add XCom Redis backend implementation

Signed-off-by: Jakub Sokołowski <jakub@status.im>

airflow_xcom_redis/__init__.py

@@ -1,6 +1,31 @@
 # -*- coding: utf-8 -*-
-"""Module init-file.
+from uuid import uuid4
+from typing import Any
+from airflow.models.xcom import BaseXCom
+from airflow.providers.redis.hooks.redis import RedisHook
 
-The __init__.py files are required to make Python treat directories
-containing the file as packages.
-"""
+class XComRedisBackend(BaseXCom):
+    PREFIX = 'xcom_redis://'
+    # This connection needs to exist in advance
+    CONN_ID = 'xcom_cache'
+
+    @staticmethod
+    def serialize_value(value: Any):
+        hook = RedisHook(redis_conn_id=XComRedisBackend.CONN_ID)
+        key = str(uuid4())
+        # We use the default serializer, which pickles or JSONs
+        hook.get_conn().set(key, BaseXCom.serialize_value(value))
+        # Add prefix to make it clear where the value is stored.
+        value = XComRedisBackend.PREFIX + key
+        return BaseXCom.serialize_value(value)
+
+    @staticmethod
+    def deserialize_value(result) -> Any:
+        result = BaseXCom.deserialize_value(result)
+        prefix = XComRedisBackend.PREFIX
+        if isinstance(result, str) and result.startswith(prefix):
+            key = result.replace(prefix, "")
+            hook = RedisHook(redis_conn_id=XComRedisBackend.CONN_ID)
+            result = hook.get_conn().get(key)
+            result = BaseXCom.deserialize_value(result)
+        return result

airflow_xcom_redis/__main__.py

@@ -1,8 +0,0 @@
-# -*- coding: utf-8 -*-
-"""Module init-file.
-
-A module's __name__ is set equal to '__main__' when read from standard input,
-a script, or from an interactive prompt.
-"""
-
-print('TODO')