indexers: generate root summaries

Root summaries are now generated at the last 50,000 block interval and
is stored in the summaries flat file state. If the summaries are not
availble on start, the summaries are generated.

blockchain/indexers/flatutreexoproofindex.go

@@ -6,6 +6,7 @@ package indexers
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"encoding/hex"
 	"fmt"
 	"os"
@@ -93,6 +94,11 @@ type FlatUtreexoProofIndex struct {
 	// It keeps all the elements of the forest in order to generate proofs.
 	utreexoState *UtreexoState
 
+	// utreexoRootsState is the accumulator for all the roots at each of the
+	// blocks. This is so that we can serve to peers the proof that a set of
+	// roots at a block is correct.
+	utreexoRootsState utreexo.Pollard
+
 	// pStats are the proof size statistics that are kept for research purposes.
 	pStats proofStats
 
@@ -166,6 +172,42 @@ func (idx *FlatUtreexoProofIndex) consistentFlatFileState(tipHeight int32) error
 	return nil
 }
 
+// initUtreexoRootsState creates an accumulator from all the existing roots and
+// holds it in memory so that the proofs for them can be generated.
+func (idx *FlatUtreexoProofIndex) initUtreexoRootsState() error {
+	idx.utreexoRootsState = utreexo.NewAccumulator()
+
+	bestHeight := idx.rootsState.BestHeight()
+	for h := int32(1); h <= bestHeight; h++ {
+		stump, err := idx.fetchRoots(h)
+		if err != nil {
+			return err
+		}
+		bytes, err := blockchain.SerializeUtreexoRoots(stump.NumLeaves, stump.Roots)
+		if err != nil {
+			return err
+		}
+		rootHash := sha256.Sum256(bytes)
+
+		err = idx.utreexoRootsState.Modify(
+			[]utreexo.Leaf{{Hash: rootHash}}, nil, utreexo.Proof{})
+		if err != nil {
+			return err
+		}
+	}
+
+	bytes, err := blockchain.SerializeUtreexoRoots(
+		idx.utreexoState.state.GetNumLeaves(),
+		idx.utreexoState.state.GetRoots(),
+	)
+	if err != nil {
+		return err
+	}
+
+	rootHash := sha256.Sum256(bytes)
+	return idx.utreexoRootsState.Modify([]utreexo.Leaf{{Hash: rootHash}}, nil, utreexo.Proof{})
+}
+
 // Init initializes the flat utreexo proof index. This is part of the Indexer
 // interface.
 func (idx *FlatUtreexoProofIndex) Init(chain *blockchain.BlockChain,
@@ -186,6 +228,11 @@ func (idx *FlatUtreexoProofIndex) Init(chain *blockchain.BlockChain,
 		return err
 	}
 
+	err = idx.initUtreexoRootsState()
+	if err != nil {
+		return err
+	}
+
 	// Nothing to do if the node is not pruned.
 	//
 	// If the node is pruned, then we need to check if it started off as
@@ -383,6 +430,11 @@ func (idx *FlatUtreexoProofIndex) ConnectBlock(dbTx database.Tx, block *btcutil.
 		return err
 	}
 
+	err = idx.updateRootsState()
+	if err != nil {
+		return err
+	}
+
 	// Don't store proofs if the node is pruned.
 	if idx.config.Pruned {
 		return nil
@@ -572,7 +624,9 @@ func (idx *FlatUtreexoProofIndex) DisconnectBlock(dbTx database.Tx, block *btcut
 		return err
 	}
 
-	return nil
+	// Re-initializes to the current accumulator roots, effectively disconnecting
+	// a block.
+	return idx.initUtreexoRootsState()
 }
 
 // PruneBlock is invoked when an older block is deleted after it's been
@@ -862,6 +916,22 @@ func (idx *FlatUtreexoProofIndex) VerifyAccProof(toProve []utreexo.Hash,
 	return idx.utreexoState.state.Verify(toProve, *proof, false)
 }
 
+// updateRootsState updates the roots accumulator state from the roots of the current accumulator.
+func (idx *FlatUtreexoProofIndex) updateRootsState() error {
+	idx.mtx.Lock()
+	numLeaves := idx.utreexoState.state.GetNumLeaves()
+	roots := idx.utreexoState.state.GetRoots()
+	idx.mtx.Unlock()
+
+	bytes, err := blockchain.SerializeUtreexoRoots(numLeaves, roots)
+	if err != nil {
+		return err
+	}
+
+	rootHash := sha256.Sum256(bytes)
+	return idx.utreexoRootsState.Modify([]utreexo.Leaf{{Hash: rootHash}}, nil, utreexo.Proof{})
+}
+
 // flatFilePath returns the path to the flatfile.
 func flatFilePath(dataDir, dataName string) string {
 	flatFileName := dataName + "_" + flatFileNameSuffix