Forwarded activities are believed as far as their origin vouches

A thread's server passes on what happens in it, signed with its own key: Mastodon forwards the replies to its
accounts' posts and their deletions, Friendica every activity in its threads. PrivaPub answered them 401, which also
tells a sender its signature failed. Now they get 202 and nothing in them is believed: a forwarded Create or Update is
taken as its object reads at the actor's origin, a Delete of a public or unlisted copy once that origin answers 404 or
410 (RemoteActorService.IsGone; FederationHttp remembers the status of a refusal), anything else is let go, and our own
activities coming back are ignored. A forwarded copy has its own dedupe key, so one that failed never hides the
author's own delivery.

A reply in the thread of someone followed here is kept, as Mastodon keeps them. Mastodon delivers a reply to the
followers of the account it answers; PrivaPub dropped those as unaddressed, which the pasture showed: the outsider's
reply its Mastodon scenario said was never delivered had been, and was thrown away.

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

PrivaPub.Tests/Federation/ForwardedTests.cs

@@ -0,0 +1,167 @@
+using MongoDB.Entities;
+
+using PrivaPub.Models.Post;
+using PrivaPub.Tests.Support;
+
+using System.Text.Json.Nodes;
+
+using static PrivaPub.Tests.Support.FederatedSeeds;
+
+namespace PrivaPub.Tests.Federation
+{
+	// Inbox forwarding: a thread's server passes on the activities in it, signed with its own key (Mastodon the replies to
+	// its accounts' posts and their deletions, Friendica everything in its threads). They used to be refused with 401.
+	[Trait("Category", "Integration")]
+	public sealed class ForwardedTests : IAsyncLifetime
+	{
+		Harness _harness;
+
+		public async ValueTask InitializeAsync()
+		{
+			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
+			_harness = await Harness.Start();
+		}
+
+		public async ValueTask DisposeAsync()
+		{
+			if (_harness != default)
+				await _harness.DisposeAsync();
+		}
+
+		PrivaPub.Models.Statistics.InteractionEvent Processed(string activity) => _harness.Ledger.Of("in").Last(e => e.Activity == activity);
+
+		PrivaPub.Models.Statistics.InteractionEvent Received(string activity) => _harness.Ledger.Of("recv").Last(e => e.Activity == activity);
+
+		Task<Post> Stored(string objectUri) =>
+			DB.Default.Find<Post>().Match(p => p.ObjectURI == objectUri).ExecuteFirstAsync(TestContext.Current.CancellationToken);
+
+		// alice follows the thread's author (on its own server), whose post she holds; bob, elsewhere, replies to it
+		async Task<(RemoteActor Owner, RemoteActor Bob, JsonObject Reply)> Thread()
+		{
+			var (_, alice) = await _harness.Persona("alice");
+			var owner = new RemoteActor(_harness.Peer, "owner", _harness.Peer.B);
+			var bob = new RemoteActor(_harness.Peer, "bob");
+			await Follows(alice.Id, owner);
+			var post = PublicNote(owner, "<p>the thread</p>");
+			await _harness.Deliver(owner, "/human-centipede", Create(owner, post));
+			Assert.NotNull(await Stored(IdOf(post)));
+
+			var reply = PublicNote(bob, "<p>bob's reply as he wrote it</p>", owner.Id);
+			reply["inReplyTo"] = IdOf(post);
+			_harness.Peer.Serve(new Uri(IdOf(reply)).AbsolutePath, reply.ToJsonString());
+			return (owner, bob, reply);
+		}
+
+		[Fact]
+		public async Task A_reply_the_threads_server_forwards_is_kept_as_its_author_wrote_it()
+		{
+			var (owner, bob, reply) = await Thread();
+			var claimed = (JsonObject)reply.DeepClone();
+			claimed["content"] = "<p>what the forwarder says bob wrote</p>";
+
+			var result = await _harness.Deliver(owner, "/human-centipede", Create(bob, claimed));
+
+			Assert.Equal((202, "forwarded"), (result.StatusCode, result.Reason));
+			var stored = await Stored(IdOf(reply));
+			Assert.NotNull(stored);
+			Assert.Equal(bob.Id, stored.ActorURI);
+			Assert.Contains("as he wrote it", stored.ContentHtml);
+			Assert.Equal(("accepted", "stored"), (Processed("Create").Outcome, Processed("Create").Reason));
+			Assert.True((await DB.Default.Find<PrivaPub.Models.Federation.ObjectRecord>().Match(r => r.ObjectURI == IdOf(reply)).ExecuteFirstAsync(TestContext.Current.CancellationToken)).Refetched);
+		}
+
+		[Fact]
+		public async Task A_forwarded_edit_applies_the_post_as_its_origin_has_it_now()
+		{
+			var (owner, bob, reply) = await Thread();
+			await _harness.Deliver(owner, "/human-centipede", Create(bob, reply));
+			var edited = (JsonObject)reply.DeepClone();
+			edited["content"] = "<p>bob's reply, edited</p>";
+			edited["updated"] = DateTime.UtcNow.AddMinutes(1).ToString("O");
+			_harness.Peer.Serve(new Uri(IdOf(reply)).AbsolutePath, edited.ToJsonString());
+			var claimed = (JsonObject)edited.DeepClone();
+			claimed["content"] = "<p>an edit bob never made</p>";
+
+			await _harness.Deliver(owner, "/human-centipede", Activity(bob, "Update", claimed));
+
+			Assert.Contains("bob's reply, edited", (await Stored(IdOf(reply))).ContentHtml);
+		}
+
+		[Fact]
+		public async Task A_forwarded_deletion_waits_for_the_origin_to_say_the_post_is_gone()
+		{
+			var (owner, bob, reply) = await Thread();
+			await _harness.Deliver(owner, "/human-centipede", Create(bob, reply));
+
+			await _harness.Deliver(owner, "/human-centipede", Activity(bob, "Delete", JsonValue.Create(IdOf(reply))!));
+			Assert.Equal(("dropped", "forwarded-not-gone"), (Processed("Delete").Outcome, Processed("Delete").Reason));
+			Assert.NotNull(await Stored(IdOf(reply)));
+
+			_harness.Peer.Answer(new Uri(IdOf(reply)).AbsolutePath, 410);
+			await _harness.Deliver(owner, "/human-centipede", Activity(bob, "Delete", JsonValue.Create(IdOf(reply))!));
+			Assert.Null(await Stored(IdOf(reply)));
+		}
+
+		// the origin answers 404 for a followers-only post to our instance actor too: only its author's server says it is gone
+		[Fact]
+		public async Task A_forwarded_deletion_of_a_followers_only_post_is_left_to_its_author()
+		{
+			var (owner, bob, reply) = await Thread();
+			await _harness.Deliver(owner, "/human-centipede", Create(bob, reply));
+			await DB.Default.Update<Post>().Match(p => p.ObjectURI == IdOf(reply)).Modify(p => p.Visibility, PostVisibility.FollowersOnly).ExecuteAsync(TestContext.Current.CancellationToken);
+			_harness.Peer.Answer(new Uri(IdOf(reply)).AbsolutePath, 404);
+
+			await _harness.Deliver(owner, "/human-centipede", Activity(bob, "Delete", JsonValue.Create(IdOf(reply))!));
+
+			Assert.Equal(("dropped", "forwarded-private"), (Processed("Delete").Outcome, Processed("Delete").Reason));
+			Assert.NotNull(await Stored(IdOf(reply)));
+		}
+
+		// a forwarded copy is kept apart from the author's own delivery, which carries what the copy could not
+		[Fact]
+		public async Task The_authors_own_delivery_is_still_taken_after_a_forwarded_copy_that_failed()
+		{
+			var (owner, bob, reply) = await Thread();
+			_harness.Peer.Answer(new Uri(IdOf(reply)).AbsolutePath, 404);
+			var create = Create(bob, reply);
+
+			await _harness.Deliver(owner, "/human-centipede", create);
+			Assert.Null(await Stored(IdOf(reply)));
+
+			var direct = await _harness.Deliver(bob, "/human-centipede", create);
+			Assert.Equal("queued", direct.Reason);
+			Assert.NotNull(await Stored(IdOf(reply)));
+		}
+
+		// what cannot be checked against its origin (a vote, a follow, someone else's post) is let go, answered 202: a 401
+		// tells the forwarder its signature failed
+		[Fact]
+		public async Task What_a_forwarder_cannot_vouch_for_is_let_go_without_an_error()
+		{
+			var (owner, bob, reply) = await Thread();
+			var like = new JsonObject { ["id"] = NewId(bob, "likes"), ["type"] = "Like", ["actor"] = bob.Id, ["object"] = IdOf(reply) };
+
+			var result = await _harness.Deliver(owner, "/human-centipede", like);
+			Assert.Equal((202, "forwarded-ignored"), (result.StatusCode, result.Reason));
+			Assert.Equal("dropped", Received("Like").Outcome);
+
+			var onTheForwardersServer = PublicNote(owner, "<p>a post of the forwarder's</p>");
+			onTheForwardersServer["attributedTo"] = bob.Id;
+			result = await _harness.Deliver(owner, "/human-centipede", Create(bob, onTheForwardersServer));
+			Assert.Equal((202, "forwarded-ignored"), (result.StatusCode, result.Reason));
+			Assert.Null(await Stored(IdOf(onTheForwardersServer)));
+
+			// our own, coming back from a thread on another server
+			var (_, carol) = await _harness.Persona("carol");
+			var ours = new JsonObject
+			{
+				["id"] = carol.Uri + "/grunts/create-" + Guid.NewGuid().ToString("N"),
+				["type"] = "Create",
+				["actor"] = carol.Uri,
+				["object"] = new JsonObject { ["id"] = carol.Uri + "/scribbles/" + Guid.NewGuid().ToString("N"), ["type"] = "Note", ["attributedTo"] = carol.Uri }
+			};
+			result = await _harness.Deliver(owner, "/human-centipede", ours);
+			Assert.Equal((202, "forwarded-ignored"), (result.StatusCode, result.Reason));
+		}
+	}
+}

PrivaPub.Tests/Support/Harness.cs

@@ -135,7 +135,8 @@ namespace PrivaPub.Tests.Support
 		public async Task<InboxResult> Deliver(RemoteActor sender, string path, JsonNode activity)
 		{
 			var result = await Receiver.Receive(sender.Post(Host, path, activity), default, CancellationToken.None);
-			var dedupe = "inbox|" + (activity is JsonObject ? activity["id"]?.GetValue<string>() : default);
+			var id = activity is JsonObject ? activity["id"]?.GetValue<string>() : default;
+			var dedupe = (result.Reason == "forwarded" ? "inbox|forwarded|" : "inbox|") + id;
 			var job = await DB.Default.Find<Job>().Match(j => j.DedupeKey == dedupe).ExecuteFirstAsync();
 			if (job != default)
 				Assert.Equal(JobResult.Done, (await Processor.Handle(job, CancellationToken.None)).Result);