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// 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
}
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