[WIP] Implement forking support with lazy loading backend

[dimartiro]

Description

This PR implements forking functionality for anvil-polkadot, allowing users to fork from a remote Substrate/Polkadot node and run local tests against live network state.

Adds the ability to fork from a running anvil-polkadot node (or compatible Substrate node) using the --fork-url flag. The implementation uses a lazy-loading approach to fetch state from the remote node on-demand, caching values locally for performance

Testing

After compiling the entire project using cargo build --release

1. Start base node

RUST_LOG=info ./target/release/anvil-polkadot --port 9970

2. Modify state on base node

./target/release/cast send 0x70997970C51812dc3A010C7d01b50e0d17dc79C8 \
    --value 5ether \
    --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 \
    --rpc-url http://localhost:9970

3. Verify modified balance

./target/release/cast balance 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 \
    --rpc-url http://localhost:9970

Expected Output: ~9995 ETH (10000 - 5 - gas)

4. Start fork node (inherits modified state)

RUST_LOG=info ./target/release/anvil-polkadot \
    --port 8545 \
    --fork-url http://localhost:9944

5. Verify fork inherited state

./target/release/cast balance 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 \
    --rpc-url http://localhost:8545

Expected Output: ~9995 ETH ✅ (matches base node)

6. Make changes on fork (doesn't affect base)

./target/release/cast send 0x70997970C51812dc3A010C7d01b50e0d17dc79C8 \
    --value 1ether \
    --private-key 0xac0974bec39a17e36ba4a6b4d238ff944bacb478cbed5efcae784d7bf4f2ff80 \
    --rpc-url http://localhost:8545

7. Verify isolation

./target/release/cast balance 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 \
    --rpc-url http://localhost:9970

Exepected Output: ~9995 ETH (unchanged)

./target/release/cast balance 0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266 \
    --rpc-url http://localhost:8545

Expected Output: ~9994 ETH (changed)

TODO

• Add new integration tests to test the fork is working
  • Fork a node with a smart contract deployed and check storage

[alindima]

I pulled in the latest changes from lazy-loading-backend branch on top of the forking-support and tried this out.
I got a panic on step 6 (after executing the balance transfer on the forked network):

2025-11-18T11:24:42.514506Z  INFO eth-rpc::client: Node does not have getAutomine RPC. Defaulting to automine=false. error: Client(JsonRpc(ErrorObject { code: MethodNotFound, message: "Method not found", data: None }))
2025-11-18T11:24:42.514559Z  INFO eth-rpc::client: 🔌 Subscribing to new blocks (BestBlocks)
2025-11-18T11:24:42.514591Z  INFO eth-rpc::client: 🔌 Subscribing to new blocks (FinalizedBlocks)
2025-11-18T11:25:02.237394Z  INFO node::user: eth_getBalance
2025-11-18T11:25:18.010246Z  INFO node::user: eth_chainId
2025-11-18T11:25:18.012071Z  INFO node::user: eth_getTransactionCount
2025-11-18T11:25:18.016610Z  INFO node::user: eth_feeHistory
2025-11-18T11:25:18.016894Z  INFO node::user: eth_estimateGas
2025-11-18T11:25:18.037629Z  INFO node::user: eth_sendRawTransaction
2025-11-18T11:25:18.049158Z  INFO node::user: eth_blockNumber
2025-11-18T11:25:18.049189Z  WARN db::blockchain: Block 0xb3618bf448f724dabb16ed70ac902c1d0929a86bd8a755396071d3d8c2c76bd4 exists in chain but not found when following all leaves backwards
2025-11-18T11:25:18.049209Z  INFO sc_basic_authorship::basic_authorship: 🙌 Starting consensus session on top of parent 0xb3618bf448f724dabb16ed70ac902c1d0929a86bd8a755396071d3d8c2c76bd4 (#1)
2025-11-18T11:25:18.049381Z  INFO node::user: eth_getTransactionReceipt
2025-11-18T11:25:18.049483Z  INFO node::user: eth_getBlockByNumber
2025-11-18T11:25:18.052559Z  INFO node::user: eth_getTransactionReceipt
2025-11-18T11:25:18.053993Z  INFO node::user: eth_getTransactionReceipt
2025-11-18T11:25:18.105454Z  INFO sc_basic_authorship::basic_authorship: 🎁 Prepared block for proposing at 2 (56 ms) hash: 0x759f42d8556ca90e0455ff873c65d4a29b308ac30f6750c9b9516febc03b30a7; parent_hash: 0xb361…6bd4; end: NoMoreTransactions; extrinsics_count: 2
2025-11-18T11:25:18.305392Z  INFO node::user: eth_blockNumber
2025-11-18T11:25:18.305517Z  INFO node::user: eth_getTransactionReceipt
2025-11-18T11:25:18.315519Z  INFO node::user: eth_getBlockByNumber
The application panicked (crashed).
Message:  Dropped receiver: Success(Object {"baseFeePerGas": String("0xf4240"), "blobGasUsed": String("0x0"), "difficulty": String("0x0"), "excessBlobGas": String("0x0"), "extraData": String("0x"), "gasLimit": String("0x1664f5b7bcc00"), "gasUsed": String("0x3333fc1ee"), "hash": String("0xd6ef90f572ef8869ff214e1d344ee76cb345958ccc52876dd76623042b564238"), "logsBloom": String("0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"), "miner": String("0x0000000000000000000000000000000000000000"), "mixHash": String("0x0000000000000000000000000000000000000000000000000008e1bc9bf04000"), "nonce": String("0x0000000000000000"), "number": String("0x2"), "parentHash": String("0x1a555946dfeeebaec3da4be474d10e65643dd6fb42cf55bde0779e7ba70258c2"), "receiptsRoot": String("0x79968af4de4ac2a0e5c85f94af50f2de6dcac16542a7802166f4e96dc0b41213"), "sha3Uncles": String("0x0000000000000000000000000000000000000000000000000000000000000000"), "size": String("0x0"), "stateRoot": String("0xc1e82001b3d608ebde06742344f9735188a785a46cd74566527995dca2bcc125"), "timestamp": String("0x691c579d"), "transactions": Array [String("0x7613ee406fabf1d4cbadbf567a4623a8a3f0dc4c0f0cd8ce76de65c179d2d8dd")], "transactionsRoot": String("0xc1e82001b3d608ebde06742344f9735188a785a46cd74566527995dca2bcc125"), "uncles": Array [], "withdrawals": Array [], "withdrawalsRoot": String("0x0000000000000000000000000000000000000000000000000000000000000000")})
Location: crates/anvil-polkadot/src/api_server/server.rs:144

This is a bug. Consider reporting it at https://github.com/foundry-rs/foundry

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Run with COLORBT_SHOW_HIDDEN=1 environment variable to disable frame filtering.
Run with RUST_BACKTRACE=full to include source snippets.
zsh: abort      RUST_LOG=info ./target/release/anvil-polkadot --port 8545 --fork-url

Don't know if I messed something up while fixing conflicts, so would he worth doing this merge yourself and testing again

[dimartiro]

I pulled in the latest changes from lazy-loading-backend branch on top of the forking-support and tried this out. I got a panic on step 6 (after executing the balance transfer on the forked network):

Don't know if I messed something up while fixing conflicts, so would he worth doing this merge yourself and testing again

Out of curiosity: did you try this flow without the lazy-loading changes, just want to confirm I don't have any special setup on my side.

Regarding the merge itself — I’m currently heads-down on the other PR to get that one landed ASAP. Once that’s done I’ll jump straight onto this one

[alindima]

Out of curiosity: did you try this flow without the lazy-loading changes, just want to confirm I don't have any special setup on my side.

You mean without pulling in the latest changes, but only with the state of this branch?

[alindima]

And let's also test with a smart contract. A simple one which stores multiple items in the state to see if the child trie state is also migrated properly

[dimartiro]

Closed in favor of paritytech#426