@txkit/arbitrum-adapter

Bridge Arbitrum specifics and @txkit/tx-protocol PreparedEnvelope. Attach L1->L2 bridge intents, retryable-ticket UX hints, and sequencer-fee previews to an envelope; decode Arbitrum-flavoured calldata.

v0.1.0-alpha - skeleton scaffolded for the Arbitrum Open House London Buildathon (June 14 deadline). Surface stable; helper bodies will harden in alpha.1 with viem integration.

Why this exists

The PreparedTransaction Envelope (ERC-8265, PR #1753) gives producers a chain-neutral way to describe a transaction before signing. Arbitrum needs a few additions on top of that base shape so wallet previews can show what is actually happening:

• L1->L2 bridge deposits are two-leg flows. The envelope is the L1 transaction; the wallet should show the expected L2 outcome ("you will receive X on Arbitrum One via Across").
• Retryable tickets carry their own gas budget plus refund-address semantics that have no analogue on a vanilla L1 transaction.
• Arbitrum's fee model splits each transaction into L2 compute + L1 calldata cost, with Nova compressing calldata via Brotli on the AnyTrust DAC. A flat gasPrice * gasLimit preview hides the L1 component entirely.
• Arbitrum-specific contracts (precompiles, the Delayed Inbox, canonical gateway routers, Hop / Across L1 entrypoints) carry intents that a generic ERC-20 decoder will not surface.

@txkit/tx-protocol reserves a meta slot on every envelope. This package puts a typed shape on meta.arbitrum, with bridge, retryable, and sequencerFee sub-keys, plus an Arbitrum-aware decoder seed.

Install

npm install @txkit/arbitrum-adapter@alpha @txkit/tx-protocol@alpha

Usage

Attach an L1->L2 bridge intent

import { createEvmTx } from '@txkit/tx-protocol'
import { attachBridgeIntent, extractBridgeIntent } from '@txkit/arbitrum-adapter'

const envelope = createEvmTx({
  chain: 'eip155:1', // L1 deposit transaction
  calls: [ { to: '0x5C7BCd6E7De5423a257D81B442095A1a6ced35C5', data: '0x...' } ],
  validity: { notAfter: Math.floor(Date.now() / 1000) + 3600 },
  description: { short: 'Bridge 0.1 ETH to Arbitrum One via Across', action: 'bridge' },
})

const withBridge = attachBridgeIntent(envelope, {
  provider: 'across',
  l1ChainId: 'eip155:1',
  l2ChainId: 'eip155:42161',
  tokenIn: 'native',
  amount: '0x16345785d8a0000',
  recipient: '0xRecipientOnL2',
})

const intent = extractBridgeIntent(withBridge)
// -> { provider: 'across', l1ChainId: 'eip155:1', l2ChainId: 'eip155:42161', ... }

Surface a retryable-ticket budget

import { attachRetryableHints } from '@txkit/arbitrum-adapter'

const withRetryable = attachRetryableHints(envelope, {
  l2Gas: '0x186a0',
  l2GasPriceBid: '0x5f5e100',
  maxSubmissionCost: '0x38d7ea4c68000',
  callValueRefundAddress: '0xRefundReceiver',
})

Preview the sequencer fee

import { attachSequencerFeePreview } from '@txkit/arbitrum-adapter'

const withFee = attachSequencerFeePreview(envelope, {
  l2GasEstimate: '0x186a0',
  l1CalldataBytes: 132,
  l1BaseFeeWei: '0x3b9aca00',
  l1FeeWei: '0x16345785d8a0000',
  l2FeeWei: '0x71afd498d0000',
  totalFeeWei: '0x1d4ab7f7c2a0000',
  isCompressed: false, // true for Arbitrum Nova
})

Decode Arbitrum-flavoured calldata

import { decodeArbitrumCall } from '@txkit/arbitrum-adapter'

const decoded = decodeArbitrumCall({
  to: '0x4dBd4fC535Ac27206064B6804B5d6C7Acb7C1aBc',
  calldata: '0x679b6ded...',
})
// -> { kind: 'retryable-create', contractLabel: 'Arbitrum Inbox' }

API

Bridge intents

• attachBridgeIntent(envelope, intent) - attach meta.arbitrum.bridge
• extractBridgeIntent(envelope) - read meta.arbitrum.bridge
• isBridgeIntent(value) - type guard

Retryable tickets

• attachRetryableHints(envelope, hints) - attach meta.arbitrum.retryable
• extractRetryableHints(envelope) - read meta.arbitrum.retryable
• isRetryableHints(value) - type guard

Sequencer-fee preview

• attachSequencerFeePreview(envelope, preview) - attach meta.arbitrum.sequencerFee
• extractSequencerFeePreview(envelope) - read meta.arbitrum.sequencerFee
• isSequencerFeePreview(value) - type guard
• previewSequencerFee({ chain, calldata, l1BaseFeeWei? }) - skeleton stub, returns null until alpha.1
• NOVA_USES_COMPRESSED_CALLDATA - constant flag (true)

Decoder

• decodeArbitrumCall({ to, calldata }) - returns ArbitrumDecodedCall | null
• KNOWN_ARBITRUM_ADDRESSES - address -> label registry (precompiles, Delayed Inbox, canonical gateway, Hop / Across L1 entrypoints)

Status

Skeleton. Helper bodies for previewSequencerFee and the decoder registry will harden in alpha.1 with viem-driven precompile reads (ArbGasInfo, NodeInterface) plus expanded coverage of Hop bonders per token, Across SpokePool per chain, Stargate routers, Camelot, GMX, Pendle, and Aave V3 on Arbitrum One.

Tracking issue: open one in github.com/txkit/mono/issues if you have a buildathon use case that needs prioritisation.

License

Apache-2.0