added method to resolve conflicts betwen nodes about the actual lengt…

…h of the blockchain

blockchain/block.go

@@ -2,6 +2,7 @@ package blockchain
 
 import (
  "crypto/sha256"
+ "encoding/hex"
  "encoding/json"
  "fmt"
  "time"
@@ -62,3 +63,24 @@ func (b *Block) MarshalJSON() ([]byte, error) {
  Transactions: b.transactions,
  })
 }
+
+func (b *Block) UnmarshalJSON(data []byte) error {
+ var previousHash string
+ v := &struct {
+ Timestamp *int64 `json: "timestamp"`
+ Nonce *int `json: "nonce"`
+ PreviousHash *string `json: "previous_hash"`
+ Transactions *[]*Transaction `json: "transactions"`
+ }{
+ Timestamp: &b.timestamp,
+ Nonce: &b.nonce,
+ PreviousHash: &previousHash,
+ Transactions: &b.transactions,
+ }
+ if err := json.Unmarshal(data, &v); err != nil {
+ return err
+ }
+ ph, _ := hex.DecodeString(*v.PreviousHash)
+ copy(b.previousHash[:], ph[:32])
+ return nil
+}

blockchain/blockchain.go

@@ -48,6 +48,10 @@ func NewBlockchain(blockchainAddress string, port uint16) *Blockchain {
  return bc
 }
 
+func (bc *Blockchain) Chain() []*Block {
+ return bc.chain
+}
+
 func (bc *Blockchain) Run() {
  bc.StartSyncNeighbors()
 }
@@ -268,6 +272,36 @@ func (bc *Blockchain) ValidChain(chain []*Block) bool {
  return true
 }
 
+func (bc *Blockchain) ResolveConflicts() bool {
+ var longestChain []*Block = nil
+ maxLength := len(bc.chain)
+
+ for _, n := range bc.neighbors {
+ endpoint := fmt.Sprintf("http://%s/chain", n)
+ resp, _ := http.Get(endpoint)
+ if resp.StatusCode == 200 {
+ var bcResponse Blockchain
+ decoder := json.NewDecoder(resp.Body)
+ _ = decoder.Decode(&bcResponse)
+
+ chain := bcResponse.Chain()
+
+ if len(chain) > maxLength && bc.ValidChain(chain) {
+ maxLength = len(chain)
+ longestChain = chain
+ }
+ }
+ }
+
+ if longestChain != nil {
+ bc.chain = longestChain
+ log.Printf("Resolved conflicts: blockchain was replaced")
+ return true
+ }
+ log.Printf("Resolved conflicts: blockchain was nor replaced")
+ return false
+}
+
 type AmountResponse struct {
  Amount float32 `json:"amount"`
 }
@@ -279,3 +313,15 @@ func (ar *AmountResponse) MarshalJSON() ([]byte, error) {
  Amount: ar.Amount,
  })
 }
+
+func (bc *Blockchain) UnmarshalJSON(data []byte) error {
+ v := &struct {
+ Blocks *[]*Block `json: "chain"`
+ }{
+ Blocks: &bc.chain,
+ }
+ if err := json.Unmarshal(data, &v); err != nil {
+ return err
+ }
+ return nil
+}

blockchain/transaction.go

@@ -35,6 +35,22 @@ func (t *Transaction) MarshalJSON() ([]byte, error) {
  })
 }
 
+func (t *Transaction) UnmarshalJSON(data []byte) error {
+ v := &struct {
+ Sender *string `json:"sender_blockchain_address"`
+ Recipient *string `json:"recipient_blockchain_address"`
+ Value *float32 `json:"value"`
+ }{
+ Sender: &t.senderBlockchainAddress,
+ Recipient: &t.recipientBlockchainAddress,
+ Value: &t.value,
+ }
+ if err := json.Unmarshal(data, &v); err != nil {
+ return err
+ }
+ return nil
+}
+
 type TransactionRequest struct {
  SenderBlockchainAddress *string `json:"sender_blockchain_address"`
  RecipientBlockchainAddress *string `json:"receipient_blockchain_address"`