From dae57d260479d867fd197b33ed9ebc4989e44de0 Mon Sep 17 00:00:00 2001
From: Randall Schmidt <randallschmidt1@gmail.com>
Date: Mon, 5 Jul 2021 22:00:12 -0400
Subject: [PATCH] make cache get used even if you make a bunch of identical
 requests immediately

---
 classes/response.js |  4 ++++
 index.js            | 43 +++++++++++++++++++++++++++----------------
 package-lock.json   |  5 +++++
 package.json        |  1 +
 test/tests.js       | 11 +++++++++++
 5 files changed, 48 insertions(+), 16 deletions(-)

diff --git a/classes/response.js b/classes/response.js
index a6c9341..04ed248 100644
--- a/classes/response.js
+++ b/classes/response.js
@@ -33,6 +33,10 @@ export class NFCResponse extends Response {
   }
 
   static fromCachedResponse(bodyStream, rawMetaData, ejectSelfFromCache) {
+    if (bodyStream.readableEnded) {
+      throw new Error('Cache returned a body stream that has already been read to end.');
+    }
+
     return new NFCResponse(bodyStream, rawMetaData, ejectSelfFromCache, true);
   }
 
diff --git a/index.js b/index.js
index f21f4fb..36020b7 100644
--- a/index.js
+++ b/index.js
@@ -2,6 +2,7 @@ import fetch from 'node-fetch';
 import fs from 'fs';
 import { URLSearchParams } from 'url';
 import crypto from 'crypto';
+import locko from 'locko';
 import { NFCResponse } from './classes/response.js';
 import { MemoryCache } from './classes/caching/memory_cache.js';
 
@@ -73,15 +74,11 @@ function getCacheKey(requestArguments) {
 
 async function getResponse(cache, requestArguments) {
   const cacheKey = getCacheKey(requestArguments);
-  const cachedValue = await cache.get(cacheKey);
+  let cachedValue = await cache.get(cacheKey);
 
   const ejectSelfFromCache = () => cache.remove(cacheKey);
 
   if (cachedValue) {
-    if (cachedValue.bodyStream.readableEnded) {
-      throw new Error('Cache returned a body stream that has already been read to end.');
-    }
-
     return NFCResponse.fromCachedResponse(
       cachedValue.bodyStream,
       cachedValue.metaData,
@@ -89,19 +86,33 @@ async function getResponse(cache, requestArguments) {
     );
   }
 
-  const fetchResponse = await fetch(...requestArguments);
-  const nfcResponse = NFCResponse.fromNodeFetchResponse(fetchResponse, ejectSelfFromCache);
-  const contentLength = Number.parseInt(nfcResponse.headers.get('content-length'), 10) || 0;
-  const nfcResponseSerialized = nfcResponse.serialize();
+  await locko.lock(cacheKey);
+  try {
+    cachedValue = await cache.get(cacheKey);
+    if (cachedValue) {
+      return NFCResponse.fromCachedResponse(
+        cachedValue.bodyStream,
+        cachedValue.metaData,
+        ejectSelfFromCache,
+      );
+    }
 
-  await cache.set(
-    cacheKey,
-    nfcResponseSerialized.bodyStream,
-    nfcResponseSerialized.metaData,
-    contentLength,
-  );
+    const fetchResponse = await fetch(...requestArguments);
+    const nfcResponse = NFCResponse.fromNodeFetchResponse(fetchResponse, ejectSelfFromCache);
+    const contentLength = Number.parseInt(nfcResponse.headers.get('content-length'), 10) || 0;
+    const nfcResponseSerialized = nfcResponse.serialize();
 
-  return nfcResponse;
+    await cache.set(
+      cacheKey,
+      nfcResponseSerialized.bodyStream,
+      nfcResponseSerialized.metaData,
+      contentLength,
+    );
+
+    return nfcResponse;
+  } finally {
+    locko.unlock(cacheKey);
+  }
 }
 
 function createFetchWithCache(cache) {
diff --git a/package-lock.json b/package-lock.json
index bdc246b..685ff4f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2323,6 +2323,11 @@
         "path-exists": "^3.0.0"
       }
     },
+    "locko": {
+      "version": "0.0.3",
+      "resolved": "https://registry.npmjs.org/locko/-/locko-0.0.3.tgz",
+      "integrity": "sha512-ekhPWcejAum9WHN2ClkFA8RAUTDyYDlRRb4dSq1wCEPhIS6IMsdSKoWHl1qineCrlMEMbeD1/o2uautG4QEc7w=="
+    },
     "lodash": {
       "version": "4.17.21",
       "resolved": "https://registry.npmjs.org/lodash/-/lodash-4.17.21.tgz",
diff --git a/package.json b/package.json
index 75ccc91..e679712 100644
--- a/package.json
+++ b/package.json
@@ -39,6 +39,7 @@
   },
   "dependencies": {
     "cacache": "^15.2.0",
+    "locko": "0.0.3",
     "node-fetch": "2.6.1"
   },
   "husky": {
diff --git a/test/tests.js b/test/tests.js
index e39bd36..dc5d16a 100644
--- a/test/tests.js
+++ b/test/tests.js
@@ -404,6 +404,16 @@ describe('Data tests', function() {
       assert(err.message.includes('Unsupported body type'));
     }
   });
+
+  it('Uses cache even if you make multiple requests at the same time', async function() {
+    const [res1, res2] = await Promise.all([
+      cachedFetch('http://httpbin.org/status/200'),
+      cachedFetch('http://httpbin.org/status/200'),
+    ]);
+
+    // One should be false, the other should be true
+    assert(res1.fromCache !== res2.fromCache);
+  });
 }).timeout(10000);
 
 describe('Memory cache tests', function() {
@@ -466,3 +476,4 @@ describe('File system cache tests', function() {
     assert.strictEqual(res.fromCache, true);
   });
 });
+console.log(process.cwd())
\ No newline at end of file