X-Opaque-Id support (#997)

* Added X-Opaque-Id support

* Updated type definitions

* Updated test

* Updated docs

lib/Transport.d.ts

@@ -38,6 +38,7 @@ interface TransportOptions {
   headers?: anyObject;
   generateRequestId?: generateRequestIdFn;
   name: string;
+  opaqueIdPrefix?: string;
 }
 
 export interface RequestEvent<T = any, C = any> {
@@ -90,6 +91,7 @@ export interface TransportRequestOptions {
   id?: any;
   context?: any;
   warnings?: [string];
+  opaqueId?: string;
 }
 
 export interface TransportRequestCallback {
@@ -121,6 +123,7 @@ export default class Transport {
   compression: 'gzip' | false;
   sniffInterval: number;
   sniffOnConnectionFault: boolean;
+  opaqueIdPrefix: string | null;
   sniffEndpoint: string;
   _sniffEnabled: boolean;
   _nextSniff: number;

lib/Transport.js

@@ -41,6 +41,7 @@ class Transport {
     this.sniffEndpoint = opts.sniffEndpoint
     this.generateRequestId = opts.generateRequestId || generateRequestId()
     this.name = opts.name
+    this.opaqueIdPrefix = opts.opaqueIdPrefix
 
     this.nodeFilter = opts.nodeFilter || defaultNodeFilter
     if (typeof opts.nodeSelector === 'function') {
@@ -114,6 +115,12 @@ class Transport {
       // TODO: make this assignment FAST
       const headers = Object.assign({}, this.headers, options.headers)
 
+      if (options.opaqueId !== undefined) {
+        headers['X-Opaque-Id'] = this.opaqueIdPrefix !== null
+          ? this.opaqueIdPrefix + options.opaqueId
+          : options.opaqueId
+      }
+
       // handle json body
       if (params.body != null) {
         if (shouldSerialize(params.body) === true) {