Correct dust limit for splice inputs (#557)

When creating a splice transaction, we should filter out inputs that are below the dust limit. But we should apply the dust limit that matches each script type, instead of the using the channel's dust limit (which is used for the outputs of the funding and commitment transactions).
ACINQ · Nov 2, 2023 · 9ffeb05 · 9ffeb05
1 parent 0c34d72
commit 9ffeb05
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Showing 3 changed files with 23 additions and 7 deletions.
diff --git a/src/commonMain/kotlin/fr/acinq/lightning/channel/InteractiveTx.kt b/src/commonMain/kotlin/fr/acinq/lightning/channel/InteractiveTx.kt
@@ -205,7 +205,8 @@ data class FundingContributions(val inputs: List<InteractiveTxInput.Outgoing>, v
         ): Either<FundingContributionFailure, FundingContributions> {
             walletInputs.forEach { (tx, txOutput) ->
                 if (tx.txOut.size <= txOutput) return Either.Left(FundingContributionFailure.InputOutOfBounds(tx.txid, txOutput))
-                if (tx.txOut[txOutput].amount < params.dustLimit) return Either.Left(FundingContributionFailure.InputBelowDust(tx.txid, txOutput, tx.txOut[txOutput].amount, params.dustLimit))
+                val dustLimit = Transactions.dustLimit(tx.txOut[txOutput].publicKeyScript)
+                if (tx.txOut[txOutput].amount < dustLimit) return Either.Left(FundingContributionFailure.InputBelowDust(tx.txid, txOutput, tx.txOut[txOutput].amount, dustLimit))
                 if (Transaction.write(tx.stripInputWitnesses()).size > 65_000) return Either.Left(FundingContributionFailure.InputTxTooLarge(tx))
             }
             val previousFundingAmount = sharedUtxo?.second?.fundingAmount ?: 0.sat
@@ -775,11 +776,11 @@ data class InteractiveTxSigningSession(
                 val signedLocalCommitTx = Transactions.addSigs(localCommit.value.commitTx, fundingKey.publicKey(), fundingParams.remoteFundingPubkey, localSigOfLocalTx, remoteCommitSig.signature)
                 when (Transactions.checkSpendable(signedLocalCommitTx)) {
                     is Try.Failure -> {
-                        logger.info { "interactiveTxSession=$this"}
-                        logger.info { "channelParams=$channelParams"}
-                        logger.info { "fundingKey=${fundingKey.publicKey()}"}
-                        logger.info { "localSigOfLocalTx=$localSigOfLocalTx"}
-                        logger.info { "signedLocalCommitTx=$signedLocalCommitTx"}
+                        logger.info { "interactiveTxSession=$this" }
+                        logger.info { "channelParams=$channelParams" }
+                        logger.info { "fundingKey=${fundingKey.publicKey()}" }
+                        logger.info { "localSigOfLocalTx=$localSigOfLocalTx" }
+                        logger.info { "signedLocalCommitTx=$signedLocalCommitTx" }
                         Pair(this, InteractiveTxSigningSessionAction.AbortFundingAttempt(InvalidCommitmentSignature(fundingParams.channelId, signedLocalCommitTx.tx.txid)))
                     }
                     is Try.Success -> {

diff --git a/src/commonMain/kotlin/fr/acinq/lightning/transactions/Transactions.kt b/src/commonMain/kotlin/fr/acinq/lightning/transactions/Transactions.kt
@@ -181,6 +181,21 @@ object Transactions {
      */
     fun fee2rate(fee: Satoshi, weight: Int): FeeratePerKw = FeeratePerKw((fee * 1000L) / weight.toLong())
 
+    /** As defined in https://github.com/lightning/bolts/blob/master/03-transactions.md#dust-limits */
+    fun dustLimit(scriptPubKey: ByteVector): Satoshi {
+        return runTrying {
+            val script = Script.parse(scriptPubKey)
+            when {
+                Script.isPay2pkh(script) -> 546.sat
+                Script.isPay2sh(script) -> 540.sat
+                Script.isPay2wpkh(script) -> 294.sat
+                Script.isPay2wsh(script) -> 330.sat
+                Script.isNativeWitnessScript(script) -> 354.sat
+                else -> 546.sat
+            }
+        }.getOrElse { 546.sat }
+    }
+
     /** Offered HTLCs below this amount will be trimmed. */
     fun offeredHtlcTrimThreshold(dustLimit: Satoshi, spec: CommitmentSpec): Satoshi = dustLimit + weight2fee(spec.feerate, Commitments.HTLC_TIMEOUT_WEIGHT)
 

diff --git a/src/commonTest/kotlin/fr/acinq/lightning/channel/InteractiveTxTestsCommon.kt b/src/commonTest/kotlin/fr/acinq/lightning/channel/InteractiveTxTestsCommon.kt
@@ -635,7 +635,7 @@ class InteractiveTxTestsCommon : LightningTestSuite() {
         val pubKey = privKey.publicKey()
         val fundingParams = InteractiveTxParams(randomBytes32(), true, 150_000.sat, 50_000.sat, pubKey, 0, 660.sat, FeeratePerKw(2500.sat))
         run {
-            val previousTx = Transaction(2, listOf(), listOf(TxOut(650.sat, Script.pay2wpkh(pubKey))), 0)
+            val previousTx = Transaction(2, listOf(), listOf(TxOut(293.sat, Script.pay2wpkh(pubKey))), 0)
             val result = FundingContributions.create(channelKeys, swapInKeys, fundingParams, listOf(WalletState.Utxo(previousTx, 0, 0))).left
             assertNotNull(result)
             assertIs<FundingContributionFailure.InputBelowDust>(result)