> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/web/get-started/faq/supporting-xrefs.md).

# Supporting XRefs

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## Supporting XRefs

XRefs (external references) are used within CAD documents to reference external documents to be loaded within a main document. WebViewer Server by default does not support these XRefs as it needs to know **context information about the location of the XRef files.**

We do provide an option `TRN_CAD_XREF_CONFIG_URL` that will allow you to provide this context information, but there are a few steps that will need to be done in order to use this option.

To use this option, you will need to do the following.

1. Determine a way to match XRefs to a document.
2. Create a server which will, given a request with a document, return the correct XRefs.
3. Add the XRef files to an accessible file location on WebViewer Server.
4. Set `TRN_CAD_XREF_CONFIG_URL` to the created server.

## Determine a way to match XRefs to a document

The most common way is by providing a header during the load document call, and then matching this header to the correct XRefs.

{% tabs %}
{% tab title="JavaScript" %}
{% code lineNumbers="true" %}

```js
WebViewer(...)
  .then(instance => {
    const options = {
      customHeaders: { MyDocIdentifier: "12345id" },
      filename: "Document.pdf"
    };
    const url = 'http://<documentserver>/mydocument.pdf'
    instance.loadDocument(url, options);
  });
});
```

{% endcode %}
{% endtab %}
{% endtabs %}

Now the server will see `MyDocIdentifier` when WebViewer Server requests it, it can then return the **XRef paths** for this document like so:

{% tabs %}
{% tab title="JSON" %}
{% code lineNumbers="true" %}

```json
{
XRefSearchPaths: ['mypath/mpath/path', 'mypath2/path/path']
}
```

{% endcode %}
{% endtab %}
{% endtabs %}

WebViewer Server would then look in these paths for XRefs.

## Create a server to return the XRefs

In the next step you will need to create a server that will do the following:

1. Accept a GET request
2. Read the a header from the request
3. Return XRefs based on this header in JSON format

**Paths returned by the server should have the following traits**

* They should be **absolute paths**
* They should point to the folder containing the external files
* The path should only be a local system path

The code below is a rough example of how you would do this. The specifics of how you implement XRef path selection will be specific to your system.

{% tabs %}
{% tab title="Python" %}
{% code lineNumbers="true" %}

```python
from http.server import BaseHTTPRequestHandler,HTTPServer
import json

xrefPaths = { 
'docId1' : ['/path/path1/path', '/path/path2'], 
'docId2' : ['/path3/path']
}

class Server(BaseHTTPRequestHandler):
    def _set_headers(self):
        self.send_response(200)
        self.send_header('Content-type', 'application/json')
        self.end_headers()

    def do_HEAD(self):
        self._set_headers()

    def do_GET(self):
        self.send_response(200)
        self._set_headers()
        # here you would get each individual XRef path based on the ID
        # and return them in JSON below
        myId = self.headers["MyDocIdentifier"]
        myPaths = xrefPaths[myId]
        self.wfile.write(json.dumps({'XRefSearchPaths': myPaths }).encode())

def run(server_class=HTTPServer, handler_class=Server, port=8008):
    server_address = ('', port)
    httpd = server_class(server_address, handler_class)

    print('Starting httpd on port %d...' % port)
    httpd.serve_forever()

if __name__ == "__main__":
    run()
```

{% endcode %}
{% endtab %}
{% endtabs %}

## Add the XRefs to the server

### Using Docker

In docker you should mount volumes at the specific XRef paths like so:

{% tabs %}
{% tab title="YAML" %}
{% code lineNumbers="true" %}

```yaml
volumes:
  /myfiledirectory/dir:/home/tomcat/xrefFiles
```

{% endcode %}
{% endtab %}
{% endtabs %}

You would then set XRefs to be looked for inside of this xrefFiles directory.

### Using Windows

On windows, you only need to provide the correct paths and your XRefs should be found.

## Set TRN\_CAD\_XREF\_CONFIG\_URL

A prerequiste to this step would be to setup your server over a local network or the internet to be accessible by WebViewer Server. In this example, the server is hosted on `192.168.1.1` under the path `getXrefs`:

{% tabs %}
{% tab title="YAML" %}
{% code lineNumbers="true" %}

```yaml
TRN_CAD_XREF_CONFIG_URL: 'http://192.168.1.1/getXrefs'
```

{% endcode %}
{% endtab %}
{% endtabs %}

If everything was done correctly, XRefs should now be appearing in your documents.


---

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