ResponseValidator & ReconnectNotify

[hermanbanken]

Given the code

// in a goroutine:
for {
	err := client.SubscribeRawWithContext(ctx, func(msg *sse.Event) {
		logger.Printf("SSE Message ID=%q Retry=%q Event=%q len(Data)=%d\n", string(msg.ID), string(msg.Retry), string(msg.Event), len(msg.Data))
	})
	if err != nil {
		logger.Println("SubscribeRawWithContext stopped:", err)
	} else {
		logger.Println("SubscribeRawWithContext done; retrying")
		time.Sleep(1 * time.Second)
	}
}

the SubscribeRawWithContext method would be called every 1 second if the HTTP request returns a StatusCode other than 200 without a stream result. This happens because the EventStreamReader.startReadLoop will convert io.EOF into a non-error. This gives the users of the SSE lib no context as to why the SubscribeRawWithContext is called every single second (and without the Sleep even continuously).

I made 2 adjustments:

• use RetryNotify of the backoff library, to enable possibly getting feedback when a retry happens
• add a ResponseValidator callback that can return an error based on an invalid HTTP response (like not text/event-stream or not 200 OK)

Users can do:

client.ResponseValidator = func(c *sse.Client, resp *http.Response) error {
	if resp.Header.Get("Content-Type") != "text/event-stream" || resp.StatusCode != 200 {
		return fmt.Errorf("Invalid StatusCode %d: %s", resp.StatusCode, resp.Status)
	}
	return nil
}

and

client.ReconnectNotify = func(err error, backoff time.Duration) {
	logger.Println("Reconnect", err, backoff)
}

Without a ResponseValidator this is fully backwards compatible.

[purehyperbole]

Awesome, thanks for submitting these changes. I'll merge now and cut a release!

[hermanbanken]

Wow that was fast. Thanks! 😄