Do not include a double slash in URLs when a base URL is not set

Emby.Server.Implementations/ApplicationHost.cs

@@ -1236,28 +1236,30 @@ namespace Emby.Server.Implementations
                 str.CopyTo(span.Slice(1));
                 span[^1] = ']';
 
-                return GetLocalApiUrl(span).ToString();
+                return GetLocalApiUrl(span);
             }
 
-            return GetLocalApiUrl(ipAddress.ToString()).ToString();
+            return GetLocalApiUrl(ipAddress.ToString());
         }
 
         /// <inheritdoc/>
-        public Uri GetLoopbackHttpApiUrl()
+        public string GetLoopbackHttpApiUrl()
         {
             return GetLocalApiUrl("127.0.0.1", Uri.UriSchemeHttp, HttpPort);
         }
 
         /// <inheritdoc/>
-        public Uri GetLocalApiUrl(ReadOnlySpan<char> host, string scheme = null, int? port = null)
+        public string GetLocalApiUrl(ReadOnlySpan<char> host, string scheme = null, int? port = null)
         {
+            // NOTE: If no BaseUrl is set then UriBuilder appends a trailing slash, but if there is no BaseUrl it does
+            // not. For consistency, always trim the trailing slash.
             return new UriBuilder
             {
                 Scheme = scheme ?? (ListenWithHttps ? Uri.UriSchemeHttps : Uri.UriSchemeHttp),
                 Host = host.ToString(),
                 Port = port ?? (ListenWithHttps ? HttpsPort : HttpPort),
                 Path = ServerConfigurationManager.Configuration.BaseUrl
-            }.Uri;
+            }.ToString().TrimEnd('/');
         }
 
         public Task<List<IPAddress>> GetLocalIpAddresses(CancellationToken cancellationToken)
@@ -1333,8 +1335,7 @@ namespace Emby.Server.Implementations
                 return true;
             }
 
-            var apiUrl = GetLocalApiUrl(address);
+            var apiUrl = GetLocalApiUrl(address) + "/system/ping";
-            apiUrl += "/system/ping";
 
             if (_validAddressResults.TryGetValue(apiUrl, out var cachedResult))
             {

Emby.Server.Implementations/Browser/BrowserLauncher.cs

@@ -31,18 +31,18 @@ namespace Emby.Server.Implementations.Browser
         /// Opens the specified URL in an external browser window. Any exceptions will be logged, but ignored.
         /// </summary>
         /// <param name="appHost">The application host.</param>
-        /// <param name="url">The URL.</param>
+        /// <param name="relativeUrl">The URL to open, relative to the server base URL.</param>
-        private static void TryOpenUrl(IServerApplicationHost appHost, string url)
+        private static void TryOpenUrl(IServerApplicationHost appHost, string relativeUrl)
         {
             try
             {
-                Uri baseUrl = appHost.GetLocalApiUrl("localhost");
+                string baseUrl = appHost.GetLocalApiUrl("localhost");
-                appHost.LaunchUrl(baseUrl + url);
+                appHost.LaunchUrl(baseUrl + relativeUrl);
             }
             catch (Exception ex)
             {
                 var logger = appHost.Resolve<ILogger>();
-                logger?.LogError(ex, "Failed to open browser window with URL {URL}", url);
+                logger?.LogError(ex, "Failed to open browser window with URL {URL}", relativeUrl);
             }
         }
     }

MediaBrowser.Controller/IServerApplicationHost.cs

@@ -76,7 +76,7 @@ namespace MediaBrowser.Controller
         /// over HTTP (not HTTPS).
         /// </summary>
         /// <returns>The API URL.</returns>
-        public Uri GetLoopbackHttpApiUrl();
+        string GetLoopbackHttpApiUrl();
 
         /// <summary>
         /// Gets a local (LAN) URL that can be used to access the API. HTTPS will be preferred when available.
@@ -98,7 +98,7 @@ namespace MediaBrowser.Controller
         /// preferring the HTTPS port, if available.
         /// </param>
         /// <returns>The API URL.</returns>
-        Uri GetLocalApiUrl(ReadOnlySpan<char> hostname, string scheme = null, int? port = null);
+        string GetLocalApiUrl(ReadOnlySpan<char> hostname, string scheme = null, int? port = null);
 
         /// <summary>
         /// Open a URL in an external browser window.