Light state

[zsfelfoldi]

This PR implements ODR capable state & trie structures for the light client.

[robotally]

Vote	Count	Reviewers
👍	2	@fjl @zelig
👎	1	@obscuren

Updated: Thu Dec 17 15:10:10 UTC 2015

[codecov-io]

Current coverage is 44.13%

Merging #2019 into develop will increase coverage by +0.25% as of fa89320

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[zsfelfoldi]

@obscuren fixed the issues you mentioned and rebased on develop

[fjl]

We need to find a way to share some of the logic with package state.
Most of the code (decoding, accessors, etc.) is simply copied from package state.

Maybe one way to do it would be to split state.StateObject into two parts, one of which doesn't
contain a DB. In that case, you could simply embed it here and get all the boring methods for free.

[fjl]

On second thought, we could also address the duplication later when the protocol is in.

[zsfelfoldi]

The highest priority is to not mess up existing stuff so I'd definitely wait with that until we have a functional light client. After everything is built up (including the VM calls) we can make better decisions about what code can be shared and how that should be done.

[zsfelfoldi]

@fjl the issues you mentioned are fixed now

[fjl]

👍

[zelig]

if you wrap the request in a struct, you can DRY up all the GetCtx redundancies.

type OdrBackend interface {
   Database() ethdb.Database
  Retrieve(req *OdrRequestWithCtx)
}
type OdrRequestWithCtx struct {
 ctx   context.Context
 OdrRequest
}

type OdrRequest interface {
  StoreResult(db ethdb.Database)
}
// GetCtx not needs to be defined exactly once not 5 times
func (req *OdrRequestWithCtx) GetCtx() context.Context { return req.ctx }


// this now does not need the ctx field and the GetCtx method to be defined
type TrieRequest struct {
    root  common.Hash
    key   []byte
    proof []rlp.RawValue
}

But the question is, do you really need the ctx embedded in the request? cant you always just pass it to Retrieve if it was OdrBackend#Retrieve(req OdrRequest, context.Context)
and eliminate the extra wrapping, GetCtx and ctx fields altogether.

[zsfelfoldi]

You're right, that was a remnant of an old design. I don't want it wrapped in a struct but contexts shouldn't be wrapped anyways so they are now directly passed to Retrieve.

[zelig]

👍 great stuff

[obscuren]

@fjl renamed a few methods in #2064 such as NewStateObjectFromBytes to DecodeObject. Please change this PR so it matching the other.

Additionally you need to document the exported methods :-)

[obscuren]

👎 (just so it shown up for @robotally and doesn't get accidentally merged)

[fjl]

@zsfelfoldi I'll update #2064 tonight so it is mergeable

[zsfelfoldi]

@obscuren I updated the entire stateobject.go with all the rlp changes and added missing comments to trie.go. I did not yet comment all the state and stateobject functions because there's a shitload of them and they're not commented in the original version either :) I'll do those too of course but maybe I should do that in the two versions together in a separate PR after both this PR and #2064 are merged.

[obscuren]

I don't see why we should neglect on commenting because someone else has a year ago (me). Since this PR adds the methods we should add the documentation in this PR.

[zsfelfoldi]

@obscuren ok, I'll do it in this PR today.

[zsfelfoldi]

@obscuren done