Modify NewBlockTemplate to accept nil pay addr.

There are certain cases such as getblocktemplate which allow external
callers to be repsonsible for creating their own coinbase to replace the
generated one.  By allowing the pay address to be nil in such cases, the
need to specify mining addresses via --miningaddr can be avoided thereby
leaving the payment address management up to the caller.

cpuminer.go

@@ -298,7 +298,7 @@ out:
 		// Create a new block template using the available transactions
 		// in the memory pool as a source of transactions to potentially
 		// include in the block.
-		template, err := NewBlockTemplate(payToAddr, m.server.txMemPool)
+		template, err := NewBlockTemplate(m.server.txMemPool, payToAddr)
 		m.submitBlockLock.Unlock()
 		if err != nil {
 			errStr := fmt.Sprintf("Failed to create new block "+

mining.go

@@ -165,9 +165,11 @@ func newTxPriorityQueue(reserve int, sortByFee bool) *txPriorityQueue {
 // details about the fees and the number of signature operations for each
 // transaction in the block.
 type BlockTemplate struct {
-	block       *btcwire.MsgBlock
-	fees        []int64
-	sigOpCounts []int64
+	block           *btcwire.MsgBlock
+	fees            []int64
+	sigOpCounts     []int64
+	height          int64
+	validPayAddress bool
 }
 
 // minInt is a helper function to return the minimum of two ints.  This avoids
@@ -203,16 +205,25 @@ func standardCoinbaseScript(nextBlockHeight int64, extraNonce uint64) []byte {
 }
 
 // createCoinbaseTx returns a coinbase transaction paying an appropriate subsidy
-// based on the passed block height to the passed public key.  It also accepts
-// an extra nonce value for the signature script.  This extra nonce helps ensure
-// the transaction is not a duplicate transaction (paying the same value to the
-// same public key address would otherwise be an identical transaction for
-// block version 1).
+// based on the passed block height to the provided address.  When the address
+// is nil, the coinbase transaction will instead be redeemable by anyone.
+//
+// See the comment for NewBlockTemplate for more information about why the nil
+// address handling is useful.
 func createCoinbaseTx(coinbaseScript []byte, nextBlockHeight int64, addr btcutil.Address) (*btcutil.Tx, error) {
-	// Create a script to pay to the specific address.
-	pkScript, err := btcscript.PayToAddrScript(addr)
-	if err != nil {
-		return nil, err
+	// Create the script to pay to the provided payment address if one was
+	// specified.  Otherwise create a script that allows the coinbase to be
+	// redeemable by anyone.
+	var pkScript []byte
+	if addr != nil {
+		var err error
+		pkScript, err = btcscript.PayToAddrScript(addr)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		scriptBuilder := btcscript.NewScriptBuilder()
+		pkScript = scriptBuilder.AddOp(btcscript.OP_TRUE).Script()
 	}
 
 	tx := btcwire.NewMsgTx()
@@ -332,16 +343,22 @@ func medianAdjustedTime(chainState *chainState) (time.Time, error) {
 	return newTimestamp, nil
 }
 
-// NewBlockTemplate returns a new block template using the transactions from the
-// passed transaction memory pool with a coinbase that pays to the passed
-// address and is ready to be solved.  The transactions selected and included
-// are prioritized according to several factors.  First, each transaction has a
-// priority calculated based on its value, age of inputs, and size.
-// Transactions which consist of larger amounts, older inputs, and small sizes
-// have the highest priority.  Second, a fee per kilobyte is calculated for each
-// transaction.  Transactions with a higher fee per kilobyte are preferred.
-// Finally, the block generation related configuration options are all taken
-// into account.
+// NewBlockTemplate returns a new block template that is ready to be solved
+// using the transactions from the passed transaction memory pool and a coinbase
+// that either pays to the passed address if it is not nil, or a coinbase that
+// is redeemable by anyone if the passed address is nil.  The nil address
+// functionality is useful since there are cases such as the getblocktemplate
+// RPC where external mining software is responsible for creating their own
+// coinbase which will replace the one generated for the block template.  Thus
+// the need to have configured address can be avoided.
+//
+// The transactions selected and included are prioritized according to several
+// factors.  First, each transaction has a priority calculated based on its
+// value, age of inputs, and size.  Transactions which consist of larger
+// amounts, older inputs, and small sizes have the highest priority.  Second, a
+// fee per kilobyte is calculated for each transaction.  Transactions with a
+// higher fee per kilobyte are preferred.  Finally, the block generation related
+// configuration options are all taken into account.
 //
 // Transactions which only spend outputs from other transactions already in the
 // block chain are immediately added to a priority queue which either
@@ -387,7 +404,7 @@ func medianAdjustedTime(chainState *chainState) (time.Time, error) {
 //  |  transactions (while block size   |   |
 //  |  <= cfg.BlockMinSize)             |   |
 //   -----------------------------------  --
-func NewBlockTemplate(payToAddress btcutil.Address, mempool *txMemPool) (*BlockTemplate, error) {
+func NewBlockTemplate(mempool *txMemPool, payToAddress btcutil.Address) (*BlockTemplate, error) {
 	blockManager := mempool.server.blockManager
 	chainState := &blockManager.chainState
 	chain := blockManager.blockChain
@@ -402,7 +419,10 @@ func NewBlockTemplate(payToAddress btcutil.Address, mempool *txMemPool) (*BlockT
 	// address.  NOTE: The coinbase value will be updated to include the
 	// fees from the selected transactions later after they have actually
 	// been selected.  It is created here to detect any errors early
-	// before potentially doing a lot of work below.
+	// before potentially doing a lot of work below.  The extra nonce helps
+	// ensure the transaction is not a duplicate transaction (paying the
+	// same value to the same public key address would otherwise be an
+	// identical transaction for block version 1).
 	extraNonce := uint64(0)
 	coinbaseScript := standardCoinbaseScript(nextBlockHeight, extraNonce)
 	coinbaseTx, err := createCoinbaseTx(coinbaseScript, nextBlockHeight,
@@ -444,8 +464,8 @@ func NewBlockTemplate(payToAddress btcutil.Address, mempool *txMemPool) (*BlockT
 	// a transaction as it is selected for inclusion in the final block.
 	// However, since the total fees aren't known yet, use a dummy value for
 	// the coinbase fee which will be updated later.
-	txFees := make([]int64, len(mempoolTxns))
-	txSigOpCounts := make([]int64, len(mempoolTxns))
+	txFees := make([]int64, 0, len(mempoolTxns))
+	txSigOpCounts := make([]int64, 0, len(mempoolTxns))
 	txFees = append(txFees, -1) // Updated once known
 	txSigOpCounts = append(txSigOpCounts, numCoinbaseSigOps)
 
@@ -776,9 +796,11 @@ mempoolLoop:
 		blockSize, btcchain.CompactToBig(msgBlock.Header.Bits))
 
 	return &BlockTemplate{
-		block:       &msgBlock,
-		fees:        txFees,
-		sigOpCounts: txSigOpCounts,
+		block:           &msgBlock,
+		fees:            txFees,
+		sigOpCounts:     txSigOpCounts,
+		height:          nextBlockHeight,
+		validPayAddress: payToAddress != nil,
 	}, nil
 }
 
@@ -813,7 +835,7 @@ func UpdateBlockTime(msgBlock *btcwire.MsgBlock, bManager *blockManager) error {
 
 // UpdateExtraNonce updates the extra nonce in the coinbase script of the passed
 // block by regenerating the coinbase script with the passed value and block
-// height.  It also recalculates and updates the new merkle root the results
+// height.  It also recalculates and updates the new merkle root that results
 // from changing the coinbase script.
 func UpdateExtraNonce(msgBlock *btcwire.MsgBlock, blockHeight int64, extraNonce uint64) error {
 	coinbaseScript := standardCoinbaseScript(blockHeight, extraNonce)

rpcserver.go

@@ -1621,7 +1621,7 @@ func handleGetWorkRequest(s *rpcServer) (interface{}, error) {
 		rand.Seed(time.Now().UnixNano())
 		payToAddr := cfg.miningAddrs[rand.Intn(len(cfg.miningAddrs))]
 
-		template, err := NewBlockTemplate(payToAddr, s.server.txMemPool)
+		template, err := NewBlockTemplate(s.server.txMemPool, payToAddr)
 		if err != nil {
 			errStr := fmt.Sprintf("Failed to create new block "+
 				"template: %v", err)