[backend/federation] Handle incoming ASMove activities (ISH-118)

Iceshrimp.Backend/Core/Extensions/QueryableExtensions.cs

@@ -16,6 +16,30 @@ namespace Iceshrimp.Backend.Core.Extensions;
 
 public static class QueryableExtensions
 {
+	/// <summary>
+	/// This helper method allows consumers to obtain the performance &amp; memory footprint benefits of chunked DB transactions,
+	/// while not requiring them to work with chunks instead of a regular enumerator.
+	/// </summary>
+	/// <remarks>
+	/// Make sure to call .OrderBy() on the query, otherwise the results will be unpredictable.
+	/// </remarks>
+	/// <returns>
+	/// The result set as an IAsyncEnumerable. Makes one DB roundtrip at the start of each chunk.
+	/// Successive items of the chunk are yielded instantaneously.
+	/// </returns>
+	public static async IAsyncEnumerable<T> AsChunkedAsyncEnumerable<T>(this IQueryable<T> query, int chunkSize)
+	{
+		var offset = 0;
+		while (true)
+		{
+			var res = await query.Skip(offset).Take(chunkSize).ToArrayAsync();
+			if (res.Length == 0) break;
+			foreach (var item in res) yield return item;
+			if (res.Length < chunkSize) break;
+			offset += chunkSize;
+		}
+	}
+
 	public static IQueryable<T> Paginate<T>(
 		this IQueryable<T> query,
 		MastodonPaginationQuery pq,

Iceshrimp.Backend/Core/Federation/ActivityPub/ActivityHandlerService.cs

@@ -76,6 +76,7 @@ public class ActivityHandlerService(
 			ASEmojiReact react  => HandleReact(react, resolvedActor),
 			ASFollow follow     => HandleFollow(follow, resolvedActor),
 			ASLike like         => HandleLike(like, resolvedActor),
+			ASMove move         => HandleMove(move, resolvedActor),
 			ASReject reject     => HandleReject(reject, resolvedActor),
 			ASUndo undo         => HandleUndo(undo, resolvedActor),
 			ASUnfollow unfollow => HandleUnfollow(unfollow, resolvedActor),
@@ -204,8 +205,13 @@ public class ActivityHandlerService(
 		                      .FirstOrDefaultAsync(p => p.Followee == actor && p.FollowerId == ids[0]);
 
 		if (request == null)
-			throw GracefulException
+		{
-				.UnprocessableEntity($"No follow request matching follower '{ids[0]}' and followee '{actor.Id}' found");
+			if (await db.Followings.AnyAsync(p => p.Followee == actor && p.FollowerId == ids[0]))
+				return;
+
+			throw GracefulException.UnprocessableEntity($"No follow request matching follower '{ids[0]}'" +
+			                                            $"and followee '{actor.Id}' found");
+		}
 
 		await userSvc.AcceptFollowRequestAsync(request);
 	}
@@ -478,6 +484,51 @@ public class ActivityHandlerService(
 		await userSvc.BlockUserAsync(resolvedActor, resolvedBlockee);
 	}
 
+	private async Task HandleMove(ASMove activity, User resolvedActor)
+	{
+		if (activity.Target.Id is null) throw GracefulException.UnprocessableEntity("Move target must have an ID");
+		var target = await userResolver.ResolveAsync(activity.Target.Id);
+		var source = await userSvc.UpdateUserAsync(resolvedActor, force: true);
+		target = await userSvc.UpdateUserAsync(target, force: true);
+
+		var sourceUri = source.Uri ?? source.GetPublicUri(config.Value.WebDomain);
+		var targetUri = target.Uri ?? target.GetPublicUri(config.Value.WebDomain);
+		var aliases   = target.AlsoKnownAs ?? [];
+		if (!aliases.Contains(sourceUri))
+			throw GracefulException.UnprocessableEntity("Refusing to process move activity:" +
+			                                            "source uri not listed in target aliases");
+
+		source.MovedToUri = targetUri;
+		await db.SaveChangesAsync();
+
+		var followers = db.Followings
+		                  .Where(p => p.Followee == source)
+		                  .Where(p => p.Follower.IsLocalUser)
+		                  .OrderBy(p => p.Id)
+		                  .Select(p => p.Follower)
+		                  .PrecomputeRelationshipData(source)
+		                  .AsChunkedAsyncEnumerable(50);
+
+		await foreach (var follower in followers)
+		{
+			try
+			{
+				await userSvc.FollowUserAsync(follower, target);
+
+				// We need to transfer the precomputed properties to the source user for each follower so that the unfollow method works correctly
+				source.PrecomputedIsFollowedBy  = follower.PrecomputedIsFollowing;
+				source.PrecomputedIsRequestedBy = follower.PrecomputedIsRequested;
+
+				await userSvc.UnfollowUserAsync(follower, source);
+			}
+			catch (Exception e)
+			{
+				logger.LogWarning("Failed to process move ({sourceUri} -> {targetUri}) for user {id}: {error}",
+				                  sourceUri, targetUri, follower.Id, e);
+			}
+		}
+	}
+
 	private async Task UnfollowAsync(ASActor followeeActor, User follower)
 	{
 		//TODO: send reject? or do we not want to copy that part of the old ap core

Iceshrimp.Backend/Core/Federation/ActivityStreams/Types/ASActivity.cs

@@ -34,6 +34,7 @@ public class ASActivity : ASObjectWithId
 		public const string Undo     = $"{Ns}#Undo";
 		public const string Like     = $"{Ns}#Like";
 		public const string Block    = $"{Ns}#Block";
+		public const string Move     = $"{Ns}#Move";
 
 		// Extensions
 		public const string Bite       = "https://ns.mia.jetzt/as#Bite";
@@ -195,3 +196,13 @@ public class ASEmojiReact : ASActivity
 	[JC(typeof(ASTagConverter))]
 	public List<ASTag>? Tags { get; set; }
 }
+
+public class ASMove : ASActivity
+{
+	public ASMove() => Type = Types.Move;
+
+	[JR]
+	[J($"{Constants.ActivityStreamsNs}#target")]
+	[JC(typeof(ASLinkConverter))]
+	public required ASLink Target { get; set; }
+}

Iceshrimp.Backend/Core/Federation/ActivityStreams/Types/ASObject.cs

@@ -53,6 +53,7 @@ public class ASObject : ASObjectBase
 						ASActivity.Types.Announce          => token.ToObject<ASAnnounce>(),
 						ASActivity.Types.EmojiReact        => token.ToObject<ASEmojiReact>(),
 						ASActivity.Types.Block             => token.ToObject<ASBlock>(),
+						ASActivity.Types.Move              => token.ToObject<ASMove>(),
 						_                                  => token.ToObject<ASObject>()
 					};
 				case JTokenType.Array:

Iceshrimp.Backend/Core/Services/UserService.cs

@@ -251,6 +251,7 @@ public class UserService(
 	public async Task<User> UpdateUserAsync(User user, ASActor? actor = null, bool force = false)
 	{
 		if (!user.NeedsUpdate && actor == null && !force) return user;
+		if (user.IsLocalUser) return user;
 		if (actor is { IsUnresolved: true } or { Username: null })
 			actor = null; // This will trigger a fetch a couple lines down