filter: add forwarder filter

Fixes: https://github.com/damus-io/noteguard/issues/10
Changelog-Added: Add forwarder filter
Signed-off-by: William Casarin <jb55@jb55.com>

src/filters/forwarder.rs

@@ -0,0 +1,107 @@
+use serde::Deserialize;
+use crate::{Note, Action, NoteFilter, InputMessage, OutputMessage};
+use futures_util::{SinkExt, StreamExt};
+use tokio::sync::mpsc::{self, Sender, Receiver};
+use tokio_tungstenite::connect_async;
+use tokio_tungstenite::tungstenite::Message;
+use tokio_tungstenite::WebSocketStream;
+use tokio::time::{sleep, timeout, Duration};
+use serde_json::json;
+use log::{error, info, debug};
+
+#[derive(Default, Deserialize)]
+pub struct Forwarder {
+    relay: String,
+
+    /// the size of our bounded queue
+    queue_size: Option<u32>,
+
+    /// The channel used for communicating with the forwarder thread
+    #[serde(skip)]
+    channel: Option<Sender<Note>>,
+}
+
+async fn client_reconnect(relay: &str) -> WebSocketStream<tokio_tungstenite::MaybeTlsStream<tokio::net::TcpStream>> {
+    loop {
+        match connect_async(relay).await {
+            Err(e) => {
+                error!("failed to connect to relay {}: {}", relay, e);
+                sleep(Duration::from_secs(5)).await;
+                continue;
+            }
+            Ok((ws, _)) => {
+                info!("connected to relay: {}", relay);
+                return ws;
+            }
+        }
+    }
+}
+
+async fn forwarder_task(relay: String, mut rx: Receiver<Note>) {
+    let stream = client_reconnect(&relay).await;
+    let (mut writer, mut reader) = stream.split();
+
+    loop {
+        tokio::select! {
+            result = timeout(Duration::from_secs(10), rx.recv()) => {
+                match result {
+                    Ok(Some(note)) => {
+                        if let Err(e) = writer.send(Message::Text(serde_json::to_string(&json!(["EVENT", note])).unwrap())).await {
+                            error!("got error: '{}', reconnecting...", e);
+                            let (w, r) = client_reconnect(&relay).await.split();
+                            writer = w;
+                            reader = r;
+                        }
+                    },
+                    Ok(None) => {
+                        // Channel has been closed, exit the loop
+                        error!("channel closed, stopping forwarder_task");
+                        break;
+                    }
+                    Err(_) => {
+                        // Timeout occurred, send a ping
+                        // try reading for pongs, etc
+                        let _r = reader.next();
+                        debug!("timeout reading note queue, sending ping");
+
+                        if let Err(e) = writer.send(Message::Ping(vec![])).await {
+                            error!("error during ping ({}), reconnecting...", e);
+                            let (w, r) = client_reconnect(&relay).await.split();
+                            writer = w;
+                            reader = r;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl NoteFilter for Forwarder {
+    fn name(&self) -> &'static str {
+        "forwarder"
+    }
+
+    fn filter_note(&mut self, input: &InputMessage) -> OutputMessage {
+        if self.channel.is_none() {
+            let (tx, rx) = mpsc::channel(self.queue_size.unwrap_or(1000) as usize);
+            let relay = self.relay.clone();
+
+            tokio::task::spawn(async move {
+                forwarder_task(relay, rx).await;
+            });
+
+            self.channel = Some(tx);
+        }
+
+        // Add code to process input and send through channel
+        if let Some(ref channel) = self.channel {
+            if let Err(e) = channel.try_send(input.event.clone()) {
+                eprintln!("could not forward note: {}", e);
+            }
+        }
+
+        // Create and return an appropriate OutputMessage
+        OutputMessage::new(input.event.id.clone(), Action::Accept, None)
+    }
+}

src/filters/mod.rs

@@ -3,7 +3,13 @@ mod protected_events;
 mod ratelimit;
 mod whitelist;
 
+#[cfg(feature = "forwarder")]
+mod forwarder;
+
 pub use kinds::Kinds;
 pub use protected_events::ProtectedEvents;
 pub use ratelimit::RateLimit;
 pub use whitelist::Whitelist;
+
+#[cfg(feature = "forwarder")]
+pub use forwarder::Forwarder;