Send an event with delay using the CloudEvents SDK

The following document will teach you how to build a simple producer with a timer to delay an Event.

Operations

Prerequisites

To send events to Vanus, you must meet the following prerequisites:

1. Have a running Vanus cluster.
2. Have vsctl.
3. Have created an Eventbus named quick-start.
4. Have exported the environment variable by running this command: export VANUS_GATEWAY=127.0.0.1:8080.

We also provide an interactive Kubernetes environment to simply deploy and try Vanus in your browser.

Example code

package main

import (
    "context"
    "fmt"
    "os"
    "strings"
    "time"

    ce "github.com/cloudevents/sdk-go/v2"
    "github.com/google/uuid"
)

const (
    httpPrefix           = "http://"
    eventbus             = "quick-start"
    xceVanusDeliveryTime = "xvanusdeliverytime"
)

var (
    endpoint = os.Getenv("VANUS_GATEWAY")
)

func main() {
    // step 1: build a CloudEvents client
    client, err := ce.NewClientHTTP()
    if err != nil {
        panic(fmt.Sprintf("new cloudevents client failed, err: %s\n", err.Error()))
    }

    var target string
    if strings.HasPrefix(endpoint, httpPrefix) {
        target = fmt.Sprintf("%s/gateway/%s", endpoint, eventbus)
    } else {
        target = fmt.Sprintf("%s%s/gateway/%s", httpPrefix, endpoint, eventbus)
    }

    // step 2: specify the target
    ctx := ce.ContextWithTarget(context.Background(), target)
    // step 3: build a CloudEvent
    event := ce.NewEvent()
    event.SetID(uuid.NewString())
    event.SetSource("event-source")
    event.SetType("event-type")
    event.SetData(ce.ApplicationJSON, map[string]string{"hello": "world"})
    // set delivery time of delay event
    timeOfRFC3339Nano := time.Now().Add(10 * time.Second).Format(time.RFC3339Nano)
    event.SetExtension(xceVanusDeliveryTime, timeOfRFC3339Nano)

    // step 4: send the CloudEvent
    if result := client.Send(ctx, event); ce.IsUndelivered(result) {
        panic(fmt.Sprintf("failed to send event, err: %s\n", result.Error()))
    }
}

Expected results By running the following command after 10s, we can guarantee that The producer successfully sent the event to the Eventbus.

$ vsctl event get quick-start

Here is the expected result:

+-----+--------------------------------------------+
| NO. |                    EVENT                   |
+-----+--------------------------------------------+
|     | Context Attributes,                        |
|     |   specversion: 1.0                         |
|     |   type: event-type                         |
|     |   source: event-source                     |
|     |   id: 299c6cbd-b3c6-4de8-8486-ef0c13d60d9e |
|     |   time: 2022-09-20T12:42:36.992825162Z     |
|  0  |   datacontenttype: text/plain              |
|     | Extensions,                                |
|     |   xvanusdeliverytime: 2022-09-20T13:00:00Z |
|     |   xvanuseventbus: quick-start              |
|     |   xvanuslogoffset: AAAAAAAAAAA=            |
|     |   xvanusstime: 2022-09-20T12:42:36.994Z    |
|     | Data,                                      |
|     |   {                                        |
|     |     "hello": "world"                       |
|     |   }                                        |
|     |                                            |
+-----+--------------------------------------------+