From 2bd1efe7f42ed7b61e2ba11d3316181f21041bfb Mon Sep 17 00:00:00 2001
From: Alexander Wong <alex@udia.ca>
Date: Sat, 30 Apr 2022 00:33:37 -0600
Subject: [PATCH] Allow configurable downgrade of ETag validator strength

---
 README.md                  |  8 ++++++++
 src/index.ts               | 12 ++++++++----
 src/test/getAssetFromKV.ts | 36 ++++++++++++++++++++++++++++++++++++
 src/types.ts               |  1 +
 4 files changed, 53 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index d5baa0a..99cee88 100644
--- a/README.md
+++ b/README.md
@@ -28,6 +28,7 @@ The Cloudflare Workers Discord server is an active place where Workers users get
       - [`bypassCache`](#bypasscache)
     - [`ASSET_NAMESPACE` (required for ES Modules)](#asset_namespace-required-for-es-modules)
     - [`ASSET_MANIFEST` (required for ES Modules)](#asset_manifest-required-for-es-modules)
+    - [`defaultETag`](#defaultetag-optional)
 
 * [Helper functions](#helper-functions)
   - [`mapRequestToAsset`](#maprequesttoasset-1)
@@ -282,6 +283,13 @@ type: string
 
 This is the default document that will be concatenated for requests ends in `'/'` or without a valid mime type like `'/about'` or `'/about.me'`. The default value is `'index.html'`.
 
+#### `defaultETag` (optional)
+
+type: `'strong' | 'weak'`
+
+This determines the format of the response [ETag header](https://developer.mozilla.org/docs/Web/HTTP/Headers/ETag). If the resource is in the cache, the ETag will always be weakened before being returned.
+The default value is `'strong'`.
+
 # Helper functions
 
 ## `mapRequestToAsset`
diff --git a/src/index.ts b/src/index.ts
index a39f143..17066dd 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -31,6 +31,7 @@ const getAssetFromKVDefaultOptions: Partial<Options> = {
   defaultMimeType: 'text/plain',
   defaultDocument: 'index.html',
   pathIsEncoded: false,
+  defaultETag: 'strong',
 }
 
 function assignOptions(options?: Partial<Options>): Options {
@@ -193,14 +194,17 @@ const getAssetFromKV = async (event: Evt, options?: Partial<Options>): Promise<R
   // is invalid, returns an empty string (instead of null) to prevent the
   // the potentially disastrous scenario where the value of the Etag resp
   // header is "null". Could be modified in future to base64 encode etc
-  const formatETag = (entityId: any = pathKey, validatorType: string = 'strong') => {
+  const formatETag = (entityId: any = pathKey, validatorType: string = options.defaultETag) => {
     if (!entityId) {
       return ''
     }
     switch (validatorType) {
       case 'weak':
         if (!entityId.startsWith('W/')) {
-          return `W/${entityId}`
+          if (entityId.startsWith(`"`) && entityId.endsWith(`"`)) {
+            return `W/${entityId}`
+          }
+          return `W/"${entityId}"`
         }
         return entityId
       case 'strong':
@@ -277,7 +281,7 @@ const getAssetFromKV = async (event: Evt, options?: Partial<Options>): Promise<R
       response.headers.set('Content-Length', String(body.byteLength))
       // set etag before cache insertion
       if (!response.headers.has('etag')) {
-        response.headers.set('etag', formatETag(pathKey, 'strong'))
+        response.headers.set('etag', formatETag(pathKey))
       }
       // determine Cloudflare cache behavior
       response.headers.set('Cache-Control', `max-age=${options.cacheControl.edgeTTL}`)
@@ -288,7 +292,7 @@ const getAssetFromKV = async (event: Evt, options?: Partial<Options>): Promise<R
   response.headers.set('Content-Type', mimeType)
 
   if (response.status === 304) {
-    let etag = formatETag(response.headers.get('etag'), 'strong')
+    let etag = formatETag(response.headers.get('etag'))
     let ifNoneMatch = cacheKey.headers.get('if-none-match')
     let proxyCacheStatus = response.headers.get('CF-Cache-Status')
     if (etag) {
diff --git a/src/test/getAssetFromKV.ts b/src/test/getAssetFromKV.ts
index 425d622..71f7d77 100644
--- a/src/test/getAssetFromKV.ts
+++ b/src/test/getAssetFromKV.ts
@@ -451,6 +451,42 @@ test('getAssetFromKV when resource in cache, etag should be weakened before retu
     t.fail('Response was undefined')
   }
 })
+test('getAssetFromKV should support weak etag override of resource', async (t) => {
+  mockRequestScope()
+  const resourceKey = 'key1.png'
+  const resourceVersion = JSON.parse(mockManifest())[resourceKey]
+  const req1 = new Request(`https://blah-weak.com/${resourceKey}`, {
+    headers: {
+      'if-none-match': `W/"${resourceVersion}"`,
+    },
+  })
+  const req2 = new Request(`https://blah-weak.com/${resourceKey}`, {
+    headers: {
+      'if-none-match': `"${resourceVersion}"`,
+    },
+  })
+  const req3 = new Request(`https://blah-weak.com/${resourceKey}`, {
+    headers: {
+      'if-none-match': `"${resourceVersion}-another-version"`,
+    },
+  })
+  const event1 = getEvent(req1)
+  const event2 = getEvent(req2)
+  const event3 = getEvent(req3)
+  const res1 = await getAssetFromKV(event1, { defaultETag: 'weak' })
+  const res2 = await getAssetFromKV(event2, { defaultETag: 'weak' })
+  const res3 = await getAssetFromKV(event3, { defaultETag: 'weak' })
+  if (res1 && res2 && res3) {
+    t.is(res1.headers.get('cf-cache-status'), 'MISS')
+    t.is(res1.headers.get('etag'), req1.headers.get('if-none-match'))
+    t.is(res2.headers.get('cf-cache-status'), 'REVALIDATED')
+    t.is(res2.headers.get('etag'), `W/${req2.headers.get('if-none-match')}`)
+    t.is(res3.headers.get('cf-cache-status'), 'MISS')
+    t.not(res3.headers.get('etag'), req2.headers.get('if-none-match'))
+  } else {
+    t.fail('Response was undefined')
+  }
+})
 
 test('getAssetFromKV if-none-match not sent but resource in cache, should return cache hit 200 OK', async (t) => {
   const resourceKey = 'cache.html'
diff --git a/src/types.ts b/src/types.ts
index c806076..db75991 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -14,6 +14,7 @@ export type Options = {
   defaultMimeType: string
   defaultDocument: string
   pathIsEncoded: boolean
+  defaultETag: 'strong' | 'weak'
 }
 
 export class KVError extends Error {