P7: feeds read as accounts, and PieFed's post Move

Lemmy 1.0's multi-communities and PieFed's feeds (`type: Feed`) resolve as accounts: the feed's `following` is kept
once a day with its counts, each community in it is read in turn, and `/api/v1/accounts/:id/following` lists them.
Lemmy's feed carries the instance's key and its text in `description`; both are taken as they are. Following a feed
answers 422 until the owner decides how a feed is followed.

A post moved to another community (PieFed's Move{object: post, origin, target}), relayed by the community it leaves,
goes there with its thread; a move into a community we host is not taken.

Checked in the pasture: a Lemmy 1.0 feed and a PieFed feed list their communities (ours among them); a PieFed post moved
from its web code arrives moved, with its comment.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Api/Mastodon/Controllers/AccountsController.cs

@@ -253,7 +253,10 @@ namespace PrivaPub.Api.Mastodon.Controllers
 		[HttpGet("/api/v1/accounts/{id}/following"), Scope("read:accounts", requiresUser: false), Microsoft.AspNetCore.Authorization.AllowAnonymous]
 		public async Task<IActionResult> Following(string id, CancellationToken token)
 		{
-			var (local, _) = await Find(id, token);
+			var (local, remote) = await Find(id, token);
+			// a feed's following is what it is: its communities, as its server lists them
+			if (remote is { AvatarType: AvatarType.Feed })
+				return Json(await AccountsFor(remote.FeedCommunities.Take(Limit(40, 80)), token));
 			if (local == default || local.Id != MyId)
 				return Json(Array.Empty<Account>());
 			var following = await Page.From(Params, Limit(40, 80))
@@ -269,6 +272,8 @@ namespace PrivaPub.Api.Mastodon.Controllers
 			var (local, remote) = await Find(id, token);
 			if (local == default && remote == default)
 				return NotFoundError();
+			if (remote is { AvatarType: AvatarType.Feed })
+				return Error(StatusCodes.Status422UnprocessableEntity, "A feed is followed through its communities");
 			var following = await _follows.FollowAs(Me, local?.Uri ?? remote.ActorURI, Params.Bool("reblogs") != false, token);
 			return following == default ? Error(StatusCodes.Status403Forbidden, "This action is not allowed") : Json(await Relationship(id, token));
 		}

PrivaPub/Federation/Actors/AccountCountsJob.cs

@@ -12,18 +12,23 @@ namespace PrivaPub.Federation.Actors
 	// A remote account's follower, following and post counts, as its own server publishes them (the totalItems of its
 	// followers, following and outbox collections), and the posts it features. Read when the account is fetched, at most
 	// once a day, never when someone looks at it; a hidden or missing collection leaves its count unknown. Mastodon and
-	// GoToSocial do the same.
+	// GoToSocial do the same. A feed's following is its communities: they are kept, and read in turn, so its list shows.
 	public class AccountCountsJob : IJobHandler
 	{
 		readonly IRemoteActorService _remoteActors;
 		readonly DbEntities _dbEntities;
 		readonly IFeaturedPosts _featured;
+		readonly ILocalActorService _localActors;
 
-		public AccountCountsJob(IRemoteActorService remoteActors, DbEntities dbEntities, IFeaturedPosts featured = default)
+		public const int MaxFeedCommunities = 50;
+
+		public AccountCountsJob(IRemoteActorService remoteActors, DbEntities dbEntities, IFeaturedPosts featured = default,
+			ILocalActorService localActors = default)
 		{
 			_remoteActors = remoteActors;
 			_dbEntities = dbEntities;
 			_featured = featured;
+			_localActors = localActors;
 		}
 
 		public JobKind Kind => JobKind.CountAccount;
@@ -38,28 +43,52 @@ namespace PrivaPub.Federation.Actors
 			var actor = await _dbEntities.ForeignAvatars.Match(a => a.ActorURI == job.Payload && !a.DeletionAt.HasValue).ExecuteFirstAsync(token);
 			if (actor == default)
 				return JobOutcome.Done;
-			await DB.Default.Update<ForeignAvatar>().MatchID(actor.ID)
-				.Modify(a => a.FollowersCount, await Total(actor, actor.FollowersURL, token))
-				.Modify(a => a.FollowingCount, await Total(actor, actor.FollowingURL, token))
-				.Modify(a => a.StatusesCount, await Total(actor, actor.OutboxURL, token))
-				.Modify(a => a.CountedAt, DateTime.UtcNow)
-				.ExecuteAsync(token);
+			var feed = actor.AvatarType == AvatarType.Feed;
+			var (following, communities) = await Read(actor, actor.FollowingURL, feed, token);
+			var update = DB.Default.Update<ForeignAvatar>().MatchID(actor.ID)
+				.Modify(a => a.FollowersCount, (await Read(actor, actor.FollowersURL, false, token)).Total)
+				.Modify(a => a.FollowingCount, following)
+				.Modify(a => a.StatusesCount, (await Read(actor, actor.OutboxURL, false, token)).Total)
+				.Modify(a => a.CountedAt, DateTime.UtcNow);
+			if (feed)
+				update = update.Modify(a => a.FeedCommunities, communities);
+			await update.ExecuteAsync(token);
+			if (feed)
+				foreach (var community in communities)
+					if (_localActors == default || !community.StartsWith(_localActors.BaseAddress + "/", StringComparison.Ordinal))
+						await _remoteActors.GetActor(community, refresh: false, token);
 			if (_featured != default)
 				await _featured.Sync(actor, token);
 			return JobOutcome.Done;
 		}
 
-		// only from the actor's own server, as everything we believe about it
-		async Task<int?> Total(ForeignAvatar actor, string collection, CancellationToken token)
+		// only from the actor's own server, as everything we believe about it: its total, and the ids it lists when asked
+		// (inline, or on its first page)
+		async Task<(int? Total, List<string> Items)> Read(ForeignAvatar actor, string collection, bool items, CancellationToken token)
 		{
+			var listed = new List<string>();
 			if (string.IsNullOrEmpty(collection) || !Origin.Same(collection, actor.ActorURI))
-				return default;
+				return (default, listed);
 			using var scope = HttpScope.For("collection");
 			using var fetched = await _remoteActors.FetchObject(collection, token);
-			return fetched != default && fetched.Root.ValueKind == System.Text.Json.JsonValueKind.Object
-				&& fetched.Root.TryGetProperty("totalItems", out var total) && total.TryGetInt32(out var count) && count >= 0
-				? count
-				: default;
+			if (fetched == default || fetched.Root.ValueKind != System.Text.Json.JsonValueKind.Object)
+				return (default, listed);
+			int? total = fetched.Root.TryGetProperty("totalItems", out var counted) && counted.TryGetInt32(out var count) && count >= 0 ? count : default;
+			if (!items)
+				return (total, listed);
+			var document = System.Text.Json.Nodes.JsonNode.Parse(fetched.Root.GetRawText());
+			var page = document["orderedItems"] ?? document["items"] ?? document["first"]?["orderedItems"] ?? document["first"]?["items"];
+			if (page == default && ActivityJson.Id(document["first"]) is { } first && Origin.Same(first, actor.ActorURI))
+			{
+				using var next = await _remoteActors.FetchObject(first, token);
+				var nextPage = next == default ? default : System.Text.Json.Nodes.JsonNode.Parse(next.Root.GetRawText());
+				page = nextPage?["orderedItems"] ?? nextPage?["items"];
+			}
+			if (page is System.Text.Json.Nodes.JsonArray array)
+				listed = array.Select(ActivityJson.Id)
+					.Where(id => Uri.TryCreate(id, UriKind.Absolute, out var uri) && uri.Scheme is "https" or "http")
+					.Distinct(StringComparer.Ordinal).Take(MaxFeedCommunities).ToList();
+			return (total, listed);
 		}
 	}
 }

PrivaPub/Federation/Actors/ActorDocument.cs

@@ -11,7 +11,7 @@ namespace PrivaPub.Federation.Actors
 
 	public sealed class ActorDocument
 	{
-		static readonly string[] ActorTypes = { "Person", "Service", "Application", "Group", "Organization" };
+		static readonly string[] ActorTypes = { "Person", "Service", "Application", "Group", "Organization", "Feed" };
 
 		public string Id { get; init; }
 		public string Type { get; init; }
@@ -74,7 +74,8 @@ namespace PrivaPub.Federation.Actors
 				Features = ActorFeatures.Detect(root),
 				PreferredUsername = RemoteActorService.Text(root, "preferredUsername"),
 				Name = RemoteActorService.Text(root, "name"),
-				Summary = RemoteActorService.Text(root, "summary"),
+				// (Lemmy's feed keeps its text in `description`)
+				Summary = RemoteActorService.Text(root, "summary") ?? (type == "Feed" ? RemoteActorService.Text(root, "description") : default),
 				Url = RemoteActorService.Text(root, "url") ?? id,
 				Inbox = Origin.Same(inbox, id) ? inbox : default,
 				Outbox = RemoteActorService.Text(root, "outbox"),

PrivaPub/Federation/Inbox/Handlers/AnnounceHandler.cs

@@ -59,7 +59,7 @@ namespace PrivaPub.Federation.Inbox.Handlers
 		public async Task Handle(JsonNode activity, ForeignAvatar actor, CancellationToken token)
 		{
 			var inner = activity["object"];
-			if (inner is JsonObject && Value(inner, "type") is "Create" or "Update" or "Delete" or "Like" or "Dislike" or "Undo" or "Add" or "Remove" or "Block" or "Lock")
+			if (inner is JsonObject && Value(inner, "type") is "Create" or "Update" or "Delete" or "Like" or "Dislike" or "Undo" or "Add" or "Remove" or "Block" or "Lock" or "Move")
 			{
 				await GroupActivity(inner, actor, token);
 				return;
@@ -242,6 +242,9 @@ namespace PrivaPub.Federation.Inbox.Handlers
 				case "Lock" when objectUri != default:
 					await Lock(objectUri, group, true, token);
 					break;
+				case "Move" when objectUri != default && Id(inner["origin"]) == group.ActorURI:
+					await Move(objectUri, Id(inner["target"]), group, token);
+					break;
 				case "Undo" when Value(inner["object"], "type") == "Lock":
 					await Lock(Id(inner["object"]?["object"]), group, false, token);
 					break;
@@ -305,6 +308,42 @@ namespace PrivaPub.Federation.Inbox.Handlers
 			Arrival.Accept(locked ? "locked" : "unlocked");
 		}
 
+		// A post moved to another community (PieFed's Move{object: post, origin, target}), relayed by the community it leaves,
+		// which vouches for what is done to its own posts as for a lock; its thread goes with it. A move into a community we
+		// host is not taken: it would be ours to announce.
+		async Task Move(string objectUri, string targetUri, ForeignAvatar group, CancellationToken token)
+		{
+			var post = await _dbEntities.Posts.Match(p => p.ObjectURI == objectUri && p.AudienceURI == group.ActorURI && !p.DeletedAt.HasValue)
+				.ExecuteFirstAsync(token);
+			if (post == default)
+			{
+				Arrival.Drop("unknown-object");
+				return;
+			}
+			Arrival.About(visibility: post.Visibility, created: post.CreationDate);
+			var target = targetUri == default || targetUri == group.ActorURI || await _localActors.FindByUri(targetUri, token) != default
+				? default
+				: await _remoteActors.GetActor(targetUri, refresh: false, token);
+			if (target is not { AvatarType: AvatarType.Group })
+			{
+				Arrival.Drop("unknown-target");
+				return;
+			}
+			var thread = new List<string> { post.ID };
+			var level = thread.ToList();
+			while (level.Count > 0 && thread.Count < MaxMoved)
+			{
+				var parents = level;
+				level = (await _dbEntities.Posts.Match(p => parents.Contains(p.AnsweringToPostId) && p.AudienceURI == group.ActorURI)
+					.Project(p => new PostEntity { ID = p.ID }).ExecuteAsync(token)).Select(p => p.ID).ToList();
+				thread.AddRange(level);
+			}
+			await DB.Default.Update<PostEntity>().Match(p => thread.Contains(p.ID)).Modify(p => p.AudienceURI, target.ActorURI).ExecuteAsync(token);
+			Arrival.Accept("moved");
+		}
+
+		const int MaxMoved = 1000;
+
 		// A community bans one of our personas (Lemmy's Block with the community as its target): kept as the community
 		// blocking the persona, so its relationship says blocked_by and nothing of the persona's is posted there until the
 		// Undo. A ban of someone from another server is no business of ours.

PrivaPub/Models/User/Avatar.cs

@@ -78,6 +78,7 @@ namespace PrivaPub.Models.User
 		public string OutboxURL { get; set; }
 		public string FeaturedURL { get; set; }//featured: the posts it pins
 		public List<PrivaPub.Models.Post.PostFlair> Flairs { get; set; } = new();//a community's labels for its posts
+		public List<string> FeedCommunities { get; set; } = new();//a feed's communities, its `following` (Lemmy's multi-communities, PieFed's feeds)
 		public List<string> SearchableBy { get; set; }//FEP-268d, when the account states it: outranks IsIndexable
 		public string ModeratorsURL { get; set; }//a community's attributedTo (Lemmy, PieFed, Mbin): the collection of its moderators
 		public List<AssertionKey> AssertionKeys { get; set; } = new();//its Ed25519 keys (FEP-521a), which prove what it sends (FEP-8b32)
@@ -152,7 +153,8 @@ namespace PrivaPub.Models.User
 		Group,
 		Organization,
 		Person,
-		Service
+		Service,
+		Feed
 	}
 
 	public enum AvatarAccountState