Podcast episodes play; servers with NodeInfo2 only are described

Castopod announces an episode with a Note that only links to the episode's page, which serves a PodcastEpisode. PrivaPub
reads PodcastEpisode (its words in description, its sound in audio, its cover in image), and a Note that is only a link
to its author's own episode takes the episode's sound, title, cover and words, so the post plays. A server that
publishes no NodeInfo is described from NodeInfo2 (/.well-known/x-nodeinfo2), as Castopod publishes.

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

PrivaPub.Tests/Federation/InboundRoutingTests.cs

@@ -212,6 +212,47 @@ namespace PrivaPub.Tests.Federation
 			Assert.False(await DB.Default.Find<PrivaPub.Models.Federation.Follower>().Match(f => f.LocalActorId == alice.Id && f.ActorURI == forte.Id).ExecuteAnyAsync(token));
 		}
 
+		// Castopod announces an episode with a note that only links to it: the post takes the episode's sound, title and cover
+		[Fact]
+		public async Task A_note_that_only_links_its_authors_episode_carries_the_episodes_sound()
+		{
+			var token = TestContext.Current.CancellationToken;
+			var (_, alice) = await _harness.Persona("alice");
+			var podcast = new RemoteActor(_harness.Peer, "pod");
+			await DB.Default.SaveAsync(new PrivaPub.Models.Social.Following
+			{
+				AvatarId = alice.Id, TargetActorURI = podcast.Id, TargetInboxURL = podcast.Id + "/inbox", State = PrivaPub.Models.Social.FollowState.Accepted
+			}, token);
+			var origin = new Uri(podcast.Id).GetLeftPart(UriPartial.Authority);
+			var episodePath = $"/episodes/{Guid.NewGuid():N}";
+			_harness.Peer.Serve(episodePath, new JsonObject
+			{
+				["id"] = origin + episodePath, ["type"] = "PodcastEpisode", ["attributedTo"] = podcast.Id, ["to"] = new JsonArray("https://www.w3.org/ns/activitystreams#Public"),
+				["description"] = new JsonObject { ["type"] = "Note", ["content"] = "the meadow", ["mediaType"] = "text/markdown" },
+				["image"] = new JsonObject { ["type"] = "Image", ["url"] = origin + "/cover.png" },
+				["audio"] = new JsonObject
+				{
+					["id"] = origin + "/one.mp3", ["type"] = "Audio", ["name"] = "Episode one", ["duration"] = 4.0,
+					["url"] = new JsonObject { ["href"] = origin + "/one.mp3", ["type"] = "Link", ["mediaType"] = "audio/mpeg" }
+				}
+			}.ToJsonString());
+			var noteId = NewId(podcast, "posts");
+
+			await _harness.Deliver(podcast, "/human-centipede", new JsonObject
+			{
+				["id"] = noteId + "/activity", ["type"] = "Create", ["actor"] = podcast.Id, ["to"] = new JsonArray("https://www.w3.org/ns/activitystreams#Public"),
+				["object"] = new JsonObject
+				{
+					["id"] = noteId, ["type"] = "Note", ["attributedTo"] = podcast.Id, ["to"] = new JsonArray("https://www.w3.org/ns/activitystreams#Public"),
+					["content"] = $"<a href=\"{origin + episodePath}\">Episode one</a><br/>", ["published"] = DateTime.UtcNow.ToString("O")
+				}
+			});
+
+			var post = await DB.Default.Find<Post>().Match(p => p.ObjectURI == noteId).ExecuteSingleAsync(token);
+			Assert.Equal(origin + "/one.mp3", Assert.Single(post.Media).RemoteURL);
+			Assert.Equal(("Episode one", origin + "/cover.png", 4.0), (post.Title, post.CoverURL, post.Audio.DurationSeconds));
+		}
+
 		[Fact]
 		public async Task A_join_of_a_local_post_is_answered_with_ignore()
 		{

PrivaPub.Tests/Federation/NoteParserTests.cs

@@ -35,6 +35,26 @@ namespace PrivaPub.Tests.Federation
 			}
 			""";
 
+		// Castopod's episode: its words in description, its sound in audio, the sound's name for a title
+		[Fact]
+		public void A_podcast_episode_is_read_with_its_words_sound_and_cover()
+		{
+			var episode = NoteParser.Parse(JsonNode.Parse("""
+				{"id":"https://castopod.test/@pod/episodes/one","type":"PodcastEpisode","published":"2026-10-06T09:08:17+00:00",
+				 "to":["https://www.w3.org/ns/activitystreams#Public"],"attributedTo":"https://castopod.test/@pod",
+				 "description":{"type":"Note","mediaType":"text/markdown","content":"Listen to the **meadow**","contentMap":{"en":"<p>Listen to the meadow</p>"}},
+				 "image":{"type":"Image","mediaType":"image/png","url":"https://castopod.test/media/cover.png"},
+				 "audio":{"id":"https://castopod.test/audio/one.mp3","type":"Audio","name":"Episode one","size":16791,"duration":4.02,
+				  "url":{"href":"https://castopod.test/audio/one.mp3","type":"Link","mediaType":"audio/mpeg"}}}
+				"""));
+
+			Assert.Equal(("PodcastEpisode", "Episode one", "https://castopod.test/media/cover.png"), (episode.Type, episode.Title, episode.CoverURL));
+			Assert.Contains("<strong>meadow</strong>", episode.ContentHtml);
+			var sound = Assert.Single(episode.Attachments);
+			Assert.Equal(("https://castopod.test/audio/one.mp3", "audio/mpeg"), (sound.RemoteURL, sound.ContentType));
+			Assert.Equal(4.02, episode.Audio.DurationSeconds);
+		}
+
 		[Fact]
 		public void Reads_a_mastodon_note()
 		{

PrivaPub.Tests/Statistics/DescribeTests.cs

@@ -48,6 +48,21 @@ namespace PrivaPub.Tests.Statistics
 			Assert.Equal("mobilizon", InstanceDocuments.NodeInfo(Json("""{"software":{"name":"Mobilizon"}}"""), "2.1").Software);
 		}
 
+		// Castopod publishes NodeInfo2 only
+		[Fact]
+		public void NodeInfo2_gives_the_server_and_its_usage()
+		{
+			var facts = InstanceDocuments.NodeInfo2(Json("""
+				{"version":"1.0","server":{"baseUrl":"https://castopod.test/","name":"Castopod","software":"Castopod","version":"1.15.5"},
+				 "protocols":["activitypub"],"openRegistrations":false,"usage":{"users":{"total":1,"activeMonth":1,"activeHalfyear":1},"localPosts":3}}
+				"""));
+
+			Assert.Equal(("castopod", "1.15.5", "Castopod", "nodeinfo2-1.0"), (facts.Software, facts.SoftwareVersion, facts.NodeName, facts.Version));
+			Assert.Equal(new[] { "activitypub" }, facts.Protocols);
+			Assert.Equal((1L, 3L), (facts.UsersTotal.Value, facts.LocalPosts.Value));
+			Assert.Null(InstanceDocuments.NodeInfo2(Json("""{"version":"1.0","server":{}}""")));
+		}
+
 		[Fact]
 		public void The_newest_https_nodeinfo_link_is_chosen()
 		{

PrivaPub/Federation/Inbox/RemotePosts.cs

@@ -83,7 +83,7 @@ namespace PrivaPub.Federation.Inbox
 		{
 			var mentions = await Mentions(note, to.Concat(cc), _localActors, token);
 
-			return new PostEntity
+			var post = new PostEntity
 			{
 				ID = PrivacyIds.Arrived(note.Published),
 				ObjectURI = note.Id,
@@ -135,6 +135,31 @@ namespace PrivaPub.Federation.Inbox
 				UpdateDate = note.Updated ?? note.Published,
 				EditedAt = note.Updated
 			};
+			await Episode(post, note, author, token);
+			return post;
+		}
+
+		static readonly System.Text.RegularExpressions.Regex Href = new(@"href=""([^""]+)""", System.Text.RegularExpressions.RegexOptions.Compiled);
+
+		// a post that is only a link to a podcast episode of its own author (Castopod announces each episode so): the
+		// episode's sound, title and cover, read from it
+		async Task Episode(PostEntity post, NoteDocument note, ForeignAvatar author, CancellationToken token)
+		{
+			if (note.Type != "Note" || post.Media.Count > 0 || string.IsNullOrEmpty(note.ContentHtml))
+				return;
+			var links = Href.Matches(note.ContentHtml).Select(m => System.Net.WebUtility.HtmlDecode(m.Groups[1].Value)).Distinct().ToList();
+			if (links.Count != 1 || links[0] == note.Id || !Origin.Same(links[0], author.ActorURI))
+				return;
+			using var scope = HttpScope.For("object");
+			using var fetched = await _remoteActors.FetchObject(links[0], token);
+			var episode = fetched == default ? default : NoteParser.Parse(JsonNode.Parse(fetched.Root.GetRawText()));
+			if (episode is not { Type: "PodcastEpisode" } || episode.AttributedTo != author.ActorURI)
+				return;
+			post.Media = episode.Attachments.ToList();
+			post.Audio = episode.Audio;
+			post.Title ??= episode.Title;
+			post.CoverURL ??= episode.CoverURL;
+			post.Excerpt ??= ObjectShapes.Text(episode.ContentHtml, 1000);
 		}
 
 		public async Task<PostEntity> Parent(string inReplyTo, int depth, CancellationToken token)

PrivaPub/Federation/Objects/InstanceDescriber.cs

@@ -75,6 +75,17 @@ namespace PrivaPub.Federation.Objects
 					else
 						error = "NodeInfo unreadable";
 				}
+				// no NodeInfo: NodeInfo2, Castopod's
+				if (facts == default && allowed("/.well-known/x-nodeinfo2"))
+				{
+					using var nodeInfo2 = await _http.GetJson(Address($"https://{host}/.well-known/x-nodeinfo2"), "application/json", sign: default, token);
+					if (nodeInfo2 != default && InstanceDocuments.NodeInfo2(nodeInfo2.Root) is { } second)
+					{
+						facts = second;
+						rawNodeInfo = nodeInfo2.Root.GetRawText();
+						error = default;
+					}
+				}
 			}
 
 			InstanceApiFacts api = default;

PrivaPub/Federation/Objects/InstanceDocuments.cs

@@ -72,6 +72,33 @@ namespace PrivaPub.Federation.Objects
 				Languages(metadata, "languages") ?? Languages(metadata, "langs"));
 		}
 
+		// NodeInfo2 (`/.well-known/x-nodeinfo2`), which Castopod publishes in place of NodeInfo: the server, its software
+		// and its usage in one document
+		public static NodeInfoFacts NodeInfo2(JsonElement root)
+		{
+			var server = Section(root, "server");
+			var usage = Section(root, "usage");
+			var users = Section(usage, "users");
+			if (Text(server, "software", 200) is not { } software)
+				return default;
+			return new NodeInfoFacts(
+				"nodeinfo2-" + (Text(root, "version", 20) ?? "1.0"),
+				software.ToLowerInvariant(),
+				Text(server, "version", 200),
+				Text(server, "name", 200),
+				default,
+				Strings(root, "protocols", 16, value => value.Length <= 40),
+				root.ValueKind == JsonValueKind.Object && root.TryGetProperty("openRegistrations", out var open) && open.ValueKind is JsonValueKind.True or JsonValueKind.False
+					? open.GetBoolean()
+					: (bool?)null,
+				Count(users, "total"),
+				Count(users, "activeMonth"),
+				Count(users, "activeHalfyear"),
+				Count(usage, "localPosts"),
+				Count(usage, "localComments"),
+				default);
+		}
+
 		public static InstanceApiFacts InstanceApi(JsonElement root)
 		{
 			var registrations = root.ValueKind == JsonValueKind.Object && root.TryGetProperty("registrations", out var r) ? r : default;

PrivaPub/Federation/Objects/NoteParser.cs

@@ -56,7 +56,7 @@ namespace PrivaPub.Federation.Objects
 
 	public static class NoteParser
 	{
-		static readonly string[] NoteTypes = { "Note", "Article", "Page", "Question", "Event", "Video", "Audio", "Image", "ChatMessage" };
+		static readonly string[] NoteTypes = { "Note", "Article", "Page", "Question", "Event", "Video", "Audio", "Image", "ChatMessage", "PodcastEpisode" };
 		const int MaxAttachments = 16;
 		const int MaxTags = 64;
 
@@ -68,6 +68,8 @@ namespace PrivaPub.Federation.Objects
 			var id = Id(note);
 			if (!NoteTypes.Contains(type) || Origin.Of(id) == default)
 				return default;
+			if (type == "PodcastEpisode")
+				note = Episode(note);
 
 			var (contentHtml, language) = Content(note);
 			var summary = Value(note, "summary");
@@ -123,13 +125,32 @@ namespace PrivaPub.Federation.Objects
 				CoverURL = ObjectShapes.Cover(note),
 				Link = ObjectShapes.Link(note),
 				Video = ObjectShapes.Video(note),
-				Audio = ObjectShapes.Audio(note),
+				Audio = ObjectShapes.Audio(type == "PodcastEpisode" ? note["audio"] as JsonObject : note),
 				Event = ObjectShapes.Event(note),
 				Place = ObjectShapes.NotePlace(note),
 				CommentsEnabled = note["commentsEnabled"] is JsonValue comments && comments.TryGetValue<bool>(out var enabled) ? enabled : null
 			};
 		}
 
+		// Castopod's PodcastEpisode: its words in `description` (a Note of its own), its sound in `audio`, its title the
+		// sound's name; read as a post with those
+		static JsonObject Episode(JsonObject episode)
+		{
+			var note = episode.DeepClone().AsObject();
+			if (note["description"] is JsonObject description)
+			{
+				note["content"] = description["content"]?.DeepClone();
+				note["contentMap"] = description["contentMap"]?.DeepClone();
+				note["mediaType"] = description["mediaType"]?.DeepClone();
+			}
+			if (note["audio"] is JsonObject audio)
+			{
+				note["name"] ??= audio["name"]?.DeepClone();
+				note["attachment"] = new JsonArray(audio.DeepClone());
+			}
+			return note;
+		}
+
 		static (string Html, string Language) Content(JsonObject note)
 		{
 			var content = Value(note, "content");