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import asyncio
import inspect
import json
from typing import Callable, Optional
import aioredis
class RedisMessageRelay:
"""A class for relaying messages across services using redis lists and pubsub."""
def __init__(
self,
name: str,
redis_pool: aioredis.Redis,
*,
redis_channel: Optional[aioredis.Channel, str] = None,
redis_list: Optional[str] = None,
) -> None:
self.name = name
self.channel = redis_channel or name
self.redis_list = redis_list or name
self.redis = redis_pool
def __repr__(self) -> str:
return f"<{self.__class__.__name__} name={self.name} channel={self.channel} list={self.redis_list}>"
class RedisMessageProducer(RedisMessageRelay):
async def relay(self, data: dict) -> int:
"""
Push message and notify consumer.
returns:
- Number of subscribers the notification was delivered to.
"""
serialised = json.dumps(data)
await self.redis.rpush(self.redis_list, serialised)
# Notify consumer about new message.
subs: int = await self.redis.publish(
self.channel,
"pushed"
)
return subs
class RedisMessageConsumer(RedisMessageRelay):
def __init__(
self,
*args,
callback: Callable,
loop: Optional[asyncio.AbstractEventLoop] = None,
**kwargs
) -> None:
super().__init__(*args, **kwargs)
self.callback = callback
self.loop = loop or asyncio.get_event_loop()
async def listen(self) -> None:
res = await self.redis.subscribe(self.channel)
self.channel = res[0]
await self.wait_until_message()
async def pre_callback(self, data: dict):
if inspect.iscoroutinefunction(self.callback):
await self.callback(data)
return
self.callback(data)
async def read_redis_list(self) -> None:
serialised = await self.redis.lpop(self.redis_list)
try:
data = json.loads(serialised)
except (json.JSONDecodeError, TypeError):
pass
else:
await self.pre_callback(data)
async def wait_until_message(self) -> None:
"""Receive message from a channel."""
# Empty queue before receiving messages.
queue: list = await self.redis.lrange(self.redis_list, 0, -1)
await self.redis.delete(self.redis_list)
for item in queue:
await self.pre_callback(item)
while await self.channel.wait_message():
data = await self.channel.get()
if data == "pushed":
await self.read_redis_list()
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