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watch.go
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watch.go
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// Copyright 2018 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"
"fmt"
"io"
"log"
"sort"
"time"
pb "cloud.google.com/go/firestore/apiv1/firestorepb"
"cloud.google.com/go/internal/btree"
"cloud.google.com/go/internal/trace"
"github.com/golang/protobuf/ptypes"
gax "github.com/googleapis/gax-go/v2"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/status"
)
// LogWatchStreams controls whether watch stream status changes are logged.
// This feature is EXPERIMENTAL and may disappear at any time.
var LogWatchStreams = false
// DocumentChangeKind describes the kind of change to a document between
// query snapshots.
type DocumentChangeKind int
const (
// DocumentAdded indicates that the document was added for the first time.
DocumentAdded DocumentChangeKind = iota
// DocumentRemoved indicates that the document was removed.
DocumentRemoved
// DocumentModified indicates that the document was modified.
DocumentModified
)
// A DocumentChange describes the change to a document from one query snapshot to the next.
type DocumentChange struct {
Kind DocumentChangeKind
Doc *DocumentSnapshot
// The zero-based index of the document in the sequence of query results prior to this change,
// or -1 if the document was not present.
OldIndex int
// The zero-based index of the document in the sequence of query results after this change,
// or -1 if the document is no longer present.
NewIndex int
}
// Implementation of realtime updates (a.k.a. watch).
// This code is closely based on the Node.js implementation,
// https://github.com/googleapis/nodejs-firestore/blob/master/src/watch.js.
// The sole target ID for all streams from this client.
// Variable for testing.
var watchTargetID int32 = 'g' + 'o'
var defaultBackoff = gax.Backoff{
// Values from https://github.com/googleapis/nodejs-firestore/blob/master/src/backoff.js.
Initial: 1 * time.Second,
Max: 60 * time.Second,
Multiplier: 1.5,
}
// not goroutine-safe
type watchStream struct {
ctx context.Context
c *Client
lc pb.Firestore_ListenClient // the gRPC stream
target *pb.Target // document or query being watched
backoff gax.Backoff // for stream retries
err error // sticky permanent error
readTime time.Time // time of most recent snapshot
current bool // saw CURRENT, but not RESET; precondition for a snapshot
hasReturned bool // have we returned a snapshot yet?
compare func(a, b *DocumentSnapshot) (int, error) // compare documents according to query
// An ordered tree where DocumentSnapshots are the keys.
docTree *btree.BTree
// Map of document name to DocumentSnapshot for the last returned snapshot.
docMap map[string]*DocumentSnapshot
// Map of document name to DocumentSnapshot for accumulated changes for the current snapshot.
// A nil value means the document was removed.
changeMap map[string]*DocumentSnapshot
}
func newWatchStreamForDocument(ctx context.Context, dr *DocumentRef) *watchStream {
// A single document is always equal to itself.
compare := func(_, _ *DocumentSnapshot) (int, error) { return 0, nil }
return newWatchStream(ctx, dr.Parent.c, compare, &pb.Target{
TargetType: &pb.Target_Documents{
Documents: &pb.Target_DocumentsTarget{Documents: []string{dr.Path}},
},
TargetId: watchTargetID,
})
}
func newWatchStreamForQuery(ctx context.Context, q Query) (*watchStream, error) {
qp, err := q.toProto()
if err != nil {
return nil, err
}
target := &pb.Target{
TargetType: &pb.Target_Query{
Query: &pb.Target_QueryTarget{
Parent: q.parentPath,
QueryType: &pb.Target_QueryTarget_StructuredQuery{qp},
},
},
TargetId: watchTargetID,
}
return newWatchStream(ctx, q.c, q.compareFunc(), target), nil
}
const btreeDegree = 4
func newWatchStream(ctx context.Context, c *Client, compare func(_, _ *DocumentSnapshot) (int, error), target *pb.Target) *watchStream {
w := &watchStream{
ctx: ctx,
c: c,
compare: compare,
target: target,
backoff: defaultBackoff,
docMap: map[string]*DocumentSnapshot{},
changeMap: map[string]*DocumentSnapshot{},
}
w.docTree = btree.New(btreeDegree, func(a, b interface{}) bool {
return w.less(a.(*DocumentSnapshot), b.(*DocumentSnapshot))
})
return w
}
func (s *watchStream) less(a, b *DocumentSnapshot) bool {
c, err := s.compare(a, b)
if err != nil {
s.err = err
return false
}
return c < 0
}
// Once nextSnapshot returns an error, it will always return the same error.
func (s *watchStream) nextSnapshot() (*btree.BTree, []DocumentChange, time.Time, error) {
if s.err != nil {
return nil, nil, time.Time{}, s.err
}
var changes []DocumentChange
for {
// Process messages until we are in a consistent state.
for !s.handleNextMessage() {
}
if s.err != nil {
_ = s.close() // ignore error
return nil, nil, time.Time{}, s.err
}
var newDocTree *btree.BTree
newDocTree, changes = s.computeSnapshot(s.docTree, s.docMap, s.changeMap, s.readTime)
if s.err != nil {
return nil, nil, time.Time{}, s.err
}
// Only return a snapshot if something has changed, or this is the first snapshot.
if !s.hasReturned || newDocTree != s.docTree {
s.docTree = newDocTree
break
}
}
s.changeMap = map[string]*DocumentSnapshot{}
s.hasReturned = true
return s.docTree, changes, s.readTime, nil
}
// Read a message from the stream and handle it. Return true when
// we're in a consistent state, or there is a permanent error.
func (s *watchStream) handleNextMessage() bool {
res, err := s.recv()
if err != nil {
s.err = err
// Errors returned by recv are permanent.
return true
}
switch r := res.ResponseType.(type) {
case *pb.ListenResponse_TargetChange:
return s.handleTargetChange(r.TargetChange)
case *pb.ListenResponse_DocumentChange:
name := r.DocumentChange.Document.Name
s.logf("DocumentChange %q", name)
if hasWatchTargetID(r.DocumentChange.TargetIds) { // document changed
ref, err := pathToDoc(name, s.c)
if err == nil {
s.changeMap[name], err = newDocumentSnapshot(ref, r.DocumentChange.Document, s.c, nil)
}
if err != nil {
s.err = err
return true
}
} else if hasWatchTargetID(r.DocumentChange.RemovedTargetIds) { // document removed
s.changeMap[name] = nil
}
case *pb.ListenResponse_DocumentDelete:
s.logf("Delete %q", r.DocumentDelete.Document)
s.changeMap[r.DocumentDelete.Document] = nil
case *pb.ListenResponse_DocumentRemove:
s.logf("Remove %q", r.DocumentRemove.Document)
s.changeMap[r.DocumentRemove.Document] = nil
case *pb.ListenResponse_Filter:
s.logf("Filter %d", r.Filter.Count)
if int(r.Filter.Count) != s.currentSize() {
s.resetDocs() // Remove all the current results.
// The filter didn't match; close the stream so it will be re-opened on the next
// call to nextSnapshot.
_ = s.close() // ignore error
s.lc = nil
}
default:
s.err = fmt.Errorf("unknown response type %T", r)
return true
}
return false
}
// Return true if in a consistent state, or there is a permanent error.
func (s *watchStream) handleTargetChange(tc *pb.TargetChange) bool {
switch tc.TargetChangeType {
case pb.TargetChange_NO_CHANGE:
s.logf("TargetNoChange %d %v", len(tc.TargetIds), tc.ReadTime)
if len(tc.TargetIds) == 0 && tc.ReadTime != nil && s.current {
// Everything is up-to-date, so we are ready to return a snapshot.
rt, err := ptypes.Timestamp(tc.ReadTime)
if err != nil {
s.err = err
return true
}
s.readTime = rt
s.target.ResumeType = &pb.Target_ResumeToken{tc.ResumeToken}
return true
}
case pb.TargetChange_ADD:
s.logf("TargetAdd")
if tc.TargetIds[0] != watchTargetID {
s.err = errors.New("unexpected target ID sent by server")
return true
}
case pb.TargetChange_REMOVE:
s.logf("TargetRemove")
// We should never see a remove.
if tc.Cause != nil {
s.err = status.Error(codes.Code(tc.Cause.Code), tc.Cause.Message)
} else {
s.err = status.Error(codes.Internal, "firestore: client saw REMOVE")
}
return true
// The targets reflect all changes committed before the targets were added
// to the stream.
case pb.TargetChange_CURRENT:
s.logf("TargetCurrent")
s.current = true
// The targets have been reset, and a new initial state for the targets will be
// returned in subsequent changes. Whatever changes have happened so far no
// longer matter.
case pb.TargetChange_RESET:
s.logf("TargetReset")
s.resetDocs()
default:
s.err = fmt.Errorf("firestore: unknown TargetChange type %s", tc.TargetChangeType)
return true
}
// If we see a resume token and our watch ID is affected, we assume the stream
// is now healthy, so we reset our backoff time to the minimum.
if tc.ResumeToken != nil && (len(tc.TargetIds) == 0 || hasWatchTargetID(tc.TargetIds)) {
s.backoff = defaultBackoff
}
return false // not in a consistent state, keep receiving
}
func (s *watchStream) resetDocs() {
s.target.ResumeType = nil // clear resume token
s.current = false
s.changeMap = map[string]*DocumentSnapshot{}
// Mark each document as deleted. If documents are not deleted, they
// will be send again by the server.
it := s.docTree.BeforeIndex(0)
for it.Next() {
s.changeMap[it.Key.(*DocumentSnapshot).Ref.Path] = nil
}
}
func (s *watchStream) currentSize() int {
_, adds, deletes := extractChanges(s.docMap, s.changeMap)
return len(s.docMap) + len(adds) - len(deletes)
}
// Return the changes that have occurred since the last snapshot.
func extractChanges(docMap, changeMap map[string]*DocumentSnapshot) (updates, adds []*DocumentSnapshot, deletes []string) {
for name, doc := range changeMap {
switch {
case doc == nil:
if _, ok := docMap[name]; ok {
deletes = append(deletes, name)
}
case docMap[name] != nil:
updates = append(updates, doc)
default:
adds = append(adds, doc)
}
}
return updates, adds, deletes
}
// For development only.
// TODO(jba): remove.
func assert(b bool) {
if !b {
panic("assertion failed")
}
}
// Applies the mutations in changeMap to both the document tree and the
// document lookup map. Modifies docMap in place and returns a new docTree.
// If there were no changes, returns docTree unmodified.
func (s *watchStream) computeSnapshot(docTree *btree.BTree, docMap, changeMap map[string]*DocumentSnapshot, readTime time.Time) (*btree.BTree, []DocumentChange) {
var changes []DocumentChange
updatedTree := docTree
assert(docTree.Len() == len(docMap))
updates, adds, deletes := extractChanges(docMap, changeMap)
if len(adds) > 0 || len(deletes) > 0 {
updatedTree = docTree.Clone()
}
// Process the sorted changes in the order that is expected by our clients
// (removals, additions, and then modifications). We also need to sort the
// individual changes to assure that oldIndex/newIndex keep incrementing.
deldocs := make([]*DocumentSnapshot, len(deletes))
for i, d := range deletes {
deldocs[i] = docMap[d]
}
sort.Sort(byLess{deldocs, s.less})
for _, oldDoc := range deldocs {
assert(oldDoc != nil)
delete(docMap, oldDoc.Ref.Path)
_, oldi := updatedTree.GetWithIndex(oldDoc)
// TODO(jba): have btree.Delete return old index
_, found := updatedTree.Delete(oldDoc)
assert(found)
changes = append(changes, DocumentChange{
Kind: DocumentRemoved,
Doc: oldDoc,
OldIndex: oldi,
NewIndex: -1,
})
}
sort.Sort(byLess{adds, s.less})
for _, newDoc := range adds {
name := newDoc.Ref.Path
assert(docMap[name] == nil)
newDoc.ReadTime = readTime
docMap[name] = newDoc
updatedTree.Set(newDoc, nil)
// TODO(jba): change btree so Set returns index as second value.
_, newi := updatedTree.GetWithIndex(newDoc)
changes = append(changes, DocumentChange{
Kind: DocumentAdded,
Doc: newDoc,
OldIndex: -1,
NewIndex: newi,
})
}
sort.Sort(byLess{updates, s.less})
for _, newDoc := range updates {
name := newDoc.Ref.Path
oldDoc := docMap[name]
assert(oldDoc != nil)
if newDoc.UpdateTime.Equal(oldDoc.UpdateTime) {
continue
}
if updatedTree == docTree {
updatedTree = docTree.Clone()
}
newDoc.ReadTime = readTime
docMap[name] = newDoc
_, oldi := updatedTree.GetWithIndex(oldDoc)
updatedTree.Delete(oldDoc)
updatedTree.Set(newDoc, nil)
_, newi := updatedTree.GetWithIndex(newDoc)
changes = append(changes, DocumentChange{
Kind: DocumentModified,
Doc: newDoc,
OldIndex: oldi,
NewIndex: newi,
})
}
assert(updatedTree.Len() == len(docMap))
return updatedTree, changes
}
type byLess struct {
s []*DocumentSnapshot
less func(a, b *DocumentSnapshot) bool
}
func (b byLess) Len() int { return len(b.s) }
func (b byLess) Swap(i, j int) { b.s[i], b.s[j] = b.s[j], b.s[i] }
func (b byLess) Less(i, j int) bool { return b.less(b.s[i], b.s[j]) }
func hasWatchTargetID(ids []int32) bool {
for _, id := range ids {
if id == watchTargetID {
return true
}
}
return false
}
func (s *watchStream) logf(format string, args ...interface{}) {
if LogWatchStreams {
log.Printf(format, args...)
}
}
// Close the stream. From this point on, calls to nextSnapshot will return
// io.EOF, or the error from CloseSend.
func (s *watchStream) stop() {
err := s.close()
if s.err != nil { // don't change existing error
return
}
if err != nil {
// if an error occurs while closing the stream
s.err = err
return
}
// if we close successfully,
s.err = io.EOF // normal shutdown
}
func (s *watchStream) close() error {
if s.lc == nil {
return nil
}
return s.lc.CloseSend()
}
// recv receives the next message from the stream. It also handles opening the stream
// initially, and reopening it on non-permanent errors.
// recv doesn't have to be goroutine-safe.
func (s *watchStream) recv() (*pb.ListenResponse, error) {
var err error
for {
if s.lc == nil {
s.lc, err = s.open()
if err != nil {
// Do not retry if open fails.
return nil, err
}
}
res, err := s.lc.Recv()
if err == nil || isPermanentWatchError(err) {
return res, err
}
// Non-permanent error. Sleep and retry.
s.changeMap = map[string]*DocumentSnapshot{} // clear changeMap
dur := s.backoff.Pause()
// If we're out of quota, wait a long time before retrying.
if status.Code(err) == codes.ResourceExhausted {
dur = s.backoff.Max
}
if err := sleep(s.ctx, dur); err != nil {
return nil, err
}
s.lc = nil
}
}
func (s *watchStream) open() (lc pb.Firestore_ListenClient, err error) {
s.ctx = trace.StartSpan(s.ctx, "cloud.google.com/go/firestore.watchStream.Listen")
defer func() { trace.EndSpan(s.ctx, err) }()
dbPath := s.c.path()
lc, err = s.c.c.Listen(withResourceHeader(s.ctx, dbPath))
if err == nil {
err = lc.Send(&pb.ListenRequest{
Database: dbPath,
TargetChange: &pb.ListenRequest_AddTarget{AddTarget: s.target},
})
}
if err != nil {
return nil, err
}
return lc, nil
}
func isPermanentWatchError(err error) bool {
if err == io.EOF {
// Retry on normal end-of-stream.
return false
}
switch status.Code(err) {
case codes.Unknown, codes.DeadlineExceeded, codes.ResourceExhausted,
codes.Internal, codes.Unavailable, codes.Unauthenticated:
return false
default:
return true
}
}