Fix Cloudflare Workers usage re:Headers weirdness (#214)

Ensure the headers has a raw() method before calling it

Author: trevor-scheer

.changeset/smart-tools-occur.md

@@ -0,0 +1,7 @@
+---
+'@apollo/datasource-rest': patch
+---
+
+Fix bug in Cloudflare Worker usage where we try to call the `.raw()` method on its response headers object when it doesn't exist.
+
+For some reason, the Cloudflare Worker's global `fetch` `HeadersList` object is passing the instanceof check against `node-fetch`'s `Headers` class, but it doesn't have the `.raw()` method we expect on it. To be sure, we can just make sure it's there before we call it.

cspell-dict.txt

@@ -14,6 +14,7 @@ direnv
 Fakeable
 falsey
 httpcache
+instanceof
 isplainobject
 keyvaluecache
 overridable

src/HTTPCache.ts

@@ -295,7 +295,12 @@ function policyResponseFrom(response: FetcherResponse) {
   return {
     status: response.status,
     headers:
-      response.headers instanceof NodeFetchHeaders
+      response.headers instanceof NodeFetchHeaders &&
+      // https://github.com/apollo-server-integrations/apollo-server-integration-cloudflare-workers/issues/37
+      // For some reason, Cloudflare Workers' `response.headers` is passing
+      // the instanceof check here but doesn't have the `raw()` method that
+      // node-fetch's headers have.
+      'raw' in response.headers
         ? nodeFetchHeadersToCachePolicyHeaders(response.headers)
         : Object.fromEntries(response.headers),
   };