> ## Documentation Index
> Fetch the complete documentation index at: https://gcore-doc-1046.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# CDN properties

CDN applications built on the Proxy-Wasm ABI interact with HTTP requests and responses through a property system. Since each hook (onRequestHeaders, onRequestBody, onResponseHeaders, onResponseBody) runs in its own isolated WASM instance, properties provide the mechanism for reading request/response data and modifying CDN behavior throughout the request lifecycle.

### How properties work

Properties are accessed through two core methods:

* **`get_property(path)`**: Reads data from the current request context
* **`set_property(path, value)`**: Modifies writable properties to customize CDN behavior

Each property is identified by a path (e.g., `request.path`, `response.status`) and has specific access permissions based on the hook where it's accessed.

### Property access patterns

**Read-only properties**: Can be read but not modified. These typically represent immutable request data or CDN internal state.

**Read-write properties**: Can be both read and modified. Use these to customize headers, adjust routing, or modify response behavior.

**Hook-specific availability**: Some properties are only accessible in certain hooks. For example, response properties are unavailable in request hooks.

### Available properties

The following table lists all available properties and their access permissions. These properties can only be written to within the onRequestHeaders hook:

| Property Path          | Type    | Access     | Description                                           |
| ---------------------- | ------- | ---------- | ----------------------------------------------------- |
| `request.url`          | String  | Read-write | Original URL path before modifications                |
| `request.host`         | String  | Read-write | Host header value                                     |
| `request.path`         | String  | Read-write | Request URL path                                      |
| `request.scheme`       | String  | Read-only  | Protocol scheme (http/https)                          |
| `request.method`       | String  | Read-only  | HTTP method (GET, POST, etc.)                         |
| `request.extension`    | String  | Read-only  | Request path extension                                |
| `request.query`        | String  | Read-write | Query string parameters                               |
| `request.country`      | String  | Read-only  | Country Code - deciphered from IP                     |
| `request.city`         | String  | Read-only  | City name - deciphered from IP                        |
| `request.asn`          | String  | Read-only  | ASN of the network/ISP associated with the request IP |
| `request.geo.lat`      | String  | Read-only  | Latitude - deciphered from IP                         |
| `request.geo.long`     | String  | Read-only  | Longitude - deciphered from IP                        |
| `request.region`       | String  | Read-only  | Region - deciphered from IP                           |
| `request.continent`    | String  | Read-only  | Continent - deciphered from IP                        |
| `request.country.name` | String  | Read-only  | Country name - deciphered from IP                     |
| `nginx.log_field1`     | String  | Write-only | Adds value to nginx access logs                       |
| `response.status`      | Integer | Read-only  | HTTP status code                                      |

#### `nginx.log_field1`

This field is write-only (onRequestHeaders). Adding a value here will ensure it is written to CDN access log, available through the Log uploader feature.

### Custom properties

You can also create custom properties within hooks. This allows you to track data between hook runs. e.g. custom property `markdown`
These custom hooks are all read-write, however they are only available from onRequestBody onwards. Anything added within onRequestHeaders will **not** be available, in future hooks.

### Example: Response modification

```rust theme={null}
// In onResponseHeaders
fn on_response_headers() {
    // Add Custom markdown property
    if let Some(content_type) = self.get_http_response_header("Content-Type") {
        if content_type.starts_with("text/plain") || content_type.starts_with("text/markdown") {
            self.set_http_response_header("Content-Length", None);
            self.set_http_response_header("Transfer-Encoding", Some("Chunked"));
            self.set_http_response_header("Content-Type", Some("text/html"));
            self.set_property(vec!["response.markdown"], Some(b"true"));
            println!("Response is markdown, on_response_body can now convert to HTML");
        }
    }
}

// In onResponseBody
fn on_http_response_body(&mut self, body_size: usize, end_of_stream: bool) -> Action {
    // only process markdown
    if None == self.get_property(vec!["response.markdown"]) {
        return Action::Continue;
    }
}
```

### Property modification best practices

**Validate before setting**: Always validate property values before modification to prevent errors.

**Use appropriate hooks**: Modify request properties only in onRequestHeaders.

**Handle missing properties**: Not all properties are available in all contexts. Use error handling when accessing optional properties.

<Info>
  **Note**

  Property paths are case-sensitive. Header names follow HTTP conventions (lowercase with hyphens).
</Info>