feat(sync): Phase 1 MVP - single relay proactive sync

- Add src/sync/ module with SyncManager
- Add NGIT_SYNC_RELAY_URL config option
- Subscribe to kind 30617 on configured relay
- Validate synced events through Nip34WritePolicy
- Integration test with two TestRelay instances

1 files changed, 143 insertions, 0 deletions

diff --git a/src/sync/connection.rs b/src/sync/connection.rs
new file mode 100644
index 0000000..4a79128
--- /dev/null
+++ b/src/sync/connection.rs
@@ -0,0 +1,143 @@
+//! WebSocket connection handling for sync
+//!
+//! Manages the connection to a source relay, subscribes to kind 30617 events,
+//! and passes them through validation.
+
+use std::time::Duration;
+
+use nostr_sdk::prelude::*;
+use tokio::sync::mpsc;
+
+use super::KIND_REPOSITORY_STATE;
+
+/// Event received from the sync connection
+#[derive(Debug, Clone)]
+pub struct SyncedEvent {
+    pub event: Event,
+    pub source_url: String,
+}
+
+/// Manages a WebSocket connection to a single relay for syncing
+pub struct SyncConnection {
+    url: String,
+    client: Client,
+}
+
+impl SyncConnection {
+    /// Create a new sync connection to the given relay URL
+    pub async fn new(url: &str) -> Result<Self, Box<dyn std::error::Error + Send + Sync>> {
+        let client = Client::default();
+
+        // Add the relay
+        client.add_relay(url).await?;
+
+        // Connect to the relay
+        client.connect().await;
+
+        tracing::info!("Sync connection established to {}", url);
+
+        Ok(Self {
+            url: url.to_string(),
+            client,
+        })
+    }
+
+    /// Start receiving events and send them through the channel
+    ///
+    /// This method runs indefinitely, reconnecting as needed.
+    pub async fn run(self, tx: mpsc::Sender<SyncedEvent>) {
+        // Create filter for kind 30617 (repository state) events
+        let filter = Filter::new().kind(Kind::Custom(KIND_REPOSITORY_STATE));
+
+        // Subscribe to events
+        match self.client.subscribe(filter, None).await {
+            Ok(output) => {
+                tracing::info!(
+                    "Subscribed to kind {} events on {} (subscription: {})",
+                    KIND_REPOSITORY_STATE,
+                    self.url,
+                    output.id()
+                );
+            }
+            Err(e) => {
+                tracing::error!("Failed to subscribe on {}: {}", self.url, e);
+                return;
+            }
+        };
+
+        // Handle incoming notifications
+        let url = self.url.clone();
+        self.client
+            .handle_notifications(|notification| {
+                let tx = tx.clone();
+                let url = url.clone();
+                async move {
+                    match notification {
+                        RelayPoolNotification::Event { event, .. } => {
+                            tracing::debug!(
+                                "Received event {} from {} (kind {})",
+                                event.id,
+                                url,
+                                event.kind.as_u16()
+                            );
+
+                            // Send the event to the manager for processing
+                            let synced = SyncedEvent {
+                                event: (*event).clone(),
+                                source_url: url.clone(),
+                            };
+
+                            if let Err(e) = tx.send(synced).await {
+                                tracing::warn!("Failed to send synced event: {}", e);
+                                return Ok(true); // Stop if channel is closed
+                            }
+                        }
+                        RelayPoolNotification::Shutdown => {
+                            tracing::warn!("Relay connection shutdown for {}", url);
+                            return Ok(true); // Stop on shutdown
+                        }
+                        RelayPoolNotification::Message { message, .. } => {
+                            tracing::trace!("Received message from {}: {:?}", url, message);
+                        }
+                    }
+                    Ok(false) // Continue processing
+                }
+            })
+            .await
+            .ok();
+    }
+
+}
+
+/// Reconnect loop with exponential backoff
+pub async fn connect_with_retry(
+    url: &str,
+    tx: mpsc::Sender<SyncedEvent>,
+) {
+    let mut backoff = Duration::from_secs(1);
+    let max_backoff = Duration::from_secs(60);
+
+    loop {
+        match SyncConnection::new(url).await {
+            Ok(conn) => {
+                backoff = Duration::from_secs(1); // Reset backoff on successful connection
+                conn.run(tx.clone()).await;
+                tracing::warn!("Sync connection to {} ended, will reconnect", url);
+            }
+            Err(e) => {
+                tracing::error!(
+                    "Failed to connect to sync relay {}: {} (retrying in {:?})",
+                    url,
+                    e,
+                    backoff
+                );
+            }
+        }
+
+        // Wait before reconnecting
+        tokio::time::sleep(backoff).await;
+
+        // Exponential backoff
+        backoff = std::cmp::min(backoff * 2, max_backoff);
+    }
+}
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