SocialPub/PrivaPub.Tests/Federation/FollowersSynchronizationTests.cs

using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging.Abstractions;

using MongoDB.Entities;

using PrivaPub.Federation.Actors;
using PrivaPub.Federation.Outbox;
using PrivaPub.Federation.Signing;
using PrivaPub.Infrastructure.Http;
using PrivaPub.Infrastructure.Jobs;
using PrivaPub.Models.Federation;
using PrivaPub.Models.Jobs;
using PrivaPub.Models.Social;
using PrivaPub.Tests.Support;
using PrivaPub.Tests.Support.Host;

using System.Net;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json.Nodes;

namespace PrivaPub.Tests.Federation
{
	// FEP-8fcf (owner decision 2026-10-06): a delivery addressed to a persona's followers tells the receiving server, in a signed
	// header, a digest of the persona's followers there; the roll-call it names lists them, to that server only
	[Trait("Category", "Integration")]
	[Xunit.Collection(nameof(Exclusive))]
	public sealed class FollowersSynchronizationTests : IAsyncLifetime
	{
		static readonly string[] PeerHosts = { "localhost", "127.0.0.1" };

		Harness _harness;

		public async ValueTask InitializeAsync()
		{
			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
			_harness = await Harness.Start();
			await DB.Default.DeleteAsync<RemoteInstance>(i => PeerHosts.Contains(i.Host));
		}

		public async ValueTask DisposeAsync()
		{
			if (_harness != default)
				await _harness.DisposeAsync();
		}

		static CancellationToken Token => TestContext.Current.CancellationToken;

		[Fact]
		public void The_digest_is_the_xor_of_each_ids_sha256_whatever_the_order()
		{
			Assert.Equal(new string('0', 64), FollowersSynchronization.Digest([]));
			Assert.Equal(FollowersSynchronization.Digest(["https://a.example/users/one", "https://a.example/users/two"]),
				FollowersSynchronization.Digest(["https://a.example/users/two", "https://a.example/users/one"]));
			Assert.Equal(Convert.ToHexStringLower(SHA256.HashData(Encoding.UTF8.GetBytes("https://a.example/users/one"))),
				FollowersSynchronization.Digest(["https://a.example/users/one"]));
		}

		async Task<HttpRequestRecord> Delivered(LocalActor signer, string inbox, JsonObject activity)
		{
			await _harness.Delivery.Enqueue(signer, new[] { inbox }, activity, Token);
			var job = await DB.Default.Find<Job>().Match(j => j.DedupeKey == $"{activity["id"]!.GetValue<string>()}|{inbox}").ExecuteSingleAsync(Token);
			var handler = new DeliveryJobHandler(_harness.Local, Peer.Http(), new HostCircuitBreaker(new MemoryCache(new MemoryCacheOptions())),
				NullLogger<DeliveryJobHandler>.Instance);
			Assert.Equal(JobResult.Done, (await handler.Handle(job, Token)).Result);
			return Assert.Single(_harness.Peer.Requests, r => r.Body?.Contains(activity["id"]!.GetValue<string>()) == true);
		}

		static JsonObject Create(LocalActor author, params string[] to) => new()
		{
			["id"] = $"{author.Uri}/grunts/{Guid.NewGuid():N}", ["type"] = "Create", ["actor"] = author.Uri, ["to"] = new JsonArray(to.Select(t => (JsonNode)t).ToArray()),
			["object"] = new JsonObject { ["type"] = "Note", ["content"] = "hi", ["to"] = new JsonArray(to.Select(t => (JsonNode)t).ToArray()) }
		};

		[Fact]
		public async Task A_delivery_to_followers_carries_a_signed_digest_of_the_followers_on_that_server_only()
		{
			var (_, alice) = await _harness.Persona("alice");
			var one = new RemoteActor(_harness.Peer, "one");
			var two = new RemoteActor(_harness.Peer, "two");
			var far = new RemoteActor(_harness.Peer, "far", _harness.Peer.B);
			await _harness.FollowedBy(alice, one);
			await _harness.FollowedBy(alice, two);
			await _harness.FollowedBy(alice, far);
			await DB.Default.SaveAsync(new Follower
			{
				LocalActorId = alice.Id, LocalActorKind = alice.Kind, ActorURI = _harness.Peer.A + "/users/asking", InboxURL = _harness.Peer.A + "/users/asking/inbox", IsAccepted = false
			}, Token);
			_harness.Peer.Answer("/inbox", 202);

			var received = await Delivered(alice, _harness.Peer.A + "/inbox", Create(alice, alice.Followers));

			Assert.Equal(alice.Followers, Value(received, "collectionId"));
			Assert.Equal(alice.Followers + "/roll-call", Value(received, "url"));
			Assert.Equal(FollowersSynchronization.Digest([one.Id, two.Id]), Value(received, "digest"));
			var signature = HttpSignatures.Parse(received.Signature);
			Assert.Equal(new[] { "(request-target)", "host", "date", "digest", "collection-synchronization" }, signature.Headers);
			var signingString = $"(request-target): post /inbox\nhost: {received.Headers["Host"]}\ndate: {received.Headers["Date"]}\ndigest: {received.Headers["Digest"]}\n"
				+ $"collection-synchronization: {received.Headers[FollowersSynchronization.Header]}";
			using var key = RSA.Create();
			key.ImportFromPem(alice.PublicKeyPem);
			Assert.True(key.VerifyData(Encoding.UTF8.GetBytes(signingString), signature.Signature, HashAlgorithmName.SHA256, RSASignaturePadding.Pkcs1));
		}

		static string Value(HttpRequestRecord received, string name)
		{
			var values = received.Headers[FollowersSynchronization.Header].Split(',', StringSplitOptions.TrimEntries)
				.Select(p => p.Split('=', 2)).ToDictionary(p => p[0], p => p[1].Trim('"'));
			return values[name];
		}

		[Fact]
		public async Task A_delivery_that_is_not_for_followers_carries_none()
		{
			var (_, alice) = await _harness.Persona("alice");
			var recipient = new RemoteActor(_harness.Peer, "recipient");
			await _harness.FollowedBy(alice, recipient);
			_harness.Peer.Answer("/inbox", 202);

			var received = await Delivered(alice, _harness.Peer.A + "/inbox", Create(alice, recipient.Id));

			Assert.False(received.Headers.ContainsKey(FollowersSynchronization.Header));
			Assert.DoesNotContain("collection-synchronization", HttpSignatures.Parse(received.Signature).Headers);
		}

		// Mastodon undoes a follow it never knew of with the same id each time ({actor}#follows//undo): when it comes again,
		// after a new follow, it ends that one too; a copy of it, with nothing to end, stays a copy
		[Fact]
		public async Task An_undo_of_a_follow_sent_again_after_a_new_follow_ends_that_one_too()
		{
			var (_, alice) = await _harness.Persona("alice");
			var bob = new RemoteActor(_harness.Peer, "bob");
			var undo = new JsonObject
			{
				["id"] = bob.Id + "#follows//undo", ["type"] = "Undo", ["actor"] = bob.Id,
				["object"] = new JsonObject { ["id"] = bob.Id + "#follows/", ["type"] = "Follow", ["actor"] = bob.Id, ["object"] = alice.Uri }
			};
			Task<bool> Follows() => DB.Default.Find<Follower>().Match(f => f.LocalActorId == alice.Id && f.ActorURI == bob.Id).ExecuteAnyAsync(Token);

			await _harness.FollowedBy(alice, bob);
			await _harness.Deliver(bob, "/human-centipede", undo.DeepClone());
			Assert.False(await Follows());

			await _harness.FollowedBy(alice, bob);
			await _harness.Deliver(bob, "/human-centipede", undo.DeepClone());
			Assert.False(await Follows());

			Assert.Equal("duplicate", (await _harness.Deliver(bob, "/human-centipede", undo.DeepClone())).Reason);
		}

		// received: bob's delivery claims a digest of his followers here, and lists them at his own synchronisation URL
		async Task Claimed(RemoteActor bob, string digest, params string[] listed)
		{
			var path = new Uri(bob.Id).AbsolutePath + "/followers/sync";
			_harness.Peer.Serve(path, new JsonObject
			{
				["id"] = bob.Id + "/followers/sync", ["type"] = "OrderedCollection",
				["orderedItems"] = new JsonArray(listed.Select(l => (JsonNode)l).ToArray())
			}.ToJsonString());
			var note = $"{bob.Id}/notes/{Guid.NewGuid():N}";
			var request = bob.Post(Harness.Host, "/human-centipede", new JsonObject
			{
				["id"] = note + "/activity", ["type"] = "Create", ["actor"] = bob.Id, ["to"] = new JsonArray(bob.Id + "/followers"),
				["object"] = new JsonObject { ["id"] = note, ["type"] = "Note", ["attributedTo"] = bob.Id, ["to"] = new JsonArray(bob.Id + "/followers"), ["content"] = "hi" }
			});
			request.Headers[FollowersSynchronization.Header] = $"collectionId=\"{bob.Id}/followers\", url=\"{bob.Id}/followers/sync\", digest=\"{digest}\"";
			await _harness.Receiver.Receive(request, default, Token);
			var job = await DB.Default.Find<Job>().Match(j => j.Kind == JobKind.SynchronizeFollowing && j.State == JobState.Pending && j.Payload.Contains(bob.Id))
				.ExecuteSingleAsync(Token);
			var handler = new FollowingSynchronization(_harness.Db, _harness.Local, _harness.Remote, _harness.Follows, _harness.Delivery);
			Assert.Equal(JobResult.Done, (await handler.Handle(job, Token)).Result);
		}

		async Task<Following> Follows(LocalActor persona, RemoteActor bob, FollowState state)
		{
			var following = new Following
			{
				AvatarId = persona.Id, TargetActorURI = bob.Id, TargetInboxURL = bob.Id + "/inbox", State = state, FollowActivityURI = persona.ActivityUri($"follow-{Guid.NewGuid():N}")
			};
			await DB.Default.SaveAsync(following, Token);
			return following;
		}

		Task<Following> Following(LocalActor persona, RemoteActor bob) =>
			DB.Default.Find<Following>().Match(f => f.AvatarId == persona.Id && f.TargetActorURI == bob.Id).ExecuteFirstAsync(Token);

		[Fact]
		public async Task A_claim_that_differs_is_mended_from_the_accounts_own_list()
		{
			var (_, alice) = await _harness.Persona("alice");
			var (_, carol) = await _harness.Persona("carol");
			var (_, dave) = await _harness.Persona("dave");
			var bob = new RemoteActor(_harness.Peer, "bob");
			await Follows(alice, bob, FollowState.Accepted);
			await Follows(carol, bob, FollowState.Requested);

			await Claimed(bob, FollowersSynchronization.Digest([carol.Uri, dave.Uri]), carol.Uri, dave.Uri);

			Assert.Null(await Following(alice, bob));
			Assert.Equal(FollowState.Accepted, (await Following(carol, bob)).State);
			var undos = (await _harness.Outgoing(bob.Id + "/inbox")).Where(a => a["type"]!.GetValue<string>() == "Undo").ToList();
			Assert.Equal(new[] { alice.Uri, dave.Uri }.Order(), undos.Select(u => u["actor"]!.GetValue<string>()).Order());
			var daves = Assert.Single(undos, u => u["actor"]!.GetValue<string>() == dave.Uri);
			Assert.Equal(("Follow", bob.Id), (daves["object"]!["type"]!.GetValue<string>(), daves["object"]!["object"]!.GetValue<string>()));
		}

		[Fact]
		public async Task A_list_the_claim_does_not_describe_ends_no_follow()
		{
			var (_, alice) = await _harness.Persona("alice");
			var bob = new RemoteActor(_harness.Peer, "bob");
			await Follows(alice, bob, FollowState.Accepted);

			await Claimed(bob, FollowersSynchronization.Digest(["https://privapub.test/peasants/someone"]));

			Assert.Equal(FollowState.Accepted, (await Following(alice, bob)).State);
		}

		[Fact]
		public async Task A_claim_that_agrees_reads_nothing()
		{
			var (_, alice) = await _harness.Persona("alice");
			var bob = new RemoteActor(_harness.Peer, "bob");
			await Follows(alice, bob, FollowState.Accepted);

			await Claimed(bob, FollowersSynchronization.Digest([alice.Uri]));

			Assert.DoesNotContain(_harness.Peer.Requests, r => r.Path.EndsWith("/followers/sync"));
			Assert.Equal(FollowState.Accepted, (await Following(alice, bob)).State);
		}
	}

	[Trait("Category", "Integration")]
	public sealed class RollCallTests : IAsyncLifetime
	{
		PrivaPubHost _host;
		HttpClient _client;
		Peer _peer;

		public async ValueTask InitializeAsync()
		{
			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
			_host = await PrivaPubHost.Shared();
			_client = _host.Client();
			_peer = await Peer.Start();
		}

		public async ValueTask DisposeAsync()
		{
			_client?.Dispose();
			if (_peer != default)
				await _peer.DisposeAsync();
		}

		static string[] Items(JsonObject collection) => collection["orderedItems"]!.AsArray().Select(i => i!.GetValue<string>()).ToArray();

		[Fact]
		public async Task The_roll_call_lists_the_followers_on_the_signing_server_and_asks_for_a_signature()
		{
			var token = TestContext.Current.CancellationToken;
			var persona = await _host.Persona(await _host.SignUp(), "rollcall");
			var near = new RemoteActor(_peer, "near");
			var server = new RemoteActor(_peer, "instance", type: "Application");
			var far = new RemoteActor(_peer, "far", _peer.B);
			foreach (var follower in new[] { near, far })
				await DB.Default.SaveAsync(new Follower
				{
					LocalActorId = persona.Id, LocalActorKind = LocalActorKind.Person, ActorURI = follower.Id, InboxURL = follower.Id + "/inbox"
				}, token);
			var path = $"/peasants/{persona.UserName}/groupies/roll-call";

			var asServer = await _client.Fetch(server.SignedGet(path));
			var asFar = await _client.Fetch(far.SignedGet(path));

			Assert.Equal(HttpStatusCode.OK, asServer.Status);
			Assert.Equal(persona.ActorUri() + "/groupies/roll-call", asServer.Json["id"]!.GetValue<string>());
			Assert.Equal(new[] { near.Id }, Items(asServer.Json));
			Assert.Equal(new[] { far.Id }, Items(asFar.Json));
			Assert.Equal(HttpStatusCode.Unauthorized, (await _client.Fetch(path)).Status);
		}
	}
}