1 files changed, 86 insertions, 0 deletions
diff --git a/LibMatrix/Services/HomeserverResolverService.cs b/LibMatrix/Services/HomeserverResolverService.cs
new file mode 100644
index 0000000..4d3bc46
--- /dev/null
+++ b/LibMatrix/Services/HomeserverResolverService.cs
@@ -0,0 +1,86 @@
+using System.Text.Json;
+using LibMatrix.Extensions;
+using Microsoft.Extensions.Logging;
+
+namespace LibMatrix.Services;
+
+public class HomeserverResolverService {
+    private readonly MatrixHttpClient _httpClient = new();
+    private readonly ILogger<HomeserverResolverService> _logger;
+
+    private static readonly Dictionary<string, string> _wellKnownCache = new();
+    private static readonly Dictionary<string, SemaphoreSlim> _wellKnownSemaphores = new();
+
+    public HomeserverResolverService(ILogger<HomeserverResolverService> logger) {
+        _logger = logger;
+    }
+
+    public async Task<string> ResolveHomeserverFromWellKnown(string homeserver) {
+        var res = await _resolveHomeserverFromWellKnown(homeserver);
+        if (!res.StartsWith("http")) res = "https://" + res;
+        if (res.EndsWith(":443")) res = res.Substring(0, res.Length - 4);
+        return res;
+    }
+
+    private async Task<string> _resolveHomeserverFromWellKnown(string homeserver) {
+        if (homeserver is null) throw new ArgumentNullException(nameof(homeserver));
+        SemaphoreSlim sem = _wellKnownSemaphores.GetOrCreate(homeserver, _ => new SemaphoreSlim(1, 1));
+        await sem.WaitAsync();
+        if (_wellKnownCache.ContainsKey(homeserver)) {
+            sem.Release();
+            return _wellKnownCache[homeserver];
+        }
+
+        string? result = null;
+        _logger.LogInformation($"Attempting to resolve homeserver: {homeserver}");
+        result ??= await _tryResolveFromClientWellknown(homeserver);
+        result ??= await _tryResolveFromServerWellknown(homeserver);
+        result ??= await _tryCheckIfDomainHasHomeserver(homeserver);
+
+        if (result is not null) {
+            _logger.LogInformation($"Resolved homeserver: {homeserver} -> {result}");
+            _wellKnownCache[homeserver] = result;
+            sem.Release();
+            return result;
+        }
+
+        throw new InvalidDataException($"Failed to resolve homeserver for {homeserver}! Is it online and configured correctly?");
+    }
+
+    private async Task<string?> _tryResolveFromClientWellknown(string homeserver) {
+        if (!homeserver.StartsWith("http")) homeserver = "https://" + homeserver;
+        if (await _httpClient.CheckSuccessStatus($"{homeserver}/.well-known/matrix/client")) {
+            var resp = await _httpClient.GetFromJsonAsync<JsonElement>($"{homeserver}/.well-known/matrix/client");
+            var hs = resp.GetProperty("m.homeserver").GetProperty("base_url").GetString();
+            return hs;
+        }
+
+        _logger.LogInformation("No client well-known...");
+        return null;
+    }
+
+    private async Task<string?> _tryResolveFromServerWellknown(string homeserver) {
+        if (!homeserver.StartsWith("http")) homeserver = "https://" + homeserver;
+        if (await _httpClient.CheckSuccessStatus($"{homeserver}/.well-known/matrix/server")) {
+            var resp = await _httpClient.GetFromJsonAsync<JsonElement>($"{homeserver}/.well-known/matrix/server");
+            var hs = resp.GetProperty("m.server").GetString();
+            return hs;
+        }
+
+        _logger.LogInformation("No server well-known...");
+        return null;
+    }
+
+    private async Task<string?> _tryCheckIfDomainHasHomeserver(string homeserver) {
+        _logger.LogInformation($"Checking if {homeserver} hosts a homeserver...");
+        if (await _httpClient.CheckSuccessStatus($"{homeserver}/_matrix/client/versions"))
+            return homeserver;
+        _logger.LogInformation("No homeserver on shortname...");
+        return null;
+    }
+
+    private async Task<string?> _tryCheckIfSubDomainHasHomeserver(string homeserver, string subdomain) {
+        homeserver = homeserver.Replace("https://", $"https://{subdomain}.");
+        return await _tryCheckIfDomainHasHomeserver(homeserver);
+    }
+}