blockchain: enforce CSV soft-fork validation based on versionbits state

This commit modifies the existing block validation logic to examine the
current version bits state of the CSV soft-fork, enforcing the new
validation rules (BIPs 68, 112, and 113) accordingly based on the
current `ThesholdState`.

blockchain/chain.go

@@ -351,17 +351,15 @@ func (b *BlockChain) CalcSequenceLock(tx *btcutil.Tx, utxoView *UtxoViewpoint,
 	b.chainLock.Lock()
 	defer b.chainLock.Unlock()
 
-	return b.calcSequenceLock(tx, utxoView, mempool)
+	return b.calcSequenceLock(b.bestNode, tx, utxoView, mempool)
 }
 
 // calcSequenceLock computes the relative lock-times for the passed
 // transaction. See the exported version, CalcSequenceLock for further details.
 //
 // This function MUST be called with the chain state lock held (for writes).
-func (b *BlockChain) calcSequenceLock(tx *btcutil.Tx, utxoView *UtxoViewpoint,
-	mempool bool) (*SequenceLock, error) {
-
-	mTx := tx.MsgTx()
+func (b *BlockChain) calcSequenceLock(node *blockNode, tx *btcutil.Tx,
+	utxoView *UtxoViewpoint, mempool bool) (*SequenceLock, error) {
 
 	// A value of -1 for each relative lock type represents a relative time
 	// lock value that will allow a transaction to be included in a block
@@ -370,20 +368,42 @@ func (b *BlockChain) calcSequenceLock(tx *btcutil.Tx, utxoView *UtxoViewpoint,
 	// activated.
 	sequenceLock := &SequenceLock{Seconds: -1, BlockHeight: -1}
 
+	// The sequence locks semantics are always active for transactions
+	// within the mempool.
+	csvSoftforkActive := mempool
+
+	// If we're performing block validation, then we need to query the BIP9
+	// state.
+	if !csvSoftforkActive {
+		prevNode, err := b.index.PrevNodeFromNode(node)
+		if err != nil {
+			return nil, err
+		}
+
+		// Obtain the latest BIP9 version bits state for the
+		// CSV-package soft-fork deployment. The adherence of sequence
+		// locks depends on the current soft-fork state.
+		csvState, err := b.deploymentState(prevNode, chaincfg.DeploymentCSV)
+		if err != nil {
+			return nil, err
+		}
+		csvSoftforkActive = csvState == ThresholdActive
+	}
+
 	// If the transaction's version is less than 2, and BIP 68 has not yet
 	// been activated then sequence locks are disabled. Additionally,
 	// sequence locks don't apply to coinbase transactions Therefore, we
 	// return sequence lock values of -1 indicating that this transaction
 	// can be included within a block at any given height or time.
-	// TODO(roasbeef): check version bits state or pass as param
-	// * true should be replaced with a version bits state check
-	sequenceLockActive := mTx.Version >= 2 && (mempool || true)
+	mTx := tx.MsgTx()
+	sequenceLockActive := mTx.Version >= 2 && csvSoftforkActive
 	if !sequenceLockActive || IsCoinBase(tx) {
 		return sequenceLock, nil
 	}
 
-	// Grab the next height to use for inputs present in the mempool.
-	nextHeight := b.BestSnapshot().Height + 1
+	// Grab the next height from the PoV of the passed blockNode to use for
+	// inputs present in the mempool.
+	nextHeight := node.height + 1
 
 	for txInIndex, txIn := range mTx.TxIn {
 		utxo := utxoView.LookupEntry(&txIn.PreviousOutPoint.Hash)
@@ -421,9 +441,8 @@ func (b *BlockChain) calcSequenceLock(tx *btcutil.Tx, utxoView *UtxoViewpoint,
 			// compute the past median time for the block prior to
 			// the one which included this referenced output.
 			// TODO: caching should be added to keep this speedy
-			inputDepth := uint32(b.bestNode.height-inputHeight) + 1
-			blockNode, err := b.index.RelativeNode(b.bestNode,
-				inputDepth)
+			inputDepth := uint32(node.height-inputHeight) + 1
+			blockNode, err := b.index.RelativeNode(node, inputDepth)
 			if err != nil {
 				return sequenceLock, err
 			}

blockchain/chain_test.go

@@ -122,7 +122,7 @@ func TestCalcSequenceLock(t *testing.T) {
 	netParams := &chaincfg.SimNetParams
 
 	// Create a new database and chain instance to run tests against.
-	chain, teardownFunc, err := chainSetup("haveblock", netParams)
+	chain, teardownFunc, err := chainSetup("calcseqlock", netParams)
 	if err != nil {
 		t.Errorf("Failed to setup chain instance: %v", err)
 		return
@@ -190,7 +190,8 @@ func TestCalcSequenceLock(t *testing.T) {
 		prevBlock = block
 	}
 
-	// Create with all the utxos within the create created above.
+	// Create a utxo view with all the utxos within the blocks created
+	// above.
 	utxoView := blockchain.NewUtxoViewpoint()
 	for blockHeight, blockWithMTP := range blocksWithMTP {
 		for _, tx := range blockWithMTP.block.Transactions() {
@@ -200,8 +201,9 @@ func TestCalcSequenceLock(t *testing.T) {
 	utxoView.SetBestHash(blocksWithMTP[len(blocksWithMTP)-1].block.Hash())
 
 	// The median time calculated from the PoV of the best block in our
-	// test chain. For unconfirmed inputs, this value will be used since th
-	// MTP will be calculated from the PoV of the yet-to-be-mined block.
+	// test chain. For unconfirmed inputs, this value will be used since
+	// the MTP will be calculated from the PoV of the yet-to-be-mined
+	// block.
 	nextMedianTime := int64(1401292712)
 
 	// We'll refer to this utxo within each input in the transactions

blockchain/thresholdstate.go

@@ -309,14 +309,33 @@ func (b *BlockChain) thresholdState(prevNode *blockNode, checker thresholdCondit
 //
 // This function is safe for concurrent access.
 func (b *BlockChain) ThresholdState(deploymentID uint32) (ThresholdState, error) {
+	b.chainLock.Lock()
+	state, err := b.deploymentState(b.bestNode, deploymentID)
+	b.chainLock.Unlock()
+
+	return state, err
+}
+
+// deploymentState returns the current rule change threshold for a given
+// deploymentID. The threshold is evaluated from the point of view of the block
+// node passed in as the first argument to this method.
+//
+// It is important to note that, as the variable name indicates, this function
+// expects the block node prior to the block for which the deployment state is
+// desired.  In other words, the returned deployment state is for the block
+// AFTER the passed node.
+//
+// This function MUST be called with the chain state lock held (for writes).
+func (b *BlockChain) deploymentState(prevNode *blockNode,
+	deploymentID uint32) (ThresholdState, error) {
+
 	if deploymentID > uint32(len(b.chainParams.Deployments)) {
 		return ThresholdFailed, DeploymentError(deploymentID)
 	}
+
 	deployment := &b.chainParams.Deployments[deploymentID]
 	checker := deploymentChecker{deployment: deployment, chain: b}
 	cache := &b.deploymentCaches[deploymentID]
-	b.chainLock.Lock()
-	state, err := b.thresholdState(b.bestNode, checker, cache)
-	b.chainLock.Unlock()
-	return state, err
+
+	return b.thresholdState(prevNode, checker, cache)
 }

blockchain/validate.go

@@ -752,6 +752,27 @@ func (b *BlockChain) checkBlockContext(block *btcutil.Block, prevNode *blockNode
 
 	fastAdd := flags&BFFastAdd == BFFastAdd
 	if !fastAdd {
+		// Obtain the latest state of the deployed CSV soft-fork in
+		// order to properly guard the new validation behavior based on
+		// the current BIP 9 version bits state.
+		csvState, err := b.deploymentState(prevNode, chaincfg.DeploymentCSV)
+		if err != nil {
+			return err
+		}
+
+		// Once the CSV soft-fork is fully active, we'll switch to
+		// using the current median time past of the past block's
+		// timestamps for all lock-time based checks.
+		blockTime := header.Timestamp
+		if csvState == ThresholdActive {
+			medianTime, err := b.index.CalcPastMedianTime(prevNode)
+			if err != nil {
+				return err
+			}
+
+			blockTime = medianTime
+		}
+
 		// The height of this block is one more than the referenced
 		// previous block.
 		blockHeight := prevNode.height + 1
@@ -759,7 +780,7 @@ func (b *BlockChain) checkBlockContext(block *btcutil.Block, prevNode *blockNode
 		// Ensure all transactions in the block are finalized.
 		for _, tx := range block.Transactions() {
 			if !IsFinalizedTransaction(tx, blockHeight,
-				header.Timestamp) {
+				blockTime) {
 
 				str := fmt.Sprintf("block contains unfinalized "+
 					"transaction %v", tx.Hash())
@@ -1133,6 +1154,48 @@ func (b *BlockChain) checkConnectBlock(node *blockNode, block *btcutil.Block, vi
 		scriptFlags |= txscript.ScriptVerifyCheckLockTimeVerify
 	}
 
+	// Enforce CHECKSEQUENCEVERIFY during all block validation checks once
+	// the soft-fork deployment is fully active.
+	csvState, err := b.deploymentState(node.parent, chaincfg.DeploymentCSV)
+	if err != nil {
+		return err
+	}
+	if csvState == ThresholdActive {
+		// If the CSV soft-fork is now active, then modify the
+		// scriptFlags to ensure that the CSV op code is properly
+		// validated during the script checks bleow.
+		scriptFlags |= txscript.ScriptVerifyCheckSequenceVerify
+
+		// We obtain the MTP of the *previous* block in order to
+		// determine if transactions in the current block are final.
+		medianTime, err := b.index.CalcPastMedianTime(node.parent)
+		if err != nil {
+			return err
+		}
+
+		// Additionally, if the CSV soft-fork package is now active,
+		// then we also enforce the relative sequence number based
+		// lock-times within the inputs of all transactions in this
+		// candidate block.
+		for _, tx := range block.Transactions() {
+			// A transaction can only be included within a block
+			// once the sequence locks of *all* its inputs are
+			// active.
+			sequenceLock, err := b.calcSequenceLock(node, tx, view,
+				false)
+			if err != nil {
+				return err
+			}
+			if !SequenceLockActive(sequenceLock, node.height,
+				medianTime) {
+				str := fmt.Sprintf("block contains " +
+					"transaction whose input sequence " +
+					"locks are not met")
+				return ruleError(ErrUnfinalizedTx, str)
+			}
+		}
+	}
+
 	// Now that the inexpensive checks are done and have passed, verify the
 	// transactions are actually allowed to spend the coins by running the
 	// expensive ECDSA signature check scripts.  Doing this last helps