main: fix bug in getutreexoheader handling code

We were putting in the length of leafdatas for numadds instead of the
leaves that we were adding into the accumulator.

We fix the bug and refactor the function for readability.

Author: kcalvinalvin

server.go

@@ -900,91 +900,67 @@ func (sp *serverPeer) OnGetUtreexoHeader(_ *peer.Peer, msg *wire.MsgGetUtreexoHe
 		return
 	}
 
-	if !cfg.NoUtreexo {
-		height, err := sp.server.chain.BlockHeightByHash(&msg.BlockHash)
-		if err != nil {
-			chanLog.Debugf("Unable to fetch height for block hash %v: %v",
-				msg.BlockHash, err)
-			return
-		}
-
-		// If we're pruned and the requested block is beyond the point where pruned blocks
-		// are able to serve blocks, just ignore the message.
-		if cfg.Prune != 0 && height >= sp.server.chain.BestSnapshot().Height-288 {
-			return
-		}
-
-		var blockBytes []byte
-		err = sp.server.db.View(func(dbTx database.Tx) error {
-			var err error
-			blockBytes, err = dbTx.FetchBlock(&msg.BlockHash)
-			return err
-		})
-		if err != nil {
-			chanLog.Debugf("Unable to fetch block %v: %v",
-				msg.BlockHash, err)
-			return
-		}
-		var msgBlock wire.MsgBlock
-		err = msgBlock.Deserialize(bytes.NewReader(blockBytes))
-		if err != nil {
-			chanLog.Debugf("Unable to deserialize block with hash %v: %v",
-				msg.BlockHash, err)
-			return
-		}
-
-		targets := msgBlock.UData.AccProof.Targets
+	height, err := sp.server.chain.BlockHeightByHash(&msg.BlockHash)
+	if err != nil {
+		chanLog.Debugf("Unable to fetch height for block hash %v: %v",
+			msg.BlockHash, err)
+		return
+	}
 
-		var blockHeader wire.MsgUtreexoHeader
-		blockHeader.BlockHash = msg.BlockHash
-		blockHeader.NumAdds = uint16(len(msgBlock.UData.LeafDatas))
-		blockHeader.Targets = make([]uint64, len(targets))
-		copy(blockHeader.Targets, targets)
-		sp.QueueMessage(&blockHeader, nil)
+	// If we're pruned and the requested block is beyond the point where pruned blocks
+	// are able to serve blocks, just ignore the message.
+	if cfg.Prune != 0 && height >= sp.server.chain.BestSnapshot().Height-288 {
+		return
+	}
 
+	// Fetch adds.
+	block, err := sp.server.chain.BlockByHash(&msg.BlockHash)
+	if err != nil {
+		chanLog.Debugf("Unable to fetch block for block hash %v: %v",
+			msg.BlockHash, err)
+		return
+	}
+	adds, err := blockchain.ExtractAccumulatorAdds(block, []uint32{})
+	if err != nil {
+		chanLog.Debugf("Unable to extract adds for block hash %v: %v",
+			msg.BlockHash, err)
 		return
 	}
 
+	// Fetch targets.
+	var targets []uint64
+	if !cfg.NoUtreexo {
+		targets = block.MsgBlock().UData.AccProof.Targets
+	}
 	if sp.server.utreexoProofIndex != nil {
 		udata, err := sp.server.utreexoProofIndex.FetchUtreexoProof(&msg.BlockHash)
 		if err != nil {
 			chanLog.Debugf("Unable to fetch utreexo proof for block hash %v: %v",
 				msg.BlockHash, err)
 			return
 		}
-
-		var blockHeader wire.MsgUtreexoHeader
-		blockHeader.BlockHash = msg.BlockHash
-		blockHeader.NumAdds = uint16(len(udata.LeafDatas))
-		blockHeader.Targets = make([]uint64, len(udata.AccProof.Targets))
-		copy(blockHeader.Targets, udata.AccProof.Targets)
-		sp.QueueMessage(&blockHeader, nil)
-		return
+		targets = udata.AccProof.Targets
 	}
-
 	if sp.server.flatUtreexoProofIndex != nil {
-		height, err := sp.server.chain.BlockHeightByHash(&msg.BlockHash)
-		if err != nil {
-			chanLog.Debugf("Unable to fetch height for block hash %v: %v",
-				msg.BlockHash, err)
-			return
-		}
-
 		udata, err := sp.server.flatUtreexoProofIndex.FetchUtreexoProof(height)
 		if err != nil {
 			chanLog.Debugf("Unable to fetch utreexo proof for block hash %v: %v",
 				msg.BlockHash, err)
 			return
 		}
+		targets = udata.AccProof.Targets
+	}
 
-		var blockHeader wire.MsgUtreexoHeader
-		blockHeader.BlockHash = msg.BlockHash
-		blockHeader.NumAdds = uint16(len(udata.LeafDatas))
-		blockHeader.Targets = make([]uint64, len(udata.AccProof.Targets))
-		copy(blockHeader.Targets, udata.AccProof.Targets)
-		sp.QueueMessage(&blockHeader, nil)
-		return
+	// Construct the utreexo header.
+	blockHeader := wire.MsgUtreexoHeader{
+		BlockHash: msg.BlockHash,
+		NumAdds:   uint16(len(adds)),
+		Targets:   make([]uint64, len(targets)),
 	}
+	copy(blockHeader.Targets, targets)
+	sp.QueueMessage(&blockHeader, nil)
+
+	return
 }
 
 // OnGetCFilters is invoked when a peer receives a getcfilters bitcoin message.