Calculate hashes when added to blockchain

core/Block.go

@@ -1,10 +1,6 @@
 package main
 
 import (
-	"bytes"
-	"crypto/sha256"
-	"encoding/gob"
-	"encoding/hex"
 	"time"
 )
 
@@ -17,11 +13,8 @@ type Block struct {
 }
 
 // NewBlock creates a new Block
-func NewBlock(previousHash string) Block {
-	block := Block{Timestamp: time.Now(), PreviousHash: previousHash}
-
-	block.calculateHash()
-
+func NewBlock() Block {
+	block := Block{}
 	return block
 }
 
@@ -30,18 +23,3 @@ func (block *Block) AddTransaction(transaction Transaction) error {
 	block.Data = append(block.Data, transaction)
 	return nil
 }
-
-func (block *Block) calculateHash() {
-	var buffer bytes.Buffer
-	encoder := gob.NewEncoder(&buffer)
-	if err := encoder.Encode(block); err != nil {
-		panic(err)
-	}
-	hasher := sha256.New()
-	bytes := buffer.Bytes()
-	hasher.Write(bytes)
-
-	sum := hex.EncodeToString(hasher.Sum(nil))
-
-	block.Hash = string(sum)
-}

core/Blockchain.go

@@ -1,5 +1,9 @@
 package main
 
+import (
+	"log"
+)
+
 // Blockchain struct
 type Blockchain struct {
 	blocks []Block
@@ -7,29 +11,41 @@ type Blockchain struct {
 
 // AddBlock adds a block to the chain
 func (bc *Blockchain) AddBlock(block Block) {
+
+	block.PreviousHash = bc.GetLastHash()
+
+	block.Hash = calculateHash(block)
 	bc.blocks = append(bc.blocks, block)
+	log.Print("Block added: %o", block)
 }
 
 // NewBlockchain creates a new Blockchain
 func NewBlockchain() Blockchain {
+	log.Print("Creating Blockchain...")
 
 	blockchain := Blockchain{blocks: make([]Block, 0)}
 
 	genesisBlock := generateGenesisBlock()
 	blockchain.AddBlock(genesisBlock)
-
 	return blockchain
 }
 
 func generateGenesisBlock() Block {
 
-	block := NewBlock("0")
+	block := Block{PreviousHash: "0"}
 	transaction := Transaction{Amount: 0, Sender: "0", Receiver: "0", Message: "Genesis"}
 	block.AddTransaction(transaction)
+	log.Print("Genesis Block created")
 	return block
 }
 
-// GetLastBlock returns the latest block on the chain
-func (bc *Blockchain) GetLastBlock() Block {
-	return bc.blocks[len(bc.blocks)-1]
+// GetLastHash returns the hash of the latest block on the chain
+func (bc *Blockchain) GetLastHash() string {
+
+	bcLength := len(bc.blocks)
+
+	if bcLength == 0 {
+		return "0"
+	}
+	return bc.blocks[len(bc.blocks)-1].Hash
 }

core/Server.go

@@ -16,7 +16,7 @@ func StartServer() {
 	gob.Register(Blockchain{})
 
 	blockchain = NewBlockchain()
-	block := NewBlock(blockchain.GetLastBlock().Hash)
+	block := NewBlock()
 
 	transaction := Transaction{Sender: "foo", Receiver: "bar", Amount: 100}
 	block.AddTransaction(transaction)

core/crypto.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/gob"
+	"encoding/hex"
+)
+
+func calculateHash(obj interface{}) string {
+	var buffer bytes.Buffer
+	encoder := gob.NewEncoder(&buffer)
+	if err := encoder.Encode(obj); err != nil {
+		panic(err)
+	}
+	hasher := sha256.New()
+	bytes := buffer.Bytes()
+	hasher.Write(bytes)
+
+	sum := hex.EncodeToString(hasher.Sum(nil))
+
+	return string(sum)
+}