Hashes DB Content on every persist of a new TX.

Updates to version v0.3.0

cmd/tbb/balances.go

@@ -34,7 +34,7 @@ var balancesListCmd = &cobra.Command{
 		}
 		defer state.Close()
 
-		fmt.Println("Accounts balances:")
+		fmt.Printf("Accounts balances at %x:\n", state.LatestSnapshot())
 		fmt.Println("__________________")
 		fmt.Println("")
 		for account, balance := range state.Balances {

cmd/tbb/tx.go

@@ -53,13 +53,13 @@ func txAddCmd() *cobra.Command {
 				os.Exit(1)
 			}
 
-			err = state.Persist()
+			_, err = state.Persist()
 			if err != nil {
 				fmt.Fprintln(os.Stderr, err)
 				os.Exit(1)
 			}
 
-			fmt.Println("TX successfully added to the ledger.")
+			fmt.Println("TX successfully persisted to the ledger.")
 		},
 	}
 

cmd/tbb/version.go

@@ -6,9 +6,9 @@ import (
 )
 
 const Major = "0"
-const Minor = "2"
+const Minor = "3"
 const Fix = "0"
-const Verbal = "tbb tx add --data=reward"
+const Verbal = "Immutable Snapshots"
 
 var versionCmd = &cobra.Command{
 	Use:   "version",

database/state.go

@@ -1,18 +1,23 @@
 package database
 
 import (
-	"os"
-	"path/filepath"
-	"encoding/json"
 	"bufio"
+	"crypto/sha256"
+	"encoding/json"
 	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 )
 
+type Snapshot [32]byte
+
 type State struct {
-	Balances   map[Account]uint
+	Balances  map[Account]uint
 	txMempool []Tx
 
-	dbFile *os.File
+	dbFile   *os.File
+	snapshot Snapshot
 }
 
 func NewStateFromDisk() (*State, error) {
@@ -38,24 +43,36 @@ func NewStateFromDisk() (*State, error) {
 
 	scanner := bufio.NewScanner(f)
 
-	state := &State{balances, make([]Tx, 0), f}
+	state := &State{balances, make([]Tx, 0), f, Snapshot{}}
 
 	for scanner.Scan() {
 		if err := scanner.Err(); err != nil {
 			return nil, err
 		}
 
 		var tx Tx
-		json.Unmarshal(scanner.Bytes(), &tx)
+		err = json.Unmarshal(scanner.Bytes(), &tx)
+		if err != nil {
+			return nil, err
+		}
 
 		if err := state.apply(tx); err != nil {
 			return nil, err
 		}
 	}
 
+	err = state.doSnapshot()
+	if err != nil {
+		return nil, err
+	}
+
 	return state, nil
 }
 
+func (s *State) LatestSnapshot() Snapshot {
+	return s.snapshot
+}
+
 func (s *State) Add(tx Tx) error {
 	if err := s.apply(tx); err != nil {
 		return err
@@ -66,28 +83,36 @@ func (s *State) Add(tx Tx) error {
 	return nil
 }
 
-func (s *State) Persist() error {
+func (s *State) Persist() (Snapshot, error) {
 	mempool := make([]Tx, len(s.txMempool))
 	copy(mempool, s.txMempool)
 
 	for i := 0; i < len(mempool); i++ {
 		txJson, err := json.Marshal(s.txMempool[i])
 		if err != nil {
-			return err
+			return Snapshot{}, err
 		}
 
+		fmt.Printf("Persisting new TX to disk:\n")
+		fmt.Printf("\t%s\n", txJson)
 		if _, err = s.dbFile.Write(append(txJson, '\n')); err != nil {
-			return err
+			return Snapshot{}, err
 		}
 
+		err = s.doSnapshot()
+		if err != nil {
+			return Snapshot{}, err
+		}
+		fmt.Printf("New DB Snapshot: %x\n", s.snapshot)
+
 		s.txMempool = append(s.txMempool[:i], s.txMempool[i+1:]...)
 	}
 
-	return nil
+	return s.snapshot, nil
 }
 
-func (s *State) Close() {
-	s.dbFile.Close()
+func (s *State) Close() error {
+	return s.dbFile.Close()
 }
 
 func (s *State) apply(tx Tx) error {
@@ -96,12 +121,28 @@ func (s *State) apply(tx Tx) error {
 		return nil
 	}
 
-	if s.Balances[tx.From] - tx.Value < 0 {
+	if s.Balances[tx.From]-tx.Value < 0 {
 		return fmt.Errorf("insufficient balance")
 	}
 
 	s.Balances[tx.From] -= tx.Value
 	s.Balances[tx.To] += tx.Value
 
 	return nil
-}
+}
+
+func (s *State) doSnapshot() error {
+	// Re-read the whole file from the first byte
+	_, err := s.dbFile.Seek(0, 0)
+	if err != nil {
+		return err
+	}
+
+	txsData, err := ioutil.ReadAll(s.dbFile)
+	if err != nil {
+		return err
+	}
+	s.snapshot = sha256.Sum256(txsData)
+
+	return nil
+}

database/tx.db

@@ -7,3 +7,5 @@
 {"from":"babayaga","to":"andrej","value":50,"data":""}
 {"from":"andrej","to":"andrej","value":100,"data":"reward"}
 {"from":"andrej","to":"andrej","value":100,"data":"reward"}
+{"from":"andrej","to":"andrej","value":100,"data":"reward"}
+{"from":"andrej","to":"andrej","value":100,"data":"reward"}