main.go

package main

import (
	"bufio"
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"log"
	mrand "math/rand"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"

	crypto "gx/ipfs/QmPvyPwuCgJ7pDmrKDxRtsScJgBaM5h4EpRL2qQJsmXf4n/go-libp2p-crypto"
	ma "gx/ipfs/QmYmsdtJ3HsodkePE3eU3TsCaP2YvPZJ4LoXnNkDE5Tpt7/go-multiaddr"
	golog "gx/ipfs/QmZChCsSt8DctjceaL56Eibc29CVQq4dGKRXC5JRZ6Ppae/go-log"
	peer "gx/ipfs/QmbNepETomvmXfz1X5pHNFD2QuPqnqi47dTd94QJWSorQ3/go-libp2p-peer"
	gologging "gx/ipfs/QmcaSwFc5RBg8yCq54QURwEU4nwjfCpjbpmaAm4VbdGLKv/go-logging"
	host "gx/ipfs/QmeA5hsqgLryvkeyqeQdvGDqurLkYi3XEPLZP3pzuBJXh2/go-libp2p-host"
	pstore "gx/ipfs/QmfAQMFpgDU2U4BXG64qVr8HSiictfWvkSBz7Y2oDj65st/go-libp2p-peerstore"
	net "gx/ipfs/QmfDPh144WGBqRxZb1TGDHerbMnZATrHZggAPw7putNnBq/go-libp2p-net"

	"github.com/davecgh/go-spew/spew"
	libp2p "github.com/libp2p/go-libp2p"
)

// Block represents each 'item' in the blockchain
type Block struct {
	Index      int
	Timestamp  string
	BPM        int
	Hash       string
	PrevHash   string
	Difficulty int
	Nonce      string
}

// Blockchain is a series of validated Blocks
var Blockchain []Block

var mutex = &sync.Mutex{}

const difficulty = 1

func isHashValid(hash string, difficulty int) bool {
	prefix := strings.Repeat("0", difficulty)
	return strings.HasPrefix(hash, prefix)
}

// makeBasicHost creates a LibP2P host with a random peer ID listening on the
// given multiaddress. It will use secio if secio is true.
func makeBasicHost(listenPort int, secio bool, randseed int64) (host.Host, error) {

	// If the seed is zero, use real cryptographic randomness. Otherwise, use a
	// deterministic randomness source to make generated keys stay the same
	// across multiple runs
	var r io.Reader
	if randseed == 0 {
		r = rand.Reader
	} else {
		r = mrand.New(mrand.NewSource(randseed))
	}

	// Generate a key pair for this host. We will use it
	// to obtain a valid host ID.
	priv, _, err := crypto.GenerateKeyPairWithReader(crypto.RSA, 2048, r)
	if err != nil {
		return nil, err
	}

	opts := []libp2p.Option{
		libp2p.ListenAddrStrings(fmt.Sprintf("/ip4/127.0.0.1/tcp/%d", listenPort)),
		libp2p.Identity(priv),
	}

	basicHost, err := libp2p.New(context.Background(), opts...)
	if err != nil {
		return nil, err
	}

	// Build host multiaddress
	hostAddr, _ := ma.NewMultiaddr(fmt.Sprintf("/ipfs/%s", basicHost.ID().Pretty()))

	// Now we can build a full multiaddress to reach this host
	// by encapsulating both addresses:
	addr := basicHost.Addrs()[0]
	fullAddr := addr.Encapsulate(hostAddr)
	log.Printf("I am %s\n", fullAddr)
	if secio {
		log.Printf("Now run \"go run main.go -l %d -d %s -secio\" on a different terminal\n", listenPort+1, fullAddr)
	} else {
		log.Printf("Now run \"go run main.go -l %d -d %s\" on a different terminal\n", listenPort+1, fullAddr)
	}

	return basicHost, nil
}

func handleStream(s net.Stream) {

	log.Println("Got a new stream!")

	// Create a buffer stream for non blocking read and write.
	rw := bufio.NewReadWriter(bufio.NewReader(s), bufio.NewWriter(s))

	go readData(rw)
	go writeData(rw)

	// stream 's' will stay open until you close it (or the other side closes it).
}

func readData(rw *bufio.ReadWriter) {

	for {
		str, err := rw.ReadString('\n')
		if err != nil {
			log.Fatal(err)
		}

		if str == "" {
			return
		}
		if str != "\n" {

			chain := make([]Block, 0)
			if err := json.Unmarshal([]byte(str), &chain); err != nil {
				log.Fatal(err)
			}

			mutex.Lock()
			if len(chain) > len(Blockchain) {
				Blockchain = chain
				bytes, err := json.MarshalIndent(Blockchain, "", "  ")
				if err != nil {

					log.Fatal(err)
				}
				// Green console color: 	\x1b[32m
				// Reset console color: 	\x1b[0m
				fmt.Printf("\x1b[32m%s\x1b[0m> ", string(bytes))
			}
			mutex.Unlock()
		}
	}
}

func writeData(rw *bufio.ReadWriter) {

	go func() {
		for {
			time.Sleep(5 * time.Second)
			mutex.Lock()
			bytes, err := json.Marshal(Blockchain)
			if err != nil {
				log.Println(err)
			}
			mutex.Unlock()

			mutex.Lock()
			rw.WriteString(fmt.Sprintf("%s\n", string(bytes)))
			rw.Flush()
			mutex.Unlock()

		}
	}()

	stdReader := bufio.NewReader(os.Stdin)

	for {
		fmt.Print("> ")
		sendData, err := stdReader.ReadString('\n')
		if err != nil {
			log.Fatal(err)
		}

		sendData = strings.Replace(sendData, "\n", "", -1)
		bpm, err := strconv.Atoi(sendData)
		if err != nil {
			log.Fatal(err)
		}
		newBlock := generateBlock(Blockchain[len(Blockchain)-1], bpm)

		if isBlockValid(newBlock, Blockchain[len(Blockchain)-1]) {
			mutex.Lock()
			Blockchain = append(Blockchain, newBlock)
			mutex.Unlock()
		}

		bytes, err := json.Marshal(Blockchain)
		if err != nil {
			log.Println(err)
		}

		spew.Dump(Blockchain)

		mutex.Lock()
		rw.WriteString(fmt.Sprintf("%s\n", string(bytes)))
		rw.Flush()
		mutex.Unlock()
	}

}

func main() {
	t := time.Now()
	genesisBlock := Block{}
	genesisBlock = Block{0, t.String(), 0, calculateHash(genesisBlock), "", difficulty, ""}

	Blockchain = append(Blockchain, genesisBlock)

	// LibP2P code uses golog to log messages. They log with different
	// string IDs (i.e. "swarm"). We can control the verbosity level for
	// all loggers with:
	golog.SetAllLoggers(gologging.INFO) // Change to DEBUG for extra info

	// Parse options from the command line
	listenF := flag.Int("l", 0, "wait for incoming connections")
	target := flag.String("d", "", "target peer to dial")
	secio := flag.Bool("secio", false, "enable secio")
	seed := flag.Int64("seed", 0, "set random seed for id generation")
	flag.Parse()

	if *listenF == 0 {
		log.Fatal("Please provide a port to bind on with -l")
	}

	// Make a host that listens on the given multiaddress
	ha, err := makeBasicHost(*listenF, *secio, *seed)
	if err != nil {
		log.Fatal(err)
	}

	if *target == "" {
		log.Println("listening for connections")
		// Set a stream handler on host A. /p2p/1.0.0 is
		// a user-defined protocol name.
		ha.SetStreamHandler("/p2p/1.0.0", handleStream)

		select {} // hang forever
		/**** This is where the listener code ends ****/
	} else {
		ha.SetStreamHandler("/p2p/1.0.0", handleStream)

		// The following code extracts target's peer ID from the
		// given multiaddress
		ipfsaddr, err := ma.NewMultiaddr(*target)
		if err != nil {
			log.Fatalln(err)
		}

		pid, err := ipfsaddr.ValueForProtocol(ma.P_IPFS)
		if err != nil {
			log.Fatalln(err)
		}

		peerid, err := peer.IDB58Decode(pid)
		if err != nil {
			log.Fatalln(err)
		}

		// Decapsulate the /ipfs/<peerID> part from the target
		// /ip4/<a.b.c.d>/ipfs/<peer> becomes /ip4/<a.b.c.d>
		targetPeerAddr, _ := ma.NewMultiaddr(
			fmt.Sprintf("/ipfs/%s", peer.IDB58Encode(peerid)))
		targetAddr := ipfsaddr.Decapsulate(targetPeerAddr)

		// We have a peer ID and a targetAddr so we add it to the peerstore
		// so LibP2P knows how to contact it
		ha.Peerstore().AddAddr(peerid, targetAddr, pstore.PermanentAddrTTL)

		log.Println("opening stream")
		// make a new stream from host B to host A
		// it should be handled on host A by the handler we set above because
		// we use the same /p2p/1.0.0 protocol
		s, err := ha.NewStream(context.Background(), peerid, "/p2p/1.0.0")
		if err != nil {
			log.Fatalln(err)
		}
		// Create a buffered stream so that read and writes are non blocking.
		rw := bufio.NewReadWriter(bufio.NewReader(s), bufio.NewWriter(s))

		// Create a thread to read and write data.
		go writeData(rw)
		go readData(rw)

		select {} // hang forever

	}
}

// make sure block is valid by checking index, and comparing the hash of the previous block
func isBlockValid(newBlock, oldBlock Block) bool {
	if oldBlock.Index+1 != newBlock.Index {
		return false
	}

	if oldBlock.Hash != newBlock.PrevHash {
		return false
	}

	if calculateHash(newBlock) != newBlock.Hash {
		return false
	}

	return true
}

// SHA256 hashing
func calculateHash(block Block) string {
	record := strconv.Itoa(block.Index) + block.Timestamp + strconv.Itoa(block.BPM) + block.PrevHash + block.Nonce
	h := sha256.New()
	h.Write([]byte(record))
	hashed := h.Sum(nil)
	return hex.EncodeToString(hashed)
}

// create a new block using previous block's hash
func generateBlock(oldBlock Block, BPM int) Block {

	var newBlock Block

	t := time.Now()

	newBlock.Index = oldBlock.Index + 1
	newBlock.Timestamp = t.String()
	newBlock.BPM = BPM
	newBlock.PrevHash = oldBlock.Hash
	newBlock.Hash = calculateHash(newBlock)
	newBlock.Difficulty = difficulty

	for i := 0; ; i++ {
		hex := fmt.Sprintf("%x", i) // take the hex representation of i
		newBlock.Nonce = hex
		if !isHashValid(calculateHash(newBlock), newBlock.Difficulty) {
			fmt.Println(calculateHash(newBlock), " do more work!")
			time.Sleep(time.Second)
			continue
		} else {
			fmt.Println(calculateHash(newBlock), " work done!")
			newBlock.Hash = calculateHash(newBlock)
			break
		}
	}

	return newBlock
}