Funkwhale's answers, deletions and NodeInfo are understood

Three shapes Funkwhale 2.0 sends, each of which lost something:
- its Accept is named after the Follow it answers, on our origin (`…#follows/<uuid>/accept`), and was refused as off its
  actor's origin, so no follow of a channel completed: an Accept or Reject whose id extends the id of the activity it
  answers, on our origin, is now taken;
- a channel deletes its uploads in one Delete without an id, their ids in a list as the object's id: each is deleted;
- its NodeInfo discovery names the document under its swagger schema's URL: a link whose path names NodeInfo is taken
  when no rel is known.

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

PrivaPub.Tests/Federation/InboxGapTests.cs

@@ -160,6 +160,63 @@ namespace PrivaPub.Tests.Federation
 			Assert.Equal(400, (await _harness.Deliver(organiser, "/human-centipede", Create(organiser, claimed))).StatusCode);
 		}
 
+		// Funkwhale names its Accept after the Follow it answers (`<our Follow's id>/accept`), on our origin, not its own
+		[Fact]
+		public async Task An_answer_named_after_our_follow_is_taken_and_one_naming_someone_elses_is_not()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (root, alice) = await _harness.Persona("alice");
+			var channel = new RemoteActor(_harness.Peer, "channel");
+			await _harness.Follows.Follow(root, new FollowForm { AvatarId = alice.Id, Target = channel.Id }, token);
+			var following = await DB.Default.Find<Following>().Match(f => f.AvatarId == alice.Id && f.TargetActorURI == channel.Id).ExecuteSingleAsync(token);
+
+			var elsewhere = await _harness.Deliver(channel, "/human-centipede", new JsonObject
+			{
+				["id"] = "https://privapub.test/peasants/somebody/accept", ["type"] = "Accept", ["actor"] = channel.Id, ["object"] = following.FollowActivityURI
+			});
+			Assert.Equal(400, elsewhere.StatusCode);
+
+			var named = await _harness.Deliver(channel, "/human-centipede", new JsonObject
+			{
+				["id"] = following.FollowActivityURI + "/accept", ["type"] = "Accept", ["actor"] = channel.Id,
+				["object"] = new JsonObject { ["id"] = following.FollowActivityURI, ["type"] = "Follow", ["actor"] = alice.Uri, ["object"] = channel.Id }
+			});
+			Assert.Equal(202, named.StatusCode);
+			Assert.Equal(FollowState.Accepted, (await DB.Default.Find<Following>().OneAsync(following.ID, token)).State);
+		}
+
+		// Funkwhale's channel deletes its uploads in one Delete, their ids in a list as the object's id (and the Delete has
+		// no id of its own)
+		[Fact]
+		public async Task A_delete_naming_several_objects_removes_each()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var channel = new RemoteActor(_harness.Peer, "channel");
+			await Follows(alice.Id, channel);
+			var first = PublicNote(channel, "<p>a first track</p>");
+			var second = PublicNote(channel, "<p>a second track</p>");
+			await _harness.Deliver(channel, "/human-centipede", Create(channel, first));
+			await _harness.Deliver(channel, "/human-centipede", Create(channel, second));
+			Task<bool> Held(JsonObject note) => DB.Default.Find<Post>().Match(p => p.ObjectURI == IdOf(note)).ExecuteAnyAsync(token);
+			Assert.True(await Held(first) && await Held(second));
+
+			var result = await _harness.Receiver.Receive(channel.Post(Harness.Host, "/human-centipede", new JsonObject
+			{
+				["type"] = "Delete", ["actor"] = channel.Id,
+				["object"] = new JsonObject { ["id"] = new JsonArray(IdOf(first), IdOf(second)), ["type"] = "Audio" }
+			}), default, token);
+			Assert.Equal(202, result.StatusCode);
+			var listed = IdOf(first);
+			var job = await DB.Default.Find<PrivaPub.Models.Jobs.Job>().Match(j => j.Kind == PrivaPub.Models.Jobs.JobKind.ProcessInbox
+				&& j.State == PrivaPub.Models.Jobs.JobState.Pending && j.Payload.Contains(listed)).Sort(j => j.CreatedAt, MongoDB.Entities.Order.Descending)
+				.ExecuteFirstAsync(token);
+			await _harness.Processor.Handle(job, token);
+
+			Assert.False(await Held(first));
+			Assert.False(await Held(second));
+		}
+
 		[Fact]
 		public async Task A_like_naming_a_post_by_its_page_counts_and_its_undo_too()
 		{

PrivaPub.Tests/Statistics/DescribeTests.cs

@@ -59,6 +59,10 @@ namespace PrivaPub.Tests.Statistics
 
 			Assert.Equal(("https://a.example/2.2", "2.2"), InstanceDocuments.NodeInfoLink(links));
 			Assert.Equal(default, InstanceDocuments.NodeInfoLink(Json("[]")));
+			// Funkwhale 2.0 links its NodeInfo under its swagger schema's URL
+			Assert.Equal(("https://f.example/api/v2/instance/nodeinfo/2.1", "2.1"), InstanceDocuments.NodeInfoLink(Json("""
+				{"links":[{"rel":"https://docs.funkwhale.audio/swagger/schema.yml","href":"https://f.example/api/v2/instance/nodeinfo/2.1"}]}
+				""")));
 		}
 
 		[Fact]

PrivaPub/Federation/Inbox/Handlers/DeleteHandler.cs

@@ -43,11 +43,20 @@ namespace PrivaPub.Federation.Inbox.Handlers
 
 		public string Type => "Delete";
 
+		const int MaxObjects = 50;
+
 		public async Task Handle(JsonNode activity, ForeignAvatar actor, CancellationToken token)
 		{
-			var delete = activity;
+			// Funkwhale deletes several uploads at once, naming them in one list as the object's id
+			var objectUris = activity["object"] is JsonObject { } inner && inner["id"] is JsonArray ids
+				? ids.Select(Id).Where(id => id != default).Distinct(StringComparer.Ordinal).Take(MaxObjects).ToList()
+				: new List<string> { Id(activity["object"]) };
+			foreach (var objectUri in objectUris)
+				await Handle(activity, actor, objectUri, token);
+		}
 
-			var objectUri = Id(delete["object"]);
+		async Task Handle(JsonNode activity, ForeignAvatar actor, string objectUri, CancellationToken token)
+		{
 			if (!Origin.Same(objectUri, actor.ActorURI))
 			{
 				Arrival.Drop("cross-origin");

PrivaPub/Federation/Inbox/InboxReceiver.cs

@@ -222,7 +222,10 @@ namespace PrivaPub.Federation.Inbox
 		async Task<InboxResult> ShapeProblem(string type, JsonNode activity, string actorUri, CancellationToken token)
 		{
 			var activityId = Id(activity);
-			if (activityId != default && !Origin.Same(activityId, actorUri))
+			// (Funkwhale names its answer after the activity it answers: `<our Follow's id>/accept`)
+			if (activityId != default && !Origin.Same(activityId, actorUri)
+				&& !(type is "Accept" or "Reject" && Id(activity["object"]) is { } answered && Origin.Same(answered, _localActors.BaseAddress)
+					&& activityId.StartsWith(answered + "/", StringComparison.Ordinal)))
 				return new(StatusCodes.Status400BadRequest, "the activity's id is not on its actor's origin", Reason: "id-cross-origin");
 
 			var inner = activity["object"];

PrivaPub/Federation/Objects/InstanceDocuments.cs

@@ -38,6 +38,12 @@ namespace PrivaPub.Federation.Objects
 					if (link.ValueKind == JsonValueKind.Object && Text(link, "rel") == schema && Text(link, "href") is { } href
 						&& href.StartsWith("https://", StringComparison.OrdinalIgnoreCase))
 						return (href, schema[(schema.LastIndexOf('/') + 1)..]);
+			// a link to a NodeInfo document under another rel (Funkwhale 2.0 names it after its swagger schema): its path
+			// says what it is, and its last segment the version
+			foreach (var link in list.EnumerateArray())
+				if (link.ValueKind == JsonValueKind.Object && Text(link, "href") is { } href && href.StartsWith("https://", StringComparison.OrdinalIgnoreCase)
+					&& Uri.TryCreate(href, UriKind.Absolute, out var target) && target.AbsolutePath.Contains("/nodeinfo", StringComparison.OrdinalIgnoreCase))
+					return (href, target.Segments[^1].Trim('/') is var last && Schemas.Any(s => s.EndsWith("/" + last, StringComparison.Ordinal)) ? last : "2.0");
 			return default;
 		}