Reseeding & Validation

This document covers reseeding the ArbGasInfo shim with fee data and validating ArbSys / ArbGasInfo behavior in a Stylus-first workflow. Scope is limited to the shim path (no VM precompile injection).

Purpose

• Keep local tests aligned with a live Stylus network by periodically reseeding ArbGasInfoShim at 0x…6c with a 6-value tuple from RPC.
• Preserve determinism when RPC is unavailable by falling back to project configuration (precompiles.config.json) or to a safe default.
• Validate end-to-end behavior using raw precompile selectors and a minimal probe contract.

Data model

Canonical addresses

• ArbSys 0x0000000000000000000000000000000000000064
• ArbGasInfo 0x000000000000000000000000000000000000006c

Shim tuple (storage order)

ArbGasInfoShim.getPricesInWei() returns a 6-tuple in shim order:

[ l2BaseFee, l1BaseFeeEstimate, l1CalldataCost, l1StorageCost, congestionFee, aux ]

• aux is a general-purpose slot (commonly used to surface auxiliary fees such as blob base fee during experiments).
• Tuples fetched from networks with different ordering are normalized by the reseed task before storage.

Sources & priority

Reseeding uses the following priority:

1. Stylus RPC — selected via --stylus, or when stylusRpc/STYLUS_RPC is present.
2. Nitro RPC — selected via --nitro, or when nitroRpc/NITRO_RPC is present (optional parity path).
3. Project config — precompiles.config.json → gas.pricesInWei (already in shim order).
4. Built-in fallback — safe constant tuple for deterministic testing.

Configuration keys & env

• Environment

  • STYLUS_RPC (preferred public endpoint for Stylus)
  • NITRO_RPC (optional)
  • ARB_PRECOMPILES_CONFIG (path override for the JSON file)

• Project config (precompiles.config.json)

  • stylusRpc, nitroRpc
  • gas.pricesInWei — array of 6 decimal strings in shim order

Task: arb:reseed-shims

Behavior

• Confirms the shim is installed at 0x…6c.
• Selects a source using the priority rules above (flags/env/config).
• Normalizes remote tuples to shim order when required.
• Calls ArbGasInfoShim.__seed(uint256[6]).
• Prints the source used and a readback value for verification.

Flags

• --stylus — force Stylus RPC as the source.
• --nitro — force Nitro RPC as the source.

Examples

Reseed from Stylus Sepolia (public RPC)

export NODE_OPTIONS=--dns-result-order=ipv4first
export NODE_NO_HTTP2=1
export STYLUS_RPC=https://sepolia-rollup.arbitrum.io/rpc

# Persistent node flow (assumes a Hardhat node on 8549 and shims predeployed)
npx hardhat --config hardhat.config.js arb:reseed-shims --network localhost --stylus

Possible output:

ℹ️ fetched from Stylus: [
  '26440960', '188864', '2000000000000', '100000000', '0', '100000000'
]
✅ Re-seeded getPricesInWei -> [
  '26440960', '188864', '2000000000000', '100000000', '0', '100000000'
]

Fallback to config (no RPC reachable)

npx hardhat --config hardhat.config.js arb:reseed-shims --network localhost

Output:

ℹ️ using JSON/config (shim order): [ '69440','496','2000000000000','100000000','0','100000000' ]
✅ Re-seeded getPricesInWei -> [ '69440','496','2000000000000','100000000','0','100000000' ]

Nitro compatibility (optional)

export NITRO_RPC=http://127.0.0.1:8547
npx hardhat --config hardhat.config.js arb:reseed-shims --network localhost --nitro

Validation workflows

Two validation styles are provided: readback and full probe.

Readback (sanity check)

Checks the tuple stored in the shim:

npx hardhat --config hardhat.config.js run --network localhost scripts/check-gasinfo-local.js

Expected example:

[ '69440', '496', '2000000000000', '100000000', '0', '100000000' ]

Full probe (raw + contract)

Validates both precompiles and contract calls:

npx hardhat --config hardhat.config.js run --network localhost scripts/validate-precompiles.js

Typical output:

 Validating Arbitrum Precompiles in Hardhat Context...

Arbitrum patch found in HRE
 Found 2 precompile handlers:
   ArbSys: 0x0000000000000000000000000000000000000064
   ArbGasInfo: 0x000000000000000000000000000000000000006c

 Testing ArbSys arbChainID...
ArbSys arbChainID returned: 42161

⛽ Testing ArbGasInfo getL1BaseFeeEstimate...
ArbGasInfo getL1BaseFeeEstimate returned: 1000000000 wei (1 gwei)

📄 Testing contract deployment and precompile calls...
ArbProbes contract deployed at: 0x...
Contract ArbSys call returned: 42161
Contract ArbGasInfo call returned: 496

 Precompile validation completed!

Note: in shim mode, getCurrentTxL1GasFees() is bound to the estimate (slot 1) for deterministic results.

Comparative inspection (optional)

A helper task provides a quick comparison between the local tuple and a remote RPC:

# Compare local vs Stylus remote (prints per-index equality)
npx hardhat --config hardhat.config.js arb:gas-info --stylus

# Compare local vs explicit RPC
npx hardhat --config hardhat.config.js arb:gas-info --rpc https://sepolia-rollup.arbitrum.io/rpc

# Machine-readable output
npx hardhat --config hardhat.config.js arb:gas-info --stylus --json

Output includes local, remote, and an index-by-index diff with equality markers.

End-to-end local flows

Ephemeral (single-shot)

# One-shot install + verify in a fresh in-process VM
npx hardhat --config hardhat.config.js run scripts/install-and-check-shims.js

Persistent node (recommended for iterative testing)

# Terminal A
npx hardhat node --port 8549

# Terminal B
export NODE_OPTIONS=--dns-result-order=ipv4first
export NODE_NO_HTTP2=1
export STYLUS_RPC=https://sepolia-rollup.arbitrum.io/rpc

# Predeploy shims at 0x…64 / 0x…6c
npx hardhat --config hardhat.config.js run --network localhost scripts/predeploy-precompiles.js

# Reseed from Stylus
npx hardhat --config hardhat.config.js arb:reseed-shims --network localhost --stylus

# Validate
npx hardhat --config hardhat.config.js run --network localhost scripts/check-gasinfo-local.js
npx hardhat --config hardhat.config.js run --network localhost scripts/validate-precompiles.js

# (Optional) Inspect diff vs remote
npx hardhat --config hardhat.config.js arb:gas-info --stylus

Troubleshooting (quick picks)

• HH108: cannot connect to localhost Ensure a Hardhat node is running on the configured port (e.g., npx hardhat node --port 8549) and that networks.localhost.url matches.

• Public RPC fetch failures Set:

  BASH

  export NODE_OPTIONS=--dns-result-order=ipv4first
  export NODE_NO_HTTP2=1
  

  Sanity-check with:

  BASH

  curl -s https://sepolia-rollup.arbitrum.io/rpc \
    -H 'content-type: application/json' \
    --data '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}'
  

• Shims not present Run the predeploy or the one-shot installer:

  BASH

  npx hardhat --config hardhat.config.js run --network localhost scripts/predeploy-precompiles.js
  # or
  npx hardhat --config hardhat.config.js run scripts/install-and-check-shims.js
  

• Tuple order confusion precompiles.config.json must use shim order. Remote tuples with different order are normalized by the task prior to __seed.

Artifacts & scripts (expected)

• Tasks

  • tasks/arb-reseed-shims.ts → implements arb:reseed-shims
  • tasks/arb-gas-info.ts → implements arb:gas-info
  • tasks/arb-install-shims.ts→ implements arb:install-shims

• Scripts

  • scripts/predeploy-precompiles.js → writes shim bytecode at 0x…64/0x…6c
  • scripts/install-and-check-shims.js → one-shot install + readback
  • scripts/check-gasinfo-local.js → prints the tuple
  • scripts/validate-precompiles.js → raw selector + contract probe

Tasks & flags

Environment keys (honored by tasks) STYLUS_RPC, NITRO_RPC, ARB_PRECOMPILES_CONFIG, plus stability toggles NODE_OPTIONS=--dns-result-order=ipv4first, NODE_NO_HTTP2=1.