package lnwallet import ( "github.com/roasbeef/btcd/blockchain" ) const ( WitnessFactor = blockchain.WitnessScaleFactor MaxTransactionWeightPolicy = blockchain.MaxBlockCost / 10 // The weight(cost), which is different from the !size! (see BIP-141), // is calculated as: // Weight = 4 * BaseSize + WitnessSize (weight). // BaseSize - size of the transaction without witness data (bytes). // WitnessSize - witness size (bytes). // Weight - the metric for determining the cost of the transaction. // P2WSH: 34 bytes // - OP_0: 1 byte // - OP_DATA: 1 byte (WitnessScriptSHA256 length) // - WitnessScriptSHA256: 32 bytes P2WSHSize = 1 + 1 + 32 // P2WPKH: 22 bytes // - OP_0: 1 byte // - OP_DATA: 1 byte (PublicKeyHASH160 length) // - PublicKeyHASH160: 20 bytes P2WPKHSize = 1 + 1 + 20 // MultiSig: 71 bytes // - OP_2: 1 byte // - OP_DATA: 1 byte (pubKeyAlice length) // - pubKeyAlice: 33 bytes // - OP_DATA: 1 byte (pubKeyBob length) // - pubKeyBob: 33 bytes // - OP_2: 1 byte // - OP_CHECKMULTISIG: 1 byte MultiSigSize = 1 + 1 + 33 + 1 + 33 + 1 + 1 // Witness: 222 bytes // - NumberOfWitnessElements: 1 byte // - NilLength: 1 byte // - sigAliceLength: 1 byte // - sigAlice: 73 bytes // - sigBobLength: 1 byte // - sigBob: 73 bytes // - WitnessScriptLength: 1 byte // - WitnessScript (MultiSig) WitnessSize = 1 + 1 + 1 + 73 + 1 + 73 + 1 + MultiSigSize // FundingInput: 41 bytes // - PreviousOutPoint: // - Hash: 32 bytes // - Index: 4 bytes // - OP_DATA: 1 byte (ScriptSigLength) // - ScriptSig: 0 bytes // - Witness <---- we use "Witness" instead of "ScriptSig" for // transaction validation, but "Witness" is stored // separately and cost for it size is smaller. So // we separate the calculation of ordinary data // from witness data. // - Sequence: 4 bytes FundingInputSize = 32 + 4 + 1 + 4 // OutputPayingToUs: 43 bytes // - Value: 8 bytes // - VarInt: 1 byte (PkScript length) // - PkScript (P2WSH) CommitmentDelayOutput = 8 + 1 + P2WSHSize // OutputPayingToThem: 31 bytes // - Value: 8 bytes // - VarInt: 1 byte (PkScript length) // - PkScript (P2WPKH) CommitmentKeyHashOutput = 8 + 1 + P2WPKHSize // HTLCOutput: 43 bytes // - Value: 8 bytes // - VarInt: 1 byte (PkScript length) // - PkScript (PW2SH) HTLCSize = 8 + 1 + P2WSHSize // WitnessHeader: 2 bytes // - Flag: 1 byte // - Marker: 1 byte WitnessHeaderSize = 1 + 1 // CommitmentTransaction: 125 bytes // - Version: 4 bytes // - WitnessHeader <---- part of the witness data // - CountTxIn: 1 byte // - TxIn: // FundingInput // - CountTxOut: 1 byte // - TxOut: // OutputPayingToThem, // OutputPayingToUs, // ....HTLCOutputs... // - LockTime: 4 bytes BaseCommitmentTxSize = 4 + 1 + FundingInputSize + 1 + CommitmentDelayOutput + CommitmentKeyHashOutput + 4 // CommitmentTransactionCost: 500 weight BaseCommitmentTxCost = WitnessFactor * BaseCommitmentTxSize // WitnessCommitmentTxCost: 224 weight WitnessCommitmentTxCost = WitnessHeaderSize + WitnessSize // HTLCCost: 172 weight HTLCCost = WitnessFactor * HTLCSize // MaxHTLCNumber shows as the maximum number HTLCs which can be // included in commitment transaction. This numbers was calculated by // Rusty Russel in "BOLT #5: Recommendations for On-chain Transaction // Handling", based on the fact that we need to sweep all HTLCs within // one penalty transaction. MaxHTLCNumber = 1253 ) // estimateCommitTxCost estimate commitment transaction cost depending on the // precalculated cost of base transaction, witness data, which is needed for // paying for funding tx, and htlc cost multiplied by their count. func estimateCommitTxCost(count int, prediction bool) int64 { // Make prediction about the size of commitment transaction with // additional HTLC. if prediction { count++ } htlcCost := int64(count * HTLCCost) baseCost := int64(BaseCommitmentTxCost) witnessCost := int64(WitnessCommitmentTxCost) return htlcCost + baseCost + witnessCost }