@swapdk/wdk-wallet-btc

WDK wallet module for Bitcoin. Fork of @tetherto/wdk-wallet-btc that adds optional OP_RETURN memo support to sendTransaction / signTransaction, so a spending transaction can carry a swap memo (THORChain, MAYAChain) in a single PSBT output.

Everything else — BIP-84 Native SegWit by default, Electrum and Blockbook transports, BIP-32 derivation, coin-selection — is unchanged from upstream. See the upstream README for the full API.

Why this fork exists

THORChain (and MAYAChain) routes incoming BTC deposits on the OP_RETURN memo of the spending transaction. Without that memo, a deposit to the THORChain inbound vault is either refunded or treated as a pool donation. The upstream WalletAccountBtc.sendTransaction API exposes only a single recipient output (to / value / feeRate) and no way to attach an OP_RETURN payload, leaving any THORChain-routed BTC source flow blocked.

This fork adds a single optional field — memo — to the existing send/sign options. Everything else is bit-for-bit upstream. The change is intended to land upstream as a PR; this fork exists so the SwapDK BTC bridge module can ship while that review happens.

What changed

WalletAccountBtc.sendTransaction and WalletAccountBtc.signTransaction now accept an optional memo field:

import WalletManagerBtc from '@swapdk/wdk-wallet-btc'

const wallet = new WalletManagerBtc({ /* ... */ })
const account = await wallet.getAccount(0)

const { hash, fee } = await account.sendTransaction({
  to:    'bc1qayml3n2nyavx0saqjpkz07h0wcpdum59uegwr9',
  value: 1_000_000n,                       // satoshis
  memo:  '=:e:0xe89E6305…:32324827:commission/SDK:444/5'
})

The memo bytes are emitted as an extra OP_RETURN output with value 0. Standardness rules cap OP_RETURN at 80 bytes on mainnet (Bitcoin Core policy); the wallet rejects longer memos with RangeError before constructing the PSBT.

memo may be a string (encoded as UTF-8) or a Buffer / Uint8Array of raw bytes. If omitted, the behaviour is identical to upstream — no OP_RETURN output is added.

getMaxSpendable() accepts the same memo field so callers can compute "send everything" amounts that already account for the OP_RETURN output's vbytes.

Install

npm install @swapdk/wdk-wallet-btc

Upstreaming

The diff is being prepared for submission to tetherto/wdk-wallet-btc. Once it lands upstream and the relevant version is published on npm, this fork will be deprecated. Until then it is the source of truth for SwapDK's BTC source bridge module.

License

Apache-2.0. Original copyright Tether Operations Limited; modifications copyright SwapDK. See NOTICE.