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watch.go
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watch.go
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// Copyright 2016 The etcd Authors
//
// 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 clientv3
import (
"fmt"
"sync"
v3rpc "github.com/coreos/etcd/etcdserver/api/v3rpc/rpctypes"
pb "github.com/coreos/etcd/etcdserver/etcdserverpb"
mvccpb "github.com/coreos/etcd/mvcc/mvccpb"
"golang.org/x/net/context"
"google.golang.org/grpc"
)
const (
EventTypeDelete = mvccpb.DELETE
EventTypePut = mvccpb.PUT
)
type Event mvccpb.Event
type WatchChan <-chan WatchResponse
type Watcher interface {
// Watch watches on a key or prefix. The watched events will be returned
// through the returned channel.
// If the watch is slow or the required rev is compacted, the watch request
// might be canceled from the server-side and the chan will be closed.
// 'opts' can be: 'WithRev' and/or 'WitchPrefix'.
Watch(ctx context.Context, key string, opts ...OpOption) WatchChan
// Close closes the watcher and cancels all watch requests.
Close() error
}
type WatchResponse struct {
Header pb.ResponseHeader
Events []*Event
// CompactRevision is the minimum revision the watcher may receive.
CompactRevision int64
// Canceled is used to indicate watch failure.
// If the watch failed and the stream was about to close, before the channel is closed,
// the channel sends a final response that has Canceled set to true with a non-nil Err().
Canceled bool
}
// IsCreate returns true if the event tells that the key is newly created.
func (e *Event) IsCreate() bool {
return e.Type == EventTypePut && e.Kv.CreateRevision == e.Kv.ModRevision
}
// IsModify returns true if the event tells that a new value is put on existing key.
func (e *Event) IsModify() bool {
return e.Type == EventTypePut && e.Kv.CreateRevision != e.Kv.ModRevision
}
// Err is the error value if this WatchResponse holds an error.
func (wr *WatchResponse) Err() error {
if wr.CompactRevision != 0 {
return v3rpc.ErrCompacted
}
if wr.Canceled {
return v3rpc.ErrFutureRev
}
return nil
}
// IsProgressNotify returns true if the WatchResponse is progress notification.
func (wr *WatchResponse) IsProgressNotify() bool {
return len(wr.Events) == 0 && !wr.Canceled
}
// watcher implements the Watcher interface
type watcher struct {
rc *remoteClient
remote pb.WatchClient
// ctx controls internal remote.Watch requests
ctx context.Context
cancel context.CancelFunc
// streams holds all active watchers
streams map[int64]*watcherStream
// mu protects the streams map
mu sync.RWMutex
// reqc sends a watch request from Watch() to the main goroutine
reqc chan *watchRequest
// respc receives data from the watch client
respc chan *pb.WatchResponse
// stopc is sent to the main goroutine to stop all processing
stopc chan struct{}
// donec closes to broadcast shutdown
donec chan struct{}
// errc transmits errors from grpc Recv
errc chan error
}
// watchRequest is issued by the subscriber to start a new watcher
type watchRequest struct {
ctx context.Context
key string
end string
rev int64
// progressNotify is for progress updates.
progressNotify bool
// retc receives a chan WatchResponse once the watcher is established
retc chan chan WatchResponse
}
// watcherStream represents a registered watcher
type watcherStream struct {
initReq watchRequest
// outc publishes watch responses to subscriber
outc chan<- WatchResponse
// recvc buffers watch responses before publishing
recvc chan *WatchResponse
id int64
// lastRev is revision last successfully sent over outc
lastRev int64
// resumec indicates the stream must recover at a given revision
resumec chan int64
}
func NewWatcher(c *Client) Watcher {
ctx, cancel := context.WithCancel(context.Background())
w := &watcher{
ctx: ctx,
cancel: cancel,
streams: make(map[int64]*watcherStream),
respc: make(chan *pb.WatchResponse),
reqc: make(chan *watchRequest),
stopc: make(chan struct{}),
donec: make(chan struct{}),
errc: make(chan error, 1),
}
f := func(conn *grpc.ClientConn) { w.remote = pb.NewWatchClient(conn) }
w.rc = newRemoteClient(c, f)
go w.run()
return w
}
// Watch posts a watch request to run() and waits for a new watcher channel
func (w *watcher) Watch(ctx context.Context, key string, opts ...OpOption) WatchChan {
ow := opWatch(key, opts...)
retc := make(chan chan WatchResponse, 1)
wr := &watchRequest{
ctx: ctx,
key: string(ow.key),
end: string(ow.end),
rev: ow.rev,
progressNotify: ow.progressNotify,
retc: retc,
}
ok := false
// submit request
select {
case w.reqc <- wr:
ok = true
case <-wr.ctx.Done():
case <-w.donec:
}
// receive channel
if ok {
select {
case ret := <-retc:
return ret
case <-ctx.Done():
case <-w.donec:
}
}
// couldn't create channel; return closed channel
ch := make(chan WatchResponse)
close(ch)
return ch
}
func (w *watcher) Close() error {
close(w.stopc)
<-w.donec
return v3rpc.Error(<-w.errc)
}
func (w *watcher) addStream(resp *pb.WatchResponse, pendingReq *watchRequest) {
if pendingReq == nil {
// no pending request; ignore
return
}
if resp.Canceled || resp.CompactRevision != 0 {
// a cancel at id creation time means the start revision has
// been compacted out of the store
ret := make(chan WatchResponse, 1)
ret <- WatchResponse{
Header: *resp.Header,
CompactRevision: resp.CompactRevision,
Canceled: true}
close(ret)
pendingReq.retc <- ret
return
}
ret := make(chan WatchResponse)
if resp.WatchId == -1 {
// failed; no channel
close(ret)
pendingReq.retc <- ret
return
}
ws := &watcherStream{
initReq: *pendingReq,
id: resp.WatchId,
outc: ret,
// buffered so unlikely to block on sending while holding mu
recvc: make(chan *WatchResponse, 4),
resumec: make(chan int64),
}
if pendingReq.rev == 0 {
// note the header revision so that a put following a current watcher
// disconnect will arrive on the watcher channel after reconnect
ws.initReq.rev = resp.Header.Revision
}
w.mu.Lock()
w.streams[ws.id] = ws
w.mu.Unlock()
// pass back the subscriber channel for the watcher
pendingReq.retc <- ret
// send messages to subscriber
go w.serveStream(ws)
}
// closeStream closes the watcher resources and removes it
func (w *watcher) closeStream(ws *watcherStream) {
// cancels request stream; subscriber receives nil channel
close(ws.initReq.retc)
// close subscriber's channel
close(ws.outc)
// shutdown serveStream
close(ws.recvc)
delete(w.streams, ws.id)
}
// run is the root of the goroutines for managing a watcher client
func (w *watcher) run() {
var wc pb.Watch_WatchClient
var closeErr error
defer func() {
select {
case w.errc <- closeErr:
default:
}
close(w.donec)
w.cancel()
}()
// start a stream with the etcd grpc server
if wc, closeErr = w.newWatchClient(); closeErr != nil {
return
}
var pendingReq, failedReq *watchRequest
curReqC := w.reqc
cancelSet := make(map[int64]struct{})
for {
select {
// Watch() requested
case pendingReq = <-curReqC:
// no more watch requests until there's a response
curReqC = nil
if err := wc.Send(pendingReq.toPB()); err == nil {
// pendingReq now waits on w.respc
break
}
failedReq = pendingReq
// New events from the watch client
case pbresp := <-w.respc:
switch {
case pbresp.Created:
// response to pending req, try to add
w.addStream(pbresp, pendingReq)
pendingReq = nil
curReqC = w.reqc
case pbresp.Canceled:
delete(cancelSet, pbresp.WatchId)
default:
// dispatch to appropriate watch stream
if ok := w.dispatchEvent(pbresp); ok {
break
}
// watch response on unexpected watch id; cancel id
if _, ok := cancelSet[pbresp.WatchId]; ok {
break
}
cancelSet[pbresp.WatchId] = struct{}{}
cr := &pb.WatchRequest_CancelRequest{
CancelRequest: &pb.WatchCancelRequest{
WatchId: pbresp.WatchId,
},
}
req := &pb.WatchRequest{RequestUnion: cr}
wc.Send(req)
}
// watch client failed to recv; spawn another if possible
// TODO report watch client errors from errc?
case <-w.errc:
if wc, closeErr = w.newWatchClient(); closeErr != nil {
return
}
curReqC = w.reqc
if pendingReq != nil {
failedReq = pendingReq
}
cancelSet = make(map[int64]struct{})
case <-w.stopc:
return
}
// send failed; queue for retry
if failedReq != nil {
go func(wr *watchRequest) {
select {
case w.reqc <- wr:
case <-wr.ctx.Done():
case <-w.donec:
}
}(pendingReq)
failedReq = nil
pendingReq = nil
}
}
}
// dispatchEvent sends a WatchResponse to the appropriate watcher stream
func (w *watcher) dispatchEvent(pbresp *pb.WatchResponse) bool {
w.mu.RLock()
defer w.mu.RUnlock()
ws, ok := w.streams[pbresp.WatchId]
events := make([]*Event, len(pbresp.Events))
for i, ev := range pbresp.Events {
events[i] = (*Event)(ev)
}
if ok {
wr := &WatchResponse{
Header: *pbresp.Header,
Events: events,
CompactRevision: pbresp.CompactRevision,
Canceled: pbresp.Canceled}
ws.recvc <- wr
}
return ok
}
// serveWatchClient forwards messages from the grpc stream to run()
func (w *watcher) serveWatchClient(wc pb.Watch_WatchClient) {
for {
resp, err := wc.Recv()
if err != nil {
select {
case w.errc <- err:
case <-w.donec:
}
return
}
select {
case w.respc <- resp:
case <-w.donec:
return
}
}
}
// serveStream forwards watch responses from run() to the subscriber
func (w *watcher) serveStream(ws *watcherStream) {
emptyWr := &WatchResponse{}
wrs := []*WatchResponse{}
resuming := false
closing := false
for !closing {
curWr := emptyWr
outc := ws.outc
if len(wrs) > 0 {
curWr = wrs[0]
} else {
outc = nil
}
select {
case outc <- *curWr:
if wrs[0].Err() != nil {
closing = true
break
}
var newRev int64
if len(wrs[0].Events) > 0 {
newRev = wrs[0].Events[len(wrs[0].Events)-1].Kv.ModRevision
} else {
newRev = wrs[0].Header.Revision
}
if newRev != ws.lastRev {
ws.lastRev = newRev
}
wrs[0] = nil
wrs = wrs[1:]
case wr, ok := <-ws.recvc:
if !ok {
// shutdown from closeStream
return
}
// resume up to last seen event if disconnected
if resuming && wr.Err() == nil {
resuming = false
// trim events already seen
for i := 0; i < len(wr.Events); i++ {
if wr.Events[i].Kv.ModRevision > ws.lastRev {
wr.Events = wr.Events[i:]
break
}
}
// only forward new events
if wr.Events[0].Kv.ModRevision == ws.lastRev {
break
}
}
resuming = false
// TODO don't keep buffering if subscriber stops reading
wrs = append(wrs, wr)
case resumeRev := <-ws.resumec:
wrs = nil
resuming = true
if resumeRev == -1 {
// pause serving stream while resume gets set up
break
}
if resumeRev != ws.lastRev {
panic("unexpected resume revision")
}
case <-w.donec:
closing = true
case <-ws.initReq.ctx.Done():
closing = true
}
}
w.mu.Lock()
w.closeStream(ws)
w.mu.Unlock()
// lazily send cancel message if events on missing id
}
func (w *watcher) newWatchClient() (pb.Watch_WatchClient, error) {
ws, rerr := w.resume()
if rerr != nil {
return nil, rerr
}
go w.serveWatchClient(ws)
return ws, nil
}
// resume creates a new WatchClient with all current watchers reestablished
func (w *watcher) resume() (ws pb.Watch_WatchClient, err error) {
for {
if ws, err = w.openWatchClient(); err != nil {
break
} else if err = w.resumeWatchers(ws); err == nil {
break
}
}
return ws, v3rpc.Error(err)
}
// openWatchClient retries opening a watchclient until retryConnection fails
func (w *watcher) openWatchClient() (ws pb.Watch_WatchClient, err error) {
for {
select {
case <-w.stopc:
if err == nil {
err = context.Canceled
}
return nil, err
default:
}
if ws, err = w.remote.Watch(w.ctx); ws != nil && err == nil {
break
} else if isHaltErr(w.ctx, err) {
return nil, v3rpc.Error(err)
}
err = w.rc.reconnectWait(w.ctx, nil)
}
return ws, nil
}
// resumeWatchers rebuilds every registered watcher on a new client
func (w *watcher) resumeWatchers(wc pb.Watch_WatchClient) error {
streams := []*watcherStream{}
w.mu.RLock()
for _, ws := range w.streams {
streams = append(streams, ws)
}
w.mu.RUnlock()
for _, ws := range streams {
// pause serveStream
ws.resumec <- -1
// reconstruct watcher from initial request
if ws.lastRev != 0 {
ws.initReq.rev = ws.lastRev
}
if err := wc.Send(ws.initReq.toPB()); err != nil {
return err
}
// wait for request ack
resp, err := wc.Recv()
if err != nil {
return err
} else if len(resp.Events) != 0 || !resp.Created {
return fmt.Errorf("watcher: unexpected response (%+v)", resp)
}
// id may be different since new remote watcher; update map
w.mu.Lock()
delete(w.streams, ws.id)
ws.id = resp.WatchId
w.streams[ws.id] = ws
w.mu.Unlock()
// unpause serveStream
ws.resumec <- ws.lastRev
}
return nil
}
// toPB converts an internal watch request structure to its protobuf messagefunc (wr *watchRequest)
func (wr *watchRequest) toPB() *pb.WatchRequest {
req := &pb.WatchCreateRequest{
StartRevision: wr.rev,
Key: []byte(wr.key),
RangeEnd: []byte(wr.end),
ProgressNotify: wr.progressNotify,
}
cr := &pb.WatchRequest_CreateRequest{CreateRequest: req}
return &pb.WatchRequest{RequestUnion: cr}
}