[csharp-refactor] Minor csharp refactor changes (#1723)

* [csharp-refactor] Minor changes to JSON mime usage

:racehorse: This maeks the regex static to reduce GC overhead for active clients.
This also removes the lowercase call on the mimetype before evaluating,
as the regex already uses the inline modifier for case insensitivity.

* [csharp-refactor] Regenerate sample

modules/openapi-generator/src/main/resources/csharp-refactor/ClientUtils.mustache

@@ -204,7 +204,7 @@ namespace {{packageName}}.Client
 
             foreach (var contentType in contentTypes)
             {
-                if (IsJsonMime(contentType.ToLower()))
+                if (IsJsonMime(contentType))
                     return contentType;
             }
 
@@ -229,6 +229,11 @@ namespace {{packageName}}.Client
             return String.Join(",", accepts);
         }
 
+        /// <summary>
+        /// Provides a case-insensitive check that a provided content type is a known JSON-like content type.
+        /// </summary>
+        public static readonly Regex JsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
+
         /// <summary>
         /// Check if the given MIME is a JSON MIME.
         /// JSON MIME examples:
@@ -241,8 +246,9 @@ namespace {{packageName}}.Client
         /// <returns>Returns True if MIME type is json.</returns>
         public static bool IsJsonMime(String mime)
         {
-            var jsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
-            return mime != null && (jsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json"));
+            if (String.IsNullOrWhiteSpace(mime)) return false;
+
+            return JsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json");
         }
     }
 }

samples/client/petstore/csharp-refactor/OpenAPIClient/src/Org.OpenAPITools/Client/ClientUtils.cs

@@ -208,7 +208,7 @@ public static String SelectHeaderContentType(String[] contentTypes)
 
             foreach (var contentType in contentTypes)
             {
-                if (IsJsonMime(contentType.ToLower()))
+                if (IsJsonMime(contentType))
                     return contentType;
             }
 
@@ -233,6 +233,11 @@ public static String SelectHeaderAccept(String[] accepts)
             return String.Join(",", accepts);
         }
 
+        /// <summary>
+        /// Provides a case-insensitive check that a provided content type is a known JSON-like content type.
+        /// </summary>
+        public static readonly Regex JsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
+
         /// <summary>
         /// Check if the given MIME is a JSON MIME.
         /// JSON MIME examples:
@@ -245,8 +250,9 @@ public static String SelectHeaderAccept(String[] accepts)
         /// <returns>Returns True if MIME type is json.</returns>
         public static bool IsJsonMime(String mime)
         {
-            var jsonRegex = new Regex("(?i)^(application/json|[^;/ \t]+/[^;/ \t]+[+]json)[ \t]*(;.*)?$");
-            return mime != null && (jsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json"));
+            if (String.IsNullOrWhiteSpace(mime)) return false;
+
+            return JsonRegex.IsMatch(mime) || mime.Equals("application/json-patch+json");
         }
     }
 }