Add WebFinger implementation

Iceshrimp.Backend/Core/Configuration/Config.cs

@@ -2,10 +2,16 @@ namespace Iceshrimp.Backend.Core.Configuration;
 
 public sealed class Config {
 	// FIXME: This doesn't reflect config updates.
-	public static   Config          StartupConfig { get; set; } = null!;
-	
-	public required InstanceSection Instance      { get; set; }
-	public required DatabaseSection Database      { get; set; }
+	public static Config StartupConfig { get; set; } = null!;
+
+	public required InstanceSection Instance { get; set; }
+	public required DatabaseSection Database { get; set; }
+	public          StaticSection   Static = new();
+
+	public sealed class StaticSection {
+		public string Version = "0.0.1";
+		public string UserAgent => $"Iceshrimp.NET/{Version} (https://{StartupConfig.Instance.WebDomain})";
+	}
 
 	public sealed class InstanceSection {
 		public required int    ListenPort    { get; set; } = 3000;

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

@@ -0,0 +1,14 @@
+using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
+using JR = System.Text.Json.Serialization.JsonRequiredAttribute;
+
+namespace Iceshrimp.Backend.Core.Federation.WebFinger;
+
+public sealed class Link {
+	[J("href"), JR] public string  Href { get; set; } = null!;
+	[J("rel")]      public string? Rel  { get; set; }
+}
+
+public sealed class WebFingerResponse {
+	[J("links"), JR]   public List<Link> Links   { get; set; } = null!;
+	[J("subject"), JR] public string     Subject { get; set; } = null!;
+}

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

@@ -0,0 +1,105 @@
+using System.Net.Http.Headers;
+using System.Text.Encodings.Web;
+using System.Xml;
+using Iceshrimp.Backend.Core.Configuration;
+using Iceshrimp.Backend.Core.Helpers;
+
+namespace Iceshrimp.Backend.Core.Federation.WebFinger;
+
+/*
+ * There's two different WebFinger implementations out there
+ * 1. Get /.well-known/host-meta, extract the WebFinger query url template from there
+ * 2. Get /.well-known/webfinger?resource={uri} directly
+ *
+ * We have to check for host-meta first, and only fall back to the second implementation if it
+ * - doesn't exist
+ * - doesn't have a query url template
+ */
+
+public class WebFinger {
+	private readonly string  _query;
+	private readonly string  _proto;
+	private readonly string  _domain;
+	private readonly string? _username;
+	private          string? _webFingerUrl;
+
+	private string HostMetaUrl              => $"{_proto}://{_domain}/.well-known/host-meta";
+	private string DefaultWebFingerTemplate => $"{_proto}://{_domain}/.well-known/webfinger?resource={{uri}}";
+
+	public WebFinger(string query) {
+		_query = query;
+		if (_query.StartsWith("http://") || _query.StartsWith("https://")) {
+			var uri = new Uri(_query);
+			_domain = uri.Host;
+			_proto  = _query.StartsWith("http://") ? "http" : "https";
+		}
+		else if (_query.StartsWith('@')) {
+			_proto = "https";
+
+			var split = _query.Split('@');
+			if (split.Length == 2) {
+				throw new Exception("Can't run WebFinger for local user");
+			}
+
+			if (split.Length == 3) {
+				_username = split[1];
+				_domain   = split[2];
+			}
+			else {
+				throw new Exception("Invalid query");
+			}
+		}
+		else {
+			throw new Exception("Invalid query");
+		}
+	}
+
+	private string? GetWebFingerTemplateFromHostMeta() {
+		var client = HttpClientHelpers.HttpClient;
+		var request = new HttpRequestMessage {
+			RequestUri = new Uri(HostMetaUrl),
+			Method     = HttpMethod.Get,
+			Headers    = { Accept = { MediaTypeWithQualityHeaderValue.Parse("application/xrd+xml") } }
+		};
+		var res = client.SendAsync(request);
+		var xml = new XmlDocument();
+		xml.Load(res.Result.Content.ReadAsStreamAsync().Result);
+		var section = xml["XRD"]?.GetElementsByTagName("Link");
+		if (section == null) return null;
+
+		//TODO: implement https://stackoverflow.com/a/37322614/18402176 instead
+
+		for (var i = 0; i < section.Count; i++) {
+			if (section[i]?.Attributes?["rel"]?.InnerText == "lrdd") {
+				return section[i]?.Attributes?["template"]?.InnerText;
+			}
+		}
+
+		return null;
+	}
+
+	private string GetWebFingerUrl() {
+		var template = GetWebFingerTemplateFromHostMeta() ?? DefaultWebFingerTemplate;
+		var query    = _query.StartsWith('@') ? $"acct:{_query.Substring(1)}" : _query;
+		var encoded  = UrlEncoder.Default.Encode(query);
+		return template.Replace("{uri}", encoded);
+	}
+
+	public async Task<WebFingerResponse?> Resolve() {
+		_webFingerUrl = GetWebFingerUrl();
+
+		var client = HttpClientHelpers.HttpClient;
+		var request = new HttpRequestMessage {
+			RequestUri = new Uri(_webFingerUrl),
+			Method     = HttpMethod.Get,
+			Headers = {
+				Accept = {
+					MediaTypeWithQualityHeaderValue.Parse("application/jrd+json"),
+					MediaTypeWithQualityHeaderValue.Parse("application/json")
+				}
+			}
+		};
+		var res = await client.SendAsync(request);
+		return await res.Content.ReadFromJsonAsync<WebFingerResponse>();
+	}
+}

Iceshrimp.Backend/Core/Helpers/HttpClientHelpers.cs

@@ -0,0 +1,11 @@
+using System.Net.Http.Headers;
+
+namespace Iceshrimp.Backend.Core.Helpers;
+
+public static class HttpClientHelpers {
+	public static readonly HttpClient HttpClient = new() {
+		DefaultRequestHeaders = {
+			UserAgent = { ProductInfoHeaderValue.Parse("Iceshrimp.NET/0.0.1") }
+		} //FIXME (instance domain comment in parentheses doesn't work?)
+	};
+}

Iceshrimp.Backend/Core/Services/UserService.cs

@@ -0,0 +1,7 @@
+namespace Iceshrimp.Backend.Core.Services;
+
+public static class UserService {
+	public static async Task CreateUser() {
+		
+	}
+}