Add encoding to Response

Author: Churkin Anton

src/Prometheus.Client.AspNetCore/PrometheusExtensions.cs

@@ -41,12 +41,18 @@ public static IApplicationBuilder UsePrometheusServer(this IApplicationBuilder a
             if (options.UseDefaultCollectors)
                 options.CollectorRegistryInstance.UseDefaultCollectors();
 
+            var contentType = "text/plain; version=0.0.4";
+
+            if (options.ResponseEncoding != null)
+                contentType += $"; charset={options.ResponseEncoding.BodyName}";
+
             void AddMetricsHandler(IApplicationBuilder coreapp)
             {
                 coreapp.Run(async context =>
                 {
                     var response = context.Response;
-                    response.ContentType = "text/plain; version=0.0.4";
+
+                    response.ContentType = contentType;
 
                     using var outputStream = response.Body;
                     await ScrapeHandler.ProcessAsync(options.CollectorRegistryInstance, outputStream);

src/Prometheus.Client.AspNetCore/PrometheusOptions.cs

@@ -1,3 +1,4 @@
+using System.Text;
 using Prometheus.Client.Collectors;
 
 namespace Prometheus.Client.AspNetCore
@@ -26,5 +27,10 @@ public class PrometheusOptions
         ///     Use default collectors
         /// </summary>
         public bool UseDefaultCollectors { get; set; } = true;
+
+        /// <summary>
+        ///     Charset of text response.
+        /// </summary>
+        public Encoding ResponseEncoding { get; set; }
     }
 }