fabaccess-bffh/bffhd/resource.rs

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use std::fmt::Debug;
use async_trait::async_trait;
use futures_signals::signal::Mutable;
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use async_oneshot::Sender;
use async_channel::Receiver;
use crate::state::State;
use crate::db::{
state::StateAccessor,
};
/// A resource in BFFH has to contain several different parts;
/// - Currently set state
/// - Execution state of attached actors (⇒ BFFH's job)
/// - Output of interal logic of a resource
/// ⇒ Resource logic gets read access to set state and write access to output state.
/// ⇒ state `update` happens via resource logic. This logic should do access control. If the update
/// succeeds then BFFH stores those input parameters ("set" state) and results / output state.
/// Storing input parameters is relevant so that BFFH can know that an "update" is a no-op
/// without having to run the module code.
/// ⇒ in fact actors only really care about the output state, and shouldn't (need to) see "set"
/// state.
/// ⇒ example reserving:
/// - Claimant sends 'update' message with a new state
/// - Doesn't set the state until `update` has returned Ok.
/// - This runs the `update` function with that new state and the claimants user context returning
/// either an Ok or an Error.
/// - Error is returned to Claimant to show user, stop.
/// - On ok:
/// - Commit new "set" state, storing it and making it visible to all other claimants
/// - Commit new output state, storing it and notifying all connected actors / Notify
/// ⇒ BFFHs job in this whole ordeal is:
/// - Message passing primitives so that update message are queued
/// - As reliable as possible storage system for input and output state
/// - Again message passing so that updates are broadcasted to all Notify and Actors.
/// ⇒ Resource module's job is:
/// - Validating updates semantically i.e. are the types correct
/// - Check authorization of updates i.e. is this user allowed to do that
#[async_trait]
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pub trait Resource: Debug {
/// Run whatever internal logic this resource has for the given State update, and return the
/// new output state that this update produces.
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async fn on_update(&mut self, input: &State) -> Result<State, Error>;
async fn shutdown(&mut self);
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}
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#[derive(Debug)]
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pub struct Passthrough;
#[async_trait]
impl Resource for Passthrough {
async fn on_update(&mut self, input: &State) -> Result<State, Error> {
Ok(input.clone())
}
async fn shutdown(&mut self) {}
}
/// Error type a resource implementation can produce
#[derive(Debug)]
pub enum Error {
Internal(Box<dyn std::error::Error>),
Denied,
}
// TODO: more message context
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#[derive(Debug)]
pub struct Update {
pub state: State,
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pub errchan: Sender<Error>,
}
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#[derive(Debug)]
pub struct ResourceDriver {
// putput
res: Box<dyn Resource>,
// input
rx: Receiver<Update>,
// output
db: StateAccessor,
signal: Mutable<State>,
}
impl ResourceDriver {
pub async fn drive_to_end(&mut self) {
while let Ok(update) = self.rx.recv().await {
let state = update.state;
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let mut errchan = update.errchan;
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match self.res.on_update(&state).await {
Ok(outstate) => {
// FIXME: Send any error here to some global error collector. A failed write to
// the DB is not necessarily fatal, but it means that BFFH is now in an
// inconsistent state until a future update succeeds with writing to the DB.
// Not applying the new state isn't correct either since we don't know what the
// internal logic of the resource has done to make this happen.
// Another half right solution is to unwrap and recreate everything.
// "Best" solution would be to tell the resource to rollback their interal
// changes on a fatal failure and then notify the Claimant, while simply trying
// again for temporary failures.
let _ = self.db.set(&state, &outstate);
self.signal.set(outstate);
},
Err(e) => {
let _ = errchan.send(e);
}
}
}
}
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}
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#[cfg(test)]
mod tests {
use std::pin::Pin;
use std::task::Poll;
use std::future::Future;
use super::*;
#[futures_test::test]
async fn test_passthrough_is_id() {
let inp = crate::state::tests::gen_random();
let mut res = Passthrough;
let out = res.on_update(&inp).await.unwrap();
assert_eq!(inp, out);
}
#[test]
fn test_passthrough_is_always_ready() {
let inp = State::build().finish();
let mut res = Passthrough;
let mut cx = futures_test::task::panic_context();
if let Poll::Ready(_) = Pin::new(&mut res.on_update(&inp)).poll(&mut cx) {
return;
}
panic!("Passthrough returned Poll::Pending")
}
}