---
title: In-Memory
description: In-memory store backed by a Map - the test/reference adapter. Zero dependencies, isomorphic, and non-persistent. Ideal for unit tests; not for production.
---

## Installation

This adapter has no peer dependencies and no runtime requirements - it's pure JavaScript backed by a `Map`, so it runs unchanged in Node, Bun, Deno, the browser, and edge runtimes.

```package-install
files-sdk
```

## Usage

The in-memory adapter implements the same `Adapter` contract as every cloud adapter, but stores objects in a `Map` instead of touching disk or a network. That makes it the near-universal choice for testing code that uses `Files` without standing up real storage - and it doubles as the reference adapter, since it's the smallest complete implementation.

```ts lineNumbers
import { Files } from "files-sdk";
import { memory } from "files-sdk/memory";

// A fresh, empty store. Same Adapter contract as the cloud adapters,
// so you can swap it in for tests without changing any call sites.
const files = new Files({
  adapter: memory(),
});

await files.upload("hello.txt", "hi");
const file = await files.download("hello.txt");
await file.text(); // "hi"
```

### Seeding fixtures

Pass `initial` to pre-populate the store - handy when a test needs objects present up front. Each value is a body (a string or bytes) or an object that also pins `contentType` / `metadata` / `cacheControl`, the way an `upload()` call would.

```ts lineNumbers
import { memory } from "files-sdk/memory";

const adapter = memory({
  initial: {
    "users/1.json": '{"id":1}',
    "logo.png": pngBytes, // a Uint8Array
    "report.csv": {
      body: "a,b,c\n1,2,3",
      contentType: "text/csv",
      metadata: { owner: "alice" },
    },
  },
});
```

The constructor is synchronous, so seed values must convert to bytes without awaiting - that rules out `Blob`/`File` and `ReadableStream`. Seed those by calling `upload()` after construction.

## Options

<AutoTypeTable
  path="../../packages/files-sdk/src/memory/index.ts"
  name="MemoryAdapterOptions"
/>

## Inspecting the store

The `raw` escape hatch is the backing `Map`, so a test can read or reset it directly without going through the adapter:

```ts lineNumbers
const adapter = memory();
const files = new Files({ adapter });

await files.upload("a.txt", "x");
adapter.raw.size; // 1
adapter.raw.has("a.txt"); // true
adapter.raw.clear(); // wipe between tests
```

## Behavior notes

- **Non-persistent.** The store lives in the process. Everything is lost when the process exits, and two `Files` instances built from separate `memory()` calls don't share data. Not for production.
- **Value semantics.** Bodies are copied in on upload (and on seed), so mutating a `Uint8Array` you passed in later doesn't change the stored bytes.
- **Content ETag.** The `etag` is a stable hash of the bytes (a pure-JS polynomial rolling hash, no `node:crypto`), so re-uploading identical content yields the same ETag - matching how real backends behave.

## Compatibility

| Method            | Status | Notes                                                                                                                                                                                                                                                                                                                                                                                                    |
| ----------------- | :----: | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `upload`          |   ✅   | Pause/resume via `control` works in-process; a token cannot resume in a new instance (the store lives in process memory).                                                                                                                                                                                                                                                                                |
| `download`        |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `delete`          |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `list`            |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `search`          |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `head`            |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `exists`          |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `copy`            |   ✅   |                                                                                                                                                                                                                                                                                                                                                                                                          |
| `url`             |   ⚠️   | Returns an opaque, non-fetchable `memory://{key}` URL - there's no server backing the store. Throws `NotFound` for a missing key (the way a real fetch would 404). `expiresIn` and `responseContentDisposition` round-trip as query params so URL-building call sites stay testable, but nothing resolves the URL. For working dev URLs use the `fs` adapter with `urlBaseUrl`, or a real cloud adapter. |
| `signedUploadUrl` |   ⚠️   | Returns an inert `memory://{key}` placeholder PUT target - there's no real upload endpoint, so a client can't actually PUT to it. `expiresIn` round-trips into the URL and `contentType` into the returned headers so the signing flow stays testable; `maxSize` and `minSize` are ignored. Use `upload()` to write bytes.                                                                               |