A focal point is two finite numbers

float.TryParse takes "NaN" and "Infinity", and Math.Clamp keeps a NaN, so `focus=NaN,NaN` on an upload or a media PUT
was stored as given. Once the media was posted, every status and timeline response holding the post, and the Note
and its delivery, failed to serialise, for every viewer. FocalPoint.Parse takes finite numbers only (anything else is
ignored, as an unreadable focus was); the mapper and the renderer leave out a focus that isn't sound, and migration
_016 removes the ones stored before, from the uploads and from the copy each post keeps. What PrivaPub sends is
unchanged for any focus that could be sent before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LsXgEaXee4GCU1hwYgPJXw

CLAUDE.md

@@ -307,7 +307,9 @@ group www-data and reaches the private mongod; `sudo -u www-data` works too.
      and never cached. That is how remote video plays.
 
    nginx has a `/media/proxy/` location with `proxy_buffering off` and a 600 s read timeout for those streams.
-5. **Remote video and audio become one playable attachment** in the Mastodon API (`MastodonMapper.Playable`): the best MP4
+5. **A focal point is two finite numbers** within -1..1 (`FocalPoint.Parse`); anything else is ignored. A stored NaN made
+   every status, timeline and Note holding its post fail to serialise; migration `_016` removed the ones stored before.
+6. **Remote video and audio become one playable attachment** in the Mastodon API (`MastodonMapper.Playable`): the best MP4
    up to 720p that carries both sound and picture, including PeerTube's fragmented files inside an HLS entry. HLS
    playlists themselves are not rewritten.
 

PrivaPub.Tests/Http/MastodonMediaTests.cs

@@ -136,6 +136,25 @@ namespace PrivaPub.Tests.Http
 			Assert.Null((await alice.Client.Put($"/api/v1/media/{id}", ("description", ""))).Ok().Body.Text("description"));
 		}
 
+		// a focal point is two finite numbers: NaN or Infinity is ignored, never stored (it broke every timeline holding the post)
+		[Fact]
+		public async Task A_focal_point_that_is_not_a_number_is_ignored()
+		{
+			var alice = await _host.Mastodon("alice");
+			var uploaded = (await Upload(alice, "/api/v2/media", MastodonHelpers.JpegWithMetadata(32, 32), "image/jpeg", "a.jpg", ("focus", "NaN,NaN"))).Ok();
+			Assert.Null(uploaded.Body["meta"]?["focus"]);
+			var id = uploaded.Body.Text("id");
+
+			(await alice.Client.Put($"/api/v1/media/{id}", ("focus", "0.5,0.25"))).Ok();
+			foreach (var unsound in new[] { "NaN,0", "Infinity,1", "0,-Infinity" })
+			{
+				var focus = (await alice.Client.Put($"/api/v1/media/{id}", ("focus", unsound))).Ok().Body["meta"]!["focus"]!;
+				Assert.Equal((0.5, 0.25), (focus["x"]!.GetValue<double>(), focus["y"]!.GetValue<double>()));
+			}
+			var status = (await alice.Client.Post("/api/v1/statuses", ("status", "focused"), ("media_ids[]", id))).Ok();
+			Assert.Equal(0.5, status.Body["media_attachments"]![0]!["meta"]!["focus"]!["x"]!.GetValue<double>());
+		}
+
 		[Fact]
 		public async Task Unsupported_unreadable_and_missing_files_are_refused_with_422()
 		{

PrivaPub.Tests/Infrastructure/MigrationTests.cs

@@ -1,3 +1,4 @@
+using PrivaPub.Models.Media;
 using MongoDB.Bson;
 using MongoDB.Driver;
 using MongoDB.Entities;
@@ -22,6 +23,31 @@ namespace PrivaPub.Tests.Infrastructure
 	[Trait("Category", "Integration")]
 	public class MigrationTests
 	{
+		[Fact]
+		public async Task A_focal_point_that_is_not_a_number_is_removed()
+		{
+			Assert.SkipUnless(MongoFixture.Enabled, MongoFixture.Skip);
+			var token = TestContext.Current.CancellationToken;
+			var broken = new MediaAttachment { OwnerAvatarId = "a1", Focus = [float.NaN, 0f] };
+			var sound = new MediaAttachment { OwnerAvatarId = "a1", Focus = [0.5f, -0.5f] };
+			var post = new Post
+			{
+				ObjectURI = $"https://privapub.test/{Guid.NewGuid():N}",
+				Media = [new PostMedia { URL = "https://privapub.test/media/files/a.jpg", Focus = [float.PositiveInfinity, 0f] }, new PostMedia { URL = "https://privapub.test/media/files/b.jpg", Focus = [0.1f, 0.2f] }]
+			};
+			await DB.Default.SaveAsync(broken, token);
+			await DB.Default.SaveAsync(sound, token);
+			await DB.Default.SaveAsync(post, token);
+
+			await new _016_focal_points_are_finite().UpgradeAsync();
+
+			Assert.Null((await DB.Default.Find<MediaAttachment>().OneAsync(broken.ID, token)).Focus);
+			Assert.Equal(new[] { 0.5f, -0.5f }, (await DB.Default.Find<MediaAttachment>().OneAsync(sound.ID, token)).Focus);
+			var migrated = await DB.Default.Find<Post>().OneAsync(post.ID, token);
+			Assert.Null(migrated.Media[0].Focus);
+			Assert.Equal(new[] { 0.1f, 0.2f }, migrated.Media[1].Focus);
+		}
+
 		[Fact]
 		public async Task Stored_remote_content_is_sanitized_and_local_content_rendered()
 		{

PrivaPub/Api/Mastodon/Controllers/MediaController.cs

@@ -54,9 +54,8 @@ namespace PrivaPub.Api.Mastodon.Controllers
 				return NotFoundError();
 			if (Params.Has("description"))
 				attachment.Description = Params.Get("description")?.Trim() is { Length: > 0 } description ? description[..Math.Min(description.Length, 1500)] : default;
-			if (Params.Get("focus")?.Split(',') is [var x, var y]
-				&& float.TryParse(x, NumberStyles.Float, CultureInfo.InvariantCulture, out var fx) && float.TryParse(y, NumberStyles.Float, CultureInfo.InvariantCulture, out var fy))
-				attachment.Focus = new[] { Math.Clamp(fx, -1, 1), Math.Clamp(fy, -1, 1) };
+			if (FocalPoint.Parse(Params.Get("focus")) is { } focus)
+				attachment.Focus = focus;
 			await DB.Default.SaveAsync(attachment, token);
 			return Json(View(attachment));
 		}

PrivaPub/Api/Mastodon/Mappers/MastodonMapper.cs

@@ -642,7 +642,7 @@ namespace PrivaPub.Api.Mastodon.Mappers
 				meta["original"] = original;
 			if (media.DurationSeconds is { } length)
 				meta["length"] = TimeSpan.FromSeconds(length).ToString(@"h\:mm\:ss\.ff", CultureInfo.InvariantCulture);
-			if (media.Focus is { Length: 2 })
+			if (FocalPoint.IsSound(media.Focus))
 				meta["focus"] = new { x = media.Focus[0], y = media.Focus[1] };
 			return meta;
 		}

PrivaPub/Domain/Media/FocalPoint.cs

@@ -0,0 +1,21 @@
+using System.Globalization;
+
+namespace PrivaPub.Domain.Media
+{
+	// A focal point as Mastodon's API takes it ("x,y", each within -1..1): finite numbers only, clamped to the frame. A NaN
+	// once stored here made every status, timeline and Note holding the post fail to serialise, for every viewer.
+	public static class FocalPoint
+	{
+		public static float[] Parse(string value)
+		{
+			if (value?.Split(',') is not [var x, var y]
+				|| !float.TryParse(x, NumberStyles.Float, CultureInfo.InvariantCulture, out var fx) || !float.IsFinite(fx)
+				|| !float.TryParse(y, NumberStyles.Float, CultureInfo.InvariantCulture, out var fy) || !float.IsFinite(fy))
+				return default;
+			return [Math.Clamp(fx, -1, 1), Math.Clamp(fy, -1, 1)];
+		}
+
+		/// <summary>Whether a stored focal point can be written out: two finite numbers.</summary>
+		public static bool IsSound(float[] focus) => focus is [var x, var y] && float.IsFinite(x) && float.IsFinite(y);
+	}
+}

PrivaPub/Domain/Media/MediaService.cs

@@ -75,7 +75,7 @@ namespace PrivaPub.Domain.Media
 			{
 				OwnerAvatarId = owner.Id,
 				Description = Clean(description, 1500),
-				Focus = Focus(focus)
+				Focus = FocalPoint.Parse(focus)
 			};
 			if (ImageTypes.Contains(contentType))
 			{
@@ -252,15 +252,5 @@ namespace PrivaPub.Domain.Media
 
 		static string Clean(string value, int max) =>
 			string.IsNullOrWhiteSpace(value) ? default : value.Trim().Length <= max ? value.Trim() : value.Trim()[..max];
-
-		static float[] Focus(string focus)
-		{
-			var parts = focus?.Split(',');
-			if (parts is not { Length: 2 }
-				|| !float.TryParse(parts[0], NumberStyles.Float, CultureInfo.InvariantCulture, out var x)
-				|| !float.TryParse(parts[1], NumberStyles.Float, CultureInfo.InvariantCulture, out var y))
-				return default;
-			return new[] { Math.Clamp(x, -1, 1), Math.Clamp(y, -1, 1) };
-		}
 	}
 }

PrivaPub/Federation/Rendering/ActivityPubRenderer.cs

@@ -4,6 +4,7 @@ using PrivaPub.Federation.Actors;
 using PrivaPub.Federation.Objects;
 using PrivaPub.Models.Federation;
 using PrivaPub.Models.Post;
+using PrivaPub.Domain.Media;
 
 using System.Globalization;
 using System.Net;
@@ -386,7 +387,7 @@ namespace PrivaPub.Federation.Rendering
 				};
 				if (!string.IsNullOrEmpty(m.Blurhash))
 					attachment["blurhash"] = m.Blurhash;
-				if (m.Focus is { Length: 2 })
+				if (FocalPoint.IsSound(m.Focus))
 					attachment["focalPoint"] = new JsonArray(m.Focus[0], m.Focus[1]);
 				if (m.Width.HasValue && m.Height.HasValue)
 				{

PrivaPub/Infrastructure/Data/Migrations/_016_focal_points_are_finite.cs

@@ -0,0 +1,25 @@
+using MongoDB.Bson;
+using MongoDB.Driver;
+using MongoDB.Entities;
+
+using PrivaPub.Models.Media;
+
+using PostEntity = PrivaPub.Models.Post.Post;
+
+namespace PrivaPub.Infrastructure.Data.Migrations
+{
+	// A focal point of NaN or Infinity (taken as given before FocalPoint) made every status, timeline and Note holding its
+	// post fail to serialise: it goes, from the upload and from the copy each post keeps.
+	public class _016_focal_points_are_finite : IMigration
+	{
+		public async Task UpgradeAsync()
+		{
+			var unsound = new BsonDocument("$in", new BsonArray { double.NaN, double.PositiveInfinity, double.NegativeInfinity });
+			await DB.Default.Collection<MediaAttachment>().UpdateManyAsync(new BsonDocument("Focus", unsound),
+				new BsonDocument("$set", new BsonDocument("Focus", BsonNull.Value)));
+			await DB.Default.Collection<PostEntity>().UpdateManyAsync(new BsonDocument("Media.Focus", unsound),
+				new BsonDocument("$set", new BsonDocument("Media.$[m].Focus", BsonNull.Value)),
+				new UpdateOptions { ArrayFilters = [new BsonDocumentArrayFilterDefinition<BsonDocument>(new BsonDocument("m.Focus", unsound))] });
+		}
+	}
+}