feat: add support for meta memcache commands (#4362)

This is a stripped down version of supporting the memcache meta requests.

a. Not all meta flags are supported, but TTL, flags, arithmetics are supported.
b. does not include reply support.
c. does not include new semantics that are not part of the older, ascii protocol.

The parser interface has not changed significantly, and the meta commands are emulated
using the old, high level commands like ADD,REPLACE, INCR etc.

See https://raw.githubusercontent.com/memcached/memcached/refs/heads/master/doc/protocol.txt for more details
regarding the meta commands spec.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>

tests/dragonfly/memcache_meta.py

@@ -0,0 +1,21 @@
+from .instance import DflyInstance
+from . import dfly_args
+from meta_memcache import (
+    Key,
+    ServerAddress,
+    CacheClient,
+    connection_pool_factory_builder,
+)
+
+DEFAULT_ARGS = {"memcached_port": 11211, "proactor_threads": 4}
+
+
+@dfly_args(DEFAULT_ARGS)
+def test_basic(df_server: DflyInstance):
+    pool = CacheClient.cache_client_from_servers(
+        servers=[
+            ServerAddress(host="localhost", port=DEFAULT_ARGS.get("memcached_port")),
+        ],
+        connection_pool_factory_fn=connection_pool_factory_builder(),
+    )
+    # TODO: to add integration tests

tests/dragonfly/pymemcached_test.py

@@ -5,7 +5,6 @@ from redis import Redis
 import socket
 import random
 import time
-import warnings
 
 from . import dfly_args
 from .instance import DflyInstance

tests/dragonfly/requirements.txt

@@ -13,6 +13,7 @@ wrapt==1.14.1
 pytest-asyncio==0.20.1
 pytest-repeat==0.9.3
 pymemcache==4.0.0
+meta_memcache==2
 prometheus_client==0.17.0
 aiohttp==3.10.2
 numpy