Move the CustomExtension decorator from the v21.observables module

to v21.common.  Custom extensions are not specific to SCOs, so I
don't know why it was in that module.  Now, ExtensionDefinition
and CustomExtension are together in the same module, just like
MarkingDefinition and CustomMarking are together.  Made sense to
me.

stix2/v21/__init__.py

@@ -19,13 +19,13 @@ from .base import (
 )
 from .bundle import Bundle
 from .common import (
-    TLP_AMBER, TLP_GREEN, TLP_RED, TLP_WHITE, CustomMarking,
+    TLP_AMBER, TLP_GREEN, TLP_RED, TLP_WHITE, CustomExtension, CustomMarking,
     ExtensionDefinition, ExternalReference, GranularMarking, KillChainPhase,
     LanguageContent, MarkingDefinition, StatementMarking, TLPMarking,
 )
 from .observables import (
     URL, AlternateDataStream, ArchiveExt, Artifact, AutonomousSystem,
-    CustomExtension, CustomObservable, Directory, DomainName, EmailAddress,
+    CustomObservable, Directory, DomainName, EmailAddress,
     EmailMessage, EmailMIMEComponent, File, HTTPRequestExt, ICMPExt,
     IPv4Address, IPv6Address, MACAddress, Mutex, NetworkTraffic, NTFSExt,
     PDFExt, Process, RasterImageExt, SocketExt, Software, TCPExt,

stix2/v21/common.py

@@ -1,8 +1,10 @@
 """STIX 2.1 Common Data Types and Properties."""
 
 from collections import OrderedDict
+from collections.abc import Mapping
 
-from ..custom import _custom_marking_builder
+from . import _Extension
+from ..custom import _custom_marking_builder, _custom_extension_builder
 from ..exceptions import InvalidValueError, PropertyPresenceError
 from ..markings import _MarkingsMixin
 from ..markings.utils import check_tlp_marking
@@ -139,6 +141,30 @@ class ExtensionDefinition(_STIXBase21):
     ])
 
 
+def CustomExtension(type='x-custom-ext', properties=None):
+    """Custom STIX Object Extension decorator.
+    """
+    def wrapper(cls):
+
+        # Auto-create an "extension_type" property from the class attribute, if
+        # it exists.
+        extension_type = getattr(cls, "extension_type", None)
+        if extension_type:
+            extension_type_prop = EnumProperty(
+                EXTENSION_TYPE,
+                required=False,
+                fixed=extension_type,
+            )
+
+            if isinstance(properties, Mapping):
+                properties["extension_type"] = extension_type_prop
+            else:
+                properties.append(("extension_type", extension_type_prop))
+
+        return _custom_extension_builder(cls, type, properties, '2.1', _Extension)
+    return wrapper
+
+
 class TLPMarking(_STIXBase21):
     """For more detailed information on this object's properties, see
     `the STIX 2.1 specification <https://docs.oasis-open.org/cti/stix/v2.1/cs02/stix-v2.1-cs02.html#_yd3ar14ekwrs>`__.
@@ -260,7 +286,7 @@ def CustomMarking(type='x-custom-marking', properties=None, extension_name=None)
         if extension_name:
             from . import observables
 
-            @observables.CustomExtension(type=extension_name, properties=properties)
+            @CustomExtension(type=extension_name, properties=properties)
             class NameExtension:
                 extension_type = 'property-extension'
 

stix2/v21/observables.py

@@ -6,10 +6,9 @@ _Observable and do not have a ``_type`` attribute.
 """
 
 from collections import OrderedDict
-from collections.abc import Mapping
 import itertools
 
-from ..custom import _custom_extension_builder, _custom_observable_builder
+from ..custom import _custom_observable_builder
 from ..exceptions import AtLeastOnePropertyError, DependentPropertiesError
 from ..properties import (
     BinaryProperty, BooleanProperty, DictionaryProperty,
@@ -19,9 +18,9 @@ from ..properties import (
     TypeProperty,
 )
 from .base import _Extension, _Observable, _STIXBase21
-from .common import GranularMarking
+from .common import GranularMarking, CustomExtension
 from .vocab import (
-    ACCOUNT_TYPE, ENCRYPTION_ALGORITHM, EXTENSION_TYPE, HASHING_ALGORITHM,
+    ACCOUNT_TYPE, ENCRYPTION_ALGORITHM, HASHING_ALGORITHM,
     NETWORK_SOCKET_ADDRESS_FAMILY, NETWORK_SOCKET_TYPE,
     WINDOWS_INTEGRITY_LEVEL, WINDOWS_PEBINARY_TYPE, WINDOWS_REGISTRY_DATATYPE,
     WINDOWS_SERVICE_START_TYPE, WINDOWS_SERVICE_STATUS, WINDOWS_SERVICE_TYPE,
@@ -898,25 +897,3 @@ def CustomObservable(type='x-custom-observable', properties=None, id_contrib_pro
     return wrapper
 
 
-def CustomExtension(type='x-custom-observable-ext', properties=None):
-    """Custom STIX Object Extension decorator.
-    """
-    def wrapper(cls):
-
-        # Auto-create an "extension_type" property from the class attribute, if
-        # it exists.
-        extension_type = getattr(cls, "extension_type", None)
-        if extension_type:
-            extension_type_prop = EnumProperty(
-                EXTENSION_TYPE,
-                required=False,
-                fixed=extension_type,
-            )
-
-            if isinstance(properties, Mapping):
-                properties["extension_type"] = extension_type_prop
-            else:
-                properties.append(("extension_type", extension_type_prop))
-
-        return _custom_extension_builder(cls, type, properties, '2.1', _Extension)
-    return wrapper

stix2/v21/sdo.py

@@ -7,7 +7,6 @@ import warnings
 
 from stix2patterns.validator import run_validator
 
-from . import observables
 from ..custom import _custom_object_builder
 from ..exceptions import (
     InvalidValueError, PropertyPresenceError, STIXDeprecationWarning,
@@ -20,7 +19,9 @@ from ..properties import (
 )
 from ..utils import NOW
 from .base import _DomainObject
-from .common import ExternalReference, GranularMarking, KillChainPhase
+from .common import (
+    CustomExtension, ExternalReference, GranularMarking, KillChainPhase
+)
 from .vocab import (
     ATTACK_MOTIVATION, ATTACK_RESOURCE_LEVEL, GROUPING_CONTEXT, IDENTITY_CLASS,
     IMPLEMENTATION_LANGUAGE, INDICATOR_TYPE, INDUSTRY_SECTOR,
@@ -858,7 +859,7 @@ def CustomObject(type='x-custom-type', properties=None, extension_name=None, is_
             ]),
         )
         if extension_name:
-            @observables.CustomExtension(type=extension_name, properties=extension_properties)
+            @CustomExtension(type=extension_name, properties=extension_properties)
             class NameExtension:
                 if is_sdo:
                     extension_type = 'new-sdo'