From e5bc7863627ebdae5e639d88bd50e686377456c3 Mon Sep 17 00:00:00 2001
From: Erika Tharp <eem@momentohq.com>
Date: Tue, 5 Apr 2022 09:47:17 -0700
Subject: [PATCH] chore: Create new `Header` class (#66)

---
 src/Momento.ts                 | 12 +++-------
 src/MomentoCache.ts            | 17 ++++----------
 src/grpc/HeadersInterceptor.ts | 43 +++++++++++++++++++++-------------
 3 files changed, 34 insertions(+), 38 deletions(-)

diff --git a/src/Momento.ts b/src/Momento.ts
index 97e9328cc..4dba30756 100644
--- a/src/Momento.ts
+++ b/src/Momento.ts
@@ -1,5 +1,5 @@
 import {control} from '@gomomento/generated-types';
-import {HeaderInterceptor} from './grpc/HeadersInterceptor';
+import {Header, HeaderInterceptor} from './grpc/HeadersInterceptor';
 import {ClientTimeoutInterceptor} from './grpc/ClientTimeoutInterceptor';
 import {
   InvalidArgumentError,
@@ -29,14 +29,8 @@ export class Momento {
    */
   constructor(props: MomentoProps) {
     const headers = [
-      {
-        name: 'Authorization',
-        value: props.authToken,
-      },
-      {
-        name: 'Agent',
-        value: `javascript:${version}`,
-      },
+      new Header('Authorization', props.authToken),
+      new Header('Agent', `javascript:${version}`),
     ];
     this.interceptors = [
       new HeaderInterceptor(headers).addHeadersInterceptor(),
diff --git a/src/MomentoCache.ts b/src/MomentoCache.ts
index 62aecdf60..c1e20f2b0 100644
--- a/src/MomentoCache.ts
+++ b/src/MomentoCache.ts
@@ -1,7 +1,7 @@
 import {cache} from '@gomomento/generated-types';
 // older versions of node don't have the global util variables https://github.com/nodejs/node/issues/20365
 import {TextEncoder} from 'util';
-import {HeaderInterceptor} from './grpc/HeadersInterceptor';
+import {Header, HeaderInterceptor} from './grpc/HeadersInterceptor';
 import {ClientTimeoutInterceptor} from './grpc/ClientTimeoutInterceptor';
 import {CacheGetStatus, momentoResultConverter} from './messages/Result';
 import {InvalidArgumentError, UnknownServiceError} from './Errors';
@@ -166,18 +166,9 @@ export class MomentoCache {
 
   private getInterceptors(cacheName: string): Interceptor[] {
     const headers = [
-      {
-        name: 'Authorization',
-        value: this.authToken,
-      },
-      {
-        name: 'cache',
-        value: cacheName,
-      },
-      {
-        name: 'Agent',
-        value: `javascript:${version}`,
-      },
+      new Header('Authorization', this.authToken),
+      new Header('cache', cacheName),
+      new Header('Agent', `javascript:${version}`),
     ];
     return [
       new HeaderInterceptor(headers).addHeadersInterceptor(),
diff --git a/src/grpc/HeadersInterceptor.ts b/src/grpc/HeadersInterceptor.ts
index 8ba1a4d00..b5cd20398 100644
--- a/src/grpc/HeadersInterceptor.ts
+++ b/src/grpc/HeadersInterceptor.ts
@@ -1,35 +1,46 @@
 import {InterceptingCall, Interceptor} from '@grpc/grpc-js';
 
-interface Header {
-  name: string;
-  value: string;
+export class Header {
+  public readonly onceOnlyHeaders: string[] = ['Agent'];
+  public readonly name: string;
+  public readonly value: string;
+
+  /**
+   * @param {string} name
+   * @param {string} value
+   */
+  constructor(name: string, value: string) {
+    this.name = name;
+    this.value = value;
+  }
 }
 
 export class HeaderInterceptor {
-  private readonly headers: Header[];
-  private static isUserAgentSent = false;
+  private readonly headersToAddEveryTime: Header[];
+  private readonly headersToAddOnce: Header[];
+  private static areOnlyOnceHeadersSent = false;
 
   /**
    * @param {Header[]} headers
    */
   constructor(headers: Header[]) {
-    this.headers = headers;
+    this.headersToAddOnce = headers.filter(header =>
+      header.onceOnlyHeaders.includes(header.name)
+    );
+    this.headersToAddEveryTime = headers.filter(
+      header => !header.onceOnlyHeaders.includes(header.name)
+    );
   }
 
   public addHeadersInterceptor(): Interceptor {
     return (options, nextCall) => {
       return new InterceptingCall(nextCall(options), {
         start: (metadata, listener, next) => {
-          if (!HeaderInterceptor.isUserAgentSent) {
-            this.headers.forEach(h => metadata.add(h.name, h.value));
-            HeaderInterceptor.isUserAgentSent = true;
-          } else {
-            // Only add Authorization/cache metadata
-            this.headers.forEach(h => {
-              if (h.name !== 'Agent') {
-                metadata.add(h.name, h.value);
-              }
-            });
+          this.headersToAddEveryTime.forEach(h =>
+            metadata.add(h.name, h.value)
+          );
+          if (!HeaderInterceptor.areOnlyOnceHeadersSent) {
+            this.headersToAddOnce.forEach(h => metadata.add(h.name, h.value));
           }
           next(metadata, {});
         },