Initial commit (Clean history)

path/to/venv/lib/python3.12/site-packages/redis/multidb/failover.py

@@ -0,0 +1,125 @@
+import time
+from abc import ABC, abstractmethod
+
+from redis.data_structure import WeightedList
+from redis.multidb.circuit import State as CBState
+from redis.multidb.database import Databases, SyncDatabase
+from redis.multidb.exception import (
+    NoValidDatabaseException,
+    TemporaryUnavailableException,
+)
+
+DEFAULT_FAILOVER_ATTEMPTS = 10
+DEFAULT_FAILOVER_DELAY = 12
+
+
+class FailoverStrategy(ABC):
+    @abstractmethod
+    def database(self) -> SyncDatabase:
+        """Select the database according to the strategy."""
+        pass
+
+    @abstractmethod
+    def set_databases(self, databases: Databases) -> None:
+        """Set the database strategy operates on."""
+        pass
+
+
+class FailoverStrategyExecutor(ABC):
+    @property
+    @abstractmethod
+    def failover_attempts(self) -> int:
+        """The number of failover attempts."""
+        pass
+
+    @property
+    @abstractmethod
+    def failover_delay(self) -> float:
+        """The delay between failover attempts."""
+        pass
+
+    @property
+    @abstractmethod
+    def strategy(self) -> FailoverStrategy:
+        """The strategy to execute."""
+        pass
+
+    @abstractmethod
+    def execute(self) -> SyncDatabase:
+        """Execute the failover strategy."""
+        pass
+
+
+class WeightBasedFailoverStrategy(FailoverStrategy):
+    """
+    Failover strategy based on database weights.
+    """
+
+    def __init__(self) -> None:
+        self._databases = WeightedList()
+
+    def database(self) -> SyncDatabase:
+        for database, _ in self._databases:
+            if database.circuit.state == CBState.CLOSED:
+                return database
+
+        raise NoValidDatabaseException("No valid database available for communication")
+
+    def set_databases(self, databases: Databases) -> None:
+        self._databases = databases
+
+
+class DefaultFailoverStrategyExecutor(FailoverStrategyExecutor):
+    """
+    Executes given failover strategy.
+    """
+
+    def __init__(
+        self,
+        strategy: FailoverStrategy,
+        failover_attempts: int = DEFAULT_FAILOVER_ATTEMPTS,
+        failover_delay: float = DEFAULT_FAILOVER_DELAY,
+    ):
+        self._strategy = strategy
+        self._failover_attempts = failover_attempts
+        self._failover_delay = failover_delay
+        self._next_attempt_ts: int = 0
+        self._failover_counter: int = 0
+
+    @property
+    def failover_attempts(self) -> int:
+        return self._failover_attempts
+
+    @property
+    def failover_delay(self) -> float:
+        return self._failover_delay
+
+    @property
+    def strategy(self) -> FailoverStrategy:
+        return self._strategy
+
+    def execute(self) -> SyncDatabase:
+        try:
+            database = self._strategy.database()
+            self._reset()
+            return database
+        except NoValidDatabaseException as e:
+            if self._next_attempt_ts == 0:
+                self._next_attempt_ts = time.time() + self._failover_delay
+                self._failover_counter += 1
+            elif time.time() >= self._next_attempt_ts:
+                self._next_attempt_ts += self._failover_delay
+                self._failover_counter += 1
+
+            if self._failover_counter > self._failover_attempts:
+                self._reset()
+                raise e
+            else:
+                raise TemporaryUnavailableException(
+                    "No database connections currently available. "
+                    "This is a temporary condition - please retry the operation."
+                )
+
+    def _reset(self) -> None:
+        self._next_attempt_ts = 0
+        self._failover_counter = 0