Validate Addr, Exclude nodes with invalid ip address

[nidhi-ag]

Problem Statement

Recently we faced an issue with predixy during redis cluster scaling, where it was trying to connect to empty host.

Incidents

• PHP Redis client threw error message "read error on connection".

• On checking predixy logs we found
  2019-11-12 08:05:03.498123 W Handler.cpp:396 h 4 c 127.0.0.1:47187 430 handle event 1 exception Socket.cpp:120 invalid addr :6379:Name or service not known
  where addr is empty

• Predixy INFO command output
  
  here one of the slaves are registered in the server pool even though it's host is invalid.

After replicating this issue on a test cluster, we found out that at some point "cluster nodes" is returning an invalid response where it doesn't have addr though the flag is valid (slave).
D ClusterServerPool.cpp:103 redis cluster update parse node 52a144f80835728846892506bbd7942ac49bf09c :6379@1122 slave -

Solution

• To handle this case this pull request adds address validation step to discard such invalid response from the redis.

Although the redis should respond according to the protocol, I think if the redis responds with an invalid format, predixy should do validations before inserting into the pool.

[fortrue]

the host will point an invalid address

[nidhi-ag]

Now i have changed it to use mAddr data instead of pointer.