From 0833cf49d2f0839f977542e09c32f2b9746ae225 Mon Sep 17 00:00:00 2001
From: Laura Hausmann <laura@hausmann.dev>
Date: Tue, 12 Mar 2024 05:34:45 +0100
Subject: [PATCH] [backend/federation] Fall back to JRD during host-meta step
 of the WebFinger process (ISH-162)

---
 .../Schemas/HostMetaJsonResponse.cs           | 24 ++++++--
 .../Federation/WebFinger/WebFingerService.cs  | 56 ++++++++++++++++++-
 2 files changed, 72 insertions(+), 8 deletions(-)

diff --git a/Iceshrimp.Backend/Controllers/Federation/Schemas/HostMetaJsonResponse.cs b/Iceshrimp.Backend/Controllers/Federation/Schemas/HostMetaJsonResponse.cs
index f0567e8a..d376fd76 100644
--- a/Iceshrimp.Backend/Controllers/Federation/Schemas/HostMetaJsonResponse.cs
+++ b/Iceshrimp.Backend/Controllers/Federation/Schemas/HostMetaJsonResponse.cs
@@ -2,14 +2,26 @@ using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
 
 namespace Iceshrimp.Backend.Controllers.Federation.Schemas;
 
-public class HostMetaJsonResponse(string webDomain)
+public class HostMetaJsonResponse()
 {
-	[J("links")] public List<HostMetaJsonResponseLink> Links => [new HostMetaJsonResponseLink(webDomain)];
+	public HostMetaJsonResponse(string webDomain) : this()
+	{
+		Links = [new HostMetaJsonResponseLink(webDomain)];
+	}
+
+	[J("links")] public List<HostMetaJsonResponseLink>? Links { get; set; }
 }
 
-public class HostMetaJsonResponseLink(string webDomain)
+public class HostMetaJsonResponseLink()
 {
-	[J("rel")]      public string Rel      => "lrdd";
-	[J("type")]     public string Type     => "application/jrd+json";
-	[J("template")] public string Template => $"https://{webDomain}/.well-known/webfinger?resource={{uri}}";
+	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; }
 }
\ No newline at end of file
diff --git a/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs b/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs
index a05d4ac6..c3420f6f 100644
--- a/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs
+++ b/Iceshrimp.Backend/Core/Federation/WebFinger/WebFingerService.cs
@@ -1,6 +1,7 @@
 using System.Net;
 using System.Text.Encodings.Web;
 using System.Xml;
+using Iceshrimp.Backend.Controllers.Federation.Schemas;
 using Iceshrimp.Backend.Core.Middleware;
 using Iceshrimp.Backend.Core.Services;
 
@@ -75,17 +76,20 @@ public class WebFingerService(HttpClient client, HttpRequestService httpRqSvc, I
 
 	private async Task<string> GetWebFingerUrlAsync(string query, string proto, string domain)
 	{
-		var template = await GetWebFingerTemplateFromHostMetaAsync($"{proto}://{domain}/.well-known/host-meta") ??
+		var template = await GetWebFingerTemplateFromHostMetaXmlAsync(proto, domain) ??
+		               await GetWebFingerTemplateFromHostMetaJsonAsync(proto, domain) ??
 		               $"{proto}://{domain}/.well-known/webfinger?resource={{uri}}";
+
 		var finalQuery = query.StartsWith('@') ? $"acct:{query[1..]}" : query;
 		var encoded    = UrlEncoder.Default.Encode(finalQuery);
 		return template.Replace("{uri}", encoded);
 	}
 
-	private async Task<string?> GetWebFingerTemplateFromHostMetaAsync(string hostMetaUrl)
+	private async Task<string?> GetWebFingerTemplateFromHostMetaXmlAsync(string proto, string domain)
 	{
 		try
 		{
+			var hostMetaUrl = $"{proto}://{domain}/.well-known/host-meta";
 			using var res = await client.SendAsync(httpRqSvc.Get(hostMetaUrl, ["application/xrd+xml"]),
 			                                       HttpCompletionOption.ResponseHeadersRead);
 			using var stream = await res.Content.ReadAsStreamAsync();
@@ -109,4 +113,52 @@ public class WebFingerService(HttpClient client, HttpRequestService httpRqSvc, I
 			return null;
 		}
 	}
+
+	private async Task<string?> GetWebFingerTemplateFromHostMetaJsonAsync(string proto, string domain)
+	{
+		try
+		{
+			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 result = deserialized?.Links?.FirstOrDefault(p => p is
+			{
+				Rel: "lrdd",
+				Type: "application/jrd+json",
+				Template: not null
+			});
+
+			if (result?.Template != null)
+				return result.Template;
+		}
+		catch
+		{
+			// ignored
+		}
+
+		try
+		{
+			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 result = deserialized?.Links?.FirstOrDefault(p => p is
+			{
+				Rel: "lrdd",
+				Type: "application/jrd+json",
+				Template: not null
+			});
+
+			return result?.Template;
+		}
+		catch
+		{
+			// ignored
+		}
+
+		return null;
+	}
 }
\ No newline at end of file