Zack Williams | e940c7a | 2019-08-21 14:25:39 -0700 | [diff] [blame] | 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 | |
| 5 | package internal |
| 6 | |
| 7 | // This file implements hooks for applying datastore transactions. |
| 8 | |
| 9 | import ( |
| 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 | |
| 20 | var 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. |
| 25 | func 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. |
| 32 | func 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 | |
| 39 | var transactionKey = "used for *Transaction" |
| 40 | |
| 41 | func transactionFromContext(ctx netcontext.Context) *transaction { |
| 42 | t, _ := ctx.Value(&transactionKey).(*transaction) |
| 43 | return t |
| 44 | } |
| 45 | |
| 46 | func withTransaction(ctx netcontext.Context, t *transaction) netcontext.Context { |
| 47 | return netcontext.WithValue(ctx, &transactionKey, t) |
| 48 | } |
| 49 | |
| 50 | type transaction struct { |
| 51 | transaction pb.Transaction |
| 52 | finished bool |
| 53 | } |
| 54 | |
| 55 | var ErrConcurrentTransaction = errors.New("internal: concurrent transaction") |
| 56 | |
| 57 | func 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 | } |