From 5d01fc6c7219762734bfe477a1b987d5a67fdc6d Mon Sep 17 00:00:00 2001
From: Kleissner <peter@kleissner.investments>
Date: Wed, 11 Aug 2021 22:36:47 +0200
Subject: [PATCH] Initial code to read/create the users blockchain database on
 the file system.

---
 Blockchain.go | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++
 Peernet.go    |   1 +
 2 files changed, 109 insertions(+)

diff --git a/Blockchain.go b/Blockchain.go
index bdc7bb0..1d2fe43 100644
--- a/Blockchain.go
+++ b/Blockchain.go
@@ -6,8 +6,116 @@ Author:     Peter Kleissner
 
 package core
 
+import (
+	"encoding/binary"
+	"encoding/hex"
+	"os"
+	"strconv"
+
+	"github.com/PeernetOfficial/core/store"
+	"github.com/btcsuite/btcd/btcec"
+)
+
 // BlockchainHeight is the current count of blocks
 var BlockchainHeight = uint32(0)
 
 // BlockchainVersion is the version of the blockchain
 var BlockchainVersion = uint64(0)
+
+// filenameUserBlockchain is the filename/folder of the user's blockchain
+const filenameUserBlockchain = "self.blockchain"
+
+// the key names in the key/value database are constant and must not collide with block numbers (i.e. they must be >64 bit)
+const keyHeaderHeight = "header.height"
+const keyHeaderVersion = "header.version"
+const keyHeaderSignature = "header.signature"
+
+// BlockchainHeader is the virtual blockchain header. The data is not stored as single header record, but split up.
+type BlockchainHeader struct {
+	Height    uint64
+	Version   uint64
+	PublicKey *btcec.PublicKey
+}
+
+var userBlockchainDB store.Store
+var userBlockchainHeader BlockchainHeader
+
+// initUserBlockchain initializes the users blockchain. It creates the blockchain file if it does not exist already.
+// If it is corrupted, it will log the error and exit the process.
+func initUserBlockchain() {
+	// open existing blockchain file or create new one
+	blockchain, err := store.NewPebbleStore(filenameUserBlockchain)
+	if err != nil {
+		Filters.LogError("initUserBlockchain", "error opening user blockchain: %s\n", err.Error())
+		os.Exit(1)
+	}
+
+	// verify header
+	var height, version uint64
+	heightB, found1 := blockchain.Get([]byte(keyHeaderHeight))
+	versionB, found2 := blockchain.Get([]byte(keyHeaderVersion))
+	headerSignature, isSignature := blockchain.Get([]byte(keyHeaderSignature))
+
+	if found1 && len(heightB) != 8 || found2 && len(versionB) != 8 || isSignature && len(headerSignature) != 65 {
+		Filters.LogError("initUserBlockchain", "corrupt user blockchain database. Invalid header length. Height is '%s', version '%s' and signature '%s'.\n", hex.EncodeToString(heightB), hex.EncodeToString(versionB), hex.EncodeToString(headerSignature))
+		os.Exit(1)
+	}
+
+	if found1 && len(heightB) == 8 {
+		height = binary.BigEndian.Uint64(heightB)
+	}
+	if found2 && len(heightB) == 8 {
+		version = binary.BigEndian.Uint64(versionB)
+	}
+
+	if isSignature {
+		// validate header signature
+		headerA := strconv.FormatUint(height, 10) + "/" + strconv.FormatUint(version, 10)
+		headerPublicKey, _, err := btcec.RecoverCompact(btcec.S256(), headerSignature[:], hashData([]byte(headerA)))
+		if err != nil {
+			Filters.LogError("initUserBlockchain", "corrupt user blockchain database. Error decoding signature. Height is '%s', version '%s', signature '%s'. %s\n", hex.EncodeToString(heightB), hex.EncodeToString(versionB), hex.EncodeToString(headerSignature), err.Error())
+			os.Exit(1)
+		}
+		if !headerPublicKey.IsEqual(peerPublicKey) {
+			Filters.LogError("initUserBlockchain", "corrupt user blockchain database. Signature key mismatch. Height is '%s', version '%s', signature '%s'.\n", hex.EncodeToString(heightB), hex.EncodeToString(versionB), hex.EncodeToString(headerSignature))
+			os.Exit(1)
+		}
+
+		userBlockchainHeader = BlockchainHeader{Height: height, Version: version, PublicKey: headerPublicKey}
+
+	} else if !found1 && !found2 && !isSignature {
+		// First run: create header signature!
+		height = 0
+		version = 0
+		signature, _ := blockchainCreateHeaderSignature(height, version)
+		if err := blockchain.Set([]byte(keyHeaderSignature), signature); err != nil {
+			Filters.LogError("initUserBlockchain", "initializing user blockchain: %s", err.Error())
+			os.Exit(1)
+		}
+
+	} else {
+		// header signature not present, but height/version is -> corrupt data.
+		Filters.LogError("initUserBlockchain", "corrupt user blockchain database. Height is '%s', version '%s' and signature '%s'.\n", hex.EncodeToString(heightB), hex.EncodeToString(versionB), hex.EncodeToString(headerSignature))
+		os.Exit(1)
+	}
+
+	userBlockchainDB = blockchain
+}
+
+func blockchainCreateHeaderSignature(height, version uint64) (signature []byte, err error) {
+	headerA := strconv.FormatUint(height, 10) + "/" + strconv.FormatUint(version, 10)
+	signature, err = btcec.SignCompact(btcec.S256(), peerPrivateKey, hashData([]byte(headerA)), true)
+
+	if err != nil {
+		Filters.LogError("blockchainCreateHeaderSignature", "creating signature of '%s': %s\n", headerA, err.Error())
+	}
+
+	return signature, err
+}
+
+// UserBlockchainHeader returns the users blockchain header which stores the height and version number.
+func UserBlockchainHeader() (header BlockchainHeader) {
+	return userBlockchainHeader
+}
+
+// ---- low-level blockchain manipulation functions ----
diff --git a/Peernet.go b/Peernet.go
index 2f9a403..6dd6667 100644
--- a/Peernet.go
+++ b/Peernet.go
@@ -10,6 +10,7 @@ package core
 func Init() {
 	initFilters()
 	initPeerID()
+	initUserBlockchain()
 	initKademlia()
 	initMessageSequence()
 	initSeedList()