feat(arbitrum-adapter): implement previewSequencerFee via NodeInterface.gasEstimateComponents#21
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…ce.gasEstimateComponents
Turn the previewSequencerFee skeleton (returned null) into a live estimation.
- Reads NodeInterface.gasEstimateComponents (precompile 0xC8) through a
caller-supplied viem PublicClient. The precompile simulates the (to, data)
call and returns gasEstimate, gasEstimateForL1, baseFee (L2), and
l1BaseFeeEstimate. We mark the ABI `view` so viem readContract accepts the
canonically-payable method; eth_call ignores declared mutability. Verified
live against Arbitrum One mainnet.
- Fee math (Arbitrum Nitro): both components priced at the L2 base fee.
l1FeeWei = gasEstimateForL1 * baseFee; l2FeeWei = (gasEstimate -
gasEstimateForL1) * baseFee; totalFeeWei = gasEstimate * baseFee. Fills
every SequencerFeePreview field.
- Signature is now async (client, { chain, to, calldata, from?, l1BaseFeeWei? })
with a required `to` (the precompile needs a destination to simulate) and
the client injected so the function stays RPC-agnostic and testable. Any
failure (RPC down, simulated call reverts, malformed calldata) returns null;
the preview is advisory and must never block signing.
- Rename private isNova -> checkIsNova (predicate-function naming rule).
- Add viem as a peer dependency (>=2); externalized by tsup, not bundled.
- Replace the single stub test with 6 cases over a mock PublicClient: field
math, correct precompile address/function/args, Nova compression flag,
l1BaseFeeWei override, null-on-failure, calldata byte counting.
Untouched: attachSequencerFeePreview, isSequencerFeePreview,
extractSequencerFeePreview, and the bridge / retryable / decoder helpers.
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Summary
Turns the
previewSequencerFeeskeleton (which returnednull) into a live sequencer-fee estimation. This is the alpha.1 hardening the README flagged ("helper bodies harden in alpha.1 with viem"). Scope: ONE function body + its tests + deps/docs. The pure helpers (attachSequencerFeePreview,isSequencerFeePreview,extractSequencerFeePreview) and the bridge / retryable / decoder modules are untouched.How it works
previewSequencerFee(client, { chain, to, calldata, from?, l1BaseFeeWei? })reads NodeInterface.gasEstimateComponents (precompile0xC8) through a caller-supplied viemPublicClient. The precompile simulates the(to, data)call and returns(gasEstimate, gasEstimateForL1, baseFee, l1BaseFeeEstimate).Fee math (Arbitrum Nitro - both components priced at the L2 base fee, the L1 part is denominated in L2 gas units):
l1FeeWei = gasEstimateForL1 * baseFeel2FeeWei = (gasEstimate - gasEstimateForL1) * baseFeetotalFeeWei = gasEstimate * baseFeeEvery
SequencerFeePreviewfield is filled (l2GasEstimate,l1CalldataBytes,l1BaseFeeWei,l1FeeWei,l2FeeWei,totalFeeWei,isCompressed,previewBlock).Decisions
async, takes the viem client as the first arg (RPC-agnostic + testable), and requirestobecause the precompile simulates a call and needs a destination. A calldata-size-only estimate was rejected because it cannot fill the L2 compute fields.gasEstimateComponentsalone returns the L2 base fee and the L1 base-fee estimate, soArbGasInfowould be a redundant read. Confirmed with the maintainer.view-marked ABI. The canonical method ispayable, but we own the ABI and mark itviewso viemreadContractaccepts it; eth_call ignores declared mutability. Validated live against Arbitrum One mainnet before writing the code (readContractreturned[21689n, 523n, 20062000n, 4151436n], a 4-tuple, fee math sane).null. RPC down, simulated call reverts, or malformed calldata all returnnull- the preview is advisory wallet UX and must never block signing (the type was already| null).isNova->checkIsNova(predicate-function naming rule); only referenced inside this file.Verification
6 new tests over a mock
PublicClient: full field math, correct precompile address/function/args, Nova compression flag,l1BaseFeeWeioverride, null-on-failure, calldata byte counting.Deps
viemadded as a peer dependency (>=2, mirrors core/react/tx-decoder) + dev dependency (^2.48.4). tsup externalizes it - the ESM bundle keepsimport { toHex } from 'viem'and does not inline the library.Left for alpha.1
l1CalldataBytesreports the raw byte count, not the post-Brotli/DAC size (the fee itself is still accurate -gasEstimateForL1already accounts for the DAC).ArbGasInfofallback so the L1 portion can still be shown when the simulated call reverts; plus the decoder-registry expansion and a viem custom-transport integration test.Not merging - leaving open for review.