OXYGENHUB
# 8dcaeeb848c6 oxygenhub / crates / hub / src / events.rs
7.3 KiB · Rust · last changed Live pages L1: an event bus of topics, versions and a replay buffer 20 days ago source blame history raw
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//! In-process event bus: nudges the webhook worker and streams proposal
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//! updates to open pages over server-sent events (hub spec §13.1).
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use hub_api::ProposalEvent;
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use tokio::sync::broadcast;
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pub struct Events {
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    pub deliveries: broadcast::Sender<()>,
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    pub proposals: broadcast::Sender<(i64, ProposalEvent)>,
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    /// Topics for live pages (oxygenhub#203).
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    pub live: LiveBus,
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}
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impl Default for Events {
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    fn default() -> Self {
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        Events { deliveries: broadcast::channel(16).0, proposals: broadcast::channel(256).0, live: LiveBus::default() }
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    }
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}
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impl Events {
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    pub fn notify_deliveries(&self) {
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        let _ = self.deliveries.send(());
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    }
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    /// Announce something about a proposal of a repository.
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    pub fn proposal(&self, repo_id: i64, event: ProposalEvent) {
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        let _ = self.proposals.send((repo_id, event));
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    }
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}
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/// What changed, for live pages (docs/live.md, oxygenhub#203): a topic and
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/// a kind, never the data. A page that hears its topic fetches the part
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/// that changed from its normal route, which checks the viewer's access.
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#[derive(Clone, Debug, PartialEq, Eq, serde::Serialize)]
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pub struct LiveEvent {
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    /// Increasing across the hub: what `Last-Event-ID` resumes from.
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    pub id: u64,
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    pub topic: String,
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    /// The topic's own version: how many events it has had.
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    pub version: u64,
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    /// What happened: `push`, `comment`, `review`, `check`, `jobs`, ...
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    pub kind: String,
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}
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/// Topics (docs/live.md §4).
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pub mod topic {
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    pub fn repo(id: i64) -> String {
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        format!("repo:{id}")
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    }
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    pub fn proposal(repo: i64, n: i64) -> String {
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        format!("repo:{repo}/proposal:{n}")
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    }
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    pub fn issue(repo: i64, n: i64) -> String {
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        format!("repo:{repo}/issue:{n}")
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    }
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    pub fn run(id: i64) -> String {
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        format!("run:{id}")
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    }
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    pub fn user(id: i64) -> String {
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        format!("user:{id}")
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    }
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    pub fn diffusion(repo: i64) -> String {
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        format!("diffusion:{repo}")
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    }
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}
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/// Events kept for replay: a reconnecting page catches up from these, or is
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/// told to reload when it missed more.
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pub const REPLAY: usize = 1024;
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/// The live event bus: one broadcast that subscribers filter by topic, a
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/// version per topic, and the last [`REPLAY`] events.
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pub struct LiveBus {
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    tx: broadcast::Sender<LiveEvent>,
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    state: std::sync::Mutex<BusState>,
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}
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#[derive(Default)]
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struct BusState {
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    next_id: u64,
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    versions: std::collections::HashMap<String, u64>,
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    recent: std::collections::VecDeque<LiveEvent>,
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}
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impl Default for LiveBus {
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    fn default() -> Self {
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        LiveBus { tx: broadcast::channel(1024).0, state: std::sync::Mutex::new(BusState { next_id: 1, ..Default::default() }) }
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    }
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}
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/// What a reconnecting subscriber gets: the events it missed, or `Reload`
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/// when they are no longer kept.
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#[derive(Debug, PartialEq, Eq)]
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pub enum Replay {
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    Events(Vec<LiveEvent>),
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    Reload,
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}
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impl LiveBus {
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    /// Publish an event on `topic`.
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    pub fn publish(&self, topic: &str, kind: &str) -> LiveEvent {
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        let event = {
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            let mut s = self.state.lock().unwrap_or_else(|p| p.into_inner());
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            let id = s.next_id;
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            s.next_id += 1;
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            let version = {
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                let v = s.versions.entry(topic.to_string()).or_insert(0);
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                *v += 1;
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                *v
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            };
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            let e = LiveEvent { id, topic: topic.into(), version, kind: kind.into() };
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            if s.recent.len() == REPLAY {
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                s.recent.pop_front();
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            }
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            s.recent.push_back(e.clone());
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            e
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        };
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        let _ = self.tx.send(event.clone());
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        event
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    }
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    pub fn subscribe(&self) -> broadcast::Receiver<LiveEvent> {
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        self.tx.subscribe()
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    }
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    /// The newest event id (0 before any).
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    pub fn last_id(&self) -> u64 {
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        self.state.lock().unwrap_or_else(|p| p.into_inner()).next_id - 1
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    }
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    /// The events on `topics` after `last_id`, or `Reload` when some after
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    /// it are no longer kept.
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    pub fn since(&self, last_id: u64, topics: &[String]) -> Replay {
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        let s = self.state.lock().unwrap_or_else(|p| p.into_inner());
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        let oldest = s.recent.front().map(|e| e.id).unwrap_or(s.next_id);
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        if last_id + 1 < oldest {
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            return Replay::Reload;
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        }
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        Replay::Events(s.recent.iter().filter(|e| e.id > last_id && topics.contains(&e.topic)).cloned().collect())
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    }
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    /// The topics a webhook event touches: the repository always, and the
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    /// proposal or issue its data names.
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    pub fn publish_hook(&self, repo_id: i64, event: &str, data: &serde_json::Value) {
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        let kind = event.split('.').next().unwrap_or(event);
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        self.publish(&topic::repo(repo_id), kind);
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        let number = data["number"].as_i64().or_else(|| data["issue"]["number"].as_i64());
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        let is_issue = event.starts_with("issue") || event == "comment.issue";
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        let is_proposal = event.starts_with("proposal") || matches!(event, "review" | "comment" | "comment.proposal");
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        match number {
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            Some(n) if is_issue => {
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                self.publish(&topic::issue(repo_id, n), kind);
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            }
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            Some(n) if is_proposal => {
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                self.publish(&topic::proposal(repo_id, n), kind);
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            }
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            _ => {}
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        }
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    }
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}
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#[cfg(test)]
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mod tests {
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    use super::*;
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    #[test]
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    fn events_have_ids_and_versions_and_replay_or_say_reload() {
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        let bus = LiveBus::default();
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        let mut rx = bus.subscribe();
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        let a = bus.publish("repo:1", "push");
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        let b = bus.publish("repo:2", "push");
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        let c = bus.publish("repo:1", "check");
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        assert_eq!((a.id, b.id, c.id), (1, 2, 3));
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        assert_eq!((a.version, b.version, c.version), (1, 1, 2), "versions count per topic");
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        assert_eq!(rx.try_recv().unwrap(), a, "subscribers hear every event");
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        assert_eq!(bus.since(1, &["repo:1".into()]), Replay::Events(vec![c.clone()]), "only the topics asked for");
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        assert_eq!(bus.since(3, &["repo:1".into()]), Replay::Events(vec![]));
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        for _ in 0..REPLAY {
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            bus.publish("repo:3", "push");
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        }
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        assert_eq!(bus.since(1, &["repo:1".into()]), Replay::Reload, "too old to replay");
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        assert_eq!(bus.last_id(), 3 + REPLAY as u64);
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    }
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    #[test]
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    fn a_webhook_event_names_its_repository_and_its_proposal_or_issue() {
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        let bus = LiveBus::default();
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        bus.publish_hook(7, "review", &serde_json::json!({ "number": 4, "verdict": "approve" }));
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        bus.publish_hook(7, "issue.opened", &serde_json::json!({ "issue": { "number": 9 } }));
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        bus.publish_hook(7, "comment.issue", &serde_json::json!({ "number": 9 }));
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        bus.publish_hook(7, "push", &serde_json::json!({ "updates": [] }));
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        let Replay::Events(all) = bus.since(0, &["repo:7".into(), "repo:7/proposal:4".into(), "repo:7/issue:9".into()]) else { panic!() };
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        let seen: Vec<(String, String)> = all.into_iter().map(|e| (e.topic, e.kind)).collect();
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        assert_eq!(
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            seen,
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            [
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                ("repo:7", "review"),
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                ("repo:7/proposal:4", "review"),
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                ("repo:7", "issue"),
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                ("repo:7/issue:9", "issue"),
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                ("repo:7", "comment"),
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                ("repo:7/issue:9", "comment"),
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                ("repo:7", "push"),
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            ]
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            .map(|(t, k)| (t.to_string(), k.to_string()))
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        );
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    }
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}