mining: update GBT generation to include witness commitment
This commit updates the block template generation logic to only include witness transactions once the soft-fork has activated and to also include the OP_RETURN witness commitment (with additional block weight accounting).
This commit is contained in:
Olaoluwa Osuntokun
Dave Collins
parent
728c0a4398
commit
f5dec67086
1 changed files with 82 additions and 35 deletions
107
mining/mining.go
107
mining/mining.go
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@ -5,6 +5,7 @@
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package mining
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import (
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"bytes"
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"container/heap"
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"fmt"
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"time"
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@ -460,7 +461,6 @@ func (g *BlkTmplGenerator) NewBlockTemplate(payToAddress btcutil.Address) (*Bloc
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if err != nil {
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return nil, err
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}
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// TODO(roasbeef): add witnesss commitment output
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coinbaseTx, err := createCoinbaseTx(g.chainParams, coinbaseScript,
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nextBlockHeight, payToAddress)
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if err != nil {
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@ -580,7 +580,6 @@ mempoolLoop:
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nextBlockHeight)
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// Calculate the fee in Satoshi/kB.
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// TODO(roasbeef): cost accounting by weight
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prioItem.feePerKB = txDesc.FeePerKB
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prioItem.fee = txDesc.Fee
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@ -602,13 +601,22 @@ mempoolLoop:
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// The starting block size is the size of the block header plus the max
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// possible transaction count size, plus the size of the coinbase
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// transaction.
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blockWeight := uint32((blockHeaderOverhead * (blockchain.WitnessScaleFactor - 1)) + blockchain.GetTransactionWeight(coinbaseTx))
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blockWeight := uint32((blockHeaderOverhead * blockchain.WitnessScaleFactor) +
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blockchain.GetTransactionWeight(coinbaseTx))
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blockSigOpCost := coinbaseSigOpCost
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totalFees := int64(0)
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// TODO(roasbeef): should be guarded by version bits state check
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var witnessIncluded bool
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includeWitness := true
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// Query the version bits state to see if segwit has been activated, if
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// so then this means that we'll include any transactions with witness
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// data in the mempool, and also add the witness commitment as an
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// OP_RETURN output in the coinbase transaction.
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segwitState, err := g.chain.ThresholdState(chaincfg.DeploymentSegwit)
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if err != nil {
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return nil, err
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}
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segwitActive := segwitState == blockchain.ThresholdActive
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witnessIncluded := false
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// Choose which transactions make it into the block.
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for priorityQueue.Len() > 0 {
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@ -620,37 +628,38 @@ mempoolLoop:
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switch {
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// If segregated witness has not been activated yet, then we
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// shouldn't include any witness transactions in the block.
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case tx.HasWitness() && !segwitActive:
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case !segwitActive && tx.HasWitness():
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continue
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// Otherwise, Keep track of if we've included a transaction
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// with witness data or not. If so, then we'll need to include
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// the witness commitment as the last output in the coinbase
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// transaction.
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case tx.HasWitness() && segwitActive:
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case segwitActive && !witnessIncluded && tx.HasWitness():
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// If we're about to include a transaction bearing
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// witness data, then we'll also need to include a
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// witness commitment in the coinbase transaction.
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// Therefore, we account for the additional weight
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// within the block.
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if !witnessIncluded {
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// First we account for the additional witness
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// data in the witness nonce of the coinbaes
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// transaction: 32-bytes of zeroes.
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blockWeight += 2 + 32
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// Next we account for the additional flag and
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// marker bytes in the transaction
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// serialization.
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blockWeight += (1 + 1) * blockchain.WitnessScaleFactor
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// Finally we account for the weight of the
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// additional OP_RETURN output: 8-bytes (value)
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// + 1-byte (var-int) + 38-bytes (pkScript),
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// scaling up the weight as it's non-witness
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// data.
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blockWeight += (8 + 1 + 38) * blockchain.WitnessScaleFactor
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// within the block with a model coinbase tx with a
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// witness commitment.
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coinbaseCopy := btcutil.NewTx(coinbaseTx.MsgTx().Copy())
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coinbaseCopy.MsgTx().TxIn[0].Witness = [][]byte{
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bytes.Repeat([]byte("a"),
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blockchain.CoinbaseWitnessDataLen),
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}
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coinbaseCopy.MsgTx().AddTxOut(&wire.TxOut{
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PkScript: bytes.Repeat([]byte("a"),
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blockchain.CoinbaseWitnessPkScriptLength),
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})
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// In order to accurately account for the weight
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// addition due to this coinbase transaction, we'll add
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// the difference of the transaction before and after
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// the addition of the commitment to the block weight.
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weightDiff := blockchain.GetTransactionWeight(coinbaseCopy) -
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blockchain.GetTransactionWeight(coinbaseTx)
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blockWeight += uint32(weightDiff)
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witnessIncluded = true
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}
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@ -660,7 +669,7 @@ mempoolLoop:
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// Enforce maximum block size. Also check for overflow.
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txWeight := uint32(blockchain.GetTransactionWeight(tx))
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blockPlusTxWeight := uint32(blockWeight + txWeight)
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blockPlusTxWeight := blockWeight + txWeight
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if blockPlusTxWeight < blockWeight ||
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blockPlusTxWeight >= g.policy.BlockMaxWeight {
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@ -673,7 +682,7 @@ mempoolLoop:
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// Enforce maximum signature operation cost per block. Also
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// check for overflow.
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sigOpCost, err := blockchain.GetSigOpCost(tx, false,
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blockUtxos, true, includeWitness)
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blockUtxos, true, segwitActive)
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if err != nil {
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log.Tracef("Skipping tx %s due to error in "+
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"GetSigOpCost: %v", tx.Hash(), err)
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@ -789,12 +798,49 @@ mempoolLoop:
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// the total fees accordingly.
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blockWeight -= wire.MaxVarIntPayload -
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(uint32(wire.VarIntSerializeSize(uint64(len(blockTxns)))) *
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(blockchain.WitnessScaleFactor - 1))
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blockchain.WitnessScaleFactor)
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coinbaseTx.MsgTx().TxOut[0].Value += totalFees
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txFees[0] = -totalFees
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// TODO(roasbeef): add witness commitment
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// If segwit is active and we included transactions with witness data,
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// then we'll need to include a commitment to the witness data in an
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// OP_RETURN output within the coinbase transaction.
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var witnessCommitment []byte
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if witnessIncluded {
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// The witness of the coinbase transaction MUST be exactly 32-bytes
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// of all zeroes.
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var witnessNonce [blockchain.CoinbaseWitnessDataLen]byte
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coinbaseTx.MsgTx().TxIn[0].Witness = wire.TxWitness{witnessNonce[:]}
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// Next, obtain the merkle root of a tree which consists of the
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// wtxid of all transactions in the block. The coinbase
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// transaction will have a special wtxid of all zeroes.
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witnessMerkleTree := blockchain.BuildMerkleTreeStore(blockTxns,
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true)
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witnessMerkleRoot := witnessMerkleTree[len(witnessMerkleTree)-1]
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// The preimage to the witness commitment is:
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// witnessRoot || coinbaseWitness
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var witnessPreimage [64]byte
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copy(witnessPreimage[:32], witnessMerkleRoot[:])
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copy(witnessPreimage[32:], witnessNonce[:])
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// The witness commitment itself is the double-sha256 of the
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// witness preimage generated above. With the commitment
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// generated, the witness script for the output is: OP_RETURN
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// OP_DATA_36 {0xaa21a9ed || witnessCommitment}. The leading
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// prefix is refered to as the "witness magic bytes".
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witnessCommitment = chainhash.DoubleHashB(witnessPreimage[:])
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witnessScript := append(blockchain.WitnessMagicBytes, witnessCommitment...)
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// Finally, create the OP_RETURN carrying witness commitment
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// output as an additional output within the coinbase.
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commitmentOutput := &wire.TxOut{
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Value: 0,
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PkScript: witnessScript,
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}
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coinbaseTx.MsgTx().TxOut = append(coinbaseTx.MsgTx().TxOut,
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commitmentOutput)
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}
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// Calculate the required difficulty for the block. The timestamp
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@ -849,6 +895,7 @@ mempoolLoop:
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SigOpCosts: txSigOpCosts,
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Height: nextBlockHeight,
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ValidPayAddress: payToAddress != nil,
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WitnessCommitment: witnessCommitment,
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}, nil
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}
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