Fixed #33012 -- Added Redis cache backend.

Thanks Carlton Gibson, Chris Jerdonek, David Smith, Keryn Knight,
Mariusz Felisiak, and Nick Pope for reviews and mentoring this
Google Summer of Code 2021 project.

1 files changed, 224 insertions, 0 deletions

diff --git a/django/core/cache/backends/redis.py b/django/core/cache/backends/redis.py
new file mode 100644
index 0000000000..16556b1ded
--- /dev/null
+++ b/django/core/cache/backends/redis.py
@@ -0,0 +1,224 @@
+"""Redis cache backend."""
+
+import random
+import re
+
+from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
+from django.core.serializers.base import PickleSerializer
+from django.utils.functional import cached_property
+from django.utils.module_loading import import_string
+
+
+class RedisSerializer(PickleSerializer):
+    def dumps(self, obj):
+        if isinstance(obj, int):
+            return obj
+        return super().dumps(obj)
+
+    def loads(self, data):
+        try:
+            return int(data)
+        except ValueError:
+            return super().loads(data)
+
+
+class RedisCacheClient:
+    def __init__(
+        self,
+        servers,
+        serializer=None,
+        db=None,
+        pool_class=None,
+        parser_class=None,
+    ):
+        import redis
+
+        self._lib = redis
+        self._servers = servers
+        self._pools = {}
+
+        self._client = self._lib.Redis
+
+        if isinstance(pool_class, str):
+            pool_class = import_string(pool_class)
+        self._pool_class = pool_class or self._lib.ConnectionPool
+
+        if isinstance(serializer, str):
+            serializer = import_string(serializer)
+        if callable(serializer):
+            serializer = serializer()
+        self._serializer = serializer or RedisSerializer()
+
+        if isinstance(parser_class, str):
+            parser_class = import_string(parser_class)
+        parser_class = parser_class or self._lib.connection.DefaultParser
+
+        self._pool_options = {'parser_class': parser_class, 'db': db}
+
+    def _get_connection_pool_index(self, write):
+        # Write to the first server. Read from other servers if there are more,
+        # otherwise read from the first server.
+        if write or len(self._servers) == 1:
+            return 0
+        return random.randint(1, len(self._servers) - 1)
+
+    def _get_connection_pool(self, write):
+        index = self._get_connection_pool_index(write)
+        if index not in self._pools:
+            self._pools[index] = self._pool_class.from_url(
+                self._servers[index], **self._pool_options,
+            )
+        return self._pools[index]
+
+    def get_client(self, key=None, *, write=False):
+        # key is used so that the method signature remains the same and custom
+        # cache client can be implemented which might require the key to select
+        # the server, e.g. sharding.
+        pool = self._get_connection_pool(write)
+        return self._client(connection_pool=pool)
+
+    def add(self, key, value, timeout):
+        client = self.get_client(key, write=True)
+        value = self._serializer.dumps(value)
+
+        if timeout == 0:
+            if ret := bool(client.set(key, value, nx=True)):
+                client.delete(key)
+            return ret
+        else:
+            return bool(client.set(key, value, ex=timeout, nx=True))
+
+    def get(self, key, default):
+        client = self.get_client(key)
+        value = client.get(key)
+        return default if value is None else self._serializer.loads(value)
+
+    def set(self, key, value, timeout):
+        client = self.get_client(key, write=True)
+        value = self._serializer.dumps(value)
+        if timeout == 0:
+            client.delete(key)
+        else:
+            client.set(key, value, ex=timeout)
+
+    def touch(self, key, timeout):
+        client = self.get_client(key, write=True)
+        if timeout is None:
+            return bool(client.persist(key))
+        else:
+            return bool(client.expire(key, timeout))
+
+    def delete(self, key):
+        client = self.get_client(key, write=True)
+        return bool(client.delete(key))
+
+    def get_many(self, keys):
+        client = self.get_client(None)
+        ret = client.mget(keys)
+        return {
+            k: self._serializer.loads(v) for k, v in zip(keys, ret) if v is not None
+        }
+
+    def has_key(self, key):
+        client = self.get_client(key)
+        return bool(client.exists(key))
+
+    def incr(self, key, delta):
+        client = self.get_client(key)
+        if not client.exists(key):
+            raise ValueError("Key '%s' not found." % key)
+        return client.incr(key, delta)
+
+    def set_many(self, data, timeout):
+        client = self.get_client(None, write=True)
+        pipeline = client.pipeline()
+        pipeline.mset({k: self._serializer.dumps(v) for k, v in data.items()})
+
+        if timeout is not None:
+            # Setting timeout for each key as redis does not support timeout
+            # with mset().
+            for key in data:
+                pipeline.expire(key, timeout)
+        pipeline.execute()
+
+    def delete_many(self, keys):
+        client = self.get_client(None, write=True)
+        client.delete(*keys)
+
+    def clear(self):
+        client = self.get_client(None, write=True)
+        return bool(client.flushdb())
+
+
+class RedisCache(BaseCache):
+    def __init__(self, server, params):
+        super().__init__(params)
+        if isinstance(server, str):
+            self._servers = re.split('[;,]', server)
+        else:
+            self._servers = server
+
+        self._class = RedisCacheClient
+        self._options = params.get('OPTIONS', {})
+
+    @cached_property
+    def _cache(self):
+        return self._class(self._servers, **self._options)
+
+    def get_backend_timeout(self, timeout=DEFAULT_TIMEOUT):
+        if timeout == DEFAULT_TIMEOUT:
+            timeout = self.default_timeout
+        # The key will be made persistent if None used as a timeout.
+        # Non-positive values will cause the key to be deleted.
+        return None if timeout is None else max(0, int(timeout))
+
+    def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        return self._cache.add(key, value, self.get_backend_timeout(timeout))
+
+    def get(self, key, default=None, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        return self._cache.get(key, default)
+
+    def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        self._cache.set(key, value, self.get_backend_timeout(timeout))
+
+    def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        return self._cache.touch(key, self.get_backend_timeout(timeout))
+
+    def delete(self, key, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        return self._cache.delete(key)
+
+    def get_many(self, keys, version=None):
+        key_map = {self.make_and_validate_key(key, version=version): key for key in keys}
+        ret = self._cache.get_many(key_map.keys())
+        return {key_map[k]: v for k, v in ret.items()}
+
+    def has_key(self, key, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        return self._cache.has_key(key)
+
+    def incr(self, key, delta=1, version=None):
+        key = self.make_and_validate_key(key, version=version)
+        return self._cache.incr(key, delta)
+
+    def set_many(self, data, timeout=DEFAULT_TIMEOUT, version=None):
+        safe_data = {}
+        for key, value in data.items():
+            key = self.make_and_validate_key(key, version=version)
+            safe_data[key] = value
+        self._cache.set_many(safe_data, self.get_backend_timeout(timeout))
+        return []
+
+    def delete_many(self, keys, version=None):
+        safe_keys = []
+        for key in keys:
+            key = self.make_and_validate_key(key, version=version)
+            safe_keys.append(key)
+        self._cache.delete_many(safe_keys)
+
+    def clear(self):
+        return self._cache.clear()