From cede9878917bbb78146b74094c131663e2517937 Mon Sep 17 00:00:00 2001
From: Daniel Lamando <dan@danopia.net>
Date: Mon, 23 Sep 2024 22:40:53 +0200
Subject: [PATCH] Add Deno platform cache to codegen service (#47)

* Add Deno platform cache to codegen service

* register cache differently?

* Another attempt at edge caching

* Redo platform cache fetch

* add debug event

* Hmm so we need to do cache versioning?

* Add tracing event for cache hit failure

* Ok, maybe need to x- the header

* Remove debug tracing event
---
 generation/deploy/cache-platform.ts | 65 +++++++++++++++++++++++++++++
 generation/deploy/cache.ts          | 14 ++++---
 2 files changed, 74 insertions(+), 5 deletions(-)
 create mode 100644 generation/deploy/cache-platform.ts

diff --git a/generation/deploy/cache-platform.ts b/generation/deploy/cache-platform.ts
new file mode 100644
index 0000000..be53f83
--- /dev/null
+++ b/generation/deploy/cache-platform.ts
@@ -0,0 +1,65 @@
+import { Cache } from "https://deno.land/x/httpcache@0.1.2/mod.ts";
+import { trace } from "./tracer.ts";
+
+// https://docs.deno.com/deploy/manual/edge-cache
+
+function transformUrl(url: string) {
+  return url.replace(/\/\/[^\/]+\//, '//upstream-cache-v2/');
+}
+
+export async function platformCache(
+  name = 'http-policy-cache',
+): Promise<Cache> {
+
+  const nativeCache = await caches.open(name);
+
+  return new Cache({
+
+    async get(url) {
+      const cached = await nativeCache.match(transformUrl(url));
+      if (!cached) return undefined;
+
+      type CachePolicy = Parameters<ConstructorParameters<typeof Cache>[0]['set']>[1]['policy'];
+
+      const {
+        'x-cache-policy': policyHeader,
+        ...resh
+      } = Object.fromEntries(cached.headers.entries());
+
+      if (!policyHeader) {
+        trace.getActiveSpan()?.addEvent('edgecache.fail', {
+          'message': 'platform cache hit lacked policy',
+        });
+        console.warn('WARN: platform cache lacked policy', cached);
+        return undefined;
+      }
+      const policy = {
+        ...JSON.parse(policyHeader),
+        resh,
+      } as CachePolicy;
+
+      const BodyBuffer = new Uint8Array(await cached.arrayBuffer());
+
+      return {
+        policy,
+        body: BodyBuffer,
+      };
+    },
+
+    async set(url, resp) {
+      const {resh, ...rest} = resp.policy;
+      await nativeCache.put(transformUrl(url), new Response(resp.body, {
+        headers: {
+          ...resh,
+          'x-cache-policy': JSON.stringify(rest),
+        },
+      }));
+    },
+
+    async delete(url) {
+      await nativeCache.delete(transformUrl(url));
+    },
+
+    close() {},
+  });
+}
diff --git a/generation/deploy/cache.ts b/generation/deploy/cache.ts
index 9479a81..4386cff 100644
--- a/generation/deploy/cache.ts
+++ b/generation/deploy/cache.ts
@@ -1,8 +1,12 @@
-import { inMemoryCache } from "https://deno.land/x/httpcache@0.1.2/in_memory.ts";
-import type { Cache } from "https://deno.land/x/httpcache@0.1.2/mod.ts";
-import { s3Cache } from "./cache-s3.ts";
 import { S3 } from "./s3-api.ts";
 import { ApiFactory } from "../../lib/client/mod.ts";
+import { AsyncTracer, Span } from "./tracer.ts";
+
+// can maybe replace this whole dep with deno edge cache once it's out of beta
+import type { Cache } from "https://deno.land/x/httpcache@0.1.2/mod.ts";
+import { inMemoryCache } from "https://deno.land/x/httpcache@0.1.2/in_memory.ts";
+import { s3Cache } from "./cache-s3.ts";
+import { platformCache } from "./cache-platform.ts";
 
 const s3Api = new ApiFactory({
   region: Deno.env.get('HTTPCACHE_S3_REGION') || 'us-east-2',
@@ -10,11 +14,11 @@ const s3Api = new ApiFactory({
 
 const caches: Array<Cache> = [
   inMemoryCache(40),
+  await platformCache(),
   s3Cache(s3Api, Deno.env.get('HTTPCACHE_S3_BUCKET') || 'deno-httpcache'),
 ];
-const cacheLabels = ['in-memory', 's3'];
+const cacheLabels = ['in-memory', 'platform', 's3'];
 
-import { AsyncTracer, Span } from "./tracer.ts";
 const tracer = new AsyncTracer('cached-fetch');
 
 export async function cachedFetch(mode: 'immutable' | 'mutable', label: string, url: string) {