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etcd.go
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etcd.go
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package etcd
import (
"log"
"sync"
etcdcl "github.com/coreos/etcd/client"
"golang.org/x/net/context"
"google.golang.org/grpc/naming"
)
type kv struct {
key, value string
}
// recvBuffer is an unbounded channel of *kv to record all the pending changes from etcd server.
type recvBuffer struct {
c chan *kv
mu sync.Mutex
stopping bool
backlog []*kv
}
func newRecvBuffer() *recvBuffer {
b := &recvBuffer{
c: make(chan *kv, 1),
}
return b
}
func (b *recvBuffer) put(r *kv) {
b.mu.Lock()
defer b.mu.Unlock()
if b.stopping {
return
}
b.backlog = append(b.backlog, r)
select {
case b.c <- b.backlog[0]:
b.backlog = b.backlog[1:]
default:
}
}
func (b *recvBuffer) load() {
b.mu.Lock()
defer b.mu.Unlock()
if b.stopping || len(b.backlog) == 0 {
return
}
select {
case b.c <- b.backlog[0]:
b.backlog = b.backlog[1:]
default:
}
}
func (b *recvBuffer) get() <-chan *kv {
return b.c
}
// stop terminates the recvBuffer. After it is called, the recvBuffer is not usable any more.
func (b *recvBuffer) stop() {
b.mu.Lock()
b.stopping = true
close(b.c)
b.mu.Unlock()
}
type etcdNR struct {
kAPI etcdcl.KeysAPI
recv *recvBuffer
ctx context.Context
cancel context.CancelFunc
}
// NewETCDNR creates an etcd NameResolver.
func NewETCDNR(cfg etcdcl.Config) (naming.Resolver, error) {
c, err := etcdcl.New(cfg)
if err != nil {
return nil, err
}
kAPI := etcdcl.NewKeysAPI(c)
ctx, cancel := context.WithCancel(context.Background())
return &etcdNR{
kAPI: kAPI,
recv: newRecvBuffer(),
ctx: ctx,
cancel: cancel,
}, nil
}
// getNode builds the resulting key-value map starting from node recursively.
func getNode(node *etcdcl.Node, res map[string]string) {
if !node.Dir {
res[node.Key] = node.Value
return
}
for _, val := range node.Nodes {
getNode(val, res)
}
}
func (nr *etcdNR) Get(target string) map[string]string {
resp, err := nr.kAPI.Get(nr.ctx, target, &etcdcl.GetOptions{Recursive: true, Sort: true})
if err != nil {
log.Printf("etcdNR.Get(_) stopped: %v", err)
return nil
}
res := make(map[string]string)
getNode(resp.Node, res)
return res
}
func (nr *etcdNR) Watch(target string) {
watcher := nr.kAPI.Watcher(target, &etcdcl.WatcherOptions{Recursive: true})
for {
resp, err := watcher.Next(nr.ctx)
if err != nil {
log.Printf("etcdNR.Watch(_) stopped: %v", err)
break
}
if resp.Node.Dir {
continue
}
entry := &kv{key: resp.Node.Key, value: resp.Node.Value}
nr.recv.put(entry)
}
}
func (nr *etcdNR) GetUpdate() (string, string) {
i := <-nr.recv.get()
nr.recv.load()
if i == nil {
return "", ""
}
// returns key and the corresponding value of the updated kv pair
return i.key, i.value
}
func (nr *etcdNR) Stop() {
nr.recv.stop()
nr.cancel()
}