[backend] Handle incoming ASAccept activities

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

@@ -1,3 +1,4 @@
+using Iceshrimp.Backend.Core.Configuration;
 using Iceshrimp.Backend.Core.Database;
 using Iceshrimp.Backend.Core.Database.Tables;
 using Iceshrimp.Backend.Core.Federation.ActivityStreams;
@@ -7,6 +8,7 @@ using Iceshrimp.Backend.Core.Middleware;
 using Iceshrimp.Backend.Core.Queues;
 using Iceshrimp.Backend.Core.Services;
 using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Options;
 
 namespace Iceshrimp.Backend.Core.Federation.ActivityPub;
 
@@ -16,7 +18,8 @@ public class ActivityHandlerService(
 	UserResolver userResolver,
 	DatabaseContext db,
 	QueueService queueService,
-	ActivityRenderer activityRenderer
+	ActivityRenderer activityRenderer,
+	IOptions<Config.InstanceSection> config
 ) {
 	public Task PerformActivityAsync(ASActivity activity, string? inboxUserId) {
 		logger.LogDebug("Processing activity: {activity}", activity.Id);
@@ -38,6 +41,10 @@ public class ActivityHandlerService(
 				if (activity.Object is { } obj) return UnfollowAsync(obj, activity.Actor);
 				throw GracefulException.UnprocessableEntity("Unfollow activity object is invalid");
 			}
+			case ASActivity.Types.Accept: {
+				if (activity.Object is { } obj) return AcceptAsync(obj, activity.Actor);
+				throw GracefulException.UnprocessableEntity("Follow activity object is invalid");
+			}
 			case ASActivity.Types.Undo: {
 				//TODO: implement the rest
 				//TODO: test if this actually works
@@ -118,4 +125,40 @@ public class ActivityHandlerService(
 		await db.FollowRequests.Where(p => p.Follower == follower && p.Followee == followee).ExecuteDeleteAsync();
 		await db.Followings.Where(p => p.Follower == follower && p.Followee == followee).ExecuteDeleteAsync();
 	}
+
+	private async Task AcceptAsync(ASObject obj, ASObject actor) {
+		var prefix = $"https://{config.Value.WebDomain}/follows/";
+		if (!obj.Id.StartsWith(prefix))
+			throw GracefulException.UnprocessableEntity($"Object id '{obj.Id}' not a valid follow request");
+
+		var resolvedActor = await userResolver.ResolveAsync(actor.Id);
+		var ids           = obj.Id[prefix.Length..].TrimEnd('/').Split("/");
+		if (ids.Length != 2 || ids[1] != resolvedActor.Id)
+			throw GracefulException
+				.UnprocessableEntity($"Actor id '{resolvedActor.Id}' doesn't match followee id '{ids[1]}'");
+
+		var request = await db.FollowRequests
+		                      .Include(p => p.Follower)
+		                      .FirstOrDefaultAsync(p => p.Followee == resolvedActor && p.FollowerId == ids[0]);
+
+		if (request == null)
+			throw GracefulException
+				.UnprocessableEntity($"No follow request matching follower '{ids[0]}' and followee '{resolvedActor.Id}' found");
+
+		var following = new Following {
+			Id                  = IdHelpers.GenerateSlowflakeId(),
+			CreatedAt           = DateTime.UtcNow,
+			Follower            = request.Follower,
+			Followee            = resolvedActor,
+			FollowerHost        = request.FollowerHost,
+			FolloweeHost        = request.FolloweeHost,
+			FollowerInbox       = request.FollowerInbox,
+			FolloweeInbox       = request.FolloweeInbox,
+			FollowerSharedInbox = request.FollowerSharedInbox,
+			FolloweeSharedInbox = request.FolloweeSharedInbox
+		};
+		db.Remove(request);
+		await db.AddAsync(following);
+		await db.SaveChangesAsync();
+	}
 }

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

@@ -9,7 +9,7 @@ public class ActivityRenderer(IOptions<Config.InstanceSection> config) {
 	public static ASActivity RenderCreate(ASObject obj, ASObject actor) {
 		return new ASActivity {
 			Id     = $"{obj.Id}#Create",
-			Type   = "https://www.w3.org/ns/activitystreams#Create",
+			Type   = ASActivity.Types.Create,
 			Actor  = new ASActor { Id = actor.Id },
 			Object = obj
 		};
@@ -18,7 +18,7 @@ public class ActivityRenderer(IOptions<Config.InstanceSection> config) {
 	public ASActivity RenderAccept(ASObject actor, ASObject obj) {
 		return new ASActivity {
 			Id   = $"https://{config.Value.WebDomain}/activities/{Guid.NewGuid().ToString().ToLowerInvariant()}",
-			Type = "https://www.w3.org/ns/activitystreams#Accept",
+			Type = ASActivity.Types.Accept,
 			Actor = new ASActor {
 				Id = actor.Id
 			},

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

@@ -30,6 +30,14 @@ public class ASFollow : ASActivity {
 	public ASFollow() => Type = Types.Follow;
 }
 
+public class ASUnfollow : ASActivity {
+	public ASUnfollow() => Type = Types.Unfollow;
+}
+
+public class ASAccept : ASActivity {
+	public ASAccept() => Type = Types.Accept;
+}
+
 //TODO: add the rest
 
 public sealed class ASActivityConverter : ASSerializer.ListSingleObjectConverter<ASActivity>;

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

@@ -25,9 +25,9 @@ public class ASObject {
 				ASNote.Types.Note          => token.ToObject<ASNote>(),
 				ASActivity.Types.Create    => token.ToObject<ASActivity>(),
 				ASActivity.Types.Delete    => token.ToObject<ASActivity>(),
-				ASActivity.Types.Follow    => token.ToObject<ASActivity>(),
+				ASActivity.Types.Follow    => token.ToObject<ASFollow>(),
-				ASActivity.Types.Unfollow  => token.ToObject<ASActivity>(),
+				ASActivity.Types.Unfollow  => token.ToObject<ASUnfollow>(),
-				ASActivity.Types.Accept    => token.ToObject<ASActivity>(),
+				ASActivity.Types.Accept    => token.ToObject<ASAccept>(),
 				ASActivity.Types.Undo      => token.ToObject<ASActivity>(),
 				ASActivity.Types.Like      => token.ToObject<ASActivity>(),
 				_                          => token.ToObject<ASObject>()