114 lines
3.4 KiB
Markdown
114 lines
3.4 KiB
Markdown
# services
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Background services. A service owns a route key, runs as an iced
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`Subscription`, receives `common::Wire`s on its `Inbox`, and publishes
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payloads back to every module subscribed to its key. Core maps a `Service`
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route key to a subscription through `IntoSubscription`.
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Message types are shared, so they live in the `common` crate, under
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`common/src/messages/services/`. That is what lets a service and the modules
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that consume it name the same payload without either depending on the other.
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## Getting started: add a service
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1. Declare the service's route key and payload in
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`crates/common/src/messages/services/greeter.rs`:
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```rust
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//! Greeter service messages.
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use crate::Service;
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#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
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pub enum GreeterKind {
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Hello,
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}
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impl GreeterKind {
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/// Route key a module subscribes under to receive this kind's ticks.
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pub fn key(self) -> Service {
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Service(match self {
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Self::Hello => "greeter.hello",
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})
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}
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}
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#[derive(Clone)]
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pub struct GreeterPayload {
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pub value: String,
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}
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```
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2. Re-export them from `crates/common/src/messages/services/mod.rs`:
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```rust
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mod datetime;
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mod greeter;
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mod weather;
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pub use datetime::{ClockKind, ClockPayload};
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pub use greeter::{GreeterKind, GreeterPayload};
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pub use weather::*;
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```
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3. Create `crates/services/src/greeter.rs`:
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```rust
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use std::time::Duration;
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use common::{Endpoint, Inbox, Wire, GreeterPayload};
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use iced::{futures::channel::mpsc, Subscription};
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/// Route-key namespace owned by this service; keys look like `"greeter.hello"`.
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pub const NAMESPACE: &str = "greeter.";
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pub struct GreeterService;
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impl GreeterService {
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pub fn run(inbox: Inbox) -> Subscription<Wire> {
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Subscription::run_with(inbox, |inbox| {
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let key = inbox.key();
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let mut _rx = inbox.take().expect("inbox receiver is taken once");
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iced::stream::channel(0, move |mut sender: mpsc::Sender<Wire>| async move {
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let mut interval = tokio::time::interval(Duration::from_secs(5));
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loop {
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interval.tick().await;
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// Fan-out: publish to every module subscribed to `key`.
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let wire = Wire::topic(Endpoint::service(key), key, GreeterPayload {
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value: "hello".into(),
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});
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if sender.send(wire).await.is_err() {
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return;
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}
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}
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})
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})
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}
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}
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```
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4. Add one arm to the `IntoSubscription` match in `crates/services/src/lib.rs`:
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```rust
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pub mod greeter;
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impl IntoSubscription for Service {
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fn into_subscription(self, inbox: Inbox) -> Subscription<Wire> {
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match self.0 {
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key if key.starts_with(datetime::NAMESPACE) => datetime::ClockTicker::run(inbox),
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key if key.starts_with(weather::NAMESPACE) => weather::WeatherService::run(inbox),
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key if key.starts_with(greeter::NAMESPACE) => greeter::GreeterService::run(inbox),
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_ => Subscription::none(),
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}
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}
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}
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```
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Then a module subscribes by returning `GreeterKind::Hello.key()` from its
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`services()` and downcasts `GreeterPayload` in `update()`.
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`run_with(inbox, ..)` keys the subscription by the inbox route key, so the
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same subscription returned on every rebuild is not restarted. The receiver is
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taken once inside the closure — don't call `take()` anywhere else.
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