chore: es6 unmarshaller (cloudevents#108)

* chore: es6 unmarshaller
Signed-off-by: Grant Timmerman <timmerman+devrel@google.com>

Author: grant

lib/bindings/http/unmarshaller.js

@@ -4,22 +4,14 @@ const Commons = require("./commons.js");
 const STRUCTURED = "structured";
 const BINARY = "binary";
 
-const allowedBinaryContentTypes = [];
-allowedBinaryContentTypes.push(Constants.MIME_JSON);
-allowedBinaryContentTypes.push(Constants.MIME_OCTET_STREAM);
+const allowedBinaryContentTypes = [
+  Constants.MIME_JSON,
+  Constants.MIME_OCTET_STREAM
+];
 
-const allowedStructuredContentTypes = [];
-allowedStructuredContentTypes.push(Constants.MIME_CE_JSON);
-
-function validateArgs(payload, headers) {
-  if (!payload) {
-    throw new TypeError("payload is null or undefined");
-  }
-
-  if (!headers) {
-    throw new TypeError("headers is null or undefined");
-  }
-}
+const allowedStructuredContentTypes = [
+  Constants.MIME_CE_JSON
+];
 
 // Is it binary or structured?
 function resolveBindingName(payload, headers) {
@@ -47,18 +39,22 @@ function resolveBindingName(payload, headers) {
   }
 }
 
-const Unmarshaller = function(receiverByBinding) {
-  this.receiverByBinding = receiverByBinding;
-};
-
-Unmarshaller.prototype.unmarshall = function(payload, headers) {
-  return new Promise((resolve, reject) => {
-    try {
-      validateArgs(payload, headers);
+class Unmarshaller {
+  constructor(receiverByBinding) {
+    this.receiverByBinding = receiverByBinding;
+  }
 
-      const sanityHeaders = Commons.sanityAndClone(headers);
+  unmarshall(payload, headers) {
+    return new Promise((resolve, reject) => {
+      if (!payload) {
+        return reject(new TypeError("payload is null or undefined"));
+      }
+      if (!headers) {
+        return reject(new TypeError("headers is null or undefined"));
+      }
 
       // Validation level 1
+      const sanityHeaders = Commons.sanityAndClone(headers);
       if (!sanityHeaders[Constants.HEADER_CONTENT_TYPE]) {
         throw new TypeError("content-type header not found");
       }
@@ -69,10 +65,8 @@ Unmarshaller.prototype.unmarshall = function(payload, headers) {
         .parse(payload, sanityHeaders);
 
       resolve(cloudevent);
-    } catch (e) {
-      reject(e);
-    }
-  });
-};
+    });
+  }
+}
 
 module.exports = Unmarshaller;