Synapse 1.39.0rc3 (2021-07-28)

==============================
 
 Bugfixes
 --------
 
 - Fix a bug introduced in Synapse 1.38 which caused an exception at startup when SAML authentication was enabled. ([\#10477](https://github.com/matrix-org/synapse/issues/10477))
 - Fix a long-standing bug where Synapse would not inform clients that a device had exhausted its one-time-key pool, potentially causing problems decrypting events. ([\#10485](https://github.com/matrix-org/synapse/issues/10485))
 - Fix reporting old R30 stats as R30v2 stats. Introduced in v1.39.0rc1. ([\#10486](https://github.com/matrix-org/synapse/issues/10486))
 
 Internal Changes
 ----------------
 
 - Fix an error which prevented the Github Actions workflow to build the docker images from running. ([\#10461](https://github.com/matrix-org/synapse/issues/10461))
 - Fix release script to correctly version debian changelog when doing RCs. ([\#10465](https://github.com/matrix-org/synapse/issues/10465))
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Merge tag 'v1.39.0rc3' into develop

Synapse 1.39.0rc3 (2021-07-28)
==============================

Bugfixes
--------

- Fix a bug introduced in Synapse 1.38 which caused an exception at startup when SAML authentication was enabled. ([\#10477](https://github.com/matrix-org/synapse/issues/10477))
- Fix a long-standing bug where Synapse would not inform clients that a device had exhausted its one-time-key pool, potentially causing problems decrypting events. ([\#10485](https://github.com/matrix-org/synapse/issues/10485))
- Fix reporting old R30 stats as R30v2 stats. Introduced in v1.39.0rc1. ([\#10486](https://github.com/matrix-org/synapse/issues/10486))

Internal Changes
----------------

- Fix an error which prevented the Github Actions workflow to build the docker images from running. ([\#10461](https://github.com/matrix-org/synapse/issues/10461))
- Fix release script to correctly version debian changelog when doing RCs. ([\#10465](https://github.com/matrix-org/synapse/issues/10465))

synapse/storage/databases/main/end_to_end_keys.py

@@ -21,6 +21,7 @@ from canonicaljson import encode_canonical_json
 
 from twisted.enterprise.adbapi import Connection
 
+from synapse.api.constants import DeviceKeyAlgorithms
 from synapse.logging.opentracing import log_kv, set_tag, trace
 from synapse.storage._base import SQLBaseStore, db_to_json
 from synapse.storage.database import DatabasePool, make_in_list_sql_clause
@@ -381,9 +382,15 @@ class EndToEndKeyWorkerStore(EndToEndKeyBackgroundStore):
                 " GROUP BY algorithm"
             )
             txn.execute(sql, (user_id, device_id))
-            result = {}
+
+            # Initially set the key count to 0. This ensures that the client will always
+            # receive *some count*, even if it's 0.
+            result = {DeviceKeyAlgorithms.SIGNED_CURVE25519: 0}
+
+            # Override entries with the count of any keys we pulled from the database
             for algorithm, key_count in txn:
                 result[algorithm] = key_count
+
             return result
 
         return await self.db_pool.runInteraction(