mempool: transaction finality checks now use median-time-past

This coincides with the mempool only, policy change which enforces
transaction finality according to the median-time-past rather than
blockheader timestamps. The behavior is pre-cursor to full blown BIP
113 consensus deployment, and subsequent activation.

As a result, the TimeSource field in the mempoolConfig is no longer
needed so it has been removed. Additionally, checkTransactionStandard has been
modified to instead take a time.Time as the mempool is no longer explicitly
dependant on a Chain instance.

mempool/mempool.go

@@ -67,9 +67,6 @@ type Config struct {
 	// SigCache defines a signature cache to use.
 	SigCache *txscript.SigCache
 
-	// TimeSource defines the timesource to use.
-	TimeSource blockchain.MedianTimeSource
-
 	// AddrIndex defines the optional address index instance to use for
 	// indexing the unconfirmed transactions in the memory pool.
 	// This can be nil if the address index is not enabled.
@@ -551,8 +548,9 @@ func (mp *TxPool) maybeAcceptTransaction(tx *btcutil.Tx, isNew, rateLimit bool)
 	// Don't allow non-standard transactions if the network parameters
 	// forbid their relaying.
 	if !mp.cfg.Policy.RelayNonStd {
-		err := checkTransactionStandard(tx, nextBlockHeight,
-			mp.cfg.TimeSource, mp.cfg.Policy.MinRelayTxFee)
+		medianTimePast := mp.cfg.MedianTimePast()
+		err = checkTransactionStandard(tx, nextBlockHeight,
+			medianTimePast, mp.cfg.Policy.MinRelayTxFee)
 		if err != nil {
 			// Attempt to extract a reject code from the error so
 			// it can be retained.  When not possible, fall back to

mempool/policy.go

@@ -6,6 +6,7 @@ package mempool
 
 import (
 	"fmt"
+	"time"
 
 	"github.com/btcsuite/btcd/blockchain"
 	"github.com/btcsuite/btcd/txscript"
@@ -326,7 +327,9 @@ func isDust(txOut *wire.TxOut, minRelayTxFee btcutil.Amount) bool {
 // finalized, conforming to more stringent size constraints, having scripts
 // of recognized forms, and not containing "dust" outputs (those that are
 // so small it costs more to process them than they are worth).
-func checkTransactionStandard(tx *btcutil.Tx, height int32, timeSource blockchain.MedianTimeSource, minRelayTxFee btcutil.Amount) error {
+func checkTransactionStandard(tx *btcutil.Tx, height int32,
+	medianTimePast time.Time, minRelayTxFee btcutil.Amount) error {
+
 	// The transaction must be a currently supported version.
 	msgTx := tx.MsgTx()
 	if msgTx.Version > wire.TxVersion || msgTx.Version < 1 {
@@ -338,8 +341,7 @@ func checkTransactionStandard(tx *btcutil.Tx, height int32, timeSource blockchai
 
 	// The transaction must be finalized to be standard and therefore
 	// considered for inclusion in a block.
-	adjustedTime := timeSource.AdjustedTime()
-	if !blockchain.IsFinalizedTransaction(tx, height, adjustedTime) {
+	if !blockchain.IsFinalizedTransaction(tx, height, medianTimePast) {
 		return txRuleError(wire.RejectNonstandard,
 			"transaction is not finalized")
 	}

mempool/policy_test.go

@@ -7,8 +7,8 @@ package mempool
 import (
 	"bytes"
 	"testing"
+	"time"
 
-	"github.com/btcsuite/btcd/blockchain"
 	"github.com/btcsuite/btcd/btcec"
 	"github.com/btcsuite/btcd/chaincfg"
 	"github.com/btcsuite/btcd/chaincfg/chainhash"
@@ -466,11 +466,11 @@ func TestCheckTransactionStandard(t *testing.T) {
 		},
 	}
 
-	timeSource := blockchain.NewMedianTime()
+	pastMedianTime := time.Now()
 	for _, test := range tests {
 		// Ensure standardness is as expected.
 		err := checkTransactionStandard(btcutil.NewTx(&test.tx),
-			test.height, timeSource, DefaultMinRelayTxFee)
+			test.height, pastMedianTime, DefaultMinRelayTxFee)
 		if err == nil && test.isStandard {
 			// Test passes since function returned standard for a
 			// transaction which is intended to be standard.