> For the complete documentation index, see [llms.txt](https://motivlabs.gitbook.io/janus/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://motivlabs.gitbook.io/janus/plugins/request_transformer.md).

# Request Transformer

Transform the request sent by a client on the fly on Janus, before hitting the upstream server.

## Configuration

The plain request transformer config:

```javascript
"request_transformer": {
    "enabled": true,
    "config": {
        "add": {
            "headers": {
                "X-Something": "Value"
            },
            "querystring": {
                "test": "value"
            }
        },
        "append": {
            "headers": {
                "X-Something-More": "Value"
            },
            "querystring": {
                "extra": "stuff"
            }
        },
        "replace": {
            "headers": {
                "X-Something": "New Value"
            },
            "querystring": {
                "test": "new value"
            }
        },
        "remove": {
            "headers": {
                "X-Something": ""
            },
            "querystring": {
                "test": ""
            }
        }
    }
}
```

Here is a simple definition of the available configurations.

| Configuration              | Description                                                                                                                                                                          |
| -------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| name                       | Name of the plugin to use, in this case: request-transformer                                                                                                                         |
| config.remove.headers      | List of header names. Unset the headers with the given name.                                                                                                                         |
| config.remove.querystring  | List of querystring names. Remove the querystring if it is present.                                                                                                                  |
| config.replace.headers     | List of headername:value pairs. If and only if the header is already set, replace its old value with the new one. Ignored if the header is not already set.                          |
| config.replace.querystring | List of queryname:value pairs. If and only if the header is already set, replace its old value with the new one. Ignored if the header is not already set.                           |
| config.add.headers         | List of headername:value pairs. If and only if the header is not already set, set a new header with the given value. Ignored if the header is already set.                           |
| config.add.querystring     | List of queryname:value pairs. If and only if the querystring is not already set, set a new querystring with the given value. Ignored if the header is already set.                  |
| config.append.headers      | List of headername:value pairs. If the header is not set, set it with the given value. If it is already set, a new header with the same name and the new value will be set.          |
| config.append.querystring  | List of queryname:value pairs. If the querystring is not set, set it with the given value. If it is already set, a new querystring with the same name and the new value will be set. |

## Order of execution

Plugin performs the response transformation in following order

`remove --> replace --> add --> append`