Handle headers as request option

lib/Transport.d.ts

@@ -38,11 +38,16 @@ export interface SniffMeta {
   reason: string;
 }
 
+declare type anyObject = {
+  [key: string]: any;
+};
+
 export interface RequestOptions {
   ignore?: number | number[];
   requestTimeout?: number | string;
   maxRetries?: number;
   asStream?: boolean;
+  headers?: anyObject;
 }
 
 export default class Transport {

lib/Transport.js

@@ -74,7 +74,7 @@ class Transport {
         return callback(new NoLivingConnectionsError('There are not living connections'), result)
       }
 
-      params.headers = params.headers || {}
+      const headers = options.headers || {}
       // handle json body
       if (params.body != null) {
         if (shouldSerialize(params.body) === true) {
@@ -84,9 +84,9 @@ class Transport {
             return callback(err, result)
           }
         }
-        params.headers['Content-Type'] = 'application/json'
+        headers['Content-Type'] = 'application/json'
         if (isStream(params.body) === false) {
-          params.headers['Content-Length'] = '' + Buffer.byteLength(params.body)
+          headers['Content-Length'] = '' + Buffer.byteLength(params.body)
         }
       // handle ndjson body
       } else if (params.bulkBody != null) {
@@ -99,16 +99,17 @@ class Transport {
         } else {
           params.body = params.bulkBody
         }
-        params.headers['Content-Type'] = 'application/x-ndjson'
+        headers['Content-Type'] = 'application/x-ndjson'
         if (isStream(params.body) === false) {
-          params.headers['Content-Length'] = '' + Buffer.byteLength(params.body)
+          headers['Content-Length'] = '' + Buffer.byteLength(params.body)
         }
       }
 
       if (this.suggestCompression === true) {
-        params.headers['Accept-Encoding'] = 'gzip,deflate'
+        headers['Accept-Encoding'] = 'gzip,deflate'
       }
 
+      params.headers = headers
       // serializes the querystring
       params.querystring = this.serializer.qserialize(params.querystring)
       // handles request timeout