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// Copyright 2017 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package firestore
import (
"context"
"errors"
"cloud.google.com/go/internal/trace"
gax "github.com/googleapis/gax-go/v2"
pb "google.golang.org/genproto/googleapis/firestore/v1"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/status"
)
// Transaction represents a Firestore transaction.
type Transaction struct {
c *Client
ctx context.Context
id []byte
writes []*pb.Write
maxAttempts int
readOnly bool
readAfterWrite bool
}
// A TransactionOption is an option passed to Client.Transaction.
type TransactionOption interface {
config(t *Transaction)
}
// MaxAttempts is a TransactionOption that configures the maximum number of times to
// try a transaction. In defaults to DefaultTransactionMaxAttempts.
func MaxAttempts(n int) maxAttempts { return maxAttempts(n) }
type maxAttempts int
func (m maxAttempts) config(t *Transaction) { t.maxAttempts = int(m) }
// DefaultTransactionMaxAttempts is the default number of times to attempt a transaction.
const DefaultTransactionMaxAttempts = 5
// ReadOnly is a TransactionOption that makes the transaction read-only. Read-only
// transactions cannot issue write operations, but are more efficient.
var ReadOnly = ro{}
type ro struct{}
func (ro) config(t *Transaction) { t.readOnly = true }
var (
// Defined here for testing.
errReadAfterWrite = errors.New("firestore: read after write in transaction")
errWriteReadOnly = errors.New("firestore: write in read-only transaction")
errNestedTransaction = errors.New("firestore: nested transaction")
)
type transactionInProgressKey struct{}
// RunTransaction runs f in a transaction. f should use the transaction it is given
// for all Firestore operations. For any operation requiring a context, f should use
// the context it is passed, not the first argument to RunTransaction.
//
// f must not call Commit or Rollback on the provided Transaction.
//
// If f returns nil, RunTransaction commits the transaction. If the commit fails due
// to a conflicting transaction, RunTransaction retries f. It gives up and returns an
// error after a number of attempts that can be configured with the MaxAttempts
// option. If the commit succeeds, RunTransaction returns a nil error.
//
// If f returns non-nil, then the transaction will be rolled back and
// this method will return the same error. The function f is not retried.
//
// Note that when f returns, the transaction is not committed. Calling code
// must not assume that any of f's changes have been committed until
// RunTransaction returns nil.
//
// Since f may be called more than once, f should usually be idempotent – that is, it
// should have the same result when called multiple times.
func (c *Client) RunTransaction(ctx context.Context, f func(context.Context, *Transaction) error, opts ...TransactionOption) (err error) {
ctx = trace.StartSpan(ctx, "cloud.google.com/go/firestore.Client.RunTransaction")
defer func() { trace.EndSpan(ctx, err) }()
if ctx.Value(transactionInProgressKey{}) != nil {
return errNestedTransaction
}
db := c.path()
t := &Transaction{
c: c,
ctx: withResourceHeader(ctx, db),
maxAttempts: DefaultTransactionMaxAttempts,
}
for _, opt := range opts {
opt.config(t)
}
var txOpts *pb.TransactionOptions
if t.readOnly {
txOpts = &pb.TransactionOptions{
Mode: &pb.TransactionOptions_ReadOnly_{&pb.TransactionOptions_ReadOnly{}},
}
}
var backoff gax.Backoff
// TODO(jba): use other than the standard backoff parameters?
// TODO(jba): get backoff time from gRPC trailer metadata? See
// extractRetryDelay in https://code.googlesource.com/gocloud/+/master/spanner/retry.go.
for i := 0; i < t.maxAttempts; i++ {
var res *pb.BeginTransactionResponse
res, err = t.c.c.BeginTransaction(t.ctx, &pb.BeginTransactionRequest{
Database: db,
Options: txOpts,
})
if err != nil {
return err
}
t.id = res.Transaction
err = f(context.WithValue(ctx, transactionInProgressKey{}, 1), t)
// Read after write can only be checked client-side, so we make sure to check
// even if the user does not.
if err == nil && t.readAfterWrite {
err = errReadAfterWrite
}
if err != nil {
t.rollback()
// Prefer f's returned error to rollback error.
return err
}
_, err = t.c.c.Commit(t.ctx, &pb.CommitRequest{
Database: t.c.path(),
Writes: t.writes,
Transaction: t.id,
})
// If a read-write transaction returns Aborted, retry.
// On success or other failures, return here.
if t.readOnly || status.Code(err) != codes.Aborted {
// According to the Firestore team, we should not roll back here
// if err != nil. But spanner does.
// See https://code.googlesource.com/gocloud/+/master/spanner/transaction.go#740.
return err
}
if txOpts == nil {
// txOpts can only be nil if is the first retry of a read-write transaction.
// (It is only set here and in the body of "if t.readOnly" above.)
// Mention the transaction ID in BeginTransaction so the service
// knows it is a retry.
txOpts = &pb.TransactionOptions{
Mode: &pb.TransactionOptions_ReadWrite_{
&pb.TransactionOptions_ReadWrite{RetryTransaction: t.id},
},
}
}
// Use exponential backoff to avoid contention with other running
// transactions.
if cerr := sleep(ctx, backoff.Pause()); cerr != nil {
err = cerr
break
}
// Reset state for the next attempt.
t.writes = nil
}
// If we run out of retries, return the last error we saw (which should
// be the Aborted from Commit, or a context error).
if err != nil {
t.rollback()
}
return err
}
func (t *Transaction) rollback() {
_ = t.c.c.Rollback(t.ctx, &pb.RollbackRequest{
Database: t.c.path(),
Transaction: t.id,
})
// Ignore the rollback error.
// TODO(jba): Log it?
// Note: Rollback is idempotent so it will be retried by the gapic layer.
}
// Get gets the document in the context of the transaction. The transaction holds a
// pessimistic lock on the returned document.
func (t *Transaction) Get(dr *DocumentRef) (*DocumentSnapshot, error) {
docsnaps, err := t.GetAll([]*DocumentRef{dr})
if err != nil {
return nil, err
}
ds := docsnaps[0]
if !ds.Exists() {
return ds, status.Errorf(codes.NotFound, "%q not found", dr.Path)
}
return ds, nil
}
// GetAll retrieves multiple documents with a single call. The DocumentSnapshots are
// returned in the order of the given DocumentRefs. If a document is not present, the
// corresponding DocumentSnapshot's Exists method will return false. The transaction
// holds a pessimistic lock on all of the returned documents.
func (t *Transaction) GetAll(drs []*DocumentRef) ([]*DocumentSnapshot, error) {
if len(t.writes) > 0 {
t.readAfterWrite = true
return nil, errReadAfterWrite
}
return t.c.getAll(t.ctx, drs, t.id)
}
// A Queryer is a Query or a CollectionRef. CollectionRefs act as queries whose
// results are all the documents in the collection.
type Queryer interface {
query() *Query
}
// Documents returns a DocumentIterator based on given Query or CollectionRef. The
// results will be in the context of the transaction.
func (t *Transaction) Documents(q Queryer) *DocumentIterator {
if len(t.writes) > 0 {
t.readAfterWrite = true
return &DocumentIterator{err: errReadAfterWrite}
}
return &DocumentIterator{
iter: newQueryDocumentIterator(t.ctx, q.query(), t.id),
}
}
// DocumentRefs returns references to all the documents in the collection, including
// missing documents. A missing document is a document that does not exist but has
// sub-documents.
func (t *Transaction) DocumentRefs(cr *CollectionRef) *DocumentRefIterator {
if len(t.writes) > 0 {
t.readAfterWrite = true
return &DocumentRefIterator{err: errReadAfterWrite}
}
return newDocumentRefIterator(t.ctx, cr, t.id)
}
// Create adds a Create operation to the Transaction.
// See DocumentRef.Create for details.
func (t *Transaction) Create(dr *DocumentRef, data interface{}) error {
return t.addWrites(dr.newCreateWrites(data))
}
// Set adds a Set operation to the Transaction.
// See DocumentRef.Set for details.
func (t *Transaction) Set(dr *DocumentRef, data interface{}, opts ...SetOption) error {
return t.addWrites(dr.newSetWrites(data, opts))
}
// Delete adds a Delete operation to the Transaction.
// See DocumentRef.Delete for details.
func (t *Transaction) Delete(dr *DocumentRef, opts ...Precondition) error {
return t.addWrites(dr.newDeleteWrites(opts))
}
// Update adds a new Update operation to the Transaction.
// See DocumentRef.Update for details.
func (t *Transaction) Update(dr *DocumentRef, data []Update, opts ...Precondition) error {
return t.addWrites(dr.newUpdatePathWrites(data, opts))
}
func (t *Transaction) addWrites(ws []*pb.Write, err error) error {
if t.readOnly {
return errWriteReadOnly
}
if err != nil {
return err
}
t.writes = append(t.writes, ws...)
return nil
}
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