From b37f02846b935cf14e00e60fb6e540880af0bcb6 Mon Sep 17 00:00:00 2001
From: Laura Hausmann <laura@hausmann.dev>
Date: Wed, 14 Aug 2024 01:49:49 +0200
Subject: [PATCH] [backend/federation] Add support for returning xrd+xml
 WebFinger responses for local users

---
 .../Federation/WellKnownController.cs         |  8 ++++++-
 .../Core/Extensions/MvcBuilderExtensions.cs   |  2 ++
 .../Core/Federation/WebFinger/Types.cs        | 21 ++++++++++---------
 .../Federation/WebFinger/WebFingerService.cs  | 12 +++--------
 4 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/Iceshrimp.Backend/Controllers/Federation/WellKnownController.cs b/Iceshrimp.Backend/Controllers/Federation/WellKnownController.cs
index 7495aa11..4e8940b6 100644
--- a/Iceshrimp.Backend/Controllers/Federation/WellKnownController.cs
+++ b/Iceshrimp.Backend/Controllers/Federation/WellKnownController.cs
@@ -24,7 +24,7 @@ namespace Iceshrimp.Backend.Controllers.Federation;
 public class WellKnownController(IOptions<Config.InstanceSection> config, DatabaseContext db) : ControllerBase
 {
 	[HttpGet("webfinger")]
-	[Produces(MediaTypeNames.Application.Json, "application/jrd+json")]
+	[Produces("application/jrd+json", "application/json", "application/xrd+xml", "application/xml")]
 	[ProducesResults(HttpStatusCode.OK)]
 	[ProducesErrors(HttpStatusCode.NotFound)]
 	public async Task<WebFingerResponse> WebFinger([FromQuery] string resource)
@@ -66,6 +66,12 @@ public class WellKnownController(IOptions<Config.InstanceSection> config, Databa
 					Href = user.GetPublicUri(config.Value)
 				},
 				new WebFingerLink
+				{
+					Rel  = "self",
+					Type = "application/ld+json; profile=\"https://www.w3.org/ns/activitystreams\"",
+					Href = user.GetPublicUri(config.Value)
+				},
+				new WebFingerLink
 				{
 					Rel  = "http://webfinger.net/rel/profile-page",
 					Type = "text/html",
diff --git a/Iceshrimp.Backend/Core/Extensions/MvcBuilderExtensions.cs b/Iceshrimp.Backend/Core/Extensions/MvcBuilderExtensions.cs
index e75810a1..323f010f 100644
--- a/Iceshrimp.Backend/Core/Extensions/MvcBuilderExtensions.cs
+++ b/Iceshrimp.Backend/Core/Extensions/MvcBuilderExtensions.cs
@@ -1,6 +1,7 @@
 using System.Buffers;
 using System.Net;
 using System.Text.Encodings.Web;
+using System.Xml;
 using Iceshrimp.Backend.Controllers.Shared.Attributes;
 using Iceshrimp.Backend.Core.Middleware;
 using Microsoft.AspNetCore.Mvc;
@@ -35,6 +36,7 @@ public static class MvcBuilderExtensions
 
 			       opts.InputFormatters.Insert(0, new JsonInputMultiFormatter());
 			       opts.OutputFormatters.Insert(0, new JsonOutputMultiFormatter());
+			       opts.OutputFormatters.Add(new XmlSerializerOutputFormatter());
 		       });
 
 		return builder;
diff --git a/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs b/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs
index 3a1df4d0..09a097b7 100644
--- a/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs
+++ b/Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs
@@ -30,24 +30,25 @@ public sealed class WebFingerLink
 
 [SuppressMessage("ReSharper", "CollectionNeverUpdated.Global")]
 [SuppressMessage("ReSharper", "ClassNeverInstantiated.Global")]
+[XmlRoot("XRD", Namespace = "http://docs.oasis-open.org/ns/xri/xrd-1.0", IsNullable = false)]
 public sealed class WebFingerResponse
 {
-	[J("links")] [JR]   public List<WebFingerLink> Links   { get; set; } = null!;
-	[J("subject")] [JR] public string              Subject { get; set; } = null!;
+	[XmlElement("Link")]
+	[J("links")]
+	[JR]
+	public required List<WebFingerLink> Links { get; set; } = null!;
 
+	[XmlElement("Subject")]
+	[J("subject")]
+	[JR]
+	public required string Subject { get; set; } = null!;
+
+	[XmlElement("Alias")]
 	[J("aliases")]
 	[JI(Condition = JsonIgnoreCondition.WhenWritingNull)]
 	public List<string>? Aliases { get; set; }
 }
 
-[XmlRoot("XRD", Namespace = "http://docs.oasis-open.org/ns/xri/xrd-1.0", IsNullable = false)]
-public sealed class WebFingerXmlResponse
-{
-	[XmlElement("Subject")] public required string              Subject { get; set; } = null!;
-	[XmlElement("Alias")]   public          List<string>?       Aliases { get; set; }
-	[XmlElement("Link")]    public required List<WebFingerLink> Links   { get; set; }
-}
-
 public sealed class NodeInfoIndexResponse
 {
 	[J("links")] [JR] public List<WebFingerLink> Links { get; set; } = null!;
diff --git a/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs b/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs
index 3a182a10..8aef7aa7 100644
--- a/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs
+++ b/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs
@@ -59,16 +59,10 @@ public class WebFingerService(
 		if (res.Content.Headers.ContentType?.MediaType is "application/jrd+json" or "application/json")
 			return await res.Content.ReadFromJsonAsync<WebFingerResponse>(cts.Token);
 
-		var deserializer = new XmlSerializer(typeof(WebFingerXmlResponse));
-		if (deserializer.Deserialize(await res.Content.ReadAsStreamAsync(cts.Token)) is not WebFingerXmlResponse xml)
-			throw new Exception("Failed to deserialize xml payload");
+		var deserializer = new XmlSerializer(typeof(WebFingerResponse));
 
-		return new WebFingerResponse
-		{
-			Subject = xml.Subject,
-			Links   = xml.Links,
-			Aliases = xml.Aliases
-		};
+		return deserializer.Deserialize(await res.Content.ReadAsStreamAsync(cts.Token)) as WebFingerResponse ??
+		       throw new Exception("Failed to deserialize xml payload");
 	}
 
 	public static (string query, string proto, string domain) ParseQuery(string query)