use memoryview in py3

Signed-off-by: Adrian Tschira <nota@notafile.com>

synapse/storage/signatures.py

@@ -14,6 +14,7 @@
 # limitations under the License.
 
 from twisted.internet import defer
+import six
 
 from ._base import SQLBaseStore
 
@@ -21,6 +22,13 @@ from unpaddedbase64 import encode_base64
 from synapse.crypto.event_signing import compute_event_reference_hash
 from synapse.util.caches.descriptors import cached, cachedList
 
+# py2 sqlite has buffer hardcoded as only binary type, so we must use it,
+# despite being deprecated and removed in favor of memoryview
+if six.PY2:
+    db_binary_type = buffer
+else:
+    db_binary_type = memoryview
+
 
 class SignatureWorkerStore(SQLBaseStore):
     @cached()
@@ -56,7 +64,7 @@ class SignatureWorkerStore(SQLBaseStore):
             for e_id, h in hashes.items()
         }
 
-        defer.returnValue(hashes.items())
+        defer.returnValue(list(hashes.items()))
 
     def _get_event_reference_hashes_txn(self, txn, event_id):
         """Get all the hashes for a given PDU.
@@ -91,7 +99,7 @@ class SignatureStore(SignatureWorkerStore):
             vals.append({
                 "event_id": event.event_id,
                 "algorithm": ref_alg,
-                "hash": buffer(ref_hash_bytes),
+                "hash": db_binary_type(ref_hash_bytes),
             })
 
         self._simple_insert_many_txn(