Bug in hiredis Pub/Sub handling on errors in the first subscribe.

[antirez]

Hello!

if you try to subscribe to a Pub/Sub channel with the async API and the server reply with an error such as -ERR Loading... the hiredis client will crash.

My point of view is that while there is some kind of problem in hiredis that's worth fixing, in this specific case it also shows a problem with the Redis server that should instead allow to subscribe to Pub/Sub while the server is loading data. I'm fixing the server but I think it's worth fixing hiredis as well, given that the fix for the server will probably not be back ported to Redis 2.4, and there may be in the future some other reason to reply with an error to the first subscribe.

Cheers,
Salvatore

[antirez]

p.s. this likely also happens when authentication is on but no AUTH was sent. It may be a simpler way to reproduce the bug.

[pietern]

This should be fixed with 7ec4df9.

The client will now disconnect the context when it receives a spontaneous error reply. I believe this is the best strategy at this point, because it can't retry subscriptions, or do other fancy state recovery when the server starts accepting commands.

[antirez]

Hello Pieter, thanks for the fix! About the strategy, what I can say is that in Sentinel if subscribe fails what I do is, actually, to manually disconnect the channel, and retry from scratch, so at application level I reasoned likewise.