Occasionally the term “weak subjectivity period” pops up in Eth2 discussions. It’s a weird concept that you can usually just watch fly by and not miss too much. But when you’re talking about how to sync an existing Eth2 chain it becomes quite important. Probably the best resource for it is Vitalik’s post: Proof of Stake: How I Learned to Love Weak Subjectivity I’ve struggled to get my head around it and why it matters so am writing up my current understanding. There is almost certainly at least one mistake in here somewhere…

In Ethereum, there are often short forks near the head of the chain because two miners found the PoW solution for new blocks at around the same time. Only one of those chains will ultimately wind up being considered the canonical chain and any blocks from non-canonical chains wind up having no effect on the state. Non-canonical blocks may wind up being added as ommers in future blocks, but everything in this article applies regardless of whether that happens.

One subtle detail in the way Ethereum works is that there is a difference between Ommers and Non-Canonical Blocks. It’s common for people to use the term Ommer for both of these and most of the time the difference doesn’t matter but sometimes it does.

So what is a non-canonical block? Non-canonical blocks are ones which a client imports but which don’t wind up on the canonical chain. Maybe they were on the canonical chain for a while and then a re-org switched to a different chain or maybe they were imported to a fork and spent their entire life languishing there. Either way, they don’t form part of the current consensus chain and have absolutely no effect on the world state. It’s like their transactions have never been executed and no one gets any form of miner reward for them. Non-canonical blocks must be entirely valid blocks that could form part of the canonical chain, but weren’t because we found a better chain.

I’ve been upgrading Moolah after a long period of neglect. One of the tasks is to update it to WebPack 4. Mostly this went smoothly by just creating a new project with vue-cli and bringing its generated build setup over to replace the old one. Then a bunch of tweaking.

One thing that did bite however, was tests using inject-loader started failing as soon as I added vuetify-loader to the project with:

Continuing our adventures in setting up a private beacon chain… Previously we got an Eth 1 chain with the deposit contract and successfully sent a deposit to register a new validator. So far though, we have no way of telling if it actually worked. What we need is an actual beacon chain client. Enter Artemis…

Step 3 – Add a Beacon Chain Client

We’ll be using Artemis, partly because I’m incredibly biased and partly because it happens to support the exact version of the deposit contract we’ve deployed (what a coincidence!).

I’ve started a little side-project to setup a “private beacon chain”. The aim is to better understand how the beacon chain works and start to discover some of the things still required to be built or fixed in clients before it can officially launch.

So what is a private beacon chain? It’s intended to be an entirely self-contained, runs-on-my-laptop instance of the beacon chain, run as a small-scale simulation of how the real beacon chain will be fired up.

If you’re switching from a CLA model to a DCO model you may want to add a Signed-off-by line to every existing commit so that you can run automated DCO checks over the entire repository. Doing this obviously assumes that your CLA sets things up so that you are actually in a position to provide a DCO sign-off.

Once you’re happy with all the legalities, the change is a single command using git filter-branch:

I’ve written up a simple little EIP to specify some standard names and meanings for Prometheus metrics that are common across Ethereum clients: EIP-2159.
It’s pretty simple and only defines four metrics but that’s enough to create quite powerful overview dashboards that would work across multiple clients.

There’s a fun little gotcha introduced in Java 10 which causes trouble for anyone wanting to support earlier JVMs.  If you take the code:

import java.nio.ByteBuffer;

public class ProblemCode {
  public static void main(String[] args) {
    final ByteBuffer buffer = ByteBuffer.allocate(10);
    buffer.position(10);
    System.out.println("Yay it worked!");
  }
}

If you compile it on Java 8 it will run on any Java from 8 and above. If you compile it on Java 10 or above it will only work on Java 10 and above, even if you specify -target 8 -source 8.

I’ve had the opportunity to do some proof of concept development of the Ethereum state-rent proposal that Alexey Akhunov has been leading on the Pantheon code base. The proposal evolved as the work continued so the actual implementation is now a lot simpler than described in that PDF.

Note that the aim is to explore what it takes to implement the proposal, not to create production ready code.  The current work is all available on on my state-rent branch.

This week, the work I’ve been doing for the past 6 months, and that PegaSys has been working on for the past 18 months or so was released into the world. Specifically we’ve released Pantheon 0.8.1, our new MainNet compatible, Apache 2 licensed, Java-based Ethereum client. And it’s open source.

I’m pretty excited about it on a few fronts. Firstly I think it’s a pretty important thing for the Ethereum community. To be a healthy ecosystem, Ethereum needs to have diversity in its clients to avoid a bug in one client taking out or accidentally hard forking the entire network. Currently though, Geth and Parity dominate the Ethereum client landscape. Pantheon clearly won’t change that in the short term, but it is backed by significant engineering resources to help it keep up with the ever changing Ethereum landscape and be a dependable option.

There’s an exceptionally valuable set of ethereum reference tests that are run by most or all of the different Ethereum clients to ensure they actually implement the specifications in a compatible way. They’re one of the most valuable resources for anyone developing an Ethereum client.

The Aleth project maintains the official test client called testeth but it’s a little cryptic to work out how to actually run things with it and then use that to debug failures happening in the client you’re actually developing. So this is what I’ve found useful: