When a new block is mined, let everyone know

server.go

@@ -109,7 +109,18 @@ func sendBlock(addr string, b *Block) {
 func sendData(addr string, data []byte) {
 	conn, err := net.Dial(protocol, addr)
 	if err != nil {
-		log.Panic(err)
+		fmt.Printf("%s is not available\n", addr)
+		var updatedNodes []string
+
+		for _, node := range knownNodes {
+			if node != addr {
+				updatedNodes = append(updatedNodes, node)
+			}
+		}
+
+		knownNodes = updatedNodes
+
+		return
 	}
 	defer conn.Close()
 
@@ -219,7 +230,7 @@ func handleInv(request []byte, bc *Blockchain) {
 
 	fmt.Printf("Recevied inventory with %d %s\n", len(payload.Items), payload.Type)
 
-	if payload.Type == "blocks" {
+	if payload.Type == "block" {
 		blocksInTransit = payload.Items
 
 		blockHash := payload.Items[0]
@@ -255,7 +266,7 @@ func handleGetBlocks(request []byte, bc *Blockchain) {
 	}
 
 	blocks := bc.GetBlockHashes()
-	sendInv(payload.AddrFrom, "blocks", blocks)
+	sendInv(payload.AddrFrom, "block", blocks)
 }
 
 func handleGetData(request []byte, bc *Blockchain) {
@@ -319,6 +330,11 @@ func handleTx(request []byte, bc *Blockchain) {
 				}
 			}
 
+			if len(txs) == 0 {
+				fmt.Println("All transactions are invalid! Waiting for new ones...")
+				return
+			}
+
 			cbTx := NewCoinbaseTX(miningAddress, "")
 			txs = append(txs, cbTx)
 
@@ -326,10 +342,18 @@ func handleTx(request []byte, bc *Blockchain) {
 			UTXOSet := UTXOSet{bc}
 			UTXOSet.Update(newBlock)
 
+			fmt.Println("New block is mined!")
+
 			for _, tx := range txs {
 				txID := hex.EncodeToString(tx.ID)
 				delete(mempool, txID)
 			}
+
+			for _, node := range knownNodes {
+				if node != nodeAddress {
+					sendInv(node, "block", [][]byte{newBlock.Hash})
+				}
+			}
 		}
 	}
 }

transaction.go

@@ -7,12 +7,12 @@ import (
 	"crypto/rand"
 	"crypto/sha256"
 	"math/big"
+	"strings"
 
 	"encoding/gob"
 	"encoding/hex"
 	"fmt"
 	"log"
-	"strings"
 )
 
 const subsidy = 10
@@ -72,16 +72,17 @@ func (tx *Transaction) Sign(privKey ecdsa.PrivateKey, prevTXs map[string]Transac
 		prevTx := prevTXs[hex.EncodeToString(vin.Txid)]
 		txCopy.Vin[inID].Signature = nil
 		txCopy.Vin[inID].PubKey = prevTx.Vout[vin.Vout].PubKeyHash
-		txCopy.ID = txCopy.Hash()
-		txCopy.Vin[inID].PubKey = nil
 
-		r, s, err := ecdsa.Sign(rand.Reader, &privKey, txCopy.ID)
+		dataToSign := fmt.Sprintf("%x\n", txCopy)
+
+		r, s, err := ecdsa.Sign(rand.Reader, &privKey, []byte(dataToSign))
 		if err != nil {
 			log.Panic(err)
 		}
 		signature := append(r.Bytes(), s.Bytes()...)
 
 		tx.Vin[inID].Signature = signature
+		txCopy.Vin[inID].PubKey = nil
 	}
 }
 
@@ -146,8 +147,6 @@ func (tx *Transaction) Verify(prevTXs map[string]Transaction) bool {
 		prevTx := prevTXs[hex.EncodeToString(vin.Txid)]
 		txCopy.Vin[inID].Signature = nil
 		txCopy.Vin[inID].PubKey = prevTx.Vout[vin.Vout].PubKeyHash
-		txCopy.ID = txCopy.Hash()
-		txCopy.Vin[inID].PubKey = nil
 
 		r := big.Int{}
 		s := big.Int{}
@@ -161,10 +160,13 @@ func (tx *Transaction) Verify(prevTXs map[string]Transaction) bool {
 		x.SetBytes(vin.PubKey[:(keyLen / 2)])
 		y.SetBytes(vin.PubKey[(keyLen / 2):])
 
+		dataToVerify := fmt.Sprintf("%x\n", txCopy)
+
 		rawPubKey := ecdsa.PublicKey{curve, &x, &y}
-		if ecdsa.Verify(&rawPubKey, txCopy.ID, &r, &s) == false {
+		if ecdsa.Verify(&rawPubKey, []byte(dataToVerify), &r, &s) == false {
 			return false
 		}
+		txCopy.Vin[inID].PubKey = nil
 	}
 
 	return true