# Modular Storage System

The OpenAccounting server now supports multiple storage backends for file attachments. This allows you to choose between local filesystem storage for simple deployments or cloud storage for production/multi-user environments.

## Supported Storage Backends

### 1. Local Filesystem Storage
Perfect for self-hosted deployments or development environments.

**Configuration:**
```json
{
  "storage": {
    "backend": "local",
    "local": {
      "root_dir": "./uploads",
      "base_url": "https://yourapp.com/files",
      "signing_key": "your-secret-jwt-signing-key"
    }
  }
}
```

**Environment Variables:**
```bash
OA_STORAGE_BACKEND=local
OA_STORAGE_LOCAL_ROOT_DIR=./uploads
OA_STORAGE_LOCAL_BASE_URL=https://yourapp.com/files
OA_STORAGE_LOCAL_SIGNINGKEY=your-secret-jwt-signing-key
```

**Security Features:**
- **JWT Token Access**: Files are served through secure JWT tokens with 1-hour expiry
- **Secure File Permissions**: Files created with 0600 permissions (owner read/write only)
- **Time-Limited URLs**: All file access URLs expire automatically
- **Path Traversal Protection**: Comprehensive validation prevents directory traversal attacks
- **No Direct File Access**: Files cannot be accessed without valid authentication tokens

### 2. Amazon S3 Storage  
Reliable cloud storage for production deployments.

**Configuration:**
```json
{
  "storage": {
    "backend": "s3",
    "s3": {
      "region": "us-east-1",
      "bucket": "my-openaccounting-attachments",
      "prefix": "attachments",
      "access_key_id": "AKIA...",
      "secret_access_key": "...",
      "endpoint": "",
      "path_style": false
    }
  }
}
```

**Environment Variables:**
```bash
OA_STORAGE_BACKEND=s3
OA_STORAGE_S3_REGION=us-east-1
OA_STORAGE_S3_BUCKET=my-openaccounting-attachments
OA_STORAGE_S3_PREFIX=attachments
OA_STORAGE_S3_ACCESS_KEY_ID=AKIA...
OA_STORAGE_S3_SECRET_ACCESS_KEY=...
```

**Features:**
- Automatic presigned URL generation
- Configurable expiry times
- Support for S3-compatible services (MinIO, DigitalOcean Spaces)
- IAM role support (leave credentials empty to use IAM)

### 3. Backblaze B2 Storage
Cost-effective cloud storage alternative to S3.

**Configuration:**
```json
{
  "storage": {
    "backend": "b2",
    "b2": {
      "account_id": "your-b2-account-id",
      "application_key": "your-b2-application-key",
      "bucket": "my-openaccounting-attachments", 
      "prefix": "attachments"
    }
  }
}
```

**Environment Variables:**
```bash
OA_STORAGE_BACKEND=b2
OA_STORAGE_B2_ACCOUNT_ID=your-b2-account-id
OA_STORAGE_B2_APPLICATION_KEY=your-b2-application-key
OA_STORAGE_B2_BUCKET=my-openaccounting-attachments
OA_STORAGE_B2_PREFIX=attachments
```

## API Endpoints

The storage system provides both legacy and new endpoints:

### New Storage-Agnostic Endpoints

**Upload Attachment:**
```
POST /api/v1/attachments
Content-Type: multipart/form-data

transactionId: uuid
description: string (optional)
file: binary data
```

**Get Attachment Metadata:**
```
GET /api/v1/attachments/{id}
```

**Get Download URL:**
```
GET /api/v1/attachments/{id}/url
```

**Download File:**
```
GET /api/v1/attachments/{id}?download=true
```

**Delete Attachment:**
```
DELETE /api/v1/attachments/{id}
```

### Legacy Endpoints (Still Supported)
The original transaction-scoped endpoints remain available for backward compatibility:
- `GET/POST /api/v1/orgs/{orgId}/transactions/{transactionId}/attachments`

## Security Features

- **File type validation** - Only allowed MIME types are accepted
- **File size limits** - Configurable maximum file size (default 10MB)
- **Path traversal protection** - Prevents directory traversal attacks
- **Access control** - Files are linked to users and organizations
- **Time-limited access** - JWT tokens for local storage, presigned URLs for cloud storage
- **Secure file permissions** - Local files created with restricted permissions (0600)
- **Cryptographic security** - HMAC-SHA256 signed JWT tokens prevent tampering

## File Organization

Files are automatically organized by date:
```
uploads/
├── 2025/
│   ├── 01/
│   │   ├── 15/
│   │   │   ├── uuid1.pdf
│   │   │   └── uuid2.png
│   │   └── 16/
│   │       └── uuid3.jpg
```

## Configuration Examples

### Development (Local Storage)
```json
{
  "storage": {
    "backend": "local",
    "local": {
      "root_dir": "./dev-uploads",
      "signing_key": "dev-secret-key-change-in-production"
    }
  }
}
```

### Production (S3 with IAM)
```json
{
  "storage": {
    "backend": "s3", 
    "s3": {
      "region": "us-west-2",
      "bucket": "prod-openaccounting-files",
      "prefix": "attachments"
    }
  }
}
```

### Cost-Optimized (Backblaze B2)
```json
{
  "storage": {
    "backend": "b2",
    "b2": {
      "account_id": "${B2_ACCOUNT_ID}",
      "application_key": "${B2_APP_KEY}",
      "bucket": "openaccounting-prod"
    }
  }
}
```

## Local Storage Security (JWT Tokens)

Local storage now implements JWT-based security matching the security model of S3 presigned URLs:

### How It Works
1. **File Upload**: Files are stored with secure permissions (0600) in date-organized directories
2. **URL Generation**: When requesting file access, the server generates a JWT token containing:
   - File path
   - User ID and Organization ID (for audit trails)
   - Expiry time (default 1 hour)
   - Cryptographic signature (HMAC-SHA256)
3. **File Access**: Files are served through `/secure-files?token=...` endpoint with token validation
4. **Security**: Tokens expire automatically and cannot be tampered with

### JWT Token Example
```
/secure-files?token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9...
```

### Security Benefits
- **Time-Limited Access**: URLs expire after 1 hour by default
- **Tamper-Proof**: HMAC-SHA256 signatures prevent token modification
- **Audit Trail**: Tokens include user and organization context
- **No Direct Access**: Files cannot be accessed without valid tokens
- **Secure Permissions**: Files created with 0600 permissions (owner only)

### Signing Key Configuration
The signing key should be:
- **Unique per deployment** to prevent cross-deployment token reuse
- **Kept secret** and not committed to version control
- **At least 32 characters** for security (recommended)
- **Set via environment variable** `OA_STORAGE_LOCAL_SIGNINGKEY`

If no signing key is provided, the server will auto-generate one (but tokens won't persist across restarts).

## Migration Between Storage Backends

When changing storage backends, existing attachments will remain in the old storage location. The database records contain the storage path, so files can be accessed until migrated.

To migrate:
1. Update configuration to new backend
2. Restart server
3. New uploads will use the new backend
4. Optional: Run migration script to move existing files

## Environment-Specific Considerations

### Self-Hosted
- Use local storage for simplicity
- Ensure backup strategy includes upload directory
- Consider disk space management

### Cloud Deployment  
- Use S3 or B2 for reliability and scalability
- Configure proper IAM policies
- Enable versioning and lifecycle policies

### Multi-Region
- Use cloud storage with appropriate region selection
- Consider CDN integration for better performance

## Troubleshooting

**Storage backend not initialized:**
- Check configuration syntax
- Verify credentials for cloud backends
- Ensure storage directories/buckets exist

**Permission denied:**
- Check file system permissions for local storage
- Verify IAM policies for S3
- Confirm B2 application key permissions

**Large file uploads failing:**
- Check `MaxFileSize` configuration
- Verify network timeouts
- Consider multipart upload for large files