mempool: Add HeaderByHash to Config.

This adds a HeaderByHash method to the mempool Config.  This will be
used as part of the automatic ticket revocations changes in a subsequent
commit.

internal/mempool/mempool.go

@@ -106,6 +106,11 @@ type Config struct {
 	// the current best chain.
 	BestHeight func() int64
 
+	// HeaderByHash returns the block header identified by the given hash or an
+	// error if it doesn't exist.  Note that this will return headers from both
+	// the main chain and any side chains.
+	HeaderByHash func(hash *chainhash.Hash) (wire.BlockHeader, error)
+
 	// PastMedianTime defines the function to use in order to access the
 	// median time calculated from the point-of-view of the current chain
 	// tip within the best chain.

internal/mempool/mempool_test.go

@@ -157,6 +157,18 @@ func (s *fakeChain) SetHeight(height int64) {
 	s.Unlock()
 }
 
+// HeaderByHash returns the header for the block with the given hash from the
+// fake chain instance.  Blocks can be added to the instance with the AddBlock
+// function.
+func (s *fakeChain) HeaderByHash(hash *chainhash.Hash) (wire.BlockHeader, error) {
+	block, ok := s.blocks[*hash]
+	if !ok {
+		return wire.BlockHeader{}, fmt.Errorf("unable to find block %v in fake "+
+			"chain", hash)
+	}
+	return block.MsgBlock().Header, nil
+}
+
 // PastMedianTime returns the current median time associated with the fake chain
 // instance.
 func (s *fakeChain) PastMedianTime() time.Time {
@@ -818,6 +830,7 @@ func newPoolHarness(chainParams *chaincfg.Params) (*poolHarness, []spendableOutp
 			BlockByHash:           chain.BlockByHash,
 			BestHash:              chain.BestHash,
 			BestHeight:            chain.BestHeight,
+			HeaderByHash:          chain.HeaderByHash,
 			PastMedianTime:        chain.PastMedianTime,
 			CalcSequenceLock:      chain.CalcSequenceLock,
 			TSpendMinedOnAncestor: chain.TSpendMinedOnAncestor,

server.go

@@ -3558,6 +3558,7 @@ func newServer(ctx context.Context, listenAddrs []string, db database.DB,
 		BlockByHash:      s.chain.BlockByHash,
 		BestHash:         func() *chainhash.Hash { return &s.chain.BestSnapshot().Hash },
 		BestHeight:       func() int64 { return s.chain.BestSnapshot().Height },
+		HeaderByHash:     s.chain.HeaderByHash,
 		CalcSequenceLock: s.chain.CalcSequenceLock,
 		SubsidyCache:     s.subsidyCache,
 		SigCache:         s.sigCache,