Fix: errors when using rate limiting (#811)

* Fix: errors when using rate limiting
Add: QuotaExceededError class for requesting too much
Add: QuotaExceededError error code
Add: Add an error when limit is reached
Reflact: Extract GetResponseMessage method for getting default or configured response message for requ

* Fix: modify check_we_have_considered_all_errors_in_these_tests for adding a new OcelotErrorCode

src/Ocelot/Errors/OcelotErrorCode.cs

@@ -37,6 +37,7 @@
         CouldNotFindPlaceholderError,
         CouldNotFindAggregatorError,
         CannotAddPlaceholderError,
-        CannotRemovePlaceholderError
+        CannotRemovePlaceholderError,
+        QuotaExceededError
     }
 }

src/Ocelot/RateLimit/Middleware/ClientRateLimitMiddleware.cs

@@ -69,6 +69,9 @@ namespace Ocelot.RateLimit.Middleware
                     
                     // break execution
                     await ReturnQuotaExceededResponse(context.HttpContext, options, retrystring);
+                    
+                    // Set Error
+                    context.Errors.Add(new QuotaExceededError(this.GetResponseMessage(options)));
 
                     return;
                 }
@@ -117,7 +120,7 @@ namespace Ocelot.RateLimit.Middleware
         
         public virtual Task ReturnQuotaExceededResponse(HttpContext httpContext, RateLimitOptions option, string retryAfter)
         {
-            var message = string.IsNullOrEmpty(option.QuotaExceededMessage) ? $"API calls quota exceeded! maximum admitted {option.RateLimitRule.Limit} per {option.RateLimitRule.Period}." : option.QuotaExceededMessage;
+            var message = this.GetResponseMessage(option);
 
             if (!option.DisableRateLimitHeaders)
             {
@@ -128,6 +131,14 @@ namespace Ocelot.RateLimit.Middleware
             return httpContext.Response.WriteAsync(message);
         }
 
+        private string GetResponseMessage(RateLimitOptions option)
+        {
+            var message = string.IsNullOrEmpty(option.QuotaExceededMessage)
+                ? $"API calls quota exceeded! maximum admitted {option.RateLimitRule.Limit} per {option.RateLimitRule.Period}."
+                : option.QuotaExceededMessage;
+            return message;
+        }
+
         private Task SetRateLimitHeaders(object rateLimitHeaders)
         {
             var headers = (RateLimitHeaders)rateLimitHeaders;

src/Ocelot/RateLimit/QuotaExceededError.cs

@@ -0,0 +1,12 @@
+using Ocelot.Errors;
+
+namespace Ocelot.RateLimit
+{
+    public class QuotaExceededError : Error
+    {
+        public QuotaExceededError(string message)
+            : base(message, OcelotErrorCode.QuotaExceededError)
+        {
+        }
+    }
+}