A vote turned the other way replaces the first

Lemmy turns an upvote into a downvote with a Dislike alone (and back with a
Like), so the like stayed counted next to the downvote. Now an account has
one vote on a post: a Dislike takes its like away, a Like its downvote.

The Lemmy scenario's relayed votes were never failing for that reason only:
Lemmy 1.0 sends what it queued every 30 seconds, and the check gave up after
30. It waits a minute now, and both votes are plain checks: 22 pass, the
moderator's removal stays an expected failure (P7).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

CLAUDE.md

@@ -490,7 +490,8 @@ tools/pasture/run.sh down                                            # removes e
   activity at `warn` (`LEMMY_LOG` sets `RUST_LOG`); the reason is in the 400's body. It answers our community's echo of
   its own activity and every bare `Announce{object}` 400 by design, and the echo is still needed (see
   `docs/INTEROP.md`, Lemmy). A new Lemmy never sends what it queued for a server before its send worker for that
-  server started, so the scenario waits for that worker (`lm_worker`) before its first follow. 20 checks; relayed votes and a moderator's removal are expected failures (P7).
+  server started, so the scenario waits for that worker (`lm_worker`) before its first follow, and sends what it queued every 30 seconds, so a vote takes up to a minute.
+  22 checks; a moderator's removal is an expected failure (P7).
 - **Hollo (0.9.19):** Fedify's microblog server on the shared Postgres, set up through its web form (which
   checks `Origin` against `Host`, so the request names `hollo.test` without the port). It needs a 44-character
   `SECRET_KEY`, a media directory and a `themeColor`; statuses and votes go as JSON. Town only, no scenario.

PrivaPub.Tests/Federation/InteractionTests.cs

@@ -95,17 +95,43 @@ namespace PrivaPub.Tests.Federation
 				["id"] = $"{Origin(carol)}/reactions/{Guid.NewGuid():N}", ["type"] = "EmojiReact", ["actor"] = carol.Id, ["object"] = post.ObjectURI,
 				["content"] = "🔥"
 			});
+			Assert.Equal(1, (await DB.Default.Find<Post>().OneAsync(post.ID, token)).FavouritesCount);
 			await _harness.Deliver(carol, "/human-centipede", new JsonObject
 			{
 				["id"] = $"{Origin(carol)}/dislikes/{Guid.NewGuid():N}", ["type"] = "Dislike", ["actor"] = carol.Id, ["object"] = post.ObjectURI
 			});
 
+			// the downvote counts, and takes the place of carol's like (one vote each, as Lemmy votes)
 			var stored = await DB.Default.Find<Post>().OneAsync(post.ID, token);
-			Assert.Equal(1, stored.FavouritesCount);
+			Assert.Equal(0, stored.FavouritesCount);
 			Assert.Equal(1, stored.DownvotesCount);
 			Assert.True(await DB.Default.Find<Reaction>().Match(r => r.PostId == post.ID && r.ActorURI == carol.Id && r.Emoji == "🔥").ExecuteAnyAsync(token));
 		}
 
+		[Fact]
+		public async Task A_vote_turned_the_other_way_replaces_the_first_as_lemmy_sends_it()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, post) = await LocalPost();
+			var voter = new RemoteActor(_harness.Peer, "voter");
+			var other = new RemoteActor(_harness.Peer, "other");
+			JsonObject Vote(RemoteActor actor, string type) => new()
+			{
+				["id"] = $"{Origin(actor)}/{type.ToLowerInvariant()}s/{Guid.NewGuid():N}", ["type"] = type, ["actor"] = actor.Id, ["object"] = post.ObjectURI
+			};
+
+			await _harness.Deliver(other, "/human-centipede", Vote(other, "Like"));
+			await _harness.Deliver(voter, "/human-centipede", Vote(voter, "Dislike"));
+			await _harness.Deliver(voter, "/human-centipede", Vote(voter, "Like"));
+			var up = await DB.Default.Find<Post>().OneAsync(post.ID, token);
+			Assert.Equal((2, 0), (up.FavouritesCount, up.DownvotesCount));
+
+			await _harness.Deliver(voter, "/human-centipede", Vote(voter, "Dislike"));
+			var down = await DB.Default.Find<Post>().OneAsync(post.ID, token);
+			Assert.Equal((1, 1), (down.FavouritesCount, down.DownvotesCount));
+			Assert.False(await DB.Default.Find<Favourite>().Match(f => f.PostId == post.ID && f.ActorURI == voter.Id).ExecuteAnyAsync(token));
+		}
+
 		[Fact]
 		public async Task A_circle_member_likes_a_circle_post_and_an_outsider_cannot()
 		{

PrivaPub/Federation/Inbox/Handlers/DislikeHandler.cs

@@ -49,6 +49,10 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			}
 			Arrival.Accept("stored");
 			await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(b => b.Inc(p => p.DownvotesCount, 1)).ExecuteAsync(token);
+			// a vote replaces the other one: Lemmy turns an upvote into a downvote with this Dislike alone
+			if (await DB.Default.Find<Favourite>().Match(f => f.PostId == post.ID && f.ActorURI == actor.ActorURI).ExecuteFirstAsync(token) is { } liked
+				&& (await DB.Default.DeleteAsync<Favourite>(liked.ID)).DeletedCount > 0)
+				await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(b => b.Inc(p => p.FavouritesCount, -1)).ExecuteAsync(token);
 		}
 	}
 }

PrivaPub/Federation/Inbox/Handlers/LikeHandler.cs

@@ -59,6 +59,10 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			}
 			Arrival.Accept("stored");
 			await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(b => b.Inc(p => p.FavouritesCount, 1)).ExecuteAsync(token);
+			// a vote replaces the other one: Lemmy turns a downvote into an upvote with this Like alone
+			if (await DB.Default.Find<Downvote>().Match(d => d.PostId == post.ID && d.ActorURI == actor.ActorURI).ExecuteFirstAsync(token) is { } downvoted
+				&& (await DB.Default.DeleteAsync<Downvote>(downvoted.ID)).DeletedCount > 0)
+				await DB.Default.Update<PostEntity>().MatchID(post.ID).Modify(b => b.Inc(p => p.DownvotesCount, -1)).ExecuteAsync(token);
 			if (!post.IsFederatedCopy)
 				await Notifications.Add(post.GroupUserId, NotificationType.Favourite, actor.ID, actor.ActorURI, post.ID, token);
 		}

tools/pasture/scenarios/lemmy.sh

@@ -78,19 +78,14 @@ until_true 30 '[ "$(lm GET "comment/list?post_id=$lm_cats_id" | j "print(any(\"a
 	&& ok "alice's reply becomes a comment on Lemmy" || ko "PrivaPub reply missing as a Lemmy comment"
 
 echo "  votes"
-# Lemmy sends a vote only to the community, which relays it inside an Announce: P7 trusts those for the community's own posts.
+# Lemmy sends a vote only to the community, which relays it inside an Announce (trusted since ed08f80); Lemmy 1.0 sends
+# what it queued every 30 seconds, so a vote takes up to a minute
 lm POST post/like "{\"post_id\":$p_thread_on_lm,\"is_upvote\":true}" >/dev/null
-if until_true 15 '[ "$(curl -s -H "$LAH" "$P/api/v1/statuses/$p_thread_id" | j "print(d[\"favourites_count\"])")" = "1" ]'; then
+until_true 45 '[ "$(curl -s -H "$LAH" "$P/api/v1/statuses/$p_thread_id" | j "print(d[\"favourites_count\"])")" = "1" ]' \
-	ok "Lemmy's upvote counts as a like on PrivaPub"
+	&& ok "Lemmy's upvote counts as a like on PrivaPub" || ko "Lemmy's relayed upvote not counted"
-else
-	xf "Lemmy's upvote counts as a like on PrivaPub (votes relayed by a community are P7)"
-fi
 lm POST post/like "{\"post_id\":$p_thread_on_lm,\"is_upvote\":false}" >/dev/null
-if until_true 15 '[ "$(curl -s -H "$LAH" "$P/api/v1/statuses/$p_thread_id" | j "print(d[\"favourites_count\"], ((d.get(\"privapub\") or {}).get(\"votes\") or {}).get(\"down\"))")" = "0 1" ]'; then
+until_true 45 '[ "$(curl -s -H "$LAH" "$P/api/v1/statuses/$p_thread_id" | j "print(d[\"favourites_count\"], ((d.get(\"privapub\") or {}).get(\"votes\") or {}).get(\"down\"))")" = "0 1" ]' \
-	ok "Lemmy's change to a downvote reaches PrivaPub"
+	&& ok "Lemmy's change to a downvote reaches PrivaPub" || ko "Lemmy's change to a downvote not applied"
-else
-	xf "Lemmy's change to a downvote reaches PrivaPub (votes relayed by a community are P7)"
-fi
 curl -s -o /dev/null -X POST -H "$LAH" "$P/api/v1/statuses/$lm_cats_on_p/favourite"
 until_true 30 '[ "$(lm GET "post?id=$lm_cats_id" | j "print(d[\"post_view\"][\"post\"].get(\"upvotes\"))")" = "2" ]' && ok "alice's like is an upvote on Lemmy" || ko "like not counted as an upvote on Lemmy"