wasm: add TxOut.fromTransaction and rangeproofFromTransaction#160
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EvanWinget wants to merge 1 commit into
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wasm: add TxOut.fromTransaction and rangeproofFromTransaction#160EvanWinget wants to merge 1 commit into
EvanWinget wants to merge 1 commit into
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Two helpers for the common pattern of building a PSET input from a known transaction: - TxOut.fromTransaction(tx, vout) — extract TxOut at a given vout, with the witness stripped, suitable for use as witness_utxo. - TxOut.rangeproofFromTransaction(tx, vout) — extract the rangeproof bytes (or undefined for explicit outputs) for use with inUtxoRangeproof(). The witness-strip rule is non-obvious: PSET stores the rangeproof in a separate in_utxo_rangeproof field, so a TxOut used as witness_utxo must have its TxOutWitness cleared. Centralizing the strip in a named helper makes the input flow harder to misuse. The Result/Option asymmetry between the two helpers is deliberate: a missing rangeproof is a legitimate state (explicit outputs), but out-of-range vout is a programming error.
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Thank you in advance to whoever reviews this - I do have 2 more wasm changes that I'm hoping to propose, but I thought it might make sense to get feedback on this PR and #159 before opening any additional PRs |
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Two helpers for building a PSET input from a previously-broadcast or otherwise-known transaction:
TxOut.fromTransaction(tx, vout)to extract theTxOutat a given vout, with witness data stripped, suitable for use aswitness_utxo.TxOut.rangeproofFromTransaction(tx, vout)to extract the rangeproof bytes (Nonefor explicit outputs or out-of-range vout), for use withinUtxoRangeproof().Motivation
The witness section on a
TxOutmust not be carried into PSET'switness_utxofield. PSET stores the rangeproof in a dedicated input field (in_utxo_rangeproof) and the surjection proof is consumed during prior-tx verification and not re-carried. A caller who reaches intotx.outputs()[vout]and passes the result aswitness_utxoproduces a PSET that bloats serialization and may be rejected by strict-mode parsers.This rule is non-obvious because there's nothing on the type itself that hints at it, and the failure mode is silent until a downstream verifier rejects the PSET. Centralizing the strip in a named helper makes it unmissable: if you want a
witness_utxo, you go throughfromTransaction.rangeproofFromTransactionis a smaller convenience for the matching consumer (inUtxoRangeproof) — pullingtx.outputs()[vout].witness.rangeproofand serializing it is boilerplate every PSET-building caller would otherwise repeat.