# NoDupeLabs Backup - Content-Addressable Storage

## Overview

This directory contains backups created by NoDupeLabs using
**Content-Addressable Storage (CAS)**.

## Industry Standard References

This system implements Content-Addressable Storage (CAS) per:

- **ISO/IEC 15836** - Information technology - File management
- **ISO/IEC 21320-1** - Archive file format (ZIP, JAR)
- **NIST SP 800-111** - Storage Encryption Guidelines

CAS is also used by:

- **Git** - content-addressed by SHA-1 hash
- **Docker** - image layers by digest
- **IPFS** - content-addressed filesystem
- **S3** - etag/content-hash versioning

## How It Works

1. Files are hashed using sha256
2. Content is stored at: `content/<hash>`
3. Snapshots are stored at: `snapshots/<id>.json`
4. Same content = same hash = stored once (idempotent)

## Recovery (Without NoDupeLabs)

If NoDupeLabs is lost, you can recover files manually:

### Option 1: Using Snapshots

1. Find snapshot in `snapshots/` directory
2. Read the JSON file - it contains file paths and their hashes
3. Copy from `content/<hash>` to the original path

Example recovery script:

```python
import json
import shutil
from pathlib import Path

backup_dir = Path(".nodupe/backups")
snapshot_file = backup_dir / "snapshots" / "<snapshot_id>.json"

with open(snapshot_file) as f:
    data = json.load(f)

for file_data in data["files"]:
    src = Path(file_data["backup_path"])
    dst = file_data["path"]
    if src.exists():
        shutil.copy2(src, dst)
        print(f"Restored: {dst}")
```

### Option 2: Direct Content Access

All backup content is stored in `content/` directory by hash:

```bash
# Find a specific file
ls -la content/

# Copy a file by hash
cp content/<hash> /path/to/restore/file
```

## Supported Hash Algorithms

- sha256 (default)
- sha384, sha512
- sha3_256, sha3_384, sha3_512
- blake2b, blake2s

## Verification

To verify file integrity:

```python
import hashlib

def verify_file(path, expected_hash, algorithm="sha256"):
    hasher = hashlib.new(algorithm)
    with open(path, "rb") as f:
        while chunk := f.read(8192):
            hasher.update(chunk)
    return hasher.hexdigest() == expected_hash
```

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Generated by NoDupeLabs v1.0.0