ethclient: missing mixHash in JSON block header

[lucasvo]

Geth returns 0x0 in the mixHash field when running against Rinkeby (also POA). Parity connected to Kovan doesn't return the field at all. While you could argue that parity Kovan should be fixed, I think doing such a fix on the server is more involved than doing it on the client side. However this is a discussion that should be had.

It would be great if the go-ethereum ethclient would gracefully ignore the field not being present (i.e. treat it as a null value). I don't know if there's an easy way to distinguish between POA/POW chains and only error out when interacting with a POW chain and the field is missing.

Please also refer to the parity-ethereum issue where this is discussed: openethereum/parity-ethereum#8841

System information

Geth version: 1.8.15
OS & Version: Linux

Expected behaviour

I should be able to use ethclient to communicate with a parity node connected to the kovan POA testnet.

Actual behaviour

Geth returns 0x0 in the mixHash field when running against Rinkeby (also POA). It would be great if the go-ethereum ethclient would gracefully ignore the field not being present (i.e. treat it as a null value). I don't know if there's an easy way to distinguish between POA/POW chains and only error out when interacting with a POW chain and the field is missing.

Steps to reproduce the behaviour

Submit a transaction to a parity node connected to kovan. The implications of this bug are identical to #3230 but #3230 was due to an incompatibility of the parity client in general when this field was added to the endpoint in the first place.

[gitcoinbot]

Issue Status: 1. Open 2. Started 3. Submitted 4. Done

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[SomniaStellarum]

I have an initial commit to demonstrate this fix. It has a bug right now but it shows what the idea is at least. Here is ethclient after the changes. https://github.com/SomniaStellarum/go-ethereum/tree/ethclientFixForParity/ethclient

And here is the commit:
SomniaStellarum@88da98d

[lucasvo]

@SomniaStellarum Sounds like a good idea. Most devs are on Discord, you could try asking there: https://discord.gg/xQHFXr or look for whoever touched this code last in git-blame and get their input? I'm also asking @vedhavyas to take a look at it

[holiman]

There is already a PR which fixes this differently #18166. Please give your input if that one is sufficient to solve the problem.
Also, it's no good to make changes directly to the files called gen_xxx_json.go, because those are generated by go generate based on formatting instructions in the json definitions.

[TwinbrotherPro]

Yap this is fixing the issue. I am using the fix for my own Parity PoA and it is working fine :)

[SomniaStellarum]

I was going to reach out on discord today, but looks like Martin replied here first (thanks Martin). It looks like this issue already has a fix completed in another PR. I'll stop my work on Gitcoin for it and you can likely cancel it to recover your funds.

Also, it's good to know about the gen_xxx_json.go files. I had actually generated it directly with gencodec, but I can see now how to add the go:generate comment and how that should work. I'll know for next time.

[gitcoinbot]

Issue Status: 1. Open 2. Cancelled

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