lnd.xprv/lnwallet/size.go
2017-07-30 17:49:03 -07:00

141 lines
4.3 KiB
Go

package lnwallet
import (
"github.com/roasbeef/btcd/blockchain"
)
const (
// The weight(weight), 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 weight of the transaction.
// P2WSHSize 34 bytes
// - OP_0: 1 byte
// - OP_DATA: 1 byte (WitnessScriptSHA256 length)
// - WitnessScriptSHA256: 32 bytes
P2WSHSize = 1 + 1 + 32
// P2WPKHSize 22 bytes
// - OP_0: 1 byte
// - OP_DATA: 1 byte (PublicKeyHASH160 length)
// - PublicKeyHASH160: 20 bytes
P2WPKHSize = 1 + 1 + 20
// MultiSigSize 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
// WitnessSize 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
// FundingInputSize 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 weight for it size is smaller. So
// we separate the calculation of ordinary data
// from witness data.
// - Sequence: 4 bytes
FundingInputSize = 32 + 4 + 1 + 4
// CommitmentDelayOutput 43 bytes
// - Value: 8 bytes
// - VarInt: 1 byte (PkScript length)
// - PkScript (P2WSH)
CommitmentDelayOutput = 8 + 1 + P2WSHSize
// CommitmentKeyHashOutput 31 bytes
// - Value: 8 bytes
// - VarInt: 1 byte (PkScript length)
// - PkScript (P2WPKH)
CommitmentKeyHashOutput = 8 + 1 + P2WPKHSize
// HTLCSize 43 bytes
// - Value: 8 bytes
// - VarInt: 1 byte (PkScript length)
// - PkScript (PW2SH)
HTLCSize = 8 + 1 + P2WSHSize
// WitnessHeaderSize 2 bytes
// - Flag: 1 byte
// - Marker: 1 byte
WitnessHeaderSize = 1 + 1
// BaseCommitmentTxSize 125 43 * num-htlc-outputs bytes
// - Version: 4 bytes
// - WitnessHeader <---- part of the witness data
// - CountTxIn: 1 byte
// - TxIn: 41 bytes
// FundingInput
// - CountTxOut: 1 byte
// - TxOut: 74 + 43 * num-htlc-outputs bytes
// OutputPayingToThem,
// OutputPayingToUs,
// ....HTLCOutputs...
// - LockTime: 4 bytes
BaseCommitmentTxSize = 4 + 1 + FundingInputSize + 1 +
CommitmentDelayOutput + CommitmentKeyHashOutput + 4
// BaseCommitmentTxWeight 500 weight
BaseCommitmentTxWeight = blockchain.WitnessScaleFactor * BaseCommitmentTxSize
// WitnessCommitmentTxWeight 224 weight
WitnessCommitmentTxWeight = WitnessHeaderSize + WitnessSize
// HTLCWeight 172 weight
HTLCWeight = blockchain.WitnessScaleFactor * HTLCSize
// HtlcTimeoutWeight is the weight of the HTLC timeout transaction
// which will transition an outgoing HTLC to the delay-and-claim state.
HtlcTimeoutWeight = 663
// HtlcSuccessWeight is the weight of the HTLC success transaction
// which will transition an incoming HTLC to the delay-and-claim state.
HtlcSuccessWeight = 703
// MaxHTLCNumber is the maximum number HTLCs which can be included in a
// commitment transaction. This limit was chosen such that, in the case
// of a contract breach, the punishment transaction is able to sweep
// all the HTLC's yet still remain below the widely used standard
// weight limits.
MaxHTLCNumber = 967
)
// estimateCommitTxWeight estimate commitment transaction weight depending on
// the precalculated weight of base transaction, witness data, which is needed
// for paying for funding tx, and htlc weight multiplied by their count.
func estimateCommitTxWeight(count int, prediction bool) int64 {
// Make prediction about the size of commitment transaction with
// additional HTLC.
if prediction {
count++
}
htlcWeight := int64(count * HTLCWeight)
baseWeight := int64(BaseCommitmentTxWeight)
witnessWeight := int64(WitnessCommitmentTxWeight)
return htlcWeight + baseWeight + witnessWeight
}