Add snapshot retrieval retries and fallback

src/nostr/client.py

@@ -407,6 +407,60 @@ class NostrClient:
             logger.info("publish_snapshot completed in %.2f seconds", duration)
         return manifest, manifest_id
 
+    async def _fetch_chunks_with_retry(
+        self, manifest_event
+    ) -> tuple[Manifest, list[bytes]] | None:
+        """Retrieve all chunks referenced by ``manifest_event`` with retries."""
+
+        pubkey = self.keys.public_key()
+        timeout = timedelta(seconds=10)
+
+        try:
+            data = json.loads(manifest_event.content())
+            manifest = Manifest(
+                ver=data["ver"],
+                algo=data["algo"],
+                chunks=[ChunkMeta(**c) for c in data["chunks"]],
+                delta_since=(
+                    int(data["delta_since"])
+                    if data.get("delta_since") is not None
+                    else None
+                ),
+            )
+        except Exception:
+            return None
+
+        chunks: list[bytes] = []
+        for meta in manifest.chunks:
+            attempt = 0
+            chunk_bytes: bytes | None = None
+            while attempt < MAX_RETRIES:
+                cf = Filter().author(pubkey).kind(Kind(KIND_SNAPSHOT_CHUNK))
+                if meta.event_id:
+                    cf = cf.id(EventId.parse(meta.event_id))
+                else:
+                    cf = cf.identifier(meta.id)
+                cf = cf.limit(1)
+                cev = (await self.client.fetch_events(cf, timeout)).to_vec()
+                if cev:
+                    candidate = base64.b64decode(cev[0].content().encode("utf-8"))
+                    if hashlib.sha256(candidate).hexdigest() == meta.hash:
+                        chunk_bytes = candidate
+                        break
+                attempt += 1
+                if attempt < MAX_RETRIES:
+                    await asyncio.sleep(RETRY_DELAY)
+            if chunk_bytes is None:
+                return None
+            chunks.append(chunk_bytes)
+
+        man_id = getattr(manifest_event, "id", None)
+        if hasattr(man_id, "to_hex"):
+            man_id = man_id.to_hex()
+        self.current_manifest = manifest
+        self.current_manifest_id = man_id
+        return manifest, chunks
+
     async def fetch_latest_snapshot(self) -> Tuple[Manifest, list[bytes]] | None:
         """Retrieve the latest manifest and all snapshot chunks."""
         if self.offline_mode or not self.relays:
@@ -414,47 +468,18 @@ class NostrClient:
         await self._connect_async()
 
         pubkey = self.keys.public_key()
-        f = Filter().author(pubkey).kind(Kind(KIND_MANIFEST)).limit(1)
+        f = Filter().author(pubkey).kind(Kind(KIND_MANIFEST)).limit(3)
         timeout = timedelta(seconds=10)
         events = (await self.client.fetch_events(f, timeout)).to_vec()
         if not events:
             return None
-        manifest_event = events[0]
-        manifest_raw = manifest_event.content()
-        data = json.loads(manifest_raw)
-        manifest = Manifest(
-            ver=data["ver"],
-            algo=data["algo"],
-            chunks=[ChunkMeta(**c) for c in data["chunks"]],
-            delta_since=(
-                int(data["delta_since"])
-                if data.get("delta_since") is not None
-                else None
-            ),
-        )
 
-        chunks: list[bytes] = []
-        for meta in manifest.chunks:
-            cf = Filter().author(pubkey).kind(Kind(KIND_SNAPSHOT_CHUNK))
-            if meta.event_id:
-                cf = cf.id(EventId.parse(meta.event_id))
-            else:
-                cf = cf.identifier(meta.id)
-            cf = cf.limit(1)
-            cev = (await self.client.fetch_events(cf, timeout)).to_vec()
-            if not cev:
-                raise ValueError(f"Missing chunk {meta.id}")
-            chunk_bytes = base64.b64decode(cev[0].content().encode("utf-8"))
-            if hashlib.sha256(chunk_bytes).hexdigest() != meta.hash:
-                raise ValueError(f"Checksum mismatch for chunk {meta.id}")
-            chunks.append(chunk_bytes)
+        for manifest_event in events:
+            result = await self._fetch_chunks_with_retry(manifest_event)
+            if result is not None:
+                return result
 
-        self.current_manifest = manifest
-        man_id = getattr(manifest_event, "id", None)
-        if hasattr(man_id, "to_hex"):
-            man_id = man_id.to_hex()
-        self.current_manifest_id = man_id
-        return manifest, chunks
+        return None
 
     async def publish_delta(self, delta_bytes: bytes, manifest_id: str) -> str:
         """Publish a delta event referencing a manifest."""

src/tests/test_nostr_dummy_client.py

@@ -65,3 +65,43 @@ def test_publish_and_fetch_deltas(dummy_nostr_client):
     assert relay.manifests[-1].delta_since == second_ts
     deltas = asyncio.run(client.fetch_deltas_since(0))
     assert deltas == [d1, d2]
+
+
+def test_fetch_snapshot_fallback_on_missing_chunk(dummy_nostr_client, monkeypatch):
+    import os
+    import gzip
+
+    client, relay = dummy_nostr_client
+    monkeypatch.setattr("nostr.client.MAX_RETRIES", 3)
+    monkeypatch.setattr("nostr.client.RETRY_DELAY", 0)
+
+    data1 = os.urandom(60000)
+    manifest1, _ = asyncio.run(client.publish_snapshot(data1))
+
+    data2 = os.urandom(60000)
+    manifest2, _ = asyncio.run(client.publish_snapshot(data2))
+
+    missing = manifest2.chunks[0]
+    if missing.event_id:
+        relay.chunks.pop(missing.event_id, None)
+    relay.chunks.pop(missing.id, None)
+
+    relay.filters.clear()
+
+    fetched_manifest, chunk_bytes = asyncio.run(client.fetch_latest_snapshot())
+
+    assert gzip.decompress(b"".join(chunk_bytes)) == data1
+    assert [c.event_id for c in fetched_manifest.chunks] == [
+        c.event_id for c in manifest1.chunks
+    ]
+
+    attempts = sum(
+        1
+        for f in relay.filters
+        if getattr(f, "kind_val", None) == KIND_SNAPSHOT_CHUNK
+        and (
+            missing.id in getattr(f, "ids", [])
+            or (missing.event_id and missing.event_id in getattr(f, "ids", []))
+        )
+    )
+    assert attempts == 3