fix: queue outgoing events when relay connection is down

When all relay connections are temporarily lost, EVENT messages published
by extensions (nostrmarket, events) are now queued in a bounded deque
(max 100) instead of being silently dropped. On reconnection, queued
events are flushed to all connected relays. Dead relay queues are also
drained before restart to preserve in-flight events.

Closes aiolabs/nostrclient#1

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nostr/relay.py

@@ -1,6 +1,9 @@
+from __future__ import annotations
+
 import asyncio
 import json
 import time
+from collections.abc import Callable
 from queue import Queue
 
 from loguru import logger
@@ -28,6 +31,7 @@ class Relay:
         self.num_subscriptions: int = 0
 
         self.queue: Queue = Queue()
+        self.on_connect: Callable[[Relay], None] | None = None
 
     def connect(self):
         self.ws = WebSocketApp(
@@ -97,6 +101,11 @@ class Relay:
         logger.info(f"[Relay: {self.url}] Connected.")
         self.connected = True
         self.shutdown = False
+        if self.on_connect:
+            try:
+                self.on_connect(self)
+            except Exception as e:
+                logger.warning(f"[Relay: {self.url}] on_connect callback error: {e}")
 
     def _on_close(self, _, status_code, message):
         logger.warning(

nostr/relay_manager.py

@@ -1,6 +1,8 @@
 import asyncio
+import json
 import threading
 import time
+from collections import deque
 from typing import List
 
 from loguru import logger
@@ -9,6 +11,8 @@ from .message_pool import MessagePool, NoticeMessage
 from .relay import Relay
 from .subscription import Subscription
 
+PENDING_EVENTS_MAX = 100
+
 
 class RelayManager:
     def __init__(self) -> None:
@@ -18,6 +22,8 @@ class RelayManager:
         self.message_pool = MessagePool()
         self._cached_subscriptions: dict[str, Subscription] = {}
         self._subscriptions_lock = threading.Lock()
+        self._pending_events: deque[str] = deque(maxlen=PENDING_EVENTS_MAX)
+        self._pending_events_lock = threading.Lock()
 
     def add_relay(self, url: str) -> Relay:
         if url in list(self.relays.keys()):
@@ -25,6 +31,7 @@ class RelayManager:
             return self.relays[url]
 
         relay = Relay(url, self.message_pool)
+        relay.on_connect = self._on_relay_connect
         self.relays[url] = relay
 
         self._open_connection(relay)
@@ -100,8 +107,19 @@ class RelayManager:
             relay.close()
 
     def publish_message(self, message: str):
-        for relay in self.relays.values():
-            relay.publish(message)
+        connected_relays = [
+            r for r in self.relays.values() if r.connected and not r.shutdown
+        ]
+        if connected_relays:
+            for relay in self.relays.values():
+                relay.publish(message)
+        else:
+            with self._pending_events_lock:
+                self._pending_events.append(message)
+            logger.warning(
+                f"No connected relays. Queued outgoing event "
+                f"({len(self._pending_events)}/{PENDING_EVENTS_MAX})."
+            )
 
     def handle_notice(self, notice: NoticeMessage):
         relay = next((r for r in self.relays.values() if r.url == notice.url))
@@ -137,7 +155,47 @@ class RelayManager:
 
         logger.info(f"Restarting connection to relay '{relay.url}'")
 
+        self._drain_relay_queue(relay)
         self.remove_relay(relay.url)
         new_relay = self.add_relay(relay.url)
         new_relay.error_counter = relay.error_counter
         new_relay.error_list = relay.error_list
+
+    def _drain_relay_queue(self, relay: Relay):
+        """Move pending EVENT messages from a dead relay's queue to the
+        manager's pending queue so they can be resent on reconnection."""
+        drained = 0
+        while not relay.queue.empty():
+            try:
+                message = relay.queue.get_nowait()
+                data = json.loads(message)
+                if data[0] == "EVENT":
+                    with self._pending_events_lock:
+                        self._pending_events.append(message)
+                    drained += 1
+            except Exception:
+                break
+        if drained:
+            logger.info(f"Drained {drained} pending event(s) from relay '{relay.url}'.")
+
+    def _on_relay_connect(self, _relay: Relay):
+        self._flush_pending_events()
+
+    def _flush_pending_events(self):
+        with self._pending_events_lock:
+            if not self._pending_events:
+                return
+            connected_relays = [
+                r for r in self.relays.values() if r.connected and not r.shutdown
+            ]
+            if not connected_relays:
+                return
+            count = len(self._pending_events)
+            while self._pending_events:
+                message = self._pending_events.popleft()
+                for relay in connected_relays:
+                    relay.publish(message)
+            logger.info(
+                f"Flushed {count} pending event(s) to "
+                f"{len(connected_relays)} relay(s)."
+            )