# Patch CDN Infrastructure & Game Update System

## Overview

The F2P launcher downloads game patches through a CDN redirect gateway hosted on the auth server. This allows instant CDN switching (e.g., for DMCA takedowns) without releasing a new launcher version.

## Architecture

```
Launcher --> GET auth.sanasol.ws/patches/manifest.json
          --> 302 --> mega.io/.../manifest.json

Launcher --> GET auth.sanasol.ws/patches/windows/amd64/release/0_to_11.pwr
          --> 302 --> mega.io/.../windows/amd64/release/0_to_11.pwr
```

The auth server acts as a pure redirect gateway (302). No bandwidth is consumed on the auth server - all actual file transfers happen directly between the launcher and the CDN.

## URLs

| URL | Purpose |
|-----|---------|
| `https://auth.sanasol.ws/patches/*` | Redirect gateway (302 -> CDN) |
| `https://auth.sanasol.ws/patches/manifest.json` | Patch manifest (redirects to CDN) |
| `https://auth.sanasol.ws/admin/page/settings` | Admin panel to change CDN URL |
| `https://auth.sanasol.ws/admin/api/settings/patches-cdn` | API to GET/POST CDN base URL |

### Default CDN (MEGA S4)

```
Base URL: https://s3.g.s4.mega.io/kcvismkrtfcalgwxzsazbq46l72dwsypqaham/hytale/patches
```

### Changing CDN (DMCA response)

1. Go to `https://auth.sanasol.ws/admin/page/settings`
2. Find "Patches CDN Base URL" section
3. Change URL to new CDN (e.g., `https://new-cdn.example.com/patches`)
4. Click "Save" - all launcher requests instantly redirect to new CDN
5. No launcher update needed

## Manifest Format

The manifest is a JSON file listing all available patch files:

```json
{
  "updated": "2026-02-20T13:20:09.776Z",
  "files": {
    "windows/amd64/release/0_to_11.pwr": { "size": 1618804736 },
    "windows/amd64/release/10_to_11.pwr": { "size": 62914560 },
    "darwin/arm64/release/0_to_11.pwr": { "size": 1617100800 },
    "server/release": { "version": "2026.02.19-1a311a592", "size": 1509949440, "sha256": "..." },
    ...
  }
}
```

### Key Structure

File keys follow the pattern: `{os}/{arch}/{branch}/{from}_to_{to}.pwr`

- **OS**: `windows`, `linux`, `darwin`
- **Arch**: `amd64`, `arm64`
- **Branch**: `release`, `pre-release`
- **Patch**: `{from}_to_{to}.pwr` (e.g., `0_to_11.pwr` for full install, `10_to_11.pwr` for differential)

Server builds use: `server/{branch}` with `version`, `size`, `sha256` fields.

## Game Update Process

### 1. Version Check

```
Launcher calls: getLatestClientVersion(branch)
  -> Fetches manifest from auth.sanasol.ws/patches/manifest.json
  -> Finds highest build number for current platform/branch
  -> Returns "v{buildNumber}" (e.g., "v11")
```

### 2. Update Plan (Optimal Patch Routing)

```
Launcher calls: getUpdatePlan(currentBuild, targetBuild, branch)
  -> Fetches manifest
  -> Finds available patches for platform
  -> Uses BFS to find optimal path (minimizes total download size)
  -> Example: build 5 -> 11 might use: 5->10 (148MB) + 10->11 (60MB)
    instead of: 0->11 (1.5GB)
```

### 3. Download & Apply

```
For each step in the update plan:
  1. Download .pwr file from auth.sanasol.ws/patches/{key}
     (redirects to CDN, supports resume via Range headers)
  2. Apply patch using butler tool:
     butler apply --staging-dir <staging> <pwr_file> <game_dir>
  3. Save version after each step
```

### 4. Fresh Install

For first-time installs (currentBuild = 0):
- Downloads `0_to_{target}.pwr` (full install, ~1.5GB)
- Applies with butler to create the full game directory

### 5. Differential Update

For existing installations:
- Finds optimal patch chain (e.g., `10_to_11.pwr` at ~60MB)
- Applies incrementally, saving progress after each step
- Falls back to full install if no patch path found

## Mirror Sync Script

The mirror script (`scripts/hytale-mirror.js`) downloads patches from the official Hytale API and uploads to MEGA S4.

### Usage

```bash
cd scripts
node hytale-mirror.js download   # Download patches locally
node hytale-mirror.js upload     # Upload to MEGA S4 via rclone
node hytale-mirror.js sync       # Download + Upload in one step
```

### What It Does

1. **Discovery**: Calls Hytale API to find available patches for all platforms
2. **Download**: Downloads .pwr files to `scripts/mirror/` directory
3. **Manifest Generation**: Creates `manifest.json` with file sizes (no local paths)
4. **Upload**: Uses `rclone` to sync to MEGA S4

### SOCKS5 Proxy

- API discovery calls use SOCKS5 proxy rotation (for rate limiting)
- File downloads do NOT use proxy (too slow for large files)
- Proxy list in `proxies.json` (auto-refreshed from proxy service)

### Prerequisites

- `rclone` configured with `megas4` remote pointing to MEGA S4
- Node.js 20+
- Network access to Hytale API endpoints

## Launcher Configuration

### Environment Variables

| Variable | Default | Description |
|----------|---------|-------------|
| `HYTALE_AUTH_DOMAIN` | `auth.sanasol.ws` | Auth domain (used for patch redirects) |

### Key Files

| File | Description |
|------|-------------|
| `backend/services/versionManager.js` | Manifest fetching, version checking, update planning |
| `backend/managers/differentialUpdateManager.js` | Download orchestration, butler integration |
| `backend/utils/fileManager.js` | File download with retry, resume, stall detection |
| `backend/managers/gameLauncher.js` | Game launch with token fetch, patching, signing |

### Constants (versionManager.js)

```javascript
const AUTH_DOMAIN = process.env.HYTALE_AUTH_DOMAIN || 'auth.sanasol.ws';
const MIRROR_BASE_URL = `https://${AUTH_DOMAIN}/patches`;
const MIRROR_MANIFEST_URL = `${MIRROR_BASE_URL}/manifest.json`;
const MANIFEST_CACHE_DURATION = 60000; // 1 minute cache
const FALLBACK_LATEST_BUILD = 11; // If manifest unreachable
```

## Auth Server Implementation

### Routes

```
GET /patches/*  -> handlePatchRedirect()
  - Extracts path after /patches/
  - Reads CDN base URL from Redis settings
  - Returns 302 redirect to {baseUrl}/{path}
  - Tracks download metrics

GET /admin/api/settings/patches-cdn -> getPatchesCdnBaseUrl()
POST /admin/api/settings/patches-cdn -> setPatchesCdnBaseUrl()
```

### Redis Storage

```
settings:global -> { patchesCdnBaseUrl: "https://s3.g.s4.mega.io/..." }
metrics:downloads -> { "patch:manifest.json": count, ... }
```

## Troubleshooting

### "Invalid manifest structure" error
- Check manifest.json is valid JSON with `files` object
- Verify CDN is accessible: `curl -sL https://auth.sanasol.ws/patches/manifest.json | python3 -m json.tool`
- Check admin settings for correct CDN URL

### 0-byte downloads
- Verify redirect works: `curl -sI https://auth.sanasol.ws/patches/darwin/arm64/release/0_to_11.pwr`
- Should show `302` with `Location` header
- Test actual download: `curl -sL -o /dev/null -w "%{size_download}" -r 0-1023 <url>`

### Manifest has local paths
- Regenerate manifest: `node scripts/hytale-mirror.js download` (re-scans files)
- Re-upload: `node scripts/hytale-mirror.js upload`
- Verify: entries should only have `{ size: <bytes> }`, no `path` field

### CDN switch not taking effect
- Check Redis: CDN URL stored in `settings:global`
- Verify via API: `curl https://auth.sanasol.ws/admin/api/settings/patches-cdn`
- Manifest is cached for 1 minute in launcher - wait or restart