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NATS_13:NATS Streaming案例讲解
启动服务
首先启动 go-nats-streaming 服务。为了更加能说明问题,我们启动的时候不使用默认端口号
$ nats-streaming-server -p 4242 -m 8222 -DV
编写一个简单的应用
package main import ( "log" "github.com/nats-io/go-nats-streaming" ) func main() { //stan.Connect(clusterID, clientID, ops ...Option) ns, _ := stan.Connect("test-cluster", "myID", stan.NatsURL("nats://localhost:4242")) // Simple Synchronous Publisher // does not return until an ack has been received from NATS Streaming ns.Publish("foo", []byte("Hello World")) // Simple Async Subscriber sub, _ := ns.Subscribe("foo", func(m *stan.Msg) { log.Printf("Received a message: %s\n", string(m.Data)) }, stan.StartWithLastReceived()) log.Printf("subscribing to subject ‘foo‘ \n") // Unsubscribe sub.Unsubscribe() // Close connection ns.Close() }
上面的代码使用了订阅者启动参数的 StartWithLastReceived,这个函数的含义为:读取刚才发布者最近发布的消息内容。具体还有哪些启动参数,以下列出详情:
// Subscribe starting with most recently published value sub, err := sc.Subscribe("foo", func(m *stan.Msg) { fmt.Printf("Received a message: %s\n", string(m.Data)) }, StartWithLastReceived()) // Receive all stored values in order sub, err := sc.Subscribe("foo", func(m *stan.Msg) { fmt.Printf("Received a message: %s\n", string(m.Data)) }, DeliverAllAvailable()) // Receive messages starting at a specific sequence number sub, err := sc.Subscribe("foo", func(m *stan.Msg) { fmt.Printf("Received a message: %s\n", string(m.Data)) }, StartAtSequence(22)) // Subscribe starting at a specific time var startTime time.Time ... sub, err := sc.Subscribe("foo", func(m *stan.Msg) { fmt.Printf("Received a message: %s\n", string(m.Data)) }, StartAtTime(startTime)) // Subscribe starting a specific amount of time in the past (e.g. 30 seconds ago) sub, err := sc.Subscribe("foo", func(m *stan.Msg) { fmt.Printf("Received a message: %s\n", string(m.Data)) }, StartAtTimeDelta(time.Duration(30)))
NATS_13:NATS Streaming案例讲解
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