forked from vanadium-archive/go.ref
/
database_watch.go
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/
database_watch.go
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// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package server
import (
"bytes"
"strings"
"v.io/v23/context"
"v.io/v23/naming"
"v.io/v23/rpc"
wire "v.io/v23/services/syncbase"
"v.io/v23/services/watch"
pubutil "v.io/v23/syncbase/util"
"v.io/v23/verror"
"v.io/v23/vom"
"v.io/x/ref/services/syncbase/common"
"v.io/x/ref/services/syncbase/store"
"v.io/x/ref/services/syncbase/store/watchable"
)
// GetResumeMarker implements the wire.DatabaseWatcher interface.
func (d *database) GetResumeMarker(ctx *context.T, call rpc.ServerCall, bh wire.BatchHandle) (watch.ResumeMarker, error) {
if !d.exists {
return nil, verror.New(verror.ErrNoExist, ctx, d.id)
}
var res watch.ResumeMarker
impl := func(sntx store.SnapshotOrTransaction) (err error) {
res, err = watchable.GetResumeMarker(sntx)
return err
}
if err := d.runWithExistingBatchOrNewSnapshot(ctx, bh, impl); err != nil {
return nil, err
}
return res, nil
}
// WatchGlob implements the wire.DatabaseWatcher interface.
func (d *database) WatchGlob(ctx *context.T, call watch.GlobWatcherWatchGlobServerCall, req watch.GlobRequest) error {
// TODO(rogulenko): Check permissions here and in other methods.
if !d.exists {
return verror.New(verror.ErrNoExist, ctx, d.id)
}
// Parse the pattern.
if !strings.HasSuffix(req.Pattern, "*") {
return verror.New(verror.ErrBadArg, ctx, req.Pattern)
}
collection, prefix, err := pubutil.ParseCollectionRowPair(ctx, strings.TrimSuffix(req.Pattern, "*"))
if err != nil {
return err
}
// Get the resume marker and fetch the initial state if necessary.
resumeMarker := req.ResumeMarker
c := collectionReq{
id: collection,
d: d,
}
if bytes.Equal(resumeMarker, []byte("now")) {
var err error
if resumeMarker, err = watchable.GetResumeMarker(d.st); err != nil {
return err
}
}
if len(resumeMarker) == 0 {
var err error
if resumeMarker, err = c.scanInitialState(ctx, call, prefix); err != nil {
return err
}
}
return c.watchUpdates(ctx, call, prefix, resumeMarker)
}
// scanInitialState sends the initial state of the watched prefix as one batch.
// TODO(ivanpi): Send dummy update for empty prefix to be compatible with
// v.io/v23/services/watch.
func (c *collectionReq) scanInitialState(ctx *context.T, call watch.GlobWatcherWatchGlobServerCall, prefix string) (watch.ResumeMarker, error) {
sntx := c.d.st.NewSnapshot()
defer sntx.Abort()
// Get resume marker inside snapshot.
resumeMarker, err := watchable.GetResumeMarker(sntx)
if err != nil {
return nil, err
}
// Scan initial state, sending accessible rows as single batch.
it := sntx.Scan(common.ScanPrefixArgs(common.JoinKeyParts(common.RowPrefix, c.stKeyPart()), prefix))
sender := &watchBatchSender{
send: call.SendStream().Send,
}
key, value := []byte{}, []byte{}
for it.Advance() {
key, value = it.Key(key), it.Value(value)
// Check perms.
// See comment in util/constants.go for why we use SplitNKeyParts.
parts := common.SplitNKeyParts(string(key), 3)
externalKey := parts[2]
// TODO(ivanpi): Check only once per collection.
if err := c.checkAccess(ctx, call, sntx); err != nil {
// TODO(ivanpi): Inaccessible rows are skipped. Figure out how to signal
// this to caller.
if verror.ErrorID(err) == verror.ErrNoAccess.ID {
continue
} else {
it.Cancel()
return nil, err
}
}
var valueAsRawBytes *vom.RawBytes
if err := vom.Decode(value, &valueAsRawBytes); err != nil {
it.Cancel()
return nil, err
}
if err := sender.addChange(
naming.Join(pubutil.EncodeId(c.id), externalKey),
watch.Exists,
vom.RawBytesOf(wire.StoreChange{
Value: valueAsRawBytes,
// Note: FromSync cannot be reconstructed from scan.
FromSync: false,
})); err != nil {
it.Cancel()
return nil, err
}
}
if err := it.Err(); err != nil {
return nil, verror.New(verror.ErrInternal, ctx, err)
}
// Finalize initial state batch.
if err := sender.finishBatch(resumeMarker); err != nil {
return nil, err
}
return resumeMarker, nil
}
// watchUpdates waits for database updates and sends them to the client.
// This function does two steps in a for loop:
// - scan through the watch log until the end, sending all updates to the client
// - wait for one of two signals: new updates available or the call is canceled.
// The 'new updates' signal is sent by the watcher via a Go channel.
func (c *collectionReq) watchUpdates(ctx *context.T, call watch.GlobWatcherWatchGlobServerCall, prefix string, resumeMarker watch.ResumeMarker) error {
hasUpdates, cancelWatch := watchable.WatchUpdates(c.d.st)
defer cancelWatch()
sender := &watchBatchSender{
send: call.SendStream().Send,
}
for {
// Drain the log queue.
for {
// TODO(ivanpi): Switch to streaming log batch entries? Since sync and
// conflict resolution merge batches, very large batches may not be
// unrealistic. However, sync currently also processes an entire batch at
// a time, and would need to be updated as well.
logs, nextResumeMarker, err := watchable.ReadBatchFromLog(c.d.st, resumeMarker)
if err != nil {
return err
}
if logs == nil {
// No new log records available at this time.
break
}
resumeMarker = nextResumeMarker
if err := c.processLogBatch(ctx, call, prefix, logs, sender); err != nil {
return err
}
if err := sender.finishBatch(resumeMarker); err != nil {
return err
}
}
// Wait for new updates or cancel.
select {
case _, ok := <-hasUpdates:
if !ok {
return verror.NewErrAborted(ctx)
}
case <-ctx.Done():
return ctx.Err()
}
}
}
// processLogBatch converts []*watchable.LogEntry to a watch.Change stream,
// filtering out unnecessary or inaccessible log records.
func (c *collectionReq) processLogBatch(ctx *context.T, call watch.GlobWatcherWatchGlobServerCall, prefix string, logs []*watchable.LogEntry, sender *watchBatchSender) error {
sn := c.d.st.NewSnapshot()
defer sn.Abort()
for _, logEntry := range logs {
var opKey string
var op interface{}
if err := logEntry.Op.ToValue(&op); err != nil {
return err
}
switch op := op.(type) {
case *watchable.PutOp:
opKey = string(op.Key)
case *watchable.DeleteOp:
opKey = string(op.Key)
default:
continue
}
// TODO(rogulenko): Currently we only process rows, i.e. keys of the form
// <RowPrefix>:xxx:yyy. Consider processing other keys.
if !common.IsRowKey(opKey) {
continue
}
collection, row := common.ParseRowKeyOrDie(opKey)
// Filter out unnecessary rows and rows that we can't access.
if collection != c.id || !strings.HasPrefix(row, prefix) {
continue
}
// TODO(ivanpi): Check only once per collection per batch.
if err := c.checkAccess(ctx, call, sn); err != nil {
if verror.ErrorID(err) != verror.ErrNoAccess.ID {
return err
}
continue
}
switch op := op.(type) {
case *watchable.PutOp:
rowValue, err := watchable.GetAtVersion(ctx, sn, op.Key, nil, op.Version)
if err != nil {
return err
}
var rowValueAsRawBytes *vom.RawBytes
if err := vom.Decode(rowValue, &rowValueAsRawBytes); err != nil {
return err
}
if err := sender.addChange(naming.Join(pubutil.EncodeId(collection), row),
watch.Exists,
vom.RawBytesOf(wire.StoreChange{
Value: rowValueAsRawBytes,
FromSync: logEntry.FromSync,
})); err != nil {
return err
}
case *watchable.DeleteOp:
if err := sender.addChange(naming.Join(pubutil.EncodeId(collection), row),
watch.DoesNotExist,
vom.RawBytesOf(wire.StoreChange{
FromSync: logEntry.FromSync,
})); err != nil {
return err
}
}
}
return nil
}
// watchBatchSender sends a sequence of watch changes forming a batch, delaying
// sends to allow setting the Continued flag on the last change.
type watchBatchSender struct {
// Function for sending changes to the stream. Must be set.
send func(item watch.Change) error
// Change set by previous addChange, sent by next addChange or finishBatch.
staged *watch.Change
}
// addChange sends the previously added change (if any) with Continued set to
// true and stages the new one to be sent by the next addChange or finishBatch.
func (w *watchBatchSender) addChange(name string, state int32, value *vom.RawBytes) error {
// Send previously staged change now that we know the batch is continuing.
if w.staged != nil {
w.staged.Continued = true
if err := w.send(*w.staged); err != nil {
return err
}
}
// Stage new change.
w.staged = &watch.Change{
Name: name,
State: state,
Value: value,
}
return nil
}
// finishBatch sends the previously added change (if any) with Continued set to
// false, finishing the batch.
func (w *watchBatchSender) finishBatch(resumeMarker watch.ResumeMarker) error {
// Send previously staged change as last in batch.
if w.staged != nil {
w.staged.Continued = false
w.staged.ResumeMarker = resumeMarker
if err := w.send(*w.staged); err != nil {
return err
}
}
// Clear staged change.
w.staged = nil
return nil
}