Fixed call to ZADD in Lua script (#209)

Calling ZRANGE with WITHSCORES will return list with
[member, score, member, score, ...]
Iterate over with step -2 will iterate in reverse and skip every second
index. [i] is the score, [i - 1] is the member.
ZADD syntax: ZADD key [NX|XX] [CH] [INCR] score member

Reduced delay in tests to trigger cancel with full backup q 
demonstrating issue.

Author: stefanw

CHANGELOG.txt

@@ -1,3 +1,8 @@
+UNRELEASED
+----------
+
+* Fixed error in Lua script introduced in 3.0.0.
+
 3.0.0 (2020-07-03)
 ------------------
 

channels_redis/core.py

@@ -330,9 +330,9 @@ async def _brpop_with_clean(self, index, channel, timeout):
         # of the main message queue in the proper order; BRPOP must *not* be called
         # because that would deadlock the server
         cleanup_script = """
-            local backed_up = redis.call('ZRANGE', ARGV[2], 0, -1)
-            for i = #backed_up, 1, -1 do
-                redis.call('ZADD', ARGV[1], backed_up[i])
+            local backed_up = redis.call('ZRANGE', ARGV[2], 0, -1, 'WITHSCORES')
+            for i = #backed_up, 1, -2 do
+                redis.call('ZADD', ARGV[1], backed_up[i], backed_up[i - 1])
             end
             redis.call('DEL', ARGV[2])
         """

tests/test_core.py

@@ -445,7 +445,7 @@ async def test_receive_cancel(channel_layer):
         task = asyncio.ensure_future(channel_layer.receive(channel))
         await asyncio.sleep(delay)
         task.cancel()
-        delay += 0.001
+        delay += 0.0001
 
         try:
             await asyncio.wait_for(task, None)