[backend/federation] Use content negotiation for host-meta responses

Iceshrimp.Backend/Controllers/Federation/Schemas/HostMetaJsonResponse.cs

@@ -1,27 +0,0 @@
-using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
-
-namespace Iceshrimp.Backend.Controllers.Federation.Schemas;
-
-public class HostMetaJsonResponse()
-{
-	public HostMetaJsonResponse(string webDomain) : this()
-	{
-		Links = [new HostMetaJsonResponseLink(webDomain)];
-	}
-
-	[J("links")] public List<HostMetaJsonResponseLink>? Links { get; set; }
-}
-
-public class HostMetaJsonResponseLink()
-{
-	public HostMetaJsonResponseLink(string webDomain) : this()
-	{
-		Rel      = "lrdd";
-		Type     = "application/jrd+json";
-		Template = $"https://{webDomain}/.well-known/webfinger?resource={{uri}}";
-	}
-
-	[J("rel")]      public string? Rel      { get; set; }
-	[J("type")]     public string? Type     { get; set; }
-	[J("template")] public string? Template { get; set; }
-}

Iceshrimp.Backend/Controllers/Federation/Schemas/HostMetaXmlResponse.cs

@@ -1,24 +0,0 @@
-using System.Diagnostics.CodeAnalysis;
-using System.Xml.Serialization;
-
-namespace Iceshrimp.Backend.Controllers.Federation.Schemas;
-
-[XmlRoot("XRD", Namespace = "http://docs.oasis-open.org/ns/xri/xrd-1.0", IsNullable = false)]
-public class HostMetaXmlResponse()
-{
-	[XmlElement("Link")] public required HostMetaXmlResponseLink Link;
-
-	[SetsRequiredMembers]
-	public HostMetaXmlResponse(string webDomain) : this() => Link = new HostMetaXmlResponseLink(webDomain);
-}
-
-public class HostMetaXmlResponseLink()
-{
-	[XmlAttribute("rel")]      public          string Rel = "lrdd";
-	[XmlAttribute("template")] public required string Template;
-	[XmlAttribute("type")]     public          string Type = "application/jrd+json";
-
-	[SetsRequiredMembers]
-	public HostMetaXmlResponseLink(string webDomain) : this() =>
-		Template = $"https://{webDomain}/.well-known/webfinger?resource={{uri}}";
-}

Iceshrimp.Backend/Controllers/Federation/WellKnownController.cs

@@ -1,10 +1,6 @@
 using System.Net;
-using System.Net.Http.Headers;
 using System.Net.Mime;
-using System.Text;
-using System.Xml.Serialization;
 using Iceshrimp.Backend.Controllers.Federation.Attributes;
-using Iceshrimp.Backend.Controllers.Federation.Schemas;
 using Iceshrimp.Backend.Controllers.Shared.Attributes;
 using Iceshrimp.Backend.Core.Configuration;
 using Iceshrimp.Backend.Core.Database;
@@ -24,7 +20,7 @@ namespace Iceshrimp.Backend.Controllers.Federation;
 public class WellKnownController(IOptions<Config.InstanceSection> config, DatabaseContext db) : ControllerBase
 {
 	[HttpGet("webfinger")]
-	[Produces("application/jrd+json", "application/json", "application/xrd+xml", "application/xml")]
+	[Produces("application/jrd+json", "application/xrd+xml")]
 	[ProducesResults(HttpStatusCode.OK)]
 	[ProducesErrors(HttpStatusCode.NotFound)]
 	public async Task<WebFingerResponse> WebFinger([FromQuery] string resource)
@@ -83,10 +79,7 @@ public class WellKnownController(IOptions<Config.InstanceSection> config, Databa
 					Template = $"https://{config.Value.WebDomain}/authorize-follow?acct={{uri}}"
 				}
 			],
-			Aliases = [
+			Aliases = [user.GetPublicUrl(config.Value), user.GetPublicUri(config.Value)]
-				user.GetPublicUrl(config.Value),
-				user.GetPublicUri(config.Value)
-			]
 		};
 	}
 
@@ -116,35 +109,14 @@ public class WellKnownController(IOptions<Config.InstanceSection> config, Databa
 	[HttpGet("host-meta")]
 	[Produces("application/xrd+xml", "application/jrd+json")]
 	[ProducesResults(HttpStatusCode.OK)]
-	public ActionResult<HostMetaJsonResponse> HostMeta()
+	public HostMetaResponse HostMeta()
 	{
-		var accept = Request.Headers.Accept.OfType<string>()
+		if (Request.Headers.Accept is []) Request.Headers.Accept = "application/xrd+xml";
-		                    .SelectMany(p => p.Split(","))
+		return new HostMetaResponse(config.Value.WebDomain);
-		                    .Select(MediaTypeWithQualityHeaderValue.Parse)
-		                    .Select(p => p.MediaType)
-		                    .ToList();
-
-		if (accept.Contains("application/jrd+json") || accept.Contains("application/json"))
-			return Ok(HostMetaJson());
-
-		var obj        = new HostMetaXmlResponse(config.Value.WebDomain);
-		var serializer = new XmlSerializer(obj.GetType());
-		var writer     = new Utf8StringWriter();
-
-		serializer.Serialize(writer, obj);
-		return Content(writer.ToString(), "application/xrd+xml");
 	}
 
 	[HttpGet("host-meta.json")]
 	[Produces("application/jrd+json")]
 	[ProducesResults(HttpStatusCode.OK)]
-	public HostMetaJsonResponse HostMetaJson()
+	public HostMetaResponse HostMetaJson() => new(config.Value.WebDomain);
-	{
-		return new HostMetaJsonResponse(config.Value.WebDomain);
-	}
-
-	private class Utf8StringWriter : StringWriter
-	{
-		public override Encoding Encoding => Encoding.UTF8;
-	}
 }

Iceshrimp.Backend/Core/Extensions/MvcBuilderExtensions.cs

@@ -1,11 +1,11 @@
 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;
 using Microsoft.AspNetCore.Mvc.Formatters;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.Extensions.ObjectPool;
 using Microsoft.Extensions.Options;
@@ -15,6 +15,17 @@ namespace Iceshrimp.Backend.Core.Extensions;
 
 public static class MvcBuilderExtensions
 {
+	public static IMvcBuilder AddControllersWithOptions(this IServiceCollection services)
+	{
+		services.AddSingleton<OutputFormatterSelector, AcceptHeaderOutputFormatterSelector>();
+
+		return services.AddControllers(opts =>
+		{
+			opts.RespectBrowserAcceptHeader = true;
+			opts.ReturnHttpNotAcceptable    = true;
+		});
+	}
+
 	public static IMvcBuilder AddMultiFormatter(this IMvcBuilder builder)
 	{
 		builder.Services.AddOptions<MvcOptions>()
@@ -90,4 +101,27 @@ public static class MvcBuilderExtensions
 
 		return builder;
 	}
+}
+
+/// <summary>
+/// Overrides the default OutputFormatterSelector, to make sure we return a body when content negotiation errors occur.
+/// </summary>
+public class AcceptHeaderOutputFormatterSelector(
+	IOptions<MvcOptions> options,
+	ILoggerFactory loggerFactory
+) : OutputFormatterSelector
+{
+	private readonly DefaultOutputFormatterSelector _fallbackSelector = new(options, loggerFactory);
+	private readonly List<IOutputFormatter>         _formatters       = [..options.Value.OutputFormatters];
+
+	public override IOutputFormatter? SelectFormatter(
+		OutputFormatterCanWriteContext context, IList<IOutputFormatter> formatters, MediaTypeCollection mediaTypes
+	)
+	{
+		var selectedFormatter = _fallbackSelector.SelectFormatter(context, formatters, mediaTypes);
+		if (selectedFormatter == null)
+			throw new GracefulException(HttpStatusCode.NotAcceptable, "The requested Content-Type is not acceptable.");
+
+		return selectedFormatter;
+	}
 }

Iceshrimp.Backend/Core/Federation/WebFinger/Types.cs

@@ -8,7 +8,7 @@ using JI = System.Text.Json.Serialization.JsonIgnoreAttribute;
 namespace Iceshrimp.Backend.Core.Federation.WebFinger;
 
 [SuppressMessage("ReSharper", "ClassNeverInstantiated.Global")]
-public sealed class WebFingerLink
+public class WebFingerLink
 {
 	[XmlAttribute("rel")] [J("rel")] [JR] public required string Rel { get; set; } = null!;
 
@@ -28,15 +28,10 @@ public sealed class WebFingerLink
 	public string? Template { get; set; }
 }
 
-[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
 {
-	[XmlElement("Link")]
+	[XmlElement("Link")] [J("links")] [JR] public required List<WebFingerLink> Links { get; set; } = null!;
-	[J("links")]
-	[JR]
-	public required List<WebFingerLink> Links { get; set; } = null!;
 
 	[XmlElement("Subject")]
 	[J("subject")]
@@ -49,6 +44,33 @@ public sealed class WebFingerResponse
 	public List<string>? Aliases { get; set; }
 }
 
+[XmlRoot("XRD", Namespace = "http://docs.oasis-open.org/ns/xri/xrd-1.0", IsNullable = false)]
+public class HostMetaResponse()
+{
+	[SetsRequiredMembers]
+	public HostMetaResponse(string webDomain) : this()
+	{
+		Links =
+		[
+			new HostMetaResponseLink(webDomain, "application/jrd+json"),
+			new HostMetaResponseLink(webDomain, "application/xrd+xml")
+		];
+	}
+
+	[XmlElement("Link")] [J("links")] [JR] public required List<HostMetaResponseLink> Links { get; set; }
+}
+
+public sealed class HostMetaResponseLink() : WebFingerLink
+{
+	[SetsRequiredMembers]
+	public HostMetaResponseLink(string webDomain, string type) : this()
+	{
+		Rel      = "lrdd";
+		Type     = type;
+		Template = $"https://{webDomain}/.well-known/webfinger?resource={{uri}}";
+	}
+}
+
 public sealed class NodeInfoIndexResponse
 {
 	[J("links")] [JR] public List<WebFingerLink> Links { get; set; } = null!;

Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs

@@ -3,7 +3,6 @@ using System.Net;
 using System.Text.Encodings.Web;
 using System.Xml.Linq;
 using System.Xml.Serialization;
-using Iceshrimp.Backend.Controllers.Federation.Schemas;
 using Iceshrimp.Backend.Core.Configuration;
 using Iceshrimp.Backend.Core.Middleware;
 using Iceshrimp.Backend.Core.Services;
@@ -140,9 +139,9 @@ public class WebFingerService(
 			var hostMetaUrl = $"{proto}://{domain}/.well-known/host-meta.json";
 			using var res = await client.SendAsync(httpRqSvc.Get(hostMetaUrl, ["application/jrd+json"]),
 			                                       HttpCompletionOption.ResponseHeadersRead);
-			var deserialized = await res.Content.ReadFromJsonAsync<HostMetaJsonResponse>();
+			var deserialized = await res.Content.ReadFromJsonAsync<HostMetaResponse>();
 
-			var result = deserialized?.Links?.FirstOrDefault(p => p is
+			var result = deserialized?.Links.FirstOrDefault(p => p is
 			{
 				Rel: "lrdd",
 				//Type: "application/jrd+json",
@@ -162,9 +161,9 @@ public class WebFingerService(
 			var hostMetaUrl = $"{proto}://{domain}/.well-known/host-meta";
 			using var res = await client.SendAsync(httpRqSvc.Get(hostMetaUrl, ["application/jrd+json"]),
 			                                       HttpCompletionOption.ResponseHeadersRead);
-			var deserialized = await res.Content.ReadFromJsonAsync<HostMetaJsonResponse>();
+			var deserialized = await res.Content.ReadFromJsonAsync<HostMetaResponse>();
 
-			var result = deserialized?.Links?.FirstOrDefault(p => p is
+			var result = deserialized?.Links.FirstOrDefault(p => p is
 			{
 				Rel: "lrdd",
 				//Type: "application/jrd+json",

Iceshrimp.Backend/Startup.cs

@@ -12,7 +12,8 @@ builder.Configuration.AddCustomConfiguration();
 
 await PluginLoader.LoadPlugins();
 
-builder.Services.AddControllers()
+builder.Services
+       .AddControllersWithOptions()
        .AddNewtonsoftJson() //TODO: remove once dotNetRdf switches to System.Text.Json (or we switch to LinkedData.NET)
        .ConfigureNewtonsoftJson()
        .AddMultiFormatter()