> ## Documentation Index
> Fetch the complete documentation index at: https://docs.simplehost.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Hash Deduplication

> Only upload changed files when updating a site

## How It Works

When you update an existing site, SimpleHost compares SHA-256 hashes of each file against the previous version. Files that haven't changed are copied server-side — no re-upload needed.

This makes updates fast, even for large sites with hundreds of files.

## The Flow

<Steps>
  <Step title="Send manifest with hashes">
    Include the `hash` field for each file in your update request:

    ```json theme={null}
    {
      "files": [
        {"path": "index.html", "size": 2048, "contentType": "text/html", "hash": "abc123..."},
        {"path": "style.css", "size": 512, "contentType": "text/css", "hash": "def456..."}
      ]
    }
    ```
  </Step>

  <Step title="API compares hashes">
    The API checks each file's hash against the same file path in the previous version.
  </Step>

  <Step title="Matching files are skipped">
    Files with identical hashes appear in the `skipped` array — they're copied internally, no upload needed.
  </Step>

  <Step title="Upload only changed files">
    Only files in the `uploads` array need to be uploaded.
  </Step>
</Steps>

## Example Response

If you update a site where only `index.html` changed:

```json theme={null}
{
  "upload": {
    "uploads": [
      {"path": "index.html", "url": "...", "headers": {"Content-Type": "text/html"}}
    ],
    "skipped": [
      {"path": "style.css", "reason": "hash_match"},
      {"path": "logo.png", "reason": "hash_match"},
      {"path": "app.js", "reason": "hash_match"}
    ]
  }
}
```

Only 1 file needs uploading. The other 3 are copied server-side instantly.

## Computing Hashes

The hash must be a **SHA-256 hex digest** (64 lowercase hex characters).

### macOS

```bash theme={null}
shasum -a 256 index.html | cut -d' ' -f1
```

### Linux

```bash theme={null}
sha256sum index.html | cut -d' ' -f1
```

### Node.js

```javascript theme={null}
const crypto = require('crypto');
const fs = require('fs');

const hash = crypto.createHash('sha256')
  .update(fs.readFileSync('index.html'))
  .digest('hex');
```

### Python

```python theme={null}
import hashlib

with open('index.html', 'rb') as f:
    hash = hashlib.sha256(f.read()).hexdigest()
```

<Tip>
  The `publish.sh` script handles hashing automatically. You only need to compute hashes manually if you're building a custom integration with the API.
</Tip>

## Without Hashes

If you omit the `hash` field, every file is treated as new and must be uploaded. Always include hashes when updating to get the performance benefit.