Implement the correct way of synchronizing a blockchain

Author: Jeiwan

blockchain.go

@@ -109,8 +109,24 @@ func (bc *Blockchain) AddBlock(block *Block) {
 		blockInDb := b.Get(block.Hash)
 
 		if blockInDb != nil {
-			blockData := block.Serialize()
-			b.Put(block.Hash, blockData)
+			return nil
+		}
+
+		blockData := block.Serialize()
+		err := b.Put(block.Hash, blockData)
+		if err != nil {
+			log.Panic(err)
+		}
+
+		lastHash := b.Get([]byte("l"))
+		lastBlockData := b.Get(lastHash)
+		lastBlock := DeserializeBlock(lastBlockData)
+
+		if block.Height > lastBlock.Height {
+			err = b.Put([]byte("l"), block.Hash)
+			if err != nil {
+				log.Panic(err)
+			}
 		}
 
 		return nil
@@ -192,6 +208,25 @@ func (bc *Blockchain) Iterator() *BlockchainIterator {
 	return bci
 }
 
+// GetBestHeight returns the height of the latest block
+func (bc *Blockchain) GetBestHeight() int {
+	var lastBlock Block
+
+	err := bc.db.View(func(tx *bolt.Tx) error {
+		b := tx.Bucket([]byte(blocksBucket))
+		lastHash := b.Get([]byte("l"))
+		blockData := b.Get(lastHash)
+		lastBlock = *DeserializeBlock(blockData)
+
+		return nil
+	})
+	if err != nil {
+		log.Panic(err)
+	}
+
+	return lastBlock.Height
+}
+
 // GetBlock finds a block by its hash and returns it
 func (bc *Blockchain) GetBlock(blockHash []byte) (Block, error) {
 	var block Block

server.go

@@ -11,12 +11,12 @@ import (
 )
 
 const protocol = "tcp"
-const dnsNodeID = "3000"
 const nodeVersion = 1
 const commandLength = 12
 
 var nodeAddress string
-var knownNodes []string
+var knownNodes = []string{"localhost:3000"}
+var blocksInTransit = [][]byte{}
 
 type addr struct {
 	AddrList []string
@@ -43,13 +43,10 @@ type inv struct {
 	Items    [][]byte
 }
 
-type verack struct {
-}
-
 type verzion struct {
-	Version int
-
-	AddrFrom string
+	Version    int
+	BestHeight int
+	AddrFrom   string
 }
 
 func commandToBytes(command string) []byte {
@@ -136,22 +133,15 @@ func sendGetData(address, kind string, id []byte) {
 	sendData(address, request)
 }
 
-func sendVersion(addr string) {
-	payload := gobEncode(verzion{nodeVersion, nodeAddress})
+func sendVersion(addr string, bc *Blockchain) {
+	bestHeight := bc.GetBestHeight()
+	payload := gobEncode(verzion{nodeVersion, bestHeight, nodeAddress})
 
 	request := append(commandToBytes("version"), payload...)
 
 	sendData(addr, request)
 }
 
-func sendVrack(addr string) {
-	payload := gobEncode(verack{})
-
-	request := append(commandToBytes("verack"), payload...)
-
-	sendData(addr, request)
-}
-
 func handleAddr(request []byte) {
 	var buff bytes.Buffer
 	var payload addr
@@ -184,6 +174,16 @@ func handleBlock(request []byte, bc *Blockchain) {
 
 	fmt.Println("Recevied a new block!")
 	bc.AddBlock(block)
+	fmt.Printf("Added block %x\n", block.Hash)
+	fmt.Printf("Added block %d\n", block.Height)
+
+	fmt.Println(blocksInTransit)
+	if len(blocksInTransit) > 0 {
+		blockHash := blocksInTransit[0]
+		sendGetData(payload.AddrFrom, "block", blockHash)
+
+		blocksInTransit = blocksInTransit[1:]
+	}
 }
 
 func handleInv(request []byte, bc *Blockchain) {
@@ -198,12 +198,20 @@ func handleInv(request []byte, bc *Blockchain) {
 	}
 
 	fmt.Printf("Recevied inventory with %d %s\n", len(payload.Items), payload.Type)
-	blocks := bc.GetBlockHashes()
 
-	if len(blocks) < len(payload.Items) {
-		for _, blockHash := range payload.Items {
-			sendGetData(payload.AddrFrom, "block", blockHash)
+	if payload.Type == "blocks" {
+		blocksInTransit = payload.Items
+
+		blockHash := payload.Items[0]
+		sendGetData(payload.AddrFrom, "block", blockHash)
+
+		newInTransit := [][]byte{}
+		for _, b := range blocksInTransit {
+			if bytes.Compare(b, blockHash) != 0 {
+				newInTransit = append(newInTransit, b)
+			}
 		}
+		blocksInTransit = newInTransit
 	}
 }
 
@@ -243,7 +251,7 @@ func handleGetData(request []byte, bc *Blockchain) {
 	}
 }
 
-func handleVersion(request []byte) {
+func handleVersion(request []byte, bc *Blockchain) {
 	var buff bytes.Buffer
 	var payload verzion
 
@@ -254,9 +262,19 @@ func handleVersion(request []byte) {
 		log.Panic(err)
 	}
 
-	sendVrack(payload.AddrFrom)
-	sendAddr(payload.AddrFrom)
-	knownNodes = append(knownNodes, payload.AddrFrom)
+	myBestHeight := bc.GetBestHeight()
+	foreignerBestHeight := payload.BestHeight
+
+	if myBestHeight < foreignerBestHeight {
+		sendGetBlocks(payload.AddrFrom)
+	} else {
+		sendVersion(payload.AddrFrom, bc)
+	}
+
+	// sendAddr(payload.AddrFrom)
+	if !nodeIsKnown(payload.AddrFrom) {
+		knownNodes = append(knownNodes, payload.AddrFrom)
+	}
 }
 
 func handleConnection(conn net.Conn, bc *Blockchain) {
@@ -279,9 +297,7 @@ func handleConnection(conn net.Conn, bc *Blockchain) {
 	case "getdata":
 		handleGetData(request, bc)
 	case "version":
-		handleVersion(request)
-	case "verack":
-		//
+		handleVersion(request, bc)
 	default:
 		fmt.Println("Unknown command!")
 	}
@@ -298,12 +314,12 @@ func StartServer(nodeID string) {
 	}
 	defer ln.Close()
 
-	if nodeID != dnsNodeID {
-		sendVersion(fmt.Sprintf("localhost:%s", dnsNodeID))
-	}
-
 	bc := NewBlockchain(nodeID)
 
+	if nodeAddress != knownNodes[0] {
+		sendVersion(knownNodes[0], bc)
+	}
+
 	for {
 		conn, err := ln.Accept()
 		if err != nil {
@@ -324,3 +340,13 @@ func gobEncode(data interface{}) []byte {
 
 	return buff.Bytes()
 }
+
+func nodeIsKnown(addr string) bool {
+	for _, node := range knownNodes {
+		if node == addr {
+			return true
+		}
+	}
+
+	return false
+}