**Watchers**

Watchers 在多个 enforcer 实例之间保持策略同步。当一个 enforcer 更新策略时，它会通知其他实例（通过 etcd、Redis 或 Kafka 等消息总线），它们会重新加载或更新内存中的策略。这使你可以在负载均衡器后面运行许多 enforcer，而不会出现权限过期的情况。

Watchers 在单独的包中实现，类似于适配器。下面的列表涵盖了受支持的后端。要添加新的后端，请开启一个 issue 或 PR。

Watcher	Type	Author	Description
PostgreSQL WatcherEx	Database	@IguteChung	WatcherEx for PostgreSQL
Redis WatcherEx	KV store	Casbin	WatcherEx for Redis
Redis Watcher	KV store	@billcobbler	Watcher for Redis
Etcd Watcher	KV store	Casbin	Watcher for etcd
TiKV Watcher	KV store	Casbin	Watcher for TiKV
Kafka Watcher	Messaging system	@wgarunap	Watcher for Apache Kafka
NATS Watcher	Messaging system	Soluto	Watcher for NATS
ZooKeeper Watcher	Messaging system	Grepsr	Watcher for Apache ZooKeeper
NATS, RabbitMQ, GCP Pub/Sub, AWS SNS & SQS, Kafka, InMemory	Messaging System	@rusenask	Watcher based on Go Cloud Dev Kit that works with leading cloud providers and self-hosted infrastructure
NATS, RabbitMQ, GCP Pub/Sub, AWS SNS & SQS, Kafka, InMemory	Messaging System	@bartventer	WatcherEx based on Go Cloud Dev Kit that works with leading cloud providers and self-hosted infrastructure
RocketMQ Watcher	Messaging system	@fmyxyz	Watcher for Apache RocketMQ

Watcher	Type	Author	Description
Etcd Adapter	KV store	@mapleafgo	Watcher for etcd
Redis Watcher	KV store	Casbin	Watcher for Redis
Redis WatcherEx	KV store	Casbin	WatcherEx for Redis
Lettuce-Based Redis Watcher	KV store	Casbin	Watcher for Redis based on Lettuce)
PostgreSQL Watcher	Database	Casbin	Watcher for PostgreSQL
Kafka Watcher	Messaging system	Casbin	Watcher for Apache Kafka
ZooKeeper Watcher	Messaging system	Casbin	Watcher for Apache ZooKeeper
RabbitMQ Watcher	Messaging system	Casbin	Watcher for RabbitMQ

Watcher	Type	Author	Description
Etcd Watcher	KV store	Casbin	Watcher for etcd
Redis Watcher	KV store	Casbin	Watcher for Redis
Pub/Sub Watcher	Messaging system	Casbin	Watcher for Google Cloud Pub/Sub
MongoDB Change Streams Watcher	Database	Casbin	Watcher for MongoDB Change Streams
Postgres Watcher	Database	@mcollina	Watcher for PostgreSQL

Watcher	Type	Author	Description
Etcd Watcher	KV store	Casbin	Watcher for etcd
Redis Watcher	KV store	Casbin	Watcher for Redis
Redis Watcher	KV store	ScienceLogic	Watcher for Redis
Redis Async Watcher	KV store	@kevinkelin	Watcher for Redis
PostgreSQL Watcher	Database	Casbin	Watcher for PostgreSQL
RabbitMQ Watcher	Messaging system	Casbin	Watcher for RabbitMQ
MongoDB Watcher	Database	@sanguinedab	Watcher for MongoDB

Watcher	Type	Author	Description
Redis Watcher	KV store	@Sbou	Watcher for Redis

Watcher	Type	Author	Description
Redis Watcher	KV store	CasbinRuby	Watcher for Redis
RabbitMQ Watcher	Messaging system	CasbinRuby	Watcher for RabbitMQ

Watcher	Type	Author	Description
Redis Watcher	KV store	@Tinywan	Watcher for Redis

Watcher	Type	Author	Description
Redis Watcher	KV store	Casbin	Watcher for Redis

WatcherEx

为了支持多个实例之间的增量同步，我们提供了 WatcherEx 接口。此接口可以在策略更改时通知其他实例，尽管目前尚无 WatcherEx 的实现。我们建议使用 dispatcher 来实现此功能。

与 Watcher 接口相比，WatcherEx 可以区分接收到的更新操作类型，例如 AddPolicy 与 RemovePolicy。

WatcherEx APIs:

API	描述
SetUpdateCallback(func(string)) error	SetUpdateCallback 配置 watcher 在数据库中的策略被其他实例更改时调用的回调函数。典型的回调是 Enforcer.LoadPolicy()。
Update() error	Update 调用其他实例的更新回调以同步它们的策略。通常在更改数据库中的策略后调用，例如在 Enforcer.SavePolicy()、Enforcer.AddPolicy()、Enforcer.RemovePolicy() 等之后。
Close()	Close 停止并释放 watcher。在此之后，回调函数将不再被调用。
UpdateForAddPolicy(sec, ptype string, params ...string) error	UpdateForAddPolicy 调用其他实例的更新回调以同步它们的策略。它在通过 Enforcer.AddPolicy()、Enforcer.AddNamedPolicy()、Enforcer.AddGroupingPolicy() 和 Enforcer.AddNamedGroupingPolicy() 添加策略后被调用。
UpdateForRemovePolicy(sec, ptype string, params ...string) error	UpdateForRemovePolicy 调用其他实例的更新回调以同步它们的策略。它在通过 Enforcer.RemovePolicy()、Enforcer.RemoveNamedPolicy()、Enforcer.RemoveGroupingPolicy() 和 Enforcer.RemoveNamedGroupingPolicy() 移除策略后被调用。
UpdateForRemoveFilteredPolicy(sec, ptype string, fieldIndex int, fieldValues ...string) error	UpdateForRemoveFilteredPolicy 调用其他实例的更新回调以同步它们的策略。它在 Enforcer.RemoveFilteredPolicy()、Enforcer.RemoveFilteredNamedPolicy()、Enforcer.RemoveFilteredGroupingPolicy() 和 Enforcer.RemoveFilteredNamedGroupingPolicy() 之后被调用。
UpdateForSavePolicy(model model.Model) error	UpdateForSavePolicy 调用其他实例的更新回调以同步它们的策略。它在 Enforcer.SavePolicy() 之后被调用。
UpdateForAddPolicies(sec string, ptype string, rules ...[]string) error	UpdateForAddPolicies 调用其他实例的更新回调以同步其策略。它在 Enforcer.AddPolicies()、Enforcer.AddNamedPolicies()、Enforcer.AddGroupingPolicies() 和 Enforcer.AddNamedGroupingPolicies() 之后被调用。
UpdateForRemovePolicies(sec string, ptype string, rules ...[]string) error	UpdateForRemovePolicies 调用其他实例的更新回调以同步其策略。它在 Enforcer.RemovePolicies()、Enforcer.RemoveNamedPolicies()、Enforcer.RemoveGroupingPolicies() 和 Enforcer.RemoveNamedGroupingPolicies() 之后被调用。