Extended Event filtering

[ggwpez]

Location: [backend/eth/subscription]

Problem: The event filtering of go-ethereum allows to pass a query.
A query is a set of sets of arguments, where at least on set of arguments must match. Missing parameters are treated as wildcard.

The problem is that eg. in the Adjudicator we want to filter for ChannelUpdate events with a specific ChannelID and Phase.
Since these are the first and third arguments, it does not seem possible to directly filter for them. It would work if they were the first and second arguments though.

Solution: One possibility would be to replacing the Filter [][]interface{} field with an easier to use Predicate func(Event) bool function pointer.