tendermint · githubsands · Jan 29, 2021 · Jan 29, 2021 · Jan 29, 2021 · Jan 29, 2021
diff --git a/go.mod b/go.mod
@@ -3,6 +3,7 @@ module github.com/tendermint/tm-db
 go 1.12
 
 require (
+	github.com/coreos/etcd v3.3.10+incompatible
 	github.com/dgraph-io/badger/v2 v2.2007.2
 	github.com/facebookgo/ensure v0.0.0-20160127193407-b4ab57deab51 // indirect
 	github.com/facebookgo/stack v0.0.0-20160209184415-751773369052 // indirect

diff --git a/go.sum b/go.sum
@@ -10,6 +10,7 @@ github.com/cespare/xxhash v1.1.0 h1:a6HrQnmkObjyL+Gs60czilIUGqrzKutQD6XZog3p+ko=
 github.com/cespare/xxhash v1.1.0/go.mod h1:XrSqR1VqqWfGrhpAt58auRo0WTKS1nRRg3ghfAqPWnc=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/cncf/udpa/go v0.0.0-20201120205902-5459f2c99403/go.mod h1:WmhPx2Nbnhtbo57+VJT5O0JRkEi1Wbu0z5j0R8u5Hbk=
+github.com/coreos/etcd v3.3.10+incompatible h1:jFneRYjIvLMLhDLCzuTuU4rSJUjRplcJQ7pD7MnhC04=
 github.com/coreos/etcd v3.3.10+incompatible/go.mod h1:uF7uidLiAD3TWHmW31ZFd/JWoc32PjwdhPthX9715RE=
 github.com/coreos/go-etcd v2.0.0+incompatible/go.mod h1:Jez6KQU2B/sWsbdaef3ED8NzMklzPG4d5KIOhIy30Tk=
 github.com/coreos/go-semver v0.2.0/go.mod h1:nnelYz7RCh+5ahJtPPxZlU+153eP4D4r3EedlOD2RNk=

diff --git a/transaction.go b/transaction.go
@@ -0,0 +1,105 @@
+package db
+
+import (
+	"errors"
+)
+
+var errFailedAtomicCheck = errors.New("Failed to atomically write to the database rollback completed")
+var errFailedToDeleteOnRollback = errors.New("Failed to delete during transaction rollback")
+var errDataBaseNotImplemented = errors.New("Database given is not implemented")
+var errFailedToTransact = errors.New("Failed to transact")
+
+type T interface {
+	Transact(DB) error
+}
+
+// Transaction represents one transaction that abides by ACID properties
+type Transaction struct {
+	state int            // the amount of transactions that have been completed
+	txs   []func() error // txs is a list of all txs to execute for this transaction
+	keys  [][]byte       // is a list of the keys that have been used during this transaction
+
+	atomic bool
+}
+
+func NewTransaction(db DB) Transaction {
+	return Transaction{state: 0, txs: make([]func() error, 0), keys: make([][]byte, 0), atomic: needsAtomic(db)}
+}
+
+func (t Transaction) Append(tx func() error, k []byte) {
+	t.txs = append(t.txs, tx)
+	t.saveKey(k)
+}
+
+// saveKey saves a key incase deletion needs to occur
+func (t Transaction) saveKey(k []byte) {
+	t.keys = append(t.keys, k)
+}
+
+func (t Transaction) Transact(db DB) error {
+	if !t.atomic {
+		return t.transact(db)
+	}
+
+	return t.transactAtomic(db)
+}
+
+// transact transacts
+func (t Transaction) transact(db DB) error {
+	for i := range t.txs {
+		if err := t.txs[i](); err != nil {
+			return errFailedToTransact
+		}
+
+		return nil
+	}
+
+	// shouldn't happen
+	return nil
+}
+
+// transactAtomic transacts atomically
+func (t Transaction) transactAtomic(db DB) error {
+	for i := range t.txs {
+		if err := t.txs[i](); err != nil {
+			t.rollBack(db)
+			return errFailedAtomicCheck
+		}
+
+		// increment the state so if a rollback occurs the transaction knows how many times to roll back
+		t.state++
+	}
+
+	return nil
+}
+
+// rollBack rolls the database back to what the database was before this transaction
+func (t Transaction) rollBack(db DB) {
+	// do use atomic Transaction features if the database is already atomic
+	if !t.atomic {
+		return
+	}
+
+	for i := t.state; t.state > 0 || t.state == 0; t.state-- {
+		if err := db.Delete(t.keys[i]); err != nil {
+			panic(err)
+		}
+
+		if t.state == 0 {
+			return
+		}
+	}
+}
+
+// needsAtomic checks if the database provided needs bolted on atomicity
+func needsAtomic(db DB) bool {
+	switch db.(type) {
+	case *BoltDB, ClevelDB, *PrefixDB, BadgerDB:
+		return true
+	case *GoLevelDB:
+		// atomic already set to false but explicility define here for readability
+		return false
+	default:
+		panic(errDataBaseNotImplemented)
+	}
+}