Sharing Data Between Policies

The StreamProperties injectable provides an interface to:

Consume properties set by other policies that are processing the same request.
Broadcast properties so that the other policies can consume them.

To share data, StreamProperties implements the PropertyAccessor trait:

pub trait PropertyAccessor {
    fn read_property(&self, path: &[&str]) -> Option<Bytes>;
    fn set_property(&self, path: &[&str], value: Option<&[u8]>);
}

The following example shows a simple filter that reads a property from the stream and then writes another parameter to it:

async fn request_filter(stream: StreamProperties) -> Flow<()> {
    let incoming = String::from_utf8(stream.read_property(&["incoming_property"]).unwrap_or_default()).unwrap_or_default();

    logger::info!("Recieved incoming prop {}", incoming);

    let outgoing = "outgoing".as_bytes();

    stream.set_property(&["outgoing_property"], Some(outgoing));

    Flow::Continue(())
}

#[entrypoint]
async fn configure(launcher: Launcher) -> Result<()> {
    let filter = on_request(|stream| request_filter(stream));
    launcher.launch(filter).await?;
    Ok(())
}

Sharing Data Between Policies

See Also