add event handler class

[xavdid-stripe]

Why?

We've been designing a streamlined approach to handling incoming events that is easy to get right and hard to get wrong. This PR has the initial implementation of this new system.

NOTE: final names for classes / methods are still being gaveled, so don't worry about those for now. Weigh in on this doc if you have strong feelings there!

The only other pending item is to add a method to allow handling a webhook without verifying the signature. This is good for testing and for Event Bridge, which doesn't use the signature-based verification. Otherwise, this is ready for review.

What?

• add EventHandler class
• add event handler constructor on StripeClient
• add tests
• add method for changing the context of an existing client

Example usage

public class EventNotificationWebhookHandler {
  private static final String API_KEY = System.getenv("STRIPE_API_KEY");
  private static final String WEBHOOK_SECRET = System.getenv("WEBHOOK_SECRET");

  private static final StripeClient client = new StripeClient(API_KEY);
  private static final StripeEventRouter router =
      client.router(
          WEBHOOK_SECRET, EventNotificationWebhookHandler::handleUnhandledEventNotification);

  public static void main(String[] args) throws IOException {
    router.on_V1BillingMeterErrorReportTriggeredEventNotification(
        EventNotificationWebhookHandler::handleMeterErrors);

    HttpServer server = HttpServer.create(new InetSocketAddress(4242), 0);
    server.createContext("/webhook", new WebhookHandler());
    server.setExecutor(null);
    server.start();
  }

  private static void handleUnhandledEventNotification(
      EventNotification notif, StripeClient client, UnhandledNotificationDetails details) {
    System.out.println("Received unhandled event notification type: " + notif.getType());
  }

  private static void handleMeterErrors(
      V1BillingMeterErrorReportTriggeredEventNotification notif, StripeClient client) {
    Meter meter = notif.fetchRelatedObject();
    System.out.println("Handling meter error for meter: " + meter.getDisplayName());
  }

  static class WebhookHandler implements HttpHandler {
    @Override
    public void handle(HttpExchange exchange) throws IOException {
      if ("POST".equals(exchange.getRequestMethod())) {
        InputStream requestBody = exchange.getRequestBody();
        String webhookBody = new String(requestBody.readAllBytes(), StandardCharsets.UTF_8);
        String sigHeader = exchange.getRequestHeaders().getFirst("Stripe-Signature");

        try {
          router.handle(webhookBody, sigHeader);

          exchange.sendResponseHeaders(200, -1);
        } catch (StripeException e) {
          exchange.sendResponseHeaders(400, -1);
        }
      } else {
        exchange.sendResponseHeaders(405, -1);
      }
      exchange.close();
    }
  }
}

See Also

• DEVSDK-2822
• ⚠️ Add strongly typed EventNotifications #2036

[xavdid-stripe]

I don't love this and am all ears for a better suggestion!

[mbroshi-stripe]

Meh, not much you can do. Seems like the wrong abstractions were put in place (or they made the common Java mistake of creating an interface when there was only ever going to be a single implementation)

[mbroshi-stripe]

I didn't repeat all of my comments from the Go review, but they carry over (concurrency concerns and naming, mostly). Java-specific stuff looks good to me

[mbroshi-stripe]

Meh, not much you can do. Seems like the wrong abstractions were put in place (or they made the common Java mistake of creating an interface when there was only ever going to be a single implementation)

[mbroshi-stripe]

Similar concurrency concerns as in Go: You probably want to set this to volatile or use an AtomicBoolean