Have promiseCallback make callbacks and promises behave the same

lib/utilities.js

@@ -50,10 +50,19 @@ const errorFunc = (resolve, reject) => isFunc(reject) ? reject : resolve;
 
 /**
  * Return a callback function for promise resole/reject args.
+ * Ensures that callback is called only once.
  * @returns {Function}
  */
 const promiseCallback = (resolve, reject) => {
-  return err => err ? errorFunc(resolve, reject)(err) : resolve();
+  let hasFired = false;
+  return (err) => {
+    if (hasFired) {
+      return;
+    }
+
+    hasFired = true;
+    return err ? errorFunc(resolve, reject)(err) : resolve();
+  };
 };
 
 /**
@@ -177,8 +186,9 @@ const saveBufferToFile = (buffer, filePath, callback) => {
   };
   // Setup file system writable stream.
   let fstream = fs.createWriteStream(filePath);
-  fstream.on('error', err => callback(err));
-  fstream.on('close', () => callback());
+  console.log("Calling saveBuffer");
+  fstream.on('error', err => (console.log("err cb"), callback(err)));
+  fstream.on('close', () => (console.log("close cb"), callback()));
   // Copy file via piping streams.
   readStream.pipe(fstream);
 };