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watcher.go
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watcher.go
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// Copyright 2017 The casbin Authors. All Rights Reserved.
//
// 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 etcdwatcher
import (
"context"
"runtime"
"strconv"
"sync"
"time"
"github.com/casbin/casbin/v2/persist"
client "go.etcd.io/etcd/client/v3"
)
type Watcher struct {
// lock for callback
lock sync.RWMutex
endpoints []string
client *client.Client
running bool
callback func(string)
keyName string
password string
lastSentRev int64
conf *WatcherConfig
}
type WatcherConfig struct {
Hosts []string
Key string `json:",default=casbin_watcher"`
User string
Pass string
DialKeepAliveTimeout time.Duration `json:",default=10"`
DialTimeout time.Duration `json:",default=30"`
}
// finalizer is the destructor for Watcher.
func finalizer(w *Watcher) {
w.running = false
}
// NewWatcher is the constructor for Watcher.
// endpoints is the endpoints for etcd clusters.
func NewWatcher(endpoints []string, keyName string, password ...string) (persist.Watcher, error) {
w := &Watcher{}
w.endpoints = endpoints
w.running = true
w.callback = nil
w.keyName = keyName
if len(password) > 0 {
w.password = password[0]
}
// Create the client.
err := w.createClient()
if err != nil {
return nil, err
}
// Call the destructor when the object is released.
runtime.SetFinalizer(w, finalizer)
go func() {
_ = w.startWatch()
}()
return w, nil
}
// NewWatcherWithConfig is a configurable Watcher constructor
func NewWatcherWithConfig(config WatcherConfig) (persist.Watcher, error) {
w := &Watcher{}
w.running = true
w.callback = nil
w.keyName = config.Key
w.conf = &config
// Create the client.
err := w.createClient()
if err != nil {
return nil, err
}
// Call the destructor when the object is released.
runtime.SetFinalizer(w, finalizer)
go func() {
_ = w.startWatch()
}()
return w, nil
}
// Close closes the Watcher.
func (w *Watcher) Close() {
finalizer(w)
}
func (w *Watcher) createClient() error {
cfg := client.Config{
Endpoints: w.endpoints,
// set timeout per request to fail fast when the target endpoints is unavailable
DialKeepAliveTimeout: time.Second * 10,
DialTimeout: time.Second * 30,
Password: w.password,
}
if w.conf != nil {
cfg = client.Config{
Endpoints: w.conf.Hosts,
// set timeout per request to fail fast when the target endpoints is unavailable
DialTimeout: time.Second * w.conf.DialTimeout,
DialKeepAliveTimeout: time.Second * w.conf.DialKeepAliveTimeout,
Username: w.conf.User,
Password: w.conf.Pass,
}
}
c, err := client.New(cfg)
if err != nil {
return err
}
w.client = c
return nil
}
// SetUpdateCallback sets the callback function that the watcher will call
// when the policy in DB has been changed by other instances.
// A classic callback is Enforcer.LoadPolicy().
func (w *Watcher) SetUpdateCallback(callback func(string)) error {
w.lock.Lock()
defer w.lock.Unlock()
w.callback = callback
return nil
}
// Update calls the update callback of other instances to synchronize their policy.
// It is usually called after changing the policy in DB, like Enforcer.SavePolicy(),
// Enforcer.AddPolicy(), Enforcer.RemovePolicy(), etc.
func (w *Watcher) Update() error {
w.lock.Lock()
defer w.lock.Unlock()
resp, err := w.client.Put(context.TODO(), w.keyName, "")
if err == nil {
w.lastSentRev = resp.Header.GetRevision()
}
return err
}
// startWatch is a goroutine that watches the policy change.
func (w *Watcher) startWatch() error {
watcher := w.client.Watch(context.Background(), w.keyName)
for res := range watcher {
t := res.Events[0]
if t.IsCreate() || t.IsModify() {
w.lock.RLock()
//ignore self update
if rev := t.Kv.ModRevision; rev > w.lastSentRev && w.callback != nil {
w.callback(strconv.FormatInt(rev, 10))
}
w.lock.RUnlock()
}
}
return nil
}