Bug: server actions cannot be cancelled or given abort signals

[AaronFriel]

React version: 18.2.0

Steps To Reproduce

1. As in Bug: promises passed to server actions block on promise parameters #28510, create a server action that has some long-running delay, e.g.: to simulate a large language model call.
2. There is no API on the client or server to trigger cancellation, or to detect or handle the client navigating away from the page.

Link to code example: https://codesandbox.io/p/devbox/next-14-0-3-forked-7q86s7?file=%2Fapp%2Factions.ts%3A4%2C18&workspaceId=958ee911-ec8f-4ca3-9ce1-668005ecaeb8

The current behavior

When a long-running request is fired, the server will complete it regardless of client behavior, e.g.: client hangup.

The expected behavior

An API for server actions to obtain a reference to an AbortController (or similar API) for the request, perhaps via async local context.

An API for clients to signal cancellation of a server action, perhaps via an additional return value on startTransition, perhaps as part of the transition APIs. If a transition is explicitly created, there should be a mechanism to cancel it.

[Gaurav896260]

hey,
To achieve the expected behavior, you would need to implement a mechanism on the server-side to handle this. One common approach is to use a unique token for each request. The client sends this token with each request, and if the client disconnects, it sends a cancellation request with the same token. The server then checks for cancellation requests with the same token before and during the processing of the request.

[AaronFriel]

I don't think that seems like a reasonable solution, as it relies upon:

• Follow-up requests being routed to the same server as the original request
• Infrastructure to store and poll/react to cancellation tokens globally, i.e.: redis.

Both of those seem pretty absurd, given that fetches can be aborted, the client can hang up the request. It should be possible to react to that.