feat: Support async lambda event handlers (#161)

Author: bflorian

README.md

@@ -129,8 +129,8 @@ const smartapp = new SmartApp()
     .updated(() => { ... })
     .subscribedEventHandler( ... );
 
-exports.handler = (event, context, callback) => {
-    smartapp.handleLambdaCallback(event, context, callback);
+exports.handler = (event, context) => {
+    return smartapp.handleLambdaCallback(event, context);
 };
 ```
 There are also a few Glitch examples:

lib/smart-app.js

@@ -354,12 +354,22 @@ class SmartApp {
 	/**
 	 * Use with an AWS Lambda function. No signature verification is required.
 	 *
-	 * @param {*} event
-	 * @param {*} context
-	 * @param {*} callback
+	 * @param {*} event Lambda invocation event
+	 * @param {*} context Lambda execution context
+	 * @param {*} callback optional callback function
 	 */
-	handleLambdaCallback(event, context, callback) {
-		this._handleCallback(event, responders.lambdaResponse(callback, this._log))
+	async handleLambdaCallback(event, context, callback) {
+		if (callback) {
+			return this._handleCallback(event, responders.lambdaResponse(callback, this._log))
+		}
+
+		const responder = responders.mockResponder(this._log)
+		await this._handleCallback(event, responder)
+		if (responder.response.statusCode === 200) {
+			return context.succeed(responder.response)
+		}
+
+		return context.fail(responder.response)
 	}
 
 	/**