Outbound documents speak Mastodon's dialect under PrivaPub's route names

Local text (Domain/Content/ContentRenderer): Markdig with raw HTML off and
autolinks, or plain text for API clients; then @user and @user@host are
resolved (locally or through WebFinger) into Mastodon's h-card markup and
#tags into hashtag links, skipping code, links and e-mail addresses. A
post stores the result, its mentions and its tags, and is delivered to
the mentioned actors and the parent's author as well as to followers.

Renderer:
- Mastodon's @context (toot, schema PropertyValue, discoverable,
  indexable, blurhash, focalPoint, featured, alsoKnownAs, movedTo) and
  FEP-2c59's webfinger;
- an actor's url is its HTML page, its fields are PropertyValue
  attachments, published is cut to the day and indexable is false;
- a note's content is the stored rendering; a title becomes name and a
  bold first line, a content warning without its own text is summarised
  by the title or "Content warning"; Mention and Hashtag tags, contentMap,
  updated, and to/cc by visibility.

Routes take the agreed names: /groupies, /stalking, /scribbles/{id},
/grunts/{id} (a Create resolves), /whispers/{id} for a DM's context. The
outbox is a collection with a first page, paged by max_id. A browser
asking for an actor or a note is redirected to /@user, and WebFinger's
profile-page points there.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012CzABvBkbcFqoHdmi8b9WB

PrivaPub/Federation/Rendering/ActivityPubRenderer.cs

@@ -1,33 +1,65 @@
 using Markdig;
 
+using PrivaPub.Federation.Actors;
+using PrivaPub.Federation.Objects;
 using PrivaPub.Models.Federation;
+using PrivaPub.Models.Post;
 
 using System.Globalization;
+using System.Net;
 using System.Text.Json.Nodes;
 
 using PostEntity = PrivaPub.Models.Post.Post;
-using PrivaPub.Federation.Actors;
 
 namespace PrivaPub.Federation.Rendering
 {
 	public static class ActivityPubRenderer
 	{
 		public const string ActivityStreams = "https://www.w3.org/ns/activitystreams";
-		public const string Public = "https://www.w3.org/ns/activitystreams#Public";
+		public const string Public = Addressing.Public;
+		public const string ContentWarning = "Content warning";
 
 		static readonly MarkdownPipeline Pipeline = new MarkdownPipelineBuilder().DisableHtml().Build();
 
+		public static JsonArray Context() => new(
+			ActivityStreams,
+			"https://w3id.org/security/v1",
+			new JsonObject
+			{
+				["manuallyApprovesFollowers"] = "as:manuallyApprovesFollowers",
+				["sensitive"] = "as:sensitive",
+				["Hashtag"] = "as:Hashtag",
+				["alsoKnownAs"] = new JsonObject { ["@id"] = "as:alsoKnownAs", ["@type"] = "@id" },
+				["movedTo"] = new JsonObject { ["@id"] = "as:movedTo", ["@type"] = "@id" },
+				["toot"] = "http://joinmastodon.org/ns#",
+				["featured"] = new JsonObject { ["@id"] = "toot:featured", ["@type"] = "@id" },
+				["featuredTags"] = new JsonObject { ["@id"] = "toot:featuredTags", ["@type"] = "@id" },
+				["discoverable"] = "toot:discoverable",
+				["indexable"] = "toot:indexable",
+				["blurhash"] = "toot:blurhash",
+				["focalPoint"] = new JsonObject { ["@container"] = "@list", ["@id"] = "toot:focalPoint" },
+				["schema"] = "http://schema.org#",
+				["PropertyValue"] = "schema:PropertyValue",
+				["value"] = "schema:value",
+				["webfinger"] = "https://purl.archive.org/socialweb/webfinger#webfinger"
+			});
+
 		public static string Html(string markdown) =>
 			string.IsNullOrEmpty(markdown) ? string.Empty : Markdown.ToHtml(markdown, Pipeline).Trim();
 
 		public static string Timestamp(DateTime value) =>
 			DateTime.SpecifyKind(value, DateTimeKind.Utc).ToString("yyyy-MM-ddTHH:mm:ssZ", CultureInfo.InvariantCulture);
 
+		public static string Day(DateTime value) =>
+			DateTime.SpecifyKind(value, DateTimeKind.Utc).Date.ToString("yyyy-MM-ddT00:00:00Z", CultureInfo.InvariantCulture);
+
+		public static string TagUrl(string baseAddress, string tag) => $"{baseAddress}/tags/{Uri.EscapeDataString(tag)}";
+
 		public static JsonObject Actor(LocalActor actor)
 		{
 			var document = new JsonObject
 			{
-				["@context"] = new JsonArray(ActivityStreams, "https://w3id.org/security/v1"),
+				["@context"] = Context(),
 				["id"] = actor.Uri,
 				["type"] = actor.Kind switch
 				{
@@ -38,21 +70,29 @@ namespace PrivaPub.Federation.Rendering
 				["preferredUsername"] = actor.UserName,
 				["name"] = actor.Name,
 				["summary"] = Html(actor.Summary),
-				["url"] = actor.Uri,
+				["url"] = actor.Kind == LocalActorKind.Application ? actor.Uri : actor.HtmlUrl,
 				["inbox"] = actor.Inbox,
 				["outbox"] = actor.Outbox,
 				["followers"] = actor.Followers,
 				["following"] = actor.Following,
-				["published"] = Timestamp(actor.Published),
+				["published"] = Day(actor.Published),
 				["manuallyApprovesFollowers"] = actor.ManuallyApprovesFollowers,
 				["discoverable"] = actor.Discoverable,
+				["indexable"] = false,
+				["webfinger"] = actor.Handle,
 				["endpoints"] = new JsonObject { ["sharedInbox"] = actor.SharedInbox },
 				["publicKey"] = new JsonObject
 				{
 					["id"] = actor.KeyId,
 					["owner"] = actor.Uri,
 					["publicKeyPem"] = Keys.ToSubjectPublicKeyInfoPem(actor.PublicKeyPem)
-				}
+				},
+				["attachment"] = new JsonArray(actor.Fields.Select(field => (JsonNode)new JsonObject
+				{
+					["type"] = "PropertyValue",
+					["name"] = field.Key,
+					["value"] = FieldValue(field.Value)
+				}).ToArray())
 			};
 			if (!string.IsNullOrEmpty(actor.PictureURL))
 				document["icon"] = new JsonObject { ["type"] = "Image", ["url"] = actor.PictureURL };
@@ -63,13 +103,18 @@ namespace PrivaPub.Federation.Rendering
 
 		public static JsonObject Note(PostEntity post, LocalActor author, LocalActor group, string inReplyTo)
 		{
-			var to = new JsonArray(Public);
-			var cc = new JsonArray(author.Followers);
+			var mentions = post.Mentions.Select(m => (JsonNode)m.ActorURI).ToArray();
+			var (to, cc) = post.Visibility switch
+			{
+				PostVisibility.Unlisted => (new JsonArray(author.Followers), new JsonArray(mentions.Prepend(Public).ToArray())),
+				PostVisibility.FollowersOnly => (new JsonArray(author.Followers), new JsonArray(mentions)),
+				PostVisibility.Direct => (new JsonArray(mentions), new JsonArray()),
+				_ => (new JsonArray(Public), new JsonArray(mentions.Prepend(author.Followers).ToArray()))
+			};
 			if (group != default)
 				cc.Add(group.Uri);
 
-			var note = NoteBody(author.PostUri(post.ID), author, post.Title, post.Text, post.HasContentWarning,
-				post.CreationDate, to, cc, inReplyTo);
+			var note = NoteBody(post, author, to, cc, inReplyTo);
 			if (group != default)
 				note["audience"] = group.Uri;
 			return note;
@@ -78,48 +123,84 @@ namespace PrivaPub.Federation.Rendering
 		public static JsonObject DirectNote(PostEntity post, LocalActor author, IReadOnlyList<(string Uri, string Handle)> recipients,
 			string context)
 		{
-			var note = NoteBody(author.PostUri(post.ID), author, post.Title, post.Text, post.HasContentWarning,
-				post.CreationDate, new JsonArray(recipients.Select(r => (JsonNode)r.Uri).ToArray()), new JsonArray(), default);
-			note["tag"] = new JsonArray(recipients.Select(r => (JsonNode)new JsonObject
-			{
-				["type"] = "Mention",
-				["href"] = r.Uri,
-				["name"] = "@" + r.Handle
-			}).ToArray());
-			note["content"] = string.Join(" ", recipients.Select(r => $"<span class=\"h-card\"><a href=\"{r.Uri}\" class=\"u-url mention\">@{r.Handle}</a></span>"))
-				+ " " + note["content"]!.GetValue<string>();
+			var note = NoteBody(post, author, new JsonArray(recipients.Select(r => (JsonNode)r.Uri).ToArray()), new JsonArray(), post.InReplyToURI);
+			var named = post.Mentions.Select(m => m.ActorURI).ToHashSet();
+			var tags = note["tag"]!.AsArray();
+			foreach (var recipient in recipients.Where(r => !named.Contains(r.Uri)))
+				tags.Add(new JsonObject { ["type"] = "Mention", ["href"] = recipient.Uri, ["name"] = "@" + recipient.Handle });
+			var unmentioned = recipients.Where(r => !named.Contains(r.Uri)).ToList();
+			if (unmentioned.Count > 0)
+				note["content"] = "<p>" + string.Join(" ", unmentioned.Select(r =>
+						$"<span class=\"h-card\" translate=\"no\"><a href=\"{WebUtility.HtmlEncode(r.Uri)}\" class=\"u-url mention\">@<span>{WebUtility.HtmlEncode(r.Handle.Split('@')[0])}</span></a></span>"))
+					+ "</p>" + note["content"]!.GetValue<string>();
 			if (!string.IsNullOrEmpty(context))
 				note["context"] = context;
 			return note;
 		}
 
-		static JsonObject NoteBody(string id, LocalActor author, string title, string text, bool sensitive,
-			DateTime published, JsonArray to, JsonArray cc, string inReplyTo)
+		static JsonObject NoteBody(PostEntity post, LocalActor author, JsonArray to, JsonArray cc, string inReplyTo)
 		{
+			var content = post.ContentHtml ?? Html(post.Text);
+			if (!string.IsNullOrEmpty(post.Title))
+				content = $"<p><strong>{WebUtility.HtmlEncode(post.Title)}</strong></p>{content}";
+
 			var note = new JsonObject
 			{
-				["id"] = id,
+				["id"] = author.PostUri(post.ID),
 				["type"] = "Note",
 				["attributedTo"] = author.Uri,
-				["content"] = Html(text),
-				["published"] = Timestamp(published),
-				["url"] = id,
+				["content"] = content,
+				["published"] = Timestamp(post.CreationDate),
+				["url"] = author.PostHtmlUrl(post.ID),
 				["to"] = to,
 				["cc"] = cc,
-				["sensitive"] = sensitive
+				["sensitive"] = post.HasContentWarning,
+				["tag"] = new JsonArray(post.Mentions
+					.Select(m => (JsonNode)new JsonObject { ["type"] = "Mention", ["href"] = m.ActorURI, ["name"] = MentionName(m) })
+					.Concat(post.Tags.Select(t => (JsonNode)new JsonObject
+					{
+						["type"] = "Hashtag",
+						["href"] = TagUrl(author.BaseAddress, t),
+						["name"] = "#" + t
+					}))
+					.ToArray())
 			};
-			if (sensitive && !string.IsNullOrEmpty(title))
-				note["summary"] = title;
-			else if (!string.IsNullOrEmpty(title))
-				note["name"] = title;
+			if (!string.IsNullOrEmpty(post.Language))
+				note["contentMap"] = new JsonObject { [post.Language] = content };
+			if (!string.IsNullOrEmpty(post.Title))
+				note["name"] = post.Title;
+			var summary = post.SpoilerText ?? (post.HasContentWarning ? post.Title ?? ContentWarning : default);
+			if (!string.IsNullOrEmpty(summary))
+			{
+				note["summary"] = summary;
+				note["sensitive"] = true;
+			}
 			if (!string.IsNullOrEmpty(inReplyTo))
 				note["inReplyTo"] = inReplyTo;
+			if (post.EditedAt.HasValue)
+				note["updated"] = Timestamp(post.EditedAt.Value);
 			return note;
 		}
 
+		static string MentionName(PostMention mention)
+		{
+			var handle = mention.Handle?.TrimStart('@');
+			if (string.IsNullOrEmpty(handle))
+				return "@" + mention.ActorURI;
+			return "@" + (handle.Contains('@') ? handle : $"{handle}@{new Uri(mention.ActorURI).Authority}");
+		}
+
+		static string FieldValue(string value)
+		{
+			var encoded = WebUtility.HtmlEncode(value ?? string.Empty);
+			return Uri.TryCreate(value, UriKind.Absolute, out var link) && link.Scheme is "https" or "http"
+				? $"<a href=\"{encoded}\" target=\"_blank\" rel=\"nofollow noopener noreferrer me\" translate=\"no\">{encoded}</a>"
+				: encoded;
+		}
+
 		public static JsonObject Create(LocalActor actor, JsonObject note, string activityId) => new()
 		{
-			["@context"] = ActivityStreams,
+			["@context"] = Context(),
 			["id"] = actor.ActivityUri(activityId),
 			["type"] = "Create",
 			["actor"] = actor.Uri,
@@ -161,7 +242,7 @@ namespace PrivaPub.Federation.Rendering
 			["object"] = follow.DeepClone()
 		};
 
-		public static JsonObject OrderedCollection(string id, int totalItems, IEnumerable<JsonNode> items)
+		public static JsonObject OrderedCollection(string id, int totalItems, IEnumerable<JsonNode> items, string first = default)
 		{
 			var collection = new JsonObject
 			{
@@ -170,9 +251,28 @@ namespace PrivaPub.Federation.Rendering
 				["type"] = "OrderedCollection",
 				["totalItems"] = totalItems
 			};
+			if (first != default)
+				collection["first"] = first;
 			if (items != default)
 				collection["orderedItems"] = new JsonArray(items.ToArray());
 			return collection;
 		}
+
+		public static JsonObject OrderedCollectionPage(string id, string partOf, IEnumerable<JsonNode> items, string next, string prev)
+		{
+			var page = new JsonObject
+			{
+				["@context"] = Context(),
+				["id"] = id,
+				["type"] = "OrderedCollectionPage",
+				["partOf"] = partOf,
+				["orderedItems"] = new JsonArray(items.ToArray())
+			};
+			if (next != default)
+				page["next"] = next;
+			if (prev != default)
+				page["prev"] = prev;
+			return page;
+		}
 	}
 }