partialValidation.go

package main

import (
	"bytes"
	"encoding/hex"
	"fmt"
	"net"

	"github.com/VIVelev/btcd/blockchain"
	"github.com/VIVelev/btcd/crypto/hash"
	"github.com/VIVelev/btcd/network"
	"github.com/VIVelev/btcd/utils"
)

// partialValidation validates the block headers of the first 40,000 blocks
func partialValidation() {
	// Start with the genesis block
	// https://en.bitcoin.it/wiki/Genesis_block
	previous := *new(blockchain.Block).Unmarshal(bytes.NewReader(blockchain.MainGenesisBlockBytes))

	// Now let's crawl the blockchain block headers
	conn, err := net.Dial("tcp", "mainnet.programmingbitcoin.com:8333")
	if err != nil {
		panic(err)
	}
	node := &network.Node{
		Conn:    conn,
		Testnet: false,
		Logging: true,
	}
	if err = node.Handshake(); err != nil {
		panic(err)
	}

	blocks := []blockchain.Block{previous}
	for i := 0; i < 20; i++ {
		// request the next batch of 2,000 headers
		b := previous.Marshal()
		h := hash.Hash256(b[:])
		copy(h[:], utils.Reversed(h[:]))
		getheaders := network.GetHeadersMsg{
			Version:    70015,
			NumHashes:  1,
			StartBlock: h,
			EndBlock:   [32]byte{},
		}
		node.Write(&getheaders)
		msg, err := node.WaitFor("headers")
		if err != nil {
			panic(err)
		}
		headers := msg.(*network.HeadersMsg)

		blocks = append(blocks, headers.Headers...)
		l := len(blocks)
		previous = blocks[l-1]
		fmt.Printf("received another batch of blocks, now have %d\n", l)
	}
	node.Close()
	// we now have 40,001 blocks total, 80 bytes each in raw, so total of ~3.2MB of data

	// now (partially) validate the blockchain integrity
	fmt.Println("Validating the blockchain... (partially)")
	for i, block := range blocks {
		// validate PoW
		if !block.VerifyPoW() {
			panic("PoW not valid")
		}

		// validate ptr to prev block
		var expectedPrevBlock [32]byte
		if i > 0 {
			b, _ := hex.DecodeString(blocks[i-1].Id())
			copy(expectedPrevBlock[:], b)
		}
		if !bytes.Equal(block.PrevBlock[:], expectedPrevBlock[:]) {
			panic("Ptr to prev block not valid")
		}

		if i%1000 == 0 {
			fmt.Printf("on block %d/%d\n", i+1, len(blocks))
		}
	}

	fmt.Printf("Success! The blockchain is for sure valid up to block %d.\n", len(blocks))
}