chore: added ephemeral storage guide (supabase#30791)

* chore: added ephemeral storage guide

* add use cases section

* remove word

* Apply suggestions from code review

Co-authored-by: Charis <[email protected]>

* prettier

---------

Co-authored-by: Charis <[email protected]>

Author: laktek

apps/docs/components/Navigation/NavigationMenu/NavigationMenu.constants.ts

@@ -1272,6 +1272,10 @@ export const functions: NavMenuConstant = {
           name: 'Background Tasks',
           url: '/guides/functions/background-tasks',
         },
+        {
+          name: 'Ephemeral Storage',
+          url: '/guides/functions/ephemeral-storage',
+        },
         {
           name: 'Running AI Models',
           url: '/guides/functions/ai-models',

apps/docs/content/guides/functions/ephemeral-storage.mdx

@@ -0,0 +1,54 @@
+---
+id: 'function-ephemeral-storage'
+title: 'Ephemeral Storage'
+description: 'Read and write from temporary directory'
+subtitle: 'Read and write from temporary directory'
+---
+
+Edge Functions provides ephemeral file storage. You can read and write files to the `/tmp` directory.
+
+Ephemeral storage will reset on each function invocation. This means the files you write during an invocation can only be read within the same invocation.
+
+### Use cases
+
+Here are some use cases where ephemeral storage can be useful:
+
+- Unzip an archive of CSVs and then add them as records to the DB
+- Custom image manipulation workflows (using [MagickWasm](https://supabase.com/docs/guides/functions/examples/image-manipulation))
+
+You can use [Background Tasks](https://supabase.com/docs/guides/functions/background-tasks) to handle slow file processing outside of a request.
+
+### How to use
+
+You can use [Deno File System APIs](https://docs.deno.com/api/deno/file-system) or the [`node:fs` module](https://docs.deno.com/api/node/fs/) to access the `/tmp` path.
+
+### Example
+
+Here is an example of how to write a user-uploaded zip file into a temporary file for further processing.
+
+```js
+Deno.serve(async (req) => {
+  if (req.headers.get('content-type') !== 'application/zip') {
+    return new Response('file must be a zip file', {
+      status: 400,
+    })
+  }
+
+  const uploadId = crypto.randomUUID()
+  await Deno.writeFile('/tmp/' + uploadId, req.body)
+
+  // do something with the written zip file
+
+  return new Response('ok')
+})
+```
+
+### Unavailable APIs
+
+Currently, the synchronous APIs (eg: `Deno.writeFileSync` or `Deno.mkdirSync`) for creating or writing files are not supported.
+
+You can use sync variations of read APIs (eg: `Deno.readFileSync`).
+
+### Limits
+
+In the hosted platform, a free project can write up to 256MB of data to ephemeral storage. A paid project can write up to 512MB.