1// Copyright 2014 Google Inc. All rights reserved.
2// Use of this source code is governed by the Apache 2.0
3// license that can be found in the LICENSE file.
4
5package internal
6
7// This file implements hooks for applying datastore transactions.
8
9import (
10 "errors"
11 "reflect"
12
13 "github.com/golang/protobuf/proto"
14 netcontext "golang.org/x/net/context"
15
16 basepb "google.golang.org/appengine/internal/base"
17 pb "google.golang.org/appengine/internal/datastore"
18)
19
20var transactionSetters = make(map[reflect.Type]reflect.Value)
21
22// RegisterTransactionSetter registers a function that sets transaction information
23// in a protocol buffer message. f should be a function with two arguments,
24// the first being a protocol buffer type, and the second being *datastore.Transaction.
25func RegisterTransactionSetter(f interface{}) {
26 v := reflect.ValueOf(f)
27 transactionSetters[v.Type().In(0)] = v
28}
29
30// applyTransaction applies the transaction t to message pb
31// by using the relevant setter passed to RegisterTransactionSetter.
32func applyTransaction(pb proto.Message, t *pb.Transaction) {
33 v := reflect.ValueOf(pb)
34 if f, ok := transactionSetters[v.Type()]; ok {
35 f.Call([]reflect.Value{v, reflect.ValueOf(t)})
36 }
37}
38
39var transactionKey = "used for *Transaction"
40
41func transactionFromContext(ctx netcontext.Context) *transaction {
42 t, _ := ctx.Value(&transactionKey).(*transaction)
43 return t
44}
45
46func withTransaction(ctx netcontext.Context, t *transaction) netcontext.Context {
47 return netcontext.WithValue(ctx, &transactionKey, t)
48}
49
50type transaction struct {
51 transaction pb.Transaction
52 finished bool
53}
54
55var ErrConcurrentTransaction = errors.New("internal: concurrent transaction")
56
57func RunTransactionOnce(c netcontext.Context, f func(netcontext.Context) error, xg bool, readOnly bool, previousTransaction *pb.Transaction) (*pb.Transaction, error) {
58 if transactionFromContext(c) != nil {
59 return nil, errors.New("nested transactions are not supported")
60 }
61
62 // Begin the transaction.
63 t := &transaction{}
64 req := &pb.BeginTransactionRequest{
65 App: proto.String(FullyQualifiedAppID(c)),
66 }
67 if xg {
68 req.AllowMultipleEg = proto.Bool(true)
69 }
70 if previousTransaction != nil {
71 req.PreviousTransaction = previousTransaction
72 }
73 if readOnly {
74 req.Mode = pb.BeginTransactionRequest_READ_ONLY.Enum()
75 } else {
76 req.Mode = pb.BeginTransactionRequest_READ_WRITE.Enum()
77 }
78 if err := Call(c, "datastore_v3", "BeginTransaction", req, &t.transaction); err != nil {
79 return nil, err
80 }
81
82 // Call f, rolling back the transaction if f returns a non-nil error, or panics.
83 // The panic is not recovered.
84 defer func() {
85 if t.finished {
86 return
87 }
88 t.finished = true
89 // Ignore the error return value, since we are already returning a non-nil
90 // error (or we're panicking).
91 Call(c, "datastore_v3", "Rollback", &t.transaction, &basepb.VoidProto{})
92 }()
93 if err := f(withTransaction(c, t)); err != nil {
94 return &t.transaction, err
95 }
96 t.finished = true
97
98 // Commit the transaction.
99 res := &pb.CommitResponse{}
100 err := Call(c, "datastore_v3", "Commit", &t.transaction, res)
101 if ae, ok := err.(*APIError); ok {
102 /* TODO: restore this conditional
103 if appengine.IsDevAppServer() {
104 */
105 // The Python Dev AppServer raises an ApplicationError with error code 2 (which is
106 // Error.CONCURRENT_TRANSACTION) and message "Concurrency exception.".
107 if ae.Code == int32(pb.Error_BAD_REQUEST) && ae.Detail == "ApplicationError: 2 Concurrency exception." {
108 return &t.transaction, ErrConcurrentTransaction
109 }
110 if ae.Code == int32(pb.Error_CONCURRENT_TRANSACTION) {
111 return &t.transaction, ErrConcurrentTransaction
112 }
113 }
114 return &t.transaction, err
115}