forked from TrueCloudLab/restic
685 lines
22 KiB
Go
685 lines
22 KiB
Go
/*
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Copyright 2017 Google Inc. All Rights Reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package spanner
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import (
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"bytes"
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"io"
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"sync/atomic"
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"time"
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log "github.com/golang/glog"
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proto "github.com/golang/protobuf/proto"
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proto3 "github.com/golang/protobuf/ptypes/struct"
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"golang.org/x/net/context"
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"google.golang.org/api/iterator"
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sppb "google.golang.org/genproto/googleapis/spanner/v1"
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"google.golang.org/grpc/codes"
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)
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// streamingReceiver is the interface for receiving data from a client side
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// stream.
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type streamingReceiver interface {
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Recv() (*sppb.PartialResultSet, error)
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}
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// errEarlyReadEnd returns error for read finishes when gRPC stream is still active.
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func errEarlyReadEnd() error {
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return spannerErrorf(codes.FailedPrecondition, "read completed with active stream")
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}
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// stream is the internal fault tolerant method for streaming data from
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// Cloud Spanner.
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func stream(ctx context.Context, rpc func(ct context.Context, resumeToken []byte) (streamingReceiver, error), setTimestamp func(time.Time), release func(error)) *RowIterator {
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ctx, cancel := context.WithCancel(ctx)
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return &RowIterator{
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streamd: newResumableStreamDecoder(ctx, rpc),
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rowd: &partialResultSetDecoder{},
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setTimestamp: setTimestamp,
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release: release,
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cancel: cancel,
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}
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}
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// RowIterator is an iterator over Rows.
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type RowIterator struct {
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streamd *resumableStreamDecoder
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rowd *partialResultSetDecoder
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setTimestamp func(time.Time)
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release func(error)
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cancel func()
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err error
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rows []*Row
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}
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// Next returns the next result. Its second return value is iterator.Done if
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// there are no more results. Once Next returns Done, all subsequent calls
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// will return Done.
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func (r *RowIterator) Next() (*Row, error) {
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if r.err != nil {
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return nil, r.err
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}
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for len(r.rows) == 0 && r.streamd.next() {
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r.rows, r.err = r.rowd.add(r.streamd.get())
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if r.err != nil {
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return nil, r.err
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}
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if !r.rowd.ts.IsZero() && r.setTimestamp != nil {
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r.setTimestamp(r.rowd.ts)
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r.setTimestamp = nil
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}
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}
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if len(r.rows) > 0 {
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row := r.rows[0]
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r.rows = r.rows[1:]
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return row, nil
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}
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if err := r.streamd.lastErr(); err != nil {
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r.err = toSpannerError(err)
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} else if !r.rowd.done() {
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r.err = errEarlyReadEnd()
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} else {
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r.err = iterator.Done
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}
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return nil, r.err
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}
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// Do calls the provided function once in sequence for each row in the iteration. If the
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// function returns a non-nil error, Do immediately returns that error.
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//
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// If there are no rows in the iterator, Do will return nil without calling the
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// provided function.
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//
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// Do always calls Stop on the iterator.
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func (r *RowIterator) Do(f func(r *Row) error) error {
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defer r.Stop()
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for {
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row, err := r.Next()
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switch err {
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case iterator.Done:
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return nil
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case nil:
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if err = f(row); err != nil {
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return err
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}
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default:
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return err
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}
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}
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}
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// Stop terminates the iteration. It should be called after every iteration.
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func (r *RowIterator) Stop() {
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if r.cancel != nil {
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r.cancel()
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}
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if r.release != nil {
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r.release(r.err)
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if r.err == nil {
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r.err = spannerErrorf(codes.FailedPrecondition, "Next called after Stop")
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}
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r.release = nil
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}
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}
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// partialResultQueue implements a simple FIFO queue. The zero value is a
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// valid queue.
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type partialResultQueue struct {
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q []*sppb.PartialResultSet
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first int
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last int
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n int // number of elements in queue
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}
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// empty returns if the partialResultQueue is empty.
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func (q *partialResultQueue) empty() bool {
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return q.n == 0
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}
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// errEmptyQueue returns error for dequeuing an empty queue.
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func errEmptyQueue() error {
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return spannerErrorf(codes.OutOfRange, "empty partialResultQueue")
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}
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// peekLast returns the last item in partialResultQueue; if the queue
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// is empty, it returns error.
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func (q *partialResultQueue) peekLast() (*sppb.PartialResultSet, error) {
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if q.empty() {
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return nil, errEmptyQueue()
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}
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return q.q[(q.last+cap(q.q)-1)%cap(q.q)], nil
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}
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// push adds an item to the tail of partialResultQueue.
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func (q *partialResultQueue) push(r *sppb.PartialResultSet) {
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if q.q == nil {
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q.q = make([]*sppb.PartialResultSet, 8 /* arbitrary */)
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}
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if q.n == cap(q.q) {
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buf := make([]*sppb.PartialResultSet, cap(q.q)*2)
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for i := 0; i < q.n; i++ {
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buf[i] = q.q[(q.first+i)%cap(q.q)]
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}
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q.q = buf
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q.first = 0
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q.last = q.n
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}
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q.q[q.last] = r
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q.last = (q.last + 1) % cap(q.q)
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q.n++
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}
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// pop removes an item from the head of partialResultQueue and returns
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// it.
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func (q *partialResultQueue) pop() *sppb.PartialResultSet {
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if q.n == 0 {
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return nil
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}
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r := q.q[q.first]
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q.q[q.first] = nil
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q.first = (q.first + 1) % cap(q.q)
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q.n--
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return r
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}
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// clear empties partialResultQueue.
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func (q *partialResultQueue) clear() {
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*q = partialResultQueue{}
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}
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// dump retrieves all items from partialResultQueue and return them in a slice.
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// It is used only in tests.
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func (q *partialResultQueue) dump() []*sppb.PartialResultSet {
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var dq []*sppb.PartialResultSet
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for i := q.first; len(dq) < q.n; i = (i + 1) % cap(q.q) {
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dq = append(dq, q.q[i])
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}
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return dq
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}
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// resumableStreamDecoderState encodes resumableStreamDecoder's status.
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// See also the comments for resumableStreamDecoder.Next.
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type resumableStreamDecoderState int
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const (
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unConnected resumableStreamDecoderState = iota // 0
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queueingRetryable // 1
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queueingUnretryable // 2
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aborted // 3
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finished // 4
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)
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// resumableStreamDecoder provides a resumable interface for receiving
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// sppb.PartialResultSet(s) from a given query wrapped by
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// resumableStreamDecoder.rpc().
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type resumableStreamDecoder struct {
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// state is the current status of resumableStreamDecoder, see also
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// the comments for resumableStreamDecoder.Next.
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state resumableStreamDecoderState
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// stateWitness when non-nil is called to observe state change,
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// used for testing.
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stateWitness func(resumableStreamDecoderState)
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// ctx is the caller's context, used for cancel/timeout Next().
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ctx context.Context
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// rpc is a factory of streamingReceiver, which might resume
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// a pervious stream from the point encoded in restartToken.
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// rpc is always a wrapper of a Cloud Spanner query which is
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// resumable.
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rpc func(ctx context.Context, restartToken []byte) (streamingReceiver, error)
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// stream is the current RPC streaming receiver.
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stream streamingReceiver
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// q buffers received yet undecoded partial results.
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q partialResultQueue
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// bytesBetweenResumeTokens is the proxy of the byte size of PartialResultSets being queued
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// between two resume tokens. Once bytesBetweenResumeTokens is greater than
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// maxBytesBetweenResumeTokens, resumableStreamDecoder goes into queueingUnretryable state.
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bytesBetweenResumeTokens int32
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// maxBytesBetweenResumeTokens is the max number of bytes that can be buffered
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// between two resume tokens. It is always copied from the global maxBytesBetweenResumeTokens
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// atomically.
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maxBytesBetweenResumeTokens int32
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// np is the next sppb.PartialResultSet ready to be returned
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// to caller of resumableStreamDecoder.Get().
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np *sppb.PartialResultSet
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// resumeToken stores the resume token that resumableStreamDecoder has
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// last revealed to caller.
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resumeToken []byte
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// retryCount is the number of retries that have been carried out so far
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retryCount int
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// err is the last error resumableStreamDecoder has encountered so far.
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err error
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// backoff to compute delays between retries.
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backoff exponentialBackoff
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}
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// newResumableStreamDecoder creates a new resumeableStreamDecoder instance.
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// Parameter rpc should be a function that creates a new stream
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// beginning at the restartToken if non-nil.
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func newResumableStreamDecoder(ctx context.Context, rpc func(ct context.Context, restartToken []byte) (streamingReceiver, error)) *resumableStreamDecoder {
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return &resumableStreamDecoder{
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ctx: ctx,
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rpc: rpc,
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maxBytesBetweenResumeTokens: atomic.LoadInt32(&maxBytesBetweenResumeTokens),
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backoff: defaultBackoff,
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}
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}
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// changeState fulfills state transition for resumableStateDecoder.
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func (d *resumableStreamDecoder) changeState(target resumableStreamDecoderState) {
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if d.state == queueingRetryable && d.state != target {
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// Reset bytesBetweenResumeTokens because it is only meaningful/changed under
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// queueingRetryable state.
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d.bytesBetweenResumeTokens = 0
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}
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d.state = target
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if d.stateWitness != nil {
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d.stateWitness(target)
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}
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}
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// isNewResumeToken returns if the observed resume token is different from
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// the one returned from server last time.
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func (d *resumableStreamDecoder) isNewResumeToken(rt []byte) bool {
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if rt == nil {
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return false
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}
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if bytes.Compare(rt, d.resumeToken) == 0 {
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return false
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}
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return true
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}
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// Next advances to the next available partial result set. If error or no
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// more, returns false, call Err to determine if an error was encountered.
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// The following diagram illustrates the state machine of resumableStreamDecoder
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// that Next() implements. Note that state transition can be only triggered by
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// RPC activities.
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/*
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rpc() fails retryable
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+---------+
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| | rpc() fails unretryable/ctx timeouts or cancelled
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| | +------------------------------------------------+
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| | | |
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| v | v
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| +---+---+---+ +--------+ +------+--+
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+-----+unConnected| |finished| | aborted |<----+
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| | ++-----+-+ +------+--+ |
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+---+----+--+ ^ ^ ^ |
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| ^ | | | |
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| | | | recv() fails |
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| |recv() fails retryable | | | |
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| |with valid ctx | | | |
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rpc() succeeds | +-----------------------+ | | |
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| | | recv EOF recv EOF | |
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v | | Queue size exceeds | | |
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+---+----+---+----+threshold +-------+-----------+ | |
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+---------->+ +--------------->+ +-+ |
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| |queueingRetryable| |queueingUnretryable| |
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| | +<---------------+ | |
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| +---+----------+--+ pop() returns +--+----+-----------+ |
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| | | resume token | ^ |
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| | | | | |
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+---------------+ | | | |
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recv() succeeds | +----+ |
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| recv() succeeds |
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+--------------------------------------------------+
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recv() fails unretryable
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*/
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var (
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// maxBytesBetweenResumeTokens is the maximum amount of bytes that resumableStreamDecoder
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// in queueingRetryable state can use to queue PartialResultSets before getting
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// into queueingUnretryable state.
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maxBytesBetweenResumeTokens = int32(128 * 1024 * 1024)
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)
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func (d *resumableStreamDecoder) next() bool {
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for {
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select {
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case <-d.ctx.Done():
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// Do context check here so that even gRPC failed to do
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// so, resumableStreamDecoder can still break the loop
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// as expected.
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d.err = errContextCanceled(d.ctx, d.err)
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d.changeState(aborted)
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default:
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}
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switch d.state {
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case unConnected:
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// If no gRPC stream is available, try to initiate one.
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if d.stream, d.err = d.rpc(d.ctx, d.resumeToken); d.err != nil {
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if isRetryable(d.err) {
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d.doBackOff()
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// Be explicit about state transition, although the
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// state doesn't actually change. State transition
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// will be triggered only by RPC activity, regardless of
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// whether there is an actual state change or not.
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d.changeState(unConnected)
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continue
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}
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d.changeState(aborted)
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continue
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}
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d.resetBackOff()
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d.changeState(queueingRetryable)
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continue
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case queueingRetryable:
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fallthrough
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case queueingUnretryable:
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// Receiving queue is not empty.
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last, err := d.q.peekLast()
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if err != nil {
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// Only the case that receiving queue is empty could cause peekLast to
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// return error and in such case, we should try to receive from stream.
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d.tryRecv()
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continue
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}
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if d.isNewResumeToken(last.ResumeToken) {
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// Got new resume token, return buffered sppb.PartialResultSets to caller.
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d.np = d.q.pop()
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if d.q.empty() {
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d.bytesBetweenResumeTokens = 0
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// The new resume token was just popped out from queue, record it.
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d.resumeToken = d.np.ResumeToken
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d.changeState(queueingRetryable)
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}
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return true
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}
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if d.bytesBetweenResumeTokens >= d.maxBytesBetweenResumeTokens && d.state == queueingRetryable {
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d.changeState(queueingUnretryable)
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continue
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}
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if d.state == queueingUnretryable {
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// When there is no resume token observed,
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// only yield sppb.PartialResultSets to caller under
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// queueingUnretryable state.
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d.np = d.q.pop()
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return true
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}
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// Needs to receive more from gRPC stream till a new resume token
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// is observed.
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d.tryRecv()
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continue
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case aborted:
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// Discard all pending items because none of them
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// should be yield to caller.
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d.q.clear()
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return false
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case finished:
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// If query has finished, check if there are still buffered messages.
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if d.q.empty() {
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// No buffered PartialResultSet.
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return false
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}
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// Although query has finished, there are still buffered PartialResultSets.
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d.np = d.q.pop()
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return true
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default:
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log.Errorf("Unexpected resumableStreamDecoder.state: %v", d.state)
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return false
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}
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}
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}
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// tryRecv attempts to receive a PartialResultSet from gRPC stream.
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func (d *resumableStreamDecoder) tryRecv() {
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var res *sppb.PartialResultSet
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if res, d.err = d.stream.Recv(); d.err != nil {
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if d.err == io.EOF {
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d.err = nil
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d.changeState(finished)
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return
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}
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if isRetryable(d.err) && d.state == queueingRetryable {
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d.err = nil
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// Discard all queue items (none have resume tokens).
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d.q.clear()
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d.stream = nil
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d.changeState(unConnected)
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d.doBackOff()
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return
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}
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d.changeState(aborted)
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return
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}
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d.q.push(res)
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if d.state == queueingRetryable && !d.isNewResumeToken(res.ResumeToken) {
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// adjusting d.bytesBetweenResumeTokens
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d.bytesBetweenResumeTokens += int32(proto.Size(res))
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}
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d.resetBackOff()
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d.changeState(d.state)
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}
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// resetBackOff clears the internal retry counter of
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// resumableStreamDecoder so that the next exponential
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// backoff will start at a fresh state.
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func (d *resumableStreamDecoder) resetBackOff() {
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d.retryCount = 0
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}
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// doBackoff does an exponential backoff sleep.
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func (d *resumableStreamDecoder) doBackOff() {
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ticker := time.NewTicker(d.backoff.delay(d.retryCount))
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defer ticker.Stop()
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d.retryCount++
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select {
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case <-d.ctx.Done():
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case <-ticker.C:
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}
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}
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// get returns the most recent PartialResultSet generated by a call to next.
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func (d *resumableStreamDecoder) get() *sppb.PartialResultSet {
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return d.np
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}
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// lastErr returns the last non-EOF error encountered.
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func (d *resumableStreamDecoder) lastErr() error {
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return d.err
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}
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// partialResultSetDecoder assembles PartialResultSet(s) into Cloud Spanner
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// Rows.
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type partialResultSetDecoder struct {
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row Row
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tx *sppb.Transaction
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chunked bool // if true, next value should be merged with last values entry.
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ts time.Time // read timestamp
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}
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// yield checks we have a complete row, and if so returns it. A row is not
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// complete if it doesn't have enough columns, or if this is a chunked response
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// and there are no further values to process.
|
|
func (p *partialResultSetDecoder) yield(chunked, last bool) *Row {
|
|
if len(p.row.vals) == len(p.row.fields) && (!chunked || !last) {
|
|
// When partialResultSetDecoder gets enough number of
|
|
// Column values, There are two cases that a new Row
|
|
// should be yield:
|
|
// 1. The incoming PartialResultSet is not chunked;
|
|
// 2. The incoming PartialResultSet is chunked, but the
|
|
// proto3.Value being merged is not the last one in
|
|
// the PartialResultSet.
|
|
//
|
|
// Use a fresh Row to simplify clients that want to use yielded results
|
|
// after the next row is retrieved. Note that fields is never changed
|
|
// so it doesn't need to be copied.
|
|
fresh := Row{
|
|
fields: p.row.fields,
|
|
vals: make([]*proto3.Value, len(p.row.vals)),
|
|
}
|
|
copy(fresh.vals, p.row.vals)
|
|
p.row.vals = p.row.vals[:0] // empty and reuse slice
|
|
return &fresh
|
|
}
|
|
return nil
|
|
}
|
|
|
|
// yieldTx returns transaction information via caller supplied callback.
|
|
func errChunkedEmptyRow() error {
|
|
return spannerErrorf(codes.FailedPrecondition, "got invalid chunked PartialResultSet with empty Row")
|
|
}
|
|
|
|
// add tries to merge a new PartialResultSet into buffered Row. It returns
|
|
// any rows that have been completed as a result.
|
|
func (p *partialResultSetDecoder) add(r *sppb.PartialResultSet) ([]*Row, error) {
|
|
var rows []*Row
|
|
if r.Metadata != nil {
|
|
// Metadata should only be returned in the first result.
|
|
if p.row.fields == nil {
|
|
p.row.fields = r.Metadata.RowType.Fields
|
|
}
|
|
if p.tx == nil && r.Metadata.Transaction != nil {
|
|
p.tx = r.Metadata.Transaction
|
|
if p.tx.ReadTimestamp != nil {
|
|
p.ts = time.Unix(p.tx.ReadTimestamp.Seconds, int64(p.tx.ReadTimestamp.Nanos))
|
|
}
|
|
}
|
|
}
|
|
if len(r.Values) == 0 {
|
|
return nil, nil
|
|
}
|
|
if p.chunked {
|
|
p.chunked = false
|
|
// Try to merge first value in r.Values into
|
|
// uncompleted row.
|
|
last := len(p.row.vals) - 1
|
|
if last < 0 { // sanity check
|
|
return nil, errChunkedEmptyRow()
|
|
}
|
|
var err error
|
|
// If p is chunked, then we should always try to merge p.last with r.first.
|
|
if p.row.vals[last], err = p.merge(p.row.vals[last], r.Values[0]); err != nil {
|
|
return nil, err
|
|
}
|
|
r.Values = r.Values[1:]
|
|
// Merge is done, try to yield a complete Row.
|
|
if row := p.yield(r.ChunkedValue, len(r.Values) == 0); row != nil {
|
|
rows = append(rows, row)
|
|
}
|
|
}
|
|
for i, v := range r.Values {
|
|
// The rest values in r can be appened into p directly.
|
|
p.row.vals = append(p.row.vals, v)
|
|
// Again, check to see if a complete Row can be yielded because of
|
|
// the newly added value.
|
|
if row := p.yield(r.ChunkedValue, i == len(r.Values)-1); row != nil {
|
|
rows = append(rows, row)
|
|
}
|
|
}
|
|
if r.ChunkedValue {
|
|
// After dealing with all values in r, if r is chunked then p must
|
|
// be also chunked.
|
|
p.chunked = true
|
|
}
|
|
return rows, nil
|
|
}
|
|
|
|
// isMergeable returns if a protobuf Value can be potentially merged with
|
|
// other protobuf Values.
|
|
func (p *partialResultSetDecoder) isMergeable(a *proto3.Value) bool {
|
|
switch a.Kind.(type) {
|
|
case *proto3.Value_StringValue:
|
|
return true
|
|
case *proto3.Value_ListValue:
|
|
return true
|
|
default:
|
|
return false
|
|
}
|
|
}
|
|
|
|
// errIncompatibleMergeTypes returns error for incompatible protobuf types
|
|
// that cannot be merged by partialResultSetDecoder.
|
|
func errIncompatibleMergeTypes(a, b *proto3.Value) error {
|
|
return spannerErrorf(codes.FailedPrecondition, "incompatible type in chunked PartialResultSet. expected (%T), got (%T)", a.Kind, b.Kind)
|
|
}
|
|
|
|
// errUnsupportedMergeType returns error for protobuf type that cannot be
|
|
// merged to other protobufs.
|
|
func errUnsupportedMergeType(a *proto3.Value) error {
|
|
return spannerErrorf(codes.FailedPrecondition, "unsupported type merge (%T)", a.Kind)
|
|
}
|
|
|
|
// merge tries to combine two protobuf Values if possible.
|
|
func (p *partialResultSetDecoder) merge(a, b *proto3.Value) (*proto3.Value, error) {
|
|
var err error
|
|
typeErr := errIncompatibleMergeTypes(a, b)
|
|
switch t := a.Kind.(type) {
|
|
case *proto3.Value_StringValue:
|
|
s, ok := b.Kind.(*proto3.Value_StringValue)
|
|
if !ok {
|
|
return nil, typeErr
|
|
}
|
|
return &proto3.Value{
|
|
Kind: &proto3.Value_StringValue{StringValue: t.StringValue + s.StringValue},
|
|
}, nil
|
|
case *proto3.Value_ListValue:
|
|
l, ok := b.Kind.(*proto3.Value_ListValue)
|
|
if !ok {
|
|
return nil, typeErr
|
|
}
|
|
if l.ListValue == nil || len(l.ListValue.Values) <= 0 {
|
|
// b is an empty list, just return a.
|
|
return a, nil
|
|
}
|
|
if t.ListValue == nil || len(t.ListValue.Values) <= 0 {
|
|
// a is an empty list, just return b.
|
|
return b, nil
|
|
}
|
|
if la := len(t.ListValue.Values) - 1; p.isMergeable(t.ListValue.Values[la]) {
|
|
// When the last item in a is of type String,
|
|
// List or Struct(encoded into List by Cloud Spanner),
|
|
// try to Merge last item in a and first item in b.
|
|
t.ListValue.Values[la], err = p.merge(t.ListValue.Values[la], l.ListValue.Values[0])
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
l.ListValue.Values = l.ListValue.Values[1:]
|
|
}
|
|
return &proto3.Value{
|
|
Kind: &proto3.Value_ListValue{
|
|
ListValue: &proto3.ListValue{
|
|
Values: append(t.ListValue.Values, l.ListValue.Values...),
|
|
},
|
|
},
|
|
}, nil
|
|
default:
|
|
return nil, errUnsupportedMergeType(a)
|
|
}
|
|
|
|
}
|
|
|
|
// Done returns if partialResultSetDecoder has already done with all buffered
|
|
// values.
|
|
func (p *partialResultSetDecoder) done() bool {
|
|
// There is no explicit end of stream marker, but ending part way
|
|
// through a row is obviously bad, or ending with the last column still
|
|
// awaiting completion.
|
|
return len(p.row.vals) == 0 && !p.chunked
|
|
}
|