Make Package.signature return str key_id

We use the attribute in many places, but it's a "bytes" object in
pgpdump that messes up the remaining logic. Let's just wrap it from the
very beginning.

main/models.py

@@ -7,7 +7,7 @@
 from django.contrib.sites.models import Site
 
 from .fields import PositiveBigIntegerField
-from .utils import set_created_field, DependStandin
+from .utils import set_created_field, DependStandin, SignatureWrapper
 from devel.models import DeveloperKey
 from packages.alpm import AlpmAPI
 
@@ -142,7 +142,7 @@ def signature(self):
             return None
         data = BinaryData(self.signature_bytes)
         packets = list(data.packets())
-        return packets[0]
+        return SignatureWrapper(packets[0])
 
     @property
     def signer(self):

main/utils.py

@@ -6,6 +6,7 @@
 import hashlib
 import markdown
 from markdown.extensions import Extension
+from pgpdump.packet import SignaturePacket
 
 from django.core.cache import cache
 from django.db import connections, router
@@ -165,4 +166,12 @@ def __init__(self, depends):
         self.deptype = first.deptype
         self.pkg = first.pkg.base_package() or PackageStandin(first.pkg)
 
+
+class SignatureWrapper(SignaturePacket):
+    'Decode key_id from raw SignaturePacket'
+    def __init__(self, packet):
+        for field in ("sig_version", "creation_time", "expiration_time"):
+            setattr(self, field, getattr(packet, field))
+        self.key_id = str(packet.key_id) if packet.key_id else None
+
 # vim: set ts=4 sw=4 et: