It is not possible to express a per-request Scope in a Handler that covers the entire request/response lifetime

[jgranstrom]

If a Handler requires a Scope with a lifetime spanning all of request/response, it is not possible to express unless using a broader Scope that is not per-request.

An example case is:

def myPeelingHandler: Handler[Scope, Nothing, Any, Response] = Handler.fromZIO {
  val someStream: ZStream[Any, Nothing, Byte] = ZStream.from(Seq(1, 2, 3).map(_.toByte))

  someStream
    .peel(ZSink.take[Byte](1))
    .map { peeled =>
      Response(body = Body.fromStream(peeled._2))
    }
}

Here we require a Scope for the handler. But we cannot ZIO.scoped within the handler as it would break the stream returned as a response. The other option is to have a higher level Scope that would not be per-request with instead the risk of leaking resources.

Expected behaviour
A proper way to have a Handler provide a Scope for the request such as Handler.scoped { } to cover these cases.

[jdegoes]

What scope do you want? You want the scope to be closed when the handler is done being used by the server?

[jdegoes]

I think the correct solution here is:

1. Define handlers to be Handler[R & Scope, ...] inside routes. This means that in addition to the user's own R, the server can supply a Scope, which is defined to be the scope of the handler.
2. Have the server supply a scope for the entire request/response cycle, which is fed into the handler.

To avoid breaking backward compatibility and avoid introducing overhead for "scope-less" handlers, this would have to be done very carefully using new methods / constructors.

[jdegoes]

/bounty $500

[algora-pbc]

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Attempt	Started (GMT+0)	Solution
🔴 @987Nabil	Nov 9, 2024, 2:24:54 AM	WIP
🔴 @Ayush9026	Nov 9, 2024, 7:32:51 PM	WIP
🟢 @jgranstrom		#3229

[987Nabil]

/attempt #3197

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[Ayush9026]

/attempt #3197

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[algora-pbc]

Note

The user @987Nabil is already attempting to complete issue #3197 and claim the bounty. We recommend checking in on @987Nabil's progress, and potentially collaborating, before starting a new solution.

[algora-pbc]

@987Nabil: Reminder that in 7 days the bounty will become up for grabs, so please submit a pull request before then 🙏

[algora-pbc]

@Ayush9026: Reminder that in 7 days the bounty will become up for grabs, so please submit a pull request before then 🙏

[algora-pbc]

The bounty is up for grabs! Everyone is welcome to /attempt #3197 🙌

[jgranstrom]

@jdegoes there's quite a bit of complexity that comes with splitting unscoped/scoped handlers. What about we always provide a request-response-lifetimed Scope to handlers? That seems very natural and should simplify it quite a bit. Using any other Scope from outside of handlers within handlers is pretty much a leak. Is there some concern with overhead unless the Scope is needed? I think splitting it will come with overhead in itself too

[jgranstrom]

/attempt #3197

[algora-pbc]

💡 @jgranstrom submitted a pull request that claims the bounty. You can visit your bounty board to reward.