feat: offline fork

[exp0nge]

Motivation

• feat(anvil): fully offline mode for anvil fork #9721
• Feature Request: Fully Offline Fork Testing via Pre-Loaded Block Header #11112

The current fork functionality calls out to the defined RPC url (internet) when either something is missing from the local state DB or misc calls like (eth_chainId).

With --load-state, this behavior doesn't change. As outlined above in the two issues, the goal of this PR is to entirely eliminate all remote RPC calls when the fork is running in --offline mode: if there is state cached: use that, if not, return default/0.

This allows the Anvil fork to become portable in environments where internet egress is not possible or unwanted due to security/reproducibility concerns (e.g. namely CI systems).

Solution

• Use a new offline fork DB
• Redirect all calls to local state or default if offline mode

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[onbjerg]

Please provide a description and a motivation for this change. Going off the original issue, you are passing a fork URL, which Anvil correctly tries to talk to. If you want to be fully offline, you should be able to just pass the chain ID, and use --load-state.

[exp0nge]

Please provide a description and a motivation for this change. Going off the original issue, you are passing a fork URL, which Anvil correctly tries to talk to. If you want to be fully offline, you should be able to just pass the chain ID, and use --load-state.

Hey, updated the description. I actually did start with that flag (re: my original issue), but the fork will always call out to the RPC for missing state.

[onbjerg]

Yes, this is expected, if you pass a fork URL it will try to reach out to get missing state and things like chain ID. It should work if you remove --fork-url and just use --load-state. That is, to use it in offline mode, use state from disk (--load-state) and don't pass a fork URL. I'm closing this PR and the issue given this is working as intended, unless there is a bug with --load-state.

[exp0nge]

Yes, this is expected, if you pass a fork URL it will try to reach out to get missing state and things like chain ID. It should work if you remove --fork-url and just use --load-state. That is, to use it in offline mode, use state from disk (--load-state) and don't pass a fork URL. I'm closing this PR and the issue given this is working as intended, unless there is a bug with --load-state.

OK, the other parts to this was missing some specific support for like debug_ rpc endpoints. Should I PR that separately?