Simplify and fix JsonContent encoding

src/Jackett/Utils/JsonContent.cs

@@ -12,29 +12,17 @@ using System.Threading.Tasks;
 
 namespace Jackett.Utils
 {
-    public class JsonContent : HttpContent
-    {
-        private readonly object _value;
-
-        public JsonContent(object value)
-        {
-            _value = value;
-            Headers.ContentType = new MediaTypeHeaderValue("application/json");
-        }
-
-        protected override async Task SerializeToStreamAsync(Stream stream,
-            TransportContext context)
-        {
-            var json = JsonConvert.SerializeObject(_value, Formatting.Indented, new JsonSerializerSettings {NullValueHandling = NullValueHandling.Ignore});
-            var writer = new StreamWriter(stream);
-            writer.Write(json);
-            await writer.FlushAsync();
-        }
-
-        protected override bool TryComputeLength(out long length)
-        {
-            length = -1;
-            return false;
-        }
+    public class JsonContent : StringContent
+    {
+        public JsonContent(object value)
+            : this(value, Encoding.UTF8)
+        {
+        }
+
+        public JsonContent(object value, Encoding encoding)
+            : base(JsonConvert.SerializeObject(value, Formatting.Indented, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore }), encoding, "application/json")
+        {
+            this.Headers.ContentType.CharSet = "utf-8";
+        }
     }
 }