channels_redis hard-requires EVAL command which fails on Pivotal's Shared Redis Release

[vanschelven]

channels_redis uses .eval() in a number of locations.

On certain redis server installations EVAL has been renamed for security reasons.

Pivotal's Shared Redis Release is an example of a pre-packaged redis that has EVAL renamed by default.

Under those circumstances, this happens:

Traceback (most recent call last):
result = task.result()
File "python/lib/python3.9/site-packages/channels_redis/core.py", line 492, in receive
message_channel, message = await self.receive_single(
File "python/lib/python3.9/site-packages/channels_redis/core.py", line 547, in receive_single
content = await self._brpop_with_clean(
File "python/lib/python3.9/site-packages/channels_redis/core.py", line 383, in _brpop_with_clean
await connection.eval(cleanup_script, keys=[], args=[channel, backup_queue])
aioredis.errors.ReplyError: ERR unknown command `EVAL`, with args beginning with: ` local backed_up = redis.call('ZRANGE', ARGV[2], 0, -1, 'WITHSCORES') for i = #backed_up, 1, -2 do `,

It would be great if EVAL could be removed as a requirement.

Tangentially related: #226

[carltongibson]

@vanschelven If you can show how these can be done without then we can remove them but otherwise I'm not sure we can do anything about this 🤔

[vanschelven]

how these can be done

I was looking into it, there's "only 3" commits in which they were introduced but I had to conclude that I'm a bit out of my depth trying to approach this without any serious understanding.

[vanschelven]

channels_redis.pubsub.RedisPubSubChannelLayer does not use EVAL, so for now that's a workable workaround (for me).

[carltongibson]

It'll be the Lua scripting... I'm not sure we can do with out. 🤔