*/
package okhttp3.sse

import okhttp3.Response

abstract class EventSourceListener {
  /**
   * Invoked when an event source has been accepted by the remote peer and may begin transmitting
   * events.
   */
  open fun onOpen(
    eventSource: EventSource,
    response: Response,
  ) {
  }

  /**
   * TODO description.
   */
  open fun onEvent(
    eventSource: EventSource,
    id: String?,

```
https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

使用如下 JSON 请求体：

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

然后，您的 API 就会处理发票，并在某个点之后，发送回调请求至 `callback_url`（外部 API）：

```
https://www.external.org/events/invoices/2expen51ve
```

JSON 请求体包含如下内容：

```JSON
{

Sie definieren auch auf irgendeine Weise, zu welchen **Momenten** Ihre Anwendung diese Requests oder Events sendet.

Und **Ihre Benutzer** definieren auf irgendeine Weise (zum Beispiel irgendwo in einem Web-Dashboard) die **URL**, an die Ihre Anwendung diese Requests senden soll.

https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

mit einem JSON-Körper:

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

dann verarbeitet *Ihre API* die Rechnung und sendet irgendwann später einen Callback-Request an die `callback_url` (die *externe API*):

```
https://www.external.org/events/invoices/2expen51ve
```

	targetStats map[TargetID]targetStat
}

type targetStat struct {
	// The number of concurrent async Send calls per targets
	currentSendCalls int64
	// The number of total events per target
	totalEvents int64
	// The number of failed events per target
	failedEvents int64
}

func (list *TargetList) getStatsByTargetID(id TargetID) (stat targetStat) {
	list.statLock.RLock()
	defer list.statLock.RUnlock()

aws s3api restore-object --bucket srcbucket \
--key object \
--restore-request Days=3
```

### 4.1 Monitoring transition events

`s3:ObjectTransition:Complete` and `s3:ObjectTransition:Failed` events can be used to monitor transition events between the source cluster and transition tier. To watch lifecycle events, you can enable bucket notification on the source bucket with `mc event add`  and specify `--event ilm` flag.

	parsedQueue := queue{}
	if err := d.DecodeElement(&parsedQueue, &start); err != nil {
		return err
	}

	if len(parsedQueue.Events) == 0 {
		return errors.New("missing event name(s)")
	}

	eventStringSet := set.NewStringSet()
	for _, eventName := range parsedQueue.Events {
		if eventStringSet.Contains(eventName.String()) {
			return &ErrDuplicateEventName{eventName}
		}

   * EventListeners added by Interceptors will not see all events.
   */
  private val enforceOrder: Boolean = true,
) : ConnectionListener() {
  val eventSequence: Deque<ConnectionEvent> = ConcurrentLinkedDeque()

  private val forbiddenLocks = mutableSetOf<Any>()

  /** The timestamp of the last taken event, used to measure elapsed time between events. */
  private var lastTimestampNs: Long? = null

```
https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

⏮️ 🎻 💪:

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

⤴️ *👆 🛠️* 🔜 🛠️ 🧾, & ☝ ⏪, 📨 ⏲ 📨 `callback_url` ( *🔢 🛠️*):

```
https://www.external.org/events/invoices/2expen51ve
```

⏮️ 🎻 💪 ⚗ 🕳 💖:

```JSON
{

import okio.ForwardingSink
import okio.ForwardingSource
import okio.Sink
import okio.Source
import okio.buffer

/**
 * Transmits a single HTTP request and a response pair. This layers connection management and events
 * on [ExchangeCodec], which handles the actual I/O.
 */
class Exchange(
  internal val call: RealCall,
  internal val eventListener: EventListener,
  internal val finder: ExchangeFinder,