Added the possibility to manage the placeholders from outside ocelot (#724)

src/Ocelot/Errors/OcelotErrorCode.cs

@@ -35,6 +35,8 @@
         FileValidationFailedError,
         UnableToFindDelegatingHandlerProviderError,
         CouldNotFindPlaceholderError,
-        CouldNotFindAggregatorError
+        CouldNotFindAggregatorError,
+        CannotAddPlaceholderError,
+        CannotRemovePlaceholderError
     }
 }

src/Ocelot/Infrastructure/CannotAddPlaceholderError.cs

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

src/Ocelot/Infrastructure/CannotRemovePlaceholderError.cs

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

src/Ocelot/Infrastructure/IPlaceholders.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Net.Http;
 using Ocelot.Request.Middleware;
 using Ocelot.Responses;
@@ -8,5 +9,7 @@ namespace Ocelot.Infrastructure
     {
         Response<string> Get(string key);
         Response<string> Get(string key, DownstreamRequest request);
+        Response Add(string key, Func<Response<string>> func);
+        Response Remove(string key);
     }
-}
+}

src/Ocelot/Infrastructure/Placeholders.cs

@@ -59,6 +59,28 @@ namespace Ocelot.Infrastructure
             return new ErrorResponse<string>(new CouldNotFindPlaceholderError(key));
         }
 
+        public Response Add(string key, Func<Response<string>> func)
+        {
+            if(_placeholders.ContainsKey(key))
+            {
+                return new ErrorResponse(new CannotAddPlaceholderError($"Unable to add placeholder: {key}, placeholder already exists"));
+            }
+            
+            _placeholders.Add(key, func);
+            return new OkResponse();
+        }
+
+        public Response Remove(string key)
+        {
+            if(!_placeholders.ContainsKey(key))
+            {
+                return new ErrorResponse(new CannotRemovePlaceholderError($"Unable to remove placeholder: {key}, placeholder does not exists"));
+            }
+            
+            _placeholders.Remove(key);
+            return new OkResponse();
+        }
+
         private Func<Response<string>> GetRemoteIpAddress()
         {
             return () =>