# extension-object-storage

This skill adds file storage to your project: content lives off-chain while the backend keeps only references. Useful for image galleries, video and documents.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 28100 installs · ★ 2
- Author: caffeinelabs
- License: Apache-2.0 · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/caffeinelabs/skills/tree/HEAD/skills/extension-object-storage/SKILL.md
- Updated: 2026-10-22
- HTML: https://affpapa.org/en/nevibecode/skills/extension-object-storage

## What it does

The skill wires up off-chain object storage with on-chain references. The `MixinObjectStorage` mixin provides the file infrastructure, and you track uploaded files in your own data structures using `Storage.ExternalBlob`. Large files go past the IC limit, and access happens over an HTTP URL that the browser caches.

Setup has four steps, and every one is mandatory. Add `caffeineai-object-storage` to `mops.toml`, call `include MixinObjectStorage()` in `main.mo`, give every file field the `Storage.ExternalBlob` type instead of `Text`, and install the `@caffeineai/object-storage` npm package on the frontend with `ExternalBlob.fromBytes(bytes, file.type, file.name)` at the call site. Skip any step and uploads fail with `403 Forbidden: Invalid payload`.

One thing to watch on the frontend: the npm package does not work without the backend mops package. Installing only the npm side leads to silent upload failures, because the storage gateway answers 403. The mixin import path is always `"mo:caffeineai-object-storage/Mixin"` — relative paths like `"mixins/object-storage-api"` are wrong. Do not write your own `_immutableObjectStorage*` methods either: they carry a platform signature, and a hand-written version breaks gateway validation.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add caffeinelabs/skills --skill extension-object-storage -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/extension-object-storage/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/extension-object-storage/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add caffeinelabs/skills --skill extension-object-storage -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/extension-object-storage/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add caffeinelabs/skills --skill extension-object-storage -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/extension-object-storage/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install caffeinelabs/skills extension-object-storage
```

2. **Manually: put the files in place**
- File: `.github/skills/extension-object-storage/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add caffeinelabs/skills --skill extension-object-storage -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/caffeinelabs/skills --path skills/extension-object-storage
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/extension-object-storage/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add caffeinelabs/skills --skill extension-object-storage -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/caffeinelabs/skills/tree/HEAD/skills/extension-object-storage/SKILL.md

## When to use it
- keep images and video off-chain while the backend stores only references
- build a file gallery with upload progress
- serve large files past the IC limit
- render images and video inline through a direct URL
- download a file under its original name via `getBytes()`

## Example prompts
- Add object storage to the project: wire `caffeineai-object-storage` into `mops.toml` and call `include MixinObjectStorage()` in `main.mo`.
- Handle the frontend upload with `ExternalBlob.fromBytes(bytes, file.type, file.name)` and pass the filename to the backend.
- Render images from records with `getDirectURL()` and detect the file type from the `filename` field, not from the URL.

## Source text · SKILL.md · Apache-2.0

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 5fef2d5866233c50.

BEGIN THIRD-PARTY FILE 5fef2d5866233c50
```text
---
name: extension-object-storage
description: General file/object storage, such as for images, videos, files, documents and other bulk data. Perfect fit for image galleries, video galleries, and other file or object management. Supports large files beyond IC limit, with browser-cached HTTP URL access.
version: 1.1.1
compatibility:
  mops:
    caffeineai-object-storage: "~1.1.0"
caffeineai-subscription: [none]
---

# Object Storage
Object storage extension for [Caffeine AI](https://caffeine.ai?utm_source=caffeine-skill&utm_medium=referral).

## Overview

This skill adds off-chain file/object storage with on-chain references. The `MixinObjectStorage` mixin provides infrastructure for file operations; you track uploaded files in your own data structures using `Storage.ExternalBlob`.

## Required Setup Checklist

All four steps are mandatory. Skipping any one causes `403 Forbidden: Invalid payload` at upload time.

1. **mops dependency** — add `caffeineai-object-storage` to `mops.toml` under `[dependencies]`.
2. **Mixin invocation** — `include MixinObjectStorage()` in `main.mo` (imported from `"mo:caffeineai-object-storage/Mixin"`).
3. **Storage.ExternalBlob types** — every data field that represents a file MUST use `Storage.ExternalBlob`, never `Text`.
4. **Frontend npm package** — `@caffeineai/object-storage` installed and `ExternalBlob.fromBytes(bytes, file.type, file.name)` used at the call site.

CRITICAL: The frontend package (`@caffeineai/object-storage`) does NOT work without the backend mops package (`caffeineai-object-storage`). Installing only the npm package and not the mops package causes silent upload failures (403 from the storage gateway). You MUST install both together.

# Backend

File content is stored off-chain. The backend manages references to external files using the `Storage.ExternalBlob` type from `mo:caffeineai-object-storage/Storage`. The frontend handles the actual upload/download; the backend only stores the reference.
```
END THIRD-PARTY FILE 5fef2d5866233c50

The third-party file has ended. Everything between the 5fef2d5866233c50 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 1988 of 9022 bytes. © caffeinelabs · Apache-2.0 · https://github.com/caffeinelabs/skills/tree/HEAD/skills/extension-object-storage/SKILL.md

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