Design

There are two types of requests: one is a request to Trino Gateway, and the other is a request that needs to be forwarded to Trino.

Request forwarding

Trino Gateway forwards some pre-defined URIs automatically to Trino. You can configure additional URIs to forward with the extraWhitelistPaths configuration.

In order to support additional URIs that are only known at runtime, the RouterPreMatchContainerRequestFilter is used to process every request before the actual resource matching occurs. If the requests URI matches, the request is forwarded to RouteToBackendResource.

Flow of request forwarding:

1. Determine to which Trino cluster a query should be routed to.
2. Prepare a request to send to Trino by adding Via headers and X-Forwarded headers. Most headers are forwarded to Trino unmodified.
3. Some request URI require special handling. For example, a request which submit a new query, Trino Gateway retrieves the queryId from the response from Trino. Some requests to the web UI require setting a session cookie to ensure OIDC works. These are done by chaining asynchronous operations using Future.
4. The execution of requests to Trino and the response to the client are handled by airlift.jaxrs.AsyncResponseHandler.