tests and small fix.

Jellyfin.Api/Controllers/SystemController.cs

@@ -84,13 +84,19 @@ namespace Jellyfin.Api.Controllers
         /// <summary>
         /// Pings the system.
         /// </summary>
+        /// <param name="params">Optional: Parameters to echo back in the response.</param>
         /// <response code="200">Information retrieved.</response>
         /// <returns>The server name.</returns>
         [HttpGet("Ping", Name = "GetPingSystem")]
         [HttpPost("Ping", Name = "PostPingSystem")]
         [ProducesResponseType(StatusCodes.Status200OK)]
-        public ActionResult<string> PingSystem()
+        public ActionResult<string> PingSystem([FromQuery]Dictionary<string, string>? @params = null)
         {
+            if (@params != null && @params.Count > 0)
+            {
+                Response.Headers.Add("querystring", string.Join("&", @params.Select(x => x.Key + "=" + x.Value)));
+            }
+
             return _appHost.Name;
         }
 

Jellyfin.Server/Middleware/UrlDecodeQueryFeature.cs

@@ -66,7 +66,14 @@ namespace Jellyfin.Server.Middleware
                 foreach (var pair in queryString)
                 {
                     var item = pair.Split('=', System.StringSplitOptions.RemoveEmptyEntries);
-                    pairs.Add(item[0], new StringValues(item.Length == 2 ? item[1] : string.Empty));
+                    if (item.Length > 0)
+                    {
+                        pairs.Add(item[0], new StringValues(item.Length == 2 ? item[1] : string.Empty));
+                    }
+                    else
+                    {
+                        pairs.Add(pair, string.Empty);
+                    }
                 }
 
                 _store = new QueryCollection(pairs);

tests/Jellyfin.Api.Tests/Controllers/EncodedQueryStringTest.cs

@@ -0,0 +1,47 @@
+using System.IO;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Jellyfin.Api.Tests.Controllers
+{
+    /// <summary>
+    /// Defines the test for encoded querystrings in the url.
+    /// </summary>
+    public class EncodedQueryStringTest : IClassFixture<JellyfinApplicationFactory>
+    {
+        private readonly JellyfinApplicationFactory _factory;
+
+        public EncodedQueryStringTest(JellyfinApplicationFactory factory)
+        {
+            _factory = factory;
+        }
+
+        [Fact]
+        public async Task Ensure_Ping_Working()
+        {
+            var client = _factory.CreateClient();
+
+            var response = await client.GetAsync("system/ping").ConfigureAwait(false);
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        }
+
+        [Theory]
+        [InlineData("a=1&b=2&c=3", "a=1&b=2&c=3")] // won't be processed as there is more than 1.
+        [InlineData("a=1", "a=1")] // won't be processed as it has a value
+        [InlineData("%3D", "==")] // will decode with an empty string value '=' = ''.
+        [InlineData("a%3D1%26b%3D2%26c%3D3", "a=1&b=2&c=3")] // will be processed.
+
+        public async Task Ensure_Decoding_Of_Urls_Is_Working(string sourceUrl, string unencodedUrl)
+        {
+            var client = _factory.CreateClient();
+
+            var response = await client.GetAsync("system/ping?" + sourceUrl).ConfigureAwait(false);
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            Assert.Equal(unencodedUrl, response.Headers.GetValues("querystring").First());
+        }
+    }
+}