fix: detect ScyllaDB via SUPPORTED protocol extensions, not shard count

The driver previously identified ScyllaDB solely by the presence of
shard-related fields (SCYLLA_NR_SHARDS, SCYLLA_SHARD, etc.) in the
SUPPORTED response.  When shard-awareness is disabled on the server
side (allow_shard_aware_drivers: false), those fields are absent,
causing the driver to misidentify a ScyllaDB cluster as Cassandra.

Changes:
- Add ProtocolFeatures.detect_scylla() and is_scylla flag, set from
  known Scylla-specific extension keys (LWT, rate-limit, tablets
  routing) or sharding_info presence
- Replace sharding_info check with is_scylla for peers_v2 and
  metadata_request_timeout in cluster.py and metadata.py
- Guard int() calls against None in _ShardingInfo construction
  (c_shard_info.pyx, shard_info.py)
- Add tests for is_scylla detection and regression tests for
  missing shard fields
- Assert pf.shard_id normalization in test regressions (response
  to CodeRabbit review)

Author: mykaul

cassandra/c_shard_info.pyx

@@ -29,10 +29,10 @@ cdef class ShardingInfo():
 
     def __init__(self, shard_id, shards_count, partitioner, sharding_algorithm, sharding_ignore_msb, shard_aware_port,
                  shard_aware_port_ssl):
-        self.shards_count = int(shards_count)
+        self.shards_count = int(shards_count) if shards_count else 0
         self.partitioner = partitioner
         self.sharding_algorithm = sharding_algorithm
-        self.sharding_ignore_msb = int(sharding_ignore_msb)
+        self.sharding_ignore_msb = int(sharding_ignore_msb) if sharding_ignore_msb else 0
         self.shard_aware_port = int(shard_aware_port) if shard_aware_port else 0
         self.shard_aware_port_ssl = int(shard_aware_port_ssl) if shard_aware_port_ssl else 0
 

cassandra/cluster.py

@@ -3888,14 +3888,13 @@ def _try_connect(self, endpoint):
                   "registering watchers and refreshing schema and topology",
                   connection)
 
-        # Indirect way to determine if conencted to a ScyllaDB cluster, which does not support peers_v2
-        # If sharding information is available, it's a ScyllaDB cluster, so do not use peers_v2 table.
-        if connection.features.sharding_info is not None:
+        # ScyllaDB does not support peers_v2.  Use is_scylla (not sharding_info)
+        # so that clusters with shard-awareness disabled are still detected correctly.
+        if connection.features.is_scylla:
             self._uses_peers_v2 = False
 
-        # Only ScyllaDB supports "USING TIMEOUT"
-        # Sharding information signals it is ScyllaDB
-        self._metadata_request_timeout = None if connection.features.sharding_info is None or not self._cluster.metadata_request_timeout \
+        # Only ScyllaDB supports "USING TIMEOUT".  Use is_scylla for the same reason.
+        self._metadata_request_timeout = None if not connection.features.is_scylla or not self._cluster.metadata_request_timeout \
             else datetime.timedelta(seconds=self._cluster.metadata_request_timeout)
 
         self._tablets_routing_v1 = connection.features.tablets_routing_v1

cassandra/metadata.py

@@ -2578,8 +2578,14 @@ class SchemaParserV3(SchemaParserV22):
     _SELECT_VIEWS = "SELECT * FROM system_schema.views"
 
     def _is_not_scylla(self):
-        """Check if NOT connected to ScyllaDB by checking for shard awareness."""
-        return getattr(getattr(self.connection, 'features', None), 'shard_id', None) is None
+        """Check if NOT connected to ScyllaDB.
+
+        Uses the is_scylla flag from ProtocolFeatures, which is set from the
+        presence of Scylla-specific extension keys in the SUPPORTED response
+        (e.g. SCYLLA_LWT_ADD_METADATA_MARK, SCYLLA_RATE_LIMIT_ERROR) and
+        therefore remains True even when shard-awareness is disabled.
+        """
+        return not getattr(getattr(self.connection, 'features', None), 'is_scylla', False)
 
     _table_name_col = 'table_name'
 

cassandra/protocol_features.py

@@ -17,21 +17,43 @@ class ProtocolFeatures(object):
     sharding_info = None
     tablets_routing_v1 = False
     lwt_info = None
+    is_scylla = False
 
-    def __init__(self, rate_limit_error=None, shard_id=0, sharding_info=None, tablets_routing_v1=False, lwt_info=None):
+    def __init__(self, rate_limit_error=None, shard_id=0, sharding_info=None, tablets_routing_v1=False, lwt_info=None, is_scylla=False):
         self.rate_limit_error = rate_limit_error
         self.shard_id = shard_id
         self.sharding_info = sharding_info
         self.tablets_routing_v1 = tablets_routing_v1
         self.lwt_info = lwt_info
+        self.is_scylla = is_scylla
 
     @staticmethod
     def parse_from_supported(supported):
         rate_limit_error = ProtocolFeatures.maybe_parse_rate_limit_error(supported)
         shard_id, sharding_info = ProtocolFeatures.parse_sharding_info(supported)
         tablets_routing_v1 = ProtocolFeatures.parse_tablets_info(supported)
         lwt_info = ProtocolFeatures.parse_lwt_info(supported)
-        return ProtocolFeatures(rate_limit_error, shard_id, sharding_info, tablets_routing_v1, lwt_info)
+        is_scylla = ProtocolFeatures.detect_scylla(supported, sharding_info)
+        return ProtocolFeatures(rate_limit_error, shard_id, sharding_info, tablets_routing_v1, lwt_info, is_scylla)
+
+    @staticmethod
+    def detect_scylla(supported, sharding_info):
+        """Detect ScyllaDB from SUPPORTED extensions, independent of shard awareness.
+
+        ScyllaDB is identified by the presence of any known Scylla-specific
+        extension key in the SUPPORTED response.  Checking only shard-related
+        fields (SCYLLA_NR_SHARDS, etc.) is insufficient because those are
+        absent when shard-awareness is disabled on the server side
+        (allow_shard_aware_drivers: false), which would cause the driver to
+        misidentify a ScyllaDB cluster as Cassandra and, for example, try
+        to query the peers_v2 table that ScyllaDB does not support.
+        """
+        return (
+            LWT_ADD_METADATA_MARK in supported
+            or RATE_LIMIT_ERROR_EXTENSION in supported
+            or TABLETS_ROUTING_V1 in supported
+            or sharding_info is not None
+        )
 
     @staticmethod
     def maybe_parse_rate_limit_error(supported):
@@ -73,8 +95,12 @@ def parse_sharding_info(options):
             sharding_algorithm == "biased-token-round-robin" or sharding_ignore_msb):
             return 0, None
 
-        return int(shard_id), _ShardingInfo(shard_id, shards_count, partitioner, sharding_algorithm, sharding_ignore_msb,
-                                            shard_aware_port, shard_aware_port_ssl)
+        # SCYLLA_SHARD may be absent even when other shard fields are present
+        # (e.g. the connection landed on shard 0 and the server omits the field).
+        # Default to 0 to avoid int(None) crash.
+        resolved_shard_id = int(shard_id) if shard_id is not None else 0
+        return resolved_shard_id, _ShardingInfo(shard_id, shards_count, partitioner, sharding_algorithm, sharding_ignore_msb,
+                                                shard_aware_port, shard_aware_port_ssl)
 
 
     @staticmethod

cassandra/shard_info.py

@@ -21,10 +21,10 @@
 class _ShardingInfo(object):
 
     def __init__(self, shard_id, shards_count, partitioner, sharding_algorithm, sharding_ignore_msb, shard_aware_port, shard_aware_port_ssl):
-        self.shards_count = int(shards_count)
+        self.shards_count = int(shards_count) if shards_count else 0
         self.partitioner = partitioner
         self.sharding_algorithm = sharding_algorithm
-        self.sharding_ignore_msb = int(sharding_ignore_msb)
+        self.sharding_ignore_msb = int(sharding_ignore_msb) if sharding_ignore_msb else 0
         self.shard_aware_port = int(shard_aware_port) if shard_aware_port else None
         self.shard_aware_port_ssl = int(shard_aware_port_ssl) if shard_aware_port_ssl else None
 

tests/unit/test_protocol_features.py

@@ -22,3 +22,93 @@ class OptionsHolder(object):
         assert protocol_features.rate_limit_error == 123
         assert protocol_features.shard_id == 0
         assert protocol_features.sharding_info is None
+
+    # -----------------------------------------------------------------
+    # Tests for is_scylla detection (independent of shard awareness)
+    # Regression for: ScyllaDB misidentified as Cassandra when sharding
+    # is disabled (allow_shard_aware_drivers: false).
+    # -----------------------------------------------------------------
+
+    def test_is_scylla_detected_via_lwt(self):
+        """ScyllaDB is recognised from SCYLLA_LWT_ADD_METADATA_MARK alone."""
+        pf = ProtocolFeatures.parse_from_supported({
+            'SCYLLA_LWT_ADD_METADATA_MARK': ['LWT_OPTIMIZATION_META_BIT_MASK=8'],
+        })
+        assert pf.is_scylla is True
+        assert pf.shard_id == 0
+        assert pf.sharding_info is None  # no shard-aware connections expected
+
+    def test_is_scylla_detected_via_rate_limit(self):
+        """ScyllaDB is recognised from SCYLLA_RATE_LIMIT_ERROR alone."""
+        pf = ProtocolFeatures.parse_from_supported({
+            'SCYLLA_RATE_LIMIT_ERROR': ['ERROR_CODE=42'],
+        })
+        assert pf.is_scylla is True
+        assert pf.shard_id == 0
+        assert pf.sharding_info is None
+
+    def test_is_scylla_detected_via_tablets(self):
+        """ScyllaDB is recognised from TABLETS_ROUTING_V1 alone."""
+        pf = ProtocolFeatures.parse_from_supported({
+            'TABLETS_ROUTING_V1': [''],
+        })
+        assert pf.is_scylla is True
+        assert pf.shard_id == 0
+        assert pf.sharding_info is None
+
+    def test_is_scylla_detected_via_sharding(self):
+        """ScyllaDB with full sharding is recognised and sharding_info is populated."""
+        pf = ProtocolFeatures.parse_from_supported({
+            'SCYLLA_SHARD': ['3'],
+            'SCYLLA_NR_SHARDS': ['12'],
+            'SCYLLA_PARTITIONER': ['org.apache.cassandra.dht.Murmur3Partitioner'],
+            'SCYLLA_SHARDING_ALGORITHM': ['biased-token-round-robin'],
+            'SCYLLA_SHARDING_IGNORE_MSB': ['12'],
+            'SCYLLA_LWT_ADD_METADATA_MARK': ['LWT_OPTIMIZATION_META_BIT_MASK=8'],
+        })
+        assert pf.is_scylla is True
+        assert pf.shard_id == 3
+        assert pf.sharding_info is not None
+        assert pf.sharding_info.shards_count == 12
+
+    def test_cassandra_is_not_scylla(self):
+        """Pure Cassandra SUPPORTED response must not set is_scylla."""
+        pf = ProtocolFeatures.parse_from_supported({
+            'CQL_VERSION': ['3.0.0'],
+            'COMPRESSION': ['lz4', 'snappy'],
+        })
+        assert pf.is_scylla is False
+        assert pf.sharding_info is None
+
+    def test_scylla_without_sharding_no_crash(self):
+        """
+        Regression test for F1: SCYLLA_PARTITIONER present but SCYLLA_NR_SHARDS
+        and SCYLLA_SHARDING_IGNORE_MSB absent must not raise TypeError.
+        Mirrors the scenario where only some shard fields are advertised.
+        """
+        # Should not raise even though shards_count / sharding_ignore_msb are None.
+        pf = ProtocolFeatures.parse_from_supported({
+            'SCYLLA_PARTITIONER': ['org.apache.cassandra.dht.Murmur3Partitioner'],
+            'SCYLLA_LWT_ADD_METADATA_MARK': ['LWT_OPTIMIZATION_META_BIT_MASK=8'],
+        })
+        assert pf.is_scylla is True
+        # SCYLLA_PARTITIONER passes the sharding guard, so sharding_info is populated
+        # with zero defaults rather than crashing.
+        assert pf.shard_id == 0
+        assert pf.sharding_info is not None
+        assert pf.sharding_info.shards_count == 0
+        assert pf.sharding_info.sharding_ignore_msb == 0
+
+    def test_scylla_sharding_algorithm_only_no_crash(self):
+        """
+        Regression: SCYLLA_SHARDING_ALGORITHM present without SCYLLA_NR_SHARDS
+        must not raise TypeError.
+        """
+        pf = ProtocolFeatures.parse_from_supported({
+            'SCYLLA_SHARDING_ALGORITHM': ['biased-token-round-robin'],
+            'SCYLLA_RATE_LIMIT_ERROR': ['ERROR_CODE=42'],
+        })
+        assert pf.is_scylla is True
+        assert pf.shard_id == 0
+        assert pf.sharding_info is not None
+        assert pf.sharding_info.shards_count == 0