
+
+        elements = cls._encode_asn1ber(oid_seq)
+
+        return cls(elements=elements)
+
+    @staticmethod
+    def _encode_asn1ber(oid_seq):
+        if len(oid_seq) < 2:
+            raise ValueError("Sequence must be 2 or more elements long.")
+
+        byte_seq = bytearray([oid_seq[0] * 40 + oid_seq[1]])
+        for element in oid_seq[2:]:
+            element_seq = [element & 0x7f]
+
+            while element > 127:
+                element >>= 7
+                element_seq.insert(0, (element & 0x7f) | 0x80)
+
+            byte_seq.extend(element_seq)
+
+        return bytes(byte_seq)
+
     def __dealloc__(self):
         # NB(directxman12): MIT Kerberos has gss_release_oid
         #                   for this purpose, but it's not in the RFC

gssapi/tests/test_raw.py

@@ -800,3 +800,14 @@ def test_decode_from_bytes(self):
             o = gb.OID(elements=oid['bytes'])
             text = repr(o)
             text.should_be("<OID {0}>".format(oid['string']))
+
+    def test_encode_from_string(self):
+        for oid in TEST_OIDS.values():
+            o = gb.OID.from_int_seq(oid['string'])
+            o.__bytes__().should_be(oid['bytes'])
+
+    def test_encode_from_int_seq(self):
+        for oid in TEST_OIDS.values():
+            int_seq = oid['string'].split('.')
+            o = gb.OID.from_int_seq(int_seq)
+            o.__bytes__().should_be(oid['bytes'])

setup.py

@@ -194,7 +194,8 @@ def gssapi_modules(lst):
     keywords=['gssapi', 'security'],
     install_requires=[
         'enum34',
-        'decorator'
+        'decorator',
+        'six'
     ],
     tests_require=[
         'tox'