Previously, upstream.get_addr function returned the new address of the
upstream. Unfortunately, it was used for printing addresses. It caused
the following situation: let's imagine we have A1 and A2 where A1 was
initially selected. So the connection was performed to A1:
Current addr Selected addr
Connect+---------+ A2+------>A1 A1
|
+-+Print failure<---+ A1+------>A2 A2
| +----+
+->Mark failure+-------->+ A2 |
+----+
But the failure OP as well as log message told about `A2` where the real
problem happened with `A1`.
This commit adds distinguishing between getting the next and the current
address of the upstream resolving this issue.
Now each address has its own errors count, so rspamd will prefer upstream addrs with no errors to addrs with errors. This might help to resolve issues on systems where ipv6 does not work.
- Select ipv4/unix addresses if they exist and use ipv6 for ipv6 only
upstreams (since the support of ipv6 is poor in many OSes and
environments).
- Free IP list on upstream destruction.
- Add test cases for addresses selection.
- Allow adding of free form IP addresses to upstreams.
P value is calculated as following:
when we add/remove M upstreams from the list, the probability of hash
miss should be close to the relation N / (N + M), where N is the size of
the previous upstreams list.
So far, the algorithm described in http://arxiv.org/abs/1406.2294 shows
p value more than 0.99.
