func (e *Election) observe(ctx context.Context, ch chan<- v3.GetResponse) {
client := e.session.Client()
defer close(ch)
for {
resp, err := client.Get(ctx, e.keyPrefix, v3.WithFirstCreate()...)
if err != nil {
return
}
var kv *mvccpb.KeyValue
cctx, cancel := context.WithCancel(ctx)
if len(resp.Kvs) == 0 {
// wait for first key put on prefix
opts := []v3.OpOption{v3.WithRev(resp.Header.Revision), v3.WithPrefix()}
wch := client.Watch(cctx, e.keyPrefix, opts...)
for kv == nil {
wr, ok := <-wch
if !ok || wr.Err() != nil {
cancel()
return
}
// only accept PUTs; a DELETE will make observe() spin
for _, ev := range wr.Events {
if ev.Type == mvccpb.PUT {
kv = ev.Kv
break
}
}
}
} else {
kv = resp.Kvs[0]
}
wch := client.Watch(cctx, string(kv.Key), v3.WithRev(kv.ModRevision))
keyDeleted := false
for !keyDeleted {
wr, ok := <-wch
if !ok {
return
}
for _, ev := range wr.Events {
if ev.Type == mvccpb.DELETE {
keyDeleted = true
break
}
resp.Header = &wr.Header
resp.Kvs = []*mvccpb.KeyValue{ev.Kv}
select {
case ch <- *resp:
case <-cctx.Done():
return
}
}
}
cancel()
}
}
// Leader returns the leader value for the current election.
func (e *Election) Leader() (string, error) {
resp, err := e.kv.Get(e.ctx, e.keyPrefix, v3.WithFirstCreate()...)
if err != nil {
return "", err
} else if len(resp.Kvs) == 0 {
// no leader currently elected
return "", etcdserver.ErrNoLeader
}
return string(resp.Kvs[0].Value), nil
}
// Leader returns the leader value for the current election.
func (e *Election) Leader(ctx context.Context) (string, error) {
resp, err := e.client.Get(ctx, e.keyPrefix, v3.WithFirstCreate()...)
if err != nil {
return "", err
} else if len(resp.Kvs) == 0 {
// no leader currently elected
return "", ErrElectionNoLeader
}
return string(resp.Kvs[0].Value), nil
}
// Wait waits for a leader to be elected, returning the leader value.
func (e *Election) Wait() (string, error) {
resp, err := e.kv.Get(e.ctx, e.keyPrefix, v3.WithFirstCreate()...)
if err != nil {
return "", err
} else if len(resp.Kvs) != 0 {
// leader already exists
return string(resp.Kvs[0].Value), nil
}
_, err = WaitPrefixEvents(
e.client,
e.keyPrefix,
resp.Header.Revision,
[]storagepb.Event_EventType{storagepb.PUT})
if err != nil {
return "", err
}
return e.Wait()
}