mempool: add closure to compute median time past to config

This commit adds an additional closure function to the mempool’s config
which computes the median time past from the point of view of the best
node in the chain. The mempool test harness has also been updated to allow
setting a mock median time past for testing purposes.

In addition to increasing the testability of the mempool, this commit
should also speed up transaction and block validation for BIP 113 as
the MTP no longer needs to be re-calculated each time from scratch.

mempool/mempool.go

@@ -59,6 +59,11 @@ type Config struct {
 	// the current best chain.
 	BestHeight func() int32
 
+	// MedianTimePast defines the function to use in order to access the
+	// median time past calculated from the point-of-view of the current
+	// chain tip within the best chain.
+	MedianTimePast func() time.Time
+
 	// SigCache defines a signature cache to use.
 	SigCache *txscript.SigCache
 

mempool/mempool_test.go

@@ -9,6 +9,7 @@ import (
 	"reflect"
 	"sync"
 	"testing"
+	"time"
 
 	"github.com/btcsuite/btcd/blockchain"
 	"github.com/btcsuite/btcd/btcec"
@@ -24,8 +25,9 @@ import (
 // transations to be appear as though they are spending completely valid utxos.
 type fakeChain struct {
 	sync.RWMutex
-	utxos         *blockchain.UtxoViewpoint
-	currentHeight int32
+	utxos          *blockchain.UtxoViewpoint
+	currentHeight  int32
+	medianTimePast time.Time
 }
 
 // FetchUtxoView loads utxo details about the input transactions referenced by
@@ -72,6 +74,23 @@ func (s *fakeChain) SetHeight(height int32) {
 	s.Unlock()
 }
 
+// MedianTimePast returns the current median time past associated with the fake
+// chain instance.
+func (s *fakeChain) MedianTimePast() time.Time {
+	s.RLock()
+	mtp := s.medianTimePast
+	s.RUnlock()
+	return mtp
+}
+
+// SetMedianTimePast sets the current median time past associated with the fake
+// chain instance.
+func (s *fakeChain) SetMedianTimePast(mtp time.Time) {
+	s.Lock()
+	s.medianTimePast = mtp
+	s.Unlock()
+}
+
 // spendableOutput is a convenience type that houses a particular utxo and the
 // amount associated with it.
 type spendableOutput struct {
@@ -282,12 +301,12 @@ func newPoolHarness(chainParams *chaincfg.Params) (*poolHarness, []spendableOutp
 				MaxSigOpsPerTx:       blockchain.MaxSigOpsPerBlock / 5,
 				MinRelayTxFee:        1000, // 1 Satoshi per byte
 			},
-			ChainParams:   chainParams,
-			FetchUtxoView: chain.FetchUtxoView,
-			BestHeight:    chain.BestHeight,
-			SigCache:      nil,
-			TimeSource:    blockchain.NewMedianTime(),
-			AddrIndex:     nil,
+			ChainParams:    chainParams,
+			FetchUtxoView:  chain.FetchUtxoView,
+			BestHeight:     chain.BestHeight,
+			MedianTimePast: chain.MedianTimePast,
+			SigCache:       nil,
+			AddrIndex:      nil,
 		}),
 	}
 

server.go

@@ -2582,12 +2582,12 @@ func newServer(listenAddrs []string, db database.DB, chainParams *chaincfg.Param
 			MaxSigOpsPerTx:       blockchain.MaxSigOpsPerBlock / 5,
 			MinRelayTxFee:        cfg.minRelayTxFee,
 		},
-		ChainParams:   chainParams,
-		FetchUtxoView: s.blockManager.chain.FetchUtxoView,
-		BestHeight:    func() int32 { return bm.chain.BestSnapshot().Height },
-		SigCache:      s.sigCache,
-		TimeSource:    s.timeSource,
-		AddrIndex:     s.addrIndex,
+		ChainParams:    chainParams,
+		FetchUtxoView:  s.blockManager.chain.FetchUtxoView,
+		BestHeight:     func() int32 { return bm.chain.BestSnapshot().Height },
+		MedianTimePast: func() time.Time { return bm.chain.BestSnapshot().MedianTime },
+		SigCache:       s.sigCache,
+		AddrIndex:      s.addrIndex,
 	}
 	s.txMemPool = mempool.New(&txC)