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etcd_register.go
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etcd_register.go
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package discov
import (
"context"
"errors"
"fmt"
"sync"
"time"
"go.etcd.io/etcd/clientv3"
)
// EtcdSrvRecord is a service record to be registered to or
// unregistered from etcd.
type EtcdSrvRecord interface {
// Register registers the record to etcd.
// This method should be called when the service starts.
Register()
// Unregister unregisters the record from etcd.
// This method should be called when the service is closed.
Unregister(context.Context) error
// CatchRuntimeErrors catches runtime errors.
// Since the EtcdSrvRecord spawns goroutines to keep heartbeat
// to etcd after calling Register, some errors may occur at runtime.
CatchRuntimeErrors() <-chan error
// RegisterKvBuilder injects an EtcdKvBuilder to custom the
// format of key and value to store.
RegisterKvBuilder(EtcdKvBuilder)
}
// NewEtcdSrvRecord creates a service record.
func NewEtcdSrvRecord(cli *clientv3.Client, srvName, srvAddr string) (EtcdSrvRecord, error) {
if cli == nil {
return nil, errors.New("nil etcd client")
}
if srvName == "" {
return nil, errors.New("empty srv name")
}
if srvAddr == "" {
return nil, errors.New("empty srv addr")
}
if !isEtcdClientAvailable(cli) {
return nil, errors.New("unavailable etcd client")
}
r := &etcdSrvRecord{
cli: cli,
ctx: nil,
cancel: nil,
wg: sync.WaitGroup{},
errs: nil,
errsLock: sync.Mutex{},
srvName: srvName,
srvAddr: srvAddr,
kvBuilder: nil,
srvTTL: time.Second * 3,
}
return r, nil
}
type etcdSrvRecord struct {
cli *clientv3.Client
srvTTL time.Duration
kvBuilder EtcdKvBuilder
srvName, srvAddr string
// used as revoking checker, aliveKeeper and consumer
ctx context.Context
cancel context.CancelFunc
wg sync.WaitGroup
errs chan error // note: never close after initialization
errsLock sync.Mutex
}
func (r *etcdSrvRecord) Register() {
r.ctx, r.cancel = context.WithCancel(context.Background())
r.initErrorChannel()
if r.kvBuilder == nil {
r.RegisterKvBuilder(new(DefaultEtcdKvBuilder))
}
r.wg.Add(1)
go r.checker()
}
func (r *etcdSrvRecord) Unregister(ctx context.Context) error {
if r.cancel != nil {
r.cancel() // revokes checker, aliveKeeper and consumer
r.wg.Wait()
}
if r.kvBuilder == nil {
r.RegisterKvBuilder(new(DefaultEtcdKvBuilder))
}
key := r.kvBuilder.BuildKey(r.srvName, r.srvAddr)
_, err := r.cli.Delete(ctx, key)
if err != nil {
return fmt.Errorf("etcd client delete key(%s): %v", key, err)
}
return nil
}
func (r *etcdSrvRecord) CatchRuntimeErrors() <-chan error {
r.initErrorChannel()
return r.errs
}
// RegisterKvBuilder should be called before Register and Unregister.
func (r *etcdSrvRecord) RegisterKvBuilder(b EtcdKvBuilder) {
r.kvBuilder = b
}
func (r *etcdSrvRecord) checker() {
defer r.wg.Done()
key := r.kvBuilder.BuildKey(r.srvName, r.srvAddr)
ticker := time.NewTicker(r.srvTTL)
for {
func() {
ctx, cancel := context.WithTimeout(r.ctx, r.srvTTL)
defer cancel()
resp, err := r.cli.Get(ctx, key)
if err != nil {
r.pushErr(fmt.Errorf("CHECKER_ERROR: failed to get key: %v", err))
return
}
if resp.Count <= 0 {
lease, err := r.cli.Grant(ctx, r.srvTTL.Milliseconds()/1000)
if err != nil {
r.pushErr(fmt.Errorf("CHECKER_ERROR: failed to grant lease: %v", err))
return
}
val := r.kvBuilder.BuildValue(r.srvName, r.srvAddr)
_, err = r.cli.Put(ctx, key, val, clientv3.WithLease(lease.ID))
if err != nil {
r.pushErr(fmt.Errorf("CHECKER_ERROR: failed to put key: %v", err))
return
}
ch, err := r.cli.KeepAlive(r.ctx, lease.ID) // aliveKeeper
if err != nil {
r.pushErr(fmt.Errorf("CHECKER_ERROR: failed to keep alive: %v", err))
return
}
r.wg.Add(1)
go r.consumer(ch)
}
}()
select {
case <-r.ctx.Done():
// revoke this goroutine
ticker.Stop()
return
case <-ticker.C:
}
}
}
func (r *etcdSrvRecord) consumer(ch <-chan *clientv3.LeaseKeepAliveResponse) {
defer r.wg.Done()
for {
select {
case <-r.ctx.Done():
return
case _, ok := <-ch:
if !ok {
r.pushErr(errors.New("KEEP_ALIVE_RESP_CONSUMER_WARNING: underlying keep alive stream is interrupted"))
return
}
}
}
}
func (r *etcdSrvRecord) pushErr(err error) {
r.initErrorChannel()
select {
case r.errs <- err:
default: // channel is full, discard err
}
}
func (r *etcdSrvRecord) initErrorChannel() {
r.errsLock.Lock()
defer r.errsLock.Unlock()
if r.errs == nil {
r.errs = makeErrorChannel()
}
}