Generic Event Sub

[ggwpez]

Location: New Package [backend/eth/glue]

Motivation: As part of #19 we need a generic event subscription. It will then be used to build the generic reorg resistant event subscription.

Design: The current prototype implementation looks like this:

uml.txt
EventFactory is defined as func() EventType since otherwise i would need to use reflections to clone the EventType.

Possible extensions:

• Gas bumper
• Rebroadcasting
• Receipt polling
• Persistence

Usage: Subscribing to all ERC20Approval events of the token contract would look like this:

factory := func() glue.EventType {
	return glue.EventType{
		Name: "Approval",
		Data: new(peruntoken.ERC20Approval),
	}
}

sub, _ := glue.NewEventSub(token.Contract(), factory, nil /* Start block is 0 */) // Error handling omitted
defer sub.Close()
sink := make(chan *glue.Event, 1)
go sub.Read(ctx, sink) // Error handling omitted

for _event := range sink {
	event := _event.Data.(*peruntoken.ERC20Approval)
	// Use event…
}

Testing: I already have a test to check that emitted events are received. This should be enough in combination with the additional reorg tests that i added.