[backend/federation] Fix race condition when updating a user during a request

Iceshrimp.Backend/Core/Database/Tables/DriveFile.cs

@@ -26,7 +26,7 @@ public class DriveFile : IEntity
 	///     The created date of the DriveFile.
 	/// </summary>
 	[Column("createdAt")]
-	public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
+	public DateTime CreatedAt { get; set; }
 
 	/// <summary>
 	///     The owner ID.
@@ -188,7 +188,7 @@ public class DriveFile : IEntity
 	[Key]
 	[Column("id")]
 	[StringLength(32)]
-	public string Id { get; set; } = IdHelpers.GenerateSlowflakeId();
+	public string Id { get; set; } = null!;
 
 	public class FileProperties
 	{

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

@@ -18,9 +18,7 @@ public class ActivityDeliverService(ILogger<ActivityDeliverService> logger, Queu
 		{
 			ActorId            = actor.Id,
 			RecipientIds       = recipients.Select(p => p.Id).ToList(),
-			SerializedActivity =
+			SerializedActivity = JsonConvert.SerializeObject(activity, LdHelpers.JsonSerializerSettings),
-				JsonConvert.SerializeObject(activity,
-				                            LdHelpers.JsonSerializerSettings),
 			DeliverToFollowers = true
 		});
 	}
@@ -34,9 +32,7 @@ public class ActivityDeliverService(ILogger<ActivityDeliverService> logger, Queu
 		{
 			ActorId            = actor.Id,
 			RecipientIds       = recipients.Select(p => p.Id).ToList(),
-			SerializedActivity =
+			SerializedActivity = JsonConvert.SerializeObject(activity, LdHelpers.JsonSerializerSettings),
-				JsonConvert.SerializeObject(activity,
-				                            LdHelpers.JsonSerializerSettings),
 			DeliverToFollowers = false
 		});
 	}

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

@@ -112,13 +112,18 @@ public class UserResolver(
 	private async Task<User> GetUpdatedUser(User user)
 	{
 		if (!user.NeedsUpdate) return user;
+		user.LastFetchedAt = DateTime.UtcNow; // Prevent multiple background tasks from being started
 
 		try
 		{
 			var task = followupTaskSvc.ExecuteTask("UpdateUserAsync", async provider =>
 			{
+				// Get a fresh UserService instance in a new scope
 				var bgUserSvc = provider.GetRequiredService<UserService>();
-				await bgUserSvc.UpdateUserAsync(user);
+				
+				// Use the id overload so it doesn't attempt to insert in the main thread's DbContext
+				var fetchedUser = await bgUserSvc.UpdateUserAsync(user.Id);
+				user = fetchedUser;
 			});
 
 			// Return early, but continue execution in background

Iceshrimp.Backend/Core/Services/DriveService.cs

@@ -4,6 +4,7 @@ using Iceshrimp.Backend.Core.Configuration;
 using Iceshrimp.Backend.Core.Database;
 using Iceshrimp.Backend.Core.Database.Tables;
 using Iceshrimp.Backend.Core.Federation.Cryptography;
+using Iceshrimp.Backend.Core.Helpers;
 using Iceshrimp.Backend.Core.Middleware;
 using Iceshrimp.Backend.Core.Queues;
 using Microsoft.EntityFrameworkCore;
@@ -240,6 +241,8 @@ public class DriveService(
 
 		file = new DriveFile
 		{
+			Id                 = IdHelpers.GenerateSlowflakeId(),
+			CreatedAt          = DateTime.UtcNow,
 			User               = user,
 			UserHost           = user.Host,
 			Sha256             = digest,
@@ -332,6 +335,8 @@ file static class DriveFileExtensions
 
 		return new DriveFile
 		{
+			Id                 = IdHelpers.GenerateSlowflakeId(),
+			CreatedAt          = DateTime.UtcNow,
 			User               = user,
 			Blurhash           = file.Blurhash,
 			Type               = file.Type,

Iceshrimp.Backend/Core/Services/UserService.cs

@@ -158,9 +158,16 @@ public class UserService(
 		}
 	}
 
-	public async Task<User> UpdateUserAsync(User user, ASActor? actor = null)
+	public async Task<User> UpdateUserAsync(string id)
 	{
-		if (!user.NeedsUpdate && actor == null) return user;
+		var user = await db.Users.IncludeCommonProperties().FirstOrDefaultAsync(p => p.Id == id) ??
+		           throw new Exception("Cannot update nonexistent user");
+		return await UpdateUserAsync(user, force: true);
+	}
+
+	public async Task<User> UpdateUserAsync(User user, ASActor? actor = null, bool force = false)
+	{
+		if (!user.NeedsUpdate && actor == null && !force) return user;
 		if (actor is { IsUnresolved: true } or { Username: null })
 			actor = null; // This will trigger a fetch a couple lines down