diff --git a/vendor/google.golang.org/appengine/internal/transaction.go b/vendor/google.golang.org/appengine/internal/transaction.go
new file mode 100644
index 0000000..9006ae6
--- /dev/null
+++ b/vendor/google.golang.org/appengine/internal/transaction.go
@@ -0,0 +1,115 @@
+// Copyright 2014 Google Inc. All rights reserved.
+// Use of this source code is governed by the Apache 2.0
+// license that can be found in the LICENSE file.
+
+package internal
+
+// This file implements hooks for applying datastore transactions.
+
+import (
+	"errors"
+	"reflect"
+
+	"github.com/golang/protobuf/proto"
+	netcontext "golang.org/x/net/context"
+
+	basepb "google.golang.org/appengine/internal/base"
+	pb "google.golang.org/appengine/internal/datastore"
+)
+
+var transactionSetters = make(map[reflect.Type]reflect.Value)
+
+// RegisterTransactionSetter registers a function that sets transaction information
+// in a protocol buffer message. f should be a function with two arguments,
+// the first being a protocol buffer type, and the second being *datastore.Transaction.
+func RegisterTransactionSetter(f interface{}) {
+	v := reflect.ValueOf(f)
+	transactionSetters[v.Type().In(0)] = v
+}
+
+// applyTransaction applies the transaction t to message pb
+// by using the relevant setter passed to RegisterTransactionSetter.
+func applyTransaction(pb proto.Message, t *pb.Transaction) {
+	v := reflect.ValueOf(pb)
+	if f, ok := transactionSetters[v.Type()]; ok {
+		f.Call([]reflect.Value{v, reflect.ValueOf(t)})
+	}
+}
+
+var transactionKey = "used for *Transaction"
+
+func transactionFromContext(ctx netcontext.Context) *transaction {
+	t, _ := ctx.Value(&transactionKey).(*transaction)
+	return t
+}
+
+func withTransaction(ctx netcontext.Context, t *transaction) netcontext.Context {
+	return netcontext.WithValue(ctx, &transactionKey, t)
+}
+
+type transaction struct {
+	transaction pb.Transaction
+	finished    bool
+}
+
+var ErrConcurrentTransaction = errors.New("internal: concurrent transaction")
+
+func RunTransactionOnce(c netcontext.Context, f func(netcontext.Context) error, xg bool, readOnly bool, previousTransaction *pb.Transaction) (*pb.Transaction, error) {
+	if transactionFromContext(c) != nil {
+		return nil, errors.New("nested transactions are not supported")
+	}
+
+	// Begin the transaction.
+	t := &transaction{}
+	req := &pb.BeginTransactionRequest{
+		App: proto.String(FullyQualifiedAppID(c)),
+	}
+	if xg {
+		req.AllowMultipleEg = proto.Bool(true)
+	}
+	if previousTransaction != nil {
+		req.PreviousTransaction = previousTransaction
+	}
+	if readOnly {
+		req.Mode = pb.BeginTransactionRequest_READ_ONLY.Enum()
+	} else {
+		req.Mode = pb.BeginTransactionRequest_READ_WRITE.Enum()
+	}
+	if err := Call(c, "datastore_v3", "BeginTransaction", req, &t.transaction); err != nil {
+		return nil, err
+	}
+
+	// Call f, rolling back the transaction if f returns a non-nil error, or panics.
+	// The panic is not recovered.
+	defer func() {
+		if t.finished {
+			return
+		}
+		t.finished = true
+		// Ignore the error return value, since we are already returning a non-nil
+		// error (or we're panicking).
+		Call(c, "datastore_v3", "Rollback", &t.transaction, &basepb.VoidProto{})
+	}()
+	if err := f(withTransaction(c, t)); err != nil {
+		return &t.transaction, err
+	}
+	t.finished = true
+
+	// Commit the transaction.
+	res := &pb.CommitResponse{}
+	err := Call(c, "datastore_v3", "Commit", &t.transaction, res)
+	if ae, ok := err.(*APIError); ok {
+		/* TODO: restore this conditional
+		if appengine.IsDevAppServer() {
+		*/
+		// The Python Dev AppServer raises an ApplicationError with error code 2 (which is
+		// Error.CONCURRENT_TRANSACTION) and message "Concurrency exception.".
+		if ae.Code == int32(pb.Error_BAD_REQUEST) && ae.Detail == "ApplicationError: 2 Concurrency exception." {
+			return &t.transaction, ErrConcurrentTransaction
+		}
+		if ae.Code == int32(pb.Error_CONCURRENT_TRANSACTION) {
+			return &t.transaction, ErrConcurrentTransaction
+		}
+	}
+	return &t.transaction, err
+}