From de833ebcef66d8846ac1e121327243735f740aa1 Mon Sep 17 00:00:00 2001
From: Katja Lutz <mail@katjalutz.ch>
Date: Sun, 31 Dec 2023 17:02:43 +0100
Subject: [PATCH] feat: implement getServerFunctionMeta

Refs: nksaraf/vinxi#51
---
 docs/routes/api/server.md                   | 23 +++++++++++++++++++++
 packages/start/config/server-fns-runtime.ts |  3 +++
 packages/start/server/index.ts              |  2 +-
 packages/start/server/serverFunction.tsx    |  6 ++++++
 packages/start/server/types.ts              |  4 ++++
 5 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 packages/start/server/serverFunction.tsx

diff --git a/docs/routes/api/server.md b/docs/routes/api/server.md
index 4d1faf751..7b90a6cf7 100644
--- a/docs/routes/api/server.md
+++ b/docs/routes/api/server.md
@@ -44,3 +44,26 @@ In this example, regardless of whether we are rendering this on the server or in
 ### Serialization
 
 Server functions allow the serialization of many different data types in the response. The full list is available [here](https://github.com/lxsmnsyc/seroval/blob/main/docs/compatibility.md#supported-types).
+
+### Meta information
+
+Depending on your hosting, the server function might be running in parallel on multiple cpu cores or workers. You can use `getServerFunctionMeta` to retrieve a function-specific `id`, which is stable across all instances. 
+
+Keep in mind: this `id` can and will change between builds!
+
+```tsx twoslash
+import { getServerFunctionMeta } from "@solidjs/start/server";
+
+// or some in-memory db
+const appCache: any = globalThis;
+
+const counter = async () => {
+  "use server";
+  const { id } = getServerFunctionMeta()!;
+  const key = `counter_${id}`;
+  appCache[key] = appCache[key] ?? 0;
+  appCache[key]++;
+
+  return appCache[key] as number;
+};
+```
diff --git a/packages/start/config/server-fns-runtime.ts b/packages/start/config/server-fns-runtime.ts
index 55ad077e6..b21347c31 100644
--- a/packages/start/config/server-fns-runtime.ts
+++ b/packages/start/config/server-fns-runtime.ts
@@ -16,6 +16,9 @@ export function createServerReference(fn: Function, id: string, name: string) {
       const ogEvt = getRequestEvent();
       if (!ogEvt) throw new Error("Cannot call server function outside of a request");
       const evt = cloneEvent(ogEvt);
+      evt.locals.serverFunctionMeta = {
+        id: id + "#" + name,
+      };
       evt.serverOnly = true;
       return provideRequestEvent(evt, () => {
         return fn.apply(thisArg, args);
diff --git a/packages/start/server/index.ts b/packages/start/server/index.ts
index c34c8b4cb..25b8f3859 100644
--- a/packages/start/server/index.ts
+++ b/packages/start/server/index.ts
@@ -1,4 +1,4 @@
 export { StartServer } from "./StartServer";
 export { createHandler } from "./handler";
+export { getServerFunctionMeta } from "./serverFunction";
 export * from "./types";
-
diff --git a/packages/start/server/serverFunction.tsx b/packages/start/server/serverFunction.tsx
new file mode 100644
index 000000000..26ac8b539
--- /dev/null
+++ b/packages/start/server/serverFunction.tsx
@@ -0,0 +1,6 @@
+import { getRequestEvent } from "solid-js/web";
+import type { ServerFunctionMeta } from "./types";
+
+export function getServerFunctionMeta(): ServerFunctionMeta | undefined {
+  return getRequestEvent()?.locals.serverFunctionMeta;
+}
diff --git a/packages/start/server/types.ts b/packages/start/server/types.ts
index bbadc370f..a6bc5c4fc 100644
--- a/packages/start/server/types.ts
+++ b/packages/start/server/types.ts
@@ -71,6 +71,10 @@ export interface APIHandler {
   (event: APIEvent): Promise<any>;
 }
 
+export interface ServerFunctionMeta {
+  id: string;
+}
+
 declare module "solid-js/web" {
   interface RequestEvent extends FetchEvent {
     serverOnly?: boolean;