lemmy/crates/api_common/src/send_activity.rs

use crate::context::LemmyContext;
use activitypub_federation::config::Data;
use futures::future::BoxFuture;
use lemmy_db_schema::source::post::Post;
use lemmy_utils::{error::LemmyResult, SYNCHRONOUS_FEDERATION};
use once_cell::sync::{Lazy, OnceCell};
use tokio::{
  sync::{
    mpsc,
    mpsc::{UnboundedReceiver, UnboundedSender, WeakUnboundedSender},
    Mutex,
  },
  task::JoinHandle,
};

type MatchOutgoingActivitiesBoxed =
  Box<for<'a> fn(SendActivityData, &'a Data<LemmyContext>) -> BoxFuture<'a, LemmyResult<()>>>;

/// This static is necessary so that activities can be sent out synchronously for tests.
pub static MATCH_OUTGOING_ACTIVITIES: OnceCell<MatchOutgoingActivitiesBoxed> = OnceCell::new();

#[derive(Debug)]
pub enum SendActivityData {
  CreatePost(Post),
}

// TODO: instead of static, move this into LemmyContext. make sure that stopping the process with
//       ctrl+c still works.
static ACTIVITY_CHANNEL: Lazy<ActivityChannel> = Lazy::new(|| {
  let (sender, receiver) = mpsc::unbounded_channel();
  let weak_sender = sender.downgrade();
  ActivityChannel {
    weak_sender,
    receiver: Mutex::new(receiver),
    keepalive_sender: Mutex::new(Some(sender)),
  }
});

pub struct ActivityChannel {
  weak_sender: WeakUnboundedSender<SendActivityData>,
  receiver: Mutex<UnboundedReceiver<SendActivityData>>,
  keepalive_sender: Mutex<Option<UnboundedSender<SendActivityData>>>,
}

impl ActivityChannel {
  pub async fn retrieve_activity() -> Option<SendActivityData> {
    let mut lock = ACTIVITY_CHANNEL.receiver.lock().await;
    lock.recv().await
  }

  pub async fn submit_activity(
    data: SendActivityData,
    context: &Data<LemmyContext>,
  ) -> LemmyResult<()> {
    if *SYNCHRONOUS_FEDERATION {
      MATCH_OUTGOING_ACTIVITIES
        .get()
        .expect("retrieve function pointer")(data, context)
      .await?;
    }
    // could do `ACTIVITY_CHANNEL.keepalive_sender.lock()` instead and get rid of weak_sender,
    // not sure which way is more efficient
    else if let Some(sender) = ACTIVITY_CHANNEL.weak_sender.upgrade() {
      sender.send(data)?;
    }
    Ok(())
  }

  pub async fn close(outgoing_activities_task: JoinHandle<LemmyResult<()>>) -> LemmyResult<()> {
    ACTIVITY_CHANNEL.keepalive_sender.lock().await.take();
    outgoing_activities_task.await??;
    Ok(())
  }
}