#280 Add headers to response (#286)

* #280 can now add response headers inc trace id, now need to consolidate the header place holder stuff

* #280 changed port for linux tests

* #280 lots of hacking around to handle errors and consolidate placeholders into one class

docs/features/headerstransformation.rst

@@ -3,8 +3,32 @@ Headers Transformation
 
 Ocelot allows the user to transform headers pre and post downstream request. At the moment Ocelot only supports find and replace. This feature was requested `GitHub #190 <https://github.com/TomPallister/Ocelot/issues/190>`_ and I decided that it was going to be useful in various ways.
 
-Syntax
-^^^^^^
+Add to Response
+^^^^^^^^^^^^^^^
+
+This feature was requested in `GitHub #280 <https://github.com/TomPallister/Ocelot/issues/280>`_. I have only implemented
+for responses but could add for requests in the future.
+
+If you want to add a header to your downstream response please add the following to a ReRoute in configuration.json..
+
+.. code-block:: json
+
+    "DownstreamHeaderTransform": {
+        "Uncle": "Bob"
+    },
+
+In the example above a header with the key Uncle and value Bob would be returned by Ocelot when requesting the specific ReRoute.
+
+If you want to return the Butterfly APM trace id then do something like the following..
+
+.. code-block:: json
+
+    "DownstreamHeaderTransform": {
+        "AnyKey": "{TraceId}"
+    },
+
+Find and Replace
+^^^^^^^^^^^^^^^^
 
 In order to transform a header first we specify the header key and then the type of transform we want e.g.
 
@@ -43,6 +67,7 @@ Ocelot allows placeholders that can be used in header transformation.
 
 {BaseUrl} - This will use Ocelot's base url e.g. http://localhost:5000 as its value.
 {DownstreamBaseUrl} - This will use the downstream services base url e.g. http://localhost:5000 as its value. This only works for DownstreamHeaderTransform at the moment.
+{TraceId} - This will use the Butterfly APM Trace Id. This only works for DownstreamHeaderTransform at the moment.
 
 Handling 302 Redirects
 ^^^^^^^^^^^^^^^^^^^^^^

src/Ocelot/Configuration/Builder/DownstreamReRouteBuilder.cs

@@ -2,6 +2,7 @@ using System.Collections.Generic;
 using System.Net.Http;
 using Ocelot.Values;
 using System.Linq;
+using Ocelot.Configuration.Creator;
 
 namespace Ocelot.Configuration.Builder
 {
@@ -37,11 +38,13 @@ namespace Ocelot.Configuration.Builder
         private string _upstreamHost;
         private string _key;
         private List<string> _delegatingHandlers;
+        private List<AddHeader> _addHeadersToDownstream;
 
         public DownstreamReRouteBuilder()
         {
             _downstreamAddresses = new List<DownstreamHostAndPort>();
             _delegatingHandlers = new List<string>();
+            _addHeadersToDownstream = new List<AddHeader>();
         }
 
         public DownstreamReRouteBuilder WithDownstreamAddresses(List<DownstreamHostAndPort> downstreamAddresses)
@@ -224,6 +227,12 @@ namespace Ocelot.Configuration.Builder
             return this;
         }
 
+        public DownstreamReRouteBuilder WithAddHeadersToDownstream(List<AddHeader> addHeadersToDownstream)
+        {
+            _addHeadersToDownstream = addHeadersToDownstream;
+            return this;
+        }
+
         public DownstreamReRoute Build()
         {
             return new DownstreamReRoute(
@@ -253,7 +262,8 @@ namespace Ocelot.Configuration.Builder
                 _authenticationOptions, 
                 new PathTemplate(_downstreamPathTemplate),
                 _reRouteKey,
-                _delegatingHandlers);
+                _delegatingHandlers,
+                _addHeadersToDownstream);
         }
     }
 }

src/Ocelot/Configuration/Creator/FileOcelotConfigurationCreator.cs

@@ -213,6 +213,7 @@ namespace Ocelot.Configuration.Creator
                 .WithDownstreamHeaderFindAndReplace(hAndRs.Downstream)
                 .WithUpstreamHost(fileReRoute.UpstreamHost)
                 .WithDelegatingHandlers(fileReRoute.DelegatingHandlers)
+                .WithAddHeadersToDownstream(hAndRs.AddHeadersToDownstream)
                 .Build();
 
             return reRoute;

src/Ocelot/Configuration/Creator/HeaderFindAndReplaceCreator.cs

@@ -1,20 +1,22 @@
 using System;
 using System.Collections.Generic;
 using Ocelot.Configuration.File;
+using Ocelot.Infrastructure;
+using Ocelot.Logging;
 using Ocelot.Middleware;
+using Ocelot.Responses;
 
 namespace Ocelot.Configuration.Creator
 {
     public class HeaderFindAndReplaceCreator : IHeaderFindAndReplaceCreator
     {
-        private IBaseUrlFinder _finder;
-        private readonly Dictionary<string, Func<string>> _placeholders;
+        private IPlaceholders _placeholders;
+        private IOcelotLogger _logger;
 
-        public HeaderFindAndReplaceCreator(IBaseUrlFinder finder)
+        public HeaderFindAndReplaceCreator(IPlaceholders placeholders, IOcelotLoggerFactory factory)
         {
-            _finder = finder;
-            _placeholders = new Dictionary<string, Func<string>>();
-            _placeholders.Add("{BaseUrl}", () => _finder.Find());
+            _logger = factory.CreateLogger<HeaderFindAndReplaceCreator>();;
+            _placeholders = placeholders;
         }
 
         public HeaderTransformations Create(FileReRoute fileReRoute)
@@ -24,21 +26,43 @@ namespace Ocelot.Configuration.Creator
             foreach(var input in fileReRoute.UpstreamHeaderTransform)
             {
                 var hAndr = Map(input);
-                upstream.Add(hAndr);
+                if(!hAndr.IsError)
+                {
+                    upstream.Add(hAndr.Data);
+                }
+                else
+                {
+                    _logger.LogError($"Unable to add UpstreamHeaderTransform {input.Key}: {input.Value}");
+                }
             }
 
             var downstream = new List<HeaderFindAndReplace>();
+            var addHeadersToDownstream = new List<AddHeader>();
 
             foreach(var input in fileReRoute.DownstreamHeaderTransform)
+            {
+                if(input.Value.Contains(","))
                 {
                     var hAndr = Map(input);
-                downstream.Add(hAndr);
+                    if(!hAndr.IsError)
+                    {
+                        downstream.Add(hAndr.Data);
+                    }
+                    else
+                    {
+                        _logger.LogError($"Unable to add DownstreamHeaderTransform {input.Key}: {input.Value}");
+                    }
+                }
+                else
+                {
+                    addHeadersToDownstream.Add(new AddHeader(input.Key, input.Value));
+                }
             }
             
-            return new HeaderTransformations(upstream, downstream);
+            return new HeaderTransformations(upstream, downstream, addHeadersToDownstream);
         }
 
-        private HeaderFindAndReplace Map(KeyValuePair<string,string> input)
+        private Response<HeaderFindAndReplace> Map(KeyValuePair<string,string> input)
         {
             var findAndReplace = input.Value.Split(",");
 
@@ -51,16 +75,19 @@ namespace Ocelot.Configuration.Creator
                 
                 var placeholder = replace.Substring(startOfPlaceholder, startOfPlaceholder + (endOfPlaceholder + 1));
 
-                if(_placeholders.ContainsKey(placeholder))
+                var value = _placeholders.Get(placeholder);
+
+                if(value.IsError)
                 {
-                    var value = _placeholders[placeholder].Invoke();
-                    replace = replace.Replace(placeholder, value);
+                    return new ErrorResponse<HeaderFindAndReplace>(value.Errors);
                 }
+
+                replace = replace.Replace(placeholder, value.Data);
             }
 
             var hAndr = new HeaderFindAndReplace(input.Key, findAndReplace[0], replace, 0);
             
-            return hAndr;
+            return new OkResponse<HeaderFindAndReplace>(hAndr);
         }
     }
 }

src/Ocelot/Configuration/Creator/HeaderTransformations.cs

@@ -4,14 +4,31 @@ namespace Ocelot.Configuration.Creator
 {
     public class HeaderTransformations
     {
-        public HeaderTransformations(List<HeaderFindAndReplace> upstream, List<HeaderFindAndReplace> downstream)
+        public HeaderTransformations(
+            List<HeaderFindAndReplace> upstream, 
+            List<HeaderFindAndReplace> downstream,
+            List<AddHeader> addHeader)
         {
+            AddHeadersToDownstream = addHeader;
             Upstream = upstream;
             Downstream = downstream;
         }
 
-        public List<HeaderFindAndReplace> Upstream {get;private set;}
+        public List<HeaderFindAndReplace> Upstream { get; private set; }
 
-        public List<HeaderFindAndReplace> Downstream {get;private set;}
+        public List<HeaderFindAndReplace> Downstream { get; private set; }
+        public List<AddHeader> AddHeadersToDownstream {get;private set;}
+    }
+
+    public class AddHeader
+    {
+        public AddHeader(string key, string value)
+        {
+            this.Key = key;
+            this.Value = value;
+
+        }
+        public string Key { get; private set; }
+        public string Value { get; private set; }
     }
 }

src/Ocelot/Configuration/DownstreamReRoute.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using Ocelot.Configuration.Creator;
 using Ocelot.Values;
 
 namespace Ocelot.Configuration
@@ -32,8 +33,10 @@ namespace Ocelot.Configuration
             AuthenticationOptions authenticationOptions, 
             PathTemplate downstreamPathTemplate, 
             string reRouteKey,
-            List<string> delegatingHandlers)
+            List<string> delegatingHandlers,
+            List<AddHeader> addHeadersToDownstream)
         {
+            AddHeadersToDownstream = addHeadersToDownstream;
             DelegatingHandlers = delegatingHandlers;
             Key = key;
             UpstreamPathTemplate = upstreamPathTemplate;
@@ -90,5 +93,6 @@ namespace Ocelot.Configuration
         public PathTemplate DownstreamPathTemplate { get; private set; }
         public string ReRouteKey { get; private set; }
         public List<string> DelegatingHandlers {get;private set;}
+        public List<AddHeader> AddHeadersToDownstream {get;private set;}
     }
 }

src/Ocelot/DependencyInjection/OcelotBuilder.cs

@@ -52,6 +52,7 @@ namespace Ocelot.DependencyInjection
     using System.Linq;
     using System.Net.Http;
     using Butterfly.Client.AspNetCore;
+    using Ocelot.Infrastructure;
 
     public class OcelotBuilder : IOcelotBuilder
     {
@@ -149,6 +150,8 @@ namespace Ocelot.DependencyInjection
             // We add this here so that we can always inject something into the factory for IoC..
             _services.AddSingleton<IServiceTracer, FakeServiceTracer>();
             _services.TryAddSingleton<IConsulPollerConfiguration, InMemoryConsulPollerConfiguration>();
+            _services.TryAddSingleton<IAddHeadersToResponse, AddHeadersToResponse>();
+            _services.TryAddSingleton<IPlaceholders, Placeholders>();
         }
 
         public IOcelotAdministrationBuilder AddAdministration(string path, string secret)

src/Ocelot/Errors/OcelotErrorCode.cs

@@ -34,6 +34,7 @@
         RateLimitOptionsError,
         PathTemplateDoesntStartWithForwardSlash,
         FileValidationFailedError,
-        UnableToFindDelegatingHandlerProviderError
+        UnableToFindDelegatingHandlerProviderError,
+        CouldNotFindPlaceholderError
     }
 }

src/Ocelot/Headers/AddHeadersToRequest.cs

@@ -4,6 +4,7 @@ using Ocelot.Configuration;
 using Ocelot.Infrastructure.Claims.Parser;
 using Ocelot.Responses;
 using System.Net.Http;
+using Ocelot.Configuration.Creator;
 
 namespace Ocelot.Headers
 {

src/Ocelot/Headers/AddHeadersToResponse.cs

@@ -0,0 +1,44 @@
+namespace Ocelot.Headers
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Net.Http;
+    using Ocelot.Configuration.Creator;
+    using Ocelot.Infrastructure;
+    using Ocelot.Infrastructure.RequestData;
+    using Ocelot.Logging;
+
+    public class AddHeadersToResponse : IAddHeadersToResponse
+    {
+        private IPlaceholders _placeholders;
+        private IOcelotLogger _logger;
+
+        public AddHeadersToResponse(IPlaceholders placeholders, IOcelotLoggerFactory factory)
+        {
+            _logger = factory.CreateLogger<AddHeadersToResponse>();
+            _placeholders = placeholders;
+        }
+        public void Add(List<AddHeader> addHeaders, HttpResponseMessage response)
+        {
+            foreach(var add in addHeaders)
+            {
+                if(add.Value.StartsWith('{') && add.Value.EndsWith('}'))
+                {
+                    var value = _placeholders.Get(add.Value);
+                    
+                    if(value.IsError)
+                    {
+                        _logger.LogError($"Unable to add header to response {add.Key}: {add.Value}");
+                        continue;
+                    }
+
+                    response.Headers.TryAddWithoutValidation(add.Key, value.Data);
+                }
+                else
+                {
+                    response.Headers.TryAddWithoutValidation(add.Key, add.Value);
+                }
+            }
+        }
+    }
+}

src/Ocelot/Headers/HttpResponseHeaderReplacer.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Net.Http;
 using Ocelot.Configuration;
+using Ocelot.Infrastructure;
 using Ocelot.Infrastructure.Extensions;
 using Ocelot.Responses;
 
@@ -10,24 +11,14 @@ namespace Ocelot.Headers
 {
     public class HttpResponseHeaderReplacer : IHttpResponseHeaderReplacer
     {
-        private Dictionary<string, Func<HttpRequestMessage, string>> _placeholders;
+        private IPlaceholders _placeholders;
 
-        public HttpResponseHeaderReplacer()
+        public HttpResponseHeaderReplacer(IPlaceholders placeholders)
         {
-            _placeholders = new Dictionary<string, Func<HttpRequestMessage, string>>();
-            _placeholders.Add("{DownstreamBaseUrl}", x => {
-                var downstreamUrl = $"{x.RequestUri.Scheme}://{x.RequestUri.Host}";
-
-                if(x.RequestUri.Port != 80 && x.RequestUri.Port != 443)
-                {
-                    downstreamUrl = $"{downstreamUrl}:{x.RequestUri.Port}";
+            _placeholders = placeholders;
         }
 
-                return $"{downstreamUrl}/";
-            });
-        }
-
-        public Response Replace(HttpResponseMessage response, List<HeaderFindAndReplace> fAndRs, HttpRequestMessage httpRequestMessage)
+        public Response Replace(HttpResponseMessage response, List<HeaderFindAndReplace> fAndRs, HttpRequestMessage request)
         {
             foreach (var f in fAndRs)
             {
@@ -35,11 +26,13 @@ namespace Ocelot.Headers
                 if(response.Headers.TryGetValues(f.Key, out var values))
                 {
                     //check to see if it is a placeholder in the find...
-                    if(_placeholders.TryGetValue(f.Find, out var replacePlaceholder))
+                    var placeholderValue = _placeholders.Get(f.Find, request);
+
+                    if(!placeholderValue.IsError)
                     {
                         //if it is we need to get the value of the placeholder
-                        var find = replacePlaceholder(httpRequestMessage);
-                        var replaced = values.ToList()[f.Index].Replace(find, f.Replace.LastCharAsForwardSlash());
+                        //var find = replacePlaceholder(httpRequestMessage);
+                        var replaced = values.ToList()[f.Index].Replace(placeholderValue.Data, f.Replace.LastCharAsForwardSlash());
                         response.Headers.Remove(f.Key);
                         response.Headers.Add(f.Key, replaced);
                     }

src/Ocelot/Headers/IAddHeadersToRequest.cs

@@ -4,6 +4,8 @@
     using System.Net.Http;
 
     using Ocelot.Configuration;
+    using Ocelot.Configuration.Creator;
+    using Ocelot.Infrastructure.RequestData;
     using Ocelot.Responses;
 
     public interface IAddHeadersToRequest

src/Ocelot/Headers/IAddHeadersToResponse.cs

@@ -0,0 +1,11 @@
+namespace Ocelot.Headers
+{
+    using System.Collections.Generic;
+    using System.Net.Http;
+    using Ocelot.Configuration.Creator;
+
+    public interface IAddHeadersToResponse
+    {
+        void Add(List<AddHeader> addHeaders, HttpResponseMessage response);
+    }
+}

src/Ocelot/Headers/Middleware/HttpHeadersTransformationMiddleware.cs

@@ -13,12 +13,15 @@ namespace Ocelot.Headers.Middleware
         private readonly IOcelotLogger _logger;
         private readonly IHttpContextRequestHeaderReplacer _preReplacer;
         private readonly IHttpResponseHeaderReplacer _postReplacer;
+        private readonly IAddHeadersToResponse _addHeaders;
 
         public HttpHeadersTransformationMiddleware(OcelotRequestDelegate next,
             IOcelotLoggerFactory loggerFactory,
             IHttpContextRequestHeaderReplacer preReplacer,
-            IHttpResponseHeaderReplacer postReplacer) 
+            IHttpResponseHeaderReplacer postReplacer,
+            IAddHeadersToResponse addHeaders) 
         {
+            _addHeaders = addHeaders;
             _next = next;
             _postReplacer = postReplacer;
             _preReplacer = preReplacer;
@@ -37,6 +40,8 @@ namespace Ocelot.Headers.Middleware
             var postFAndRs = context.DownstreamReRoute.DownstreamHeadersFindAndReplace;
 
             _postReplacer.Replace(context.DownstreamResponse, postFAndRs, context.DownstreamRequest);
+
+            _addHeaders.Add(context.DownstreamReRoute.AddHeadersToDownstream, context.DownstreamResponse);
         }
     }
 }

src/Ocelot/Infrastructure/CouldNotFindPlaceholderError.cs

@@ -0,0 +1,12 @@
+using Ocelot.Errors;
+
+namespace Ocelot.Infrastructure
+{
+    public class CouldNotFindPlaceholderError : Error
+    {
+        public CouldNotFindPlaceholderError(string placeholder) 
+            : base($"Unable to find placeholder called {placeholder}", OcelotErrorCode.CouldNotFindPlaceholderError)
+            {
+            }
+    }
+}

src/Ocelot/Infrastructure/IPlaceholders.cs

@@ -0,0 +1,11 @@
+using System.Net.Http;
+using Ocelot.Responses;
+
+namespace Ocelot.Infrastructure
+{
+    public interface IPlaceholders
+    {
+        Response<string> Get(string key);
+        Response<string> Get(string key, HttpRequestMessage request);
+    }
+}

src/Ocelot/Infrastructure/Placeholders.cs

@@ -0,0 +1,70 @@
+using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using Ocelot.Infrastructure.RequestData;
+using Ocelot.Middleware;
+using Ocelot.Responses;
+
+namespace Ocelot.Infrastructure
+{
+    public class Placeholders : IPlaceholders
+    {
+        private Dictionary<string, Func<Response<string>>> _placeholders;
+        private Dictionary<string, Func<HttpRequestMessage, string>> _requestPlaceholders;
+        private readonly IBaseUrlFinder _finder;
+        private readonly IRequestScopedDataRepository _repo;
+
+        public Placeholders(IBaseUrlFinder finder, IRequestScopedDataRepository repo)
+        {
+            _repo = repo;
+            _finder = finder;
+            _placeholders = new Dictionary<string, Func<Response<string>>>();
+            _placeholders.Add("{BaseUrl}", () => new OkResponse<string>(_finder.Find()));
+            _placeholders.Add("{TraceId}", () => {
+                var traceId = _repo.Get<string>("TraceId");
+                if(traceId.IsError)
+                {
+                    return new ErrorResponse<string>(traceId.Errors);
+                }
+
+                return new OkResponse<string>(traceId.Data);
+            });
+
+            _requestPlaceholders = new Dictionary<string, Func<HttpRequestMessage, string>>();
+            _requestPlaceholders.Add("{DownstreamBaseUrl}", x => {
+                var downstreamUrl = $"{x.RequestUri.Scheme}://{x.RequestUri.Host}";
+
+                if(x.RequestUri.Port != 80 && x.RequestUri.Port != 443)
+                {
+                    downstreamUrl = $"{downstreamUrl}:{x.RequestUri.Port}";
+                }
+
+                return $"{downstreamUrl}/";
+            });
+        }
+
+        public Response<string> Get(string key)
+        {
+            if(_placeholders.ContainsKey(key))
+            {
+                var response = _placeholders[key].Invoke();
+                if(!response.IsError)
+                {
+                    return new OkResponse<string>(response.Data);
+                }
+            }
+
+            return new ErrorResponse<string>(new CouldNotFindPlaceholderError(key));
+        }
+
+        public Response<string> Get(string key, HttpRequestMessage request)
+        {
+            if(_requestPlaceholders.ContainsKey(key))
+            {
+                return new OkResponse<string>(_requestPlaceholders[key].Invoke(request));
+            }
+
+            return new ErrorResponse<string>(new CouldNotFindPlaceholderError(key));
+        }
+    }
+}

src/Ocelot/Requester/OcelotHttpTracingHandler.cs

@@ -5,26 +5,37 @@ using System.Threading;
 using System.Threading.Tasks;
 using Butterfly.Client.Tracing;
 using Butterfly.OpenTracing;
+using Ocelot.Infrastructure.RequestData;
 
 namespace Ocelot.Requester
 {
     public class OcelotHttpTracingHandler : DelegatingHandler, ITracingHandler
     {
         private readonly IServiceTracer _tracer;
+        private readonly IRequestScopedDataRepository _repo;
         private const string prefix_spanId = "ot-spanId";
 
-        public OcelotHttpTracingHandler(IServiceTracer tracer, HttpMessageHandler httpMessageHandler = null)
+        public OcelotHttpTracingHandler(
+            IServiceTracer tracer, 
+            IRequestScopedDataRepository repo,
+            HttpMessageHandler httpMessageHandler = null)
         {
+            _repo = repo;
             _tracer = tracer ?? throw new ArgumentNullException(nameof(tracer));
             InnerHandler = httpMessageHandler ?? new HttpClientHandler();
         }
 
-        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        protected override Task<HttpResponseMessage> SendAsync(
+            HttpRequestMessage request, 
+            CancellationToken cancellationToken)
         {
             return _tracer.ChildTraceAsync($"httpclient {request.Method}", DateTimeOffset.UtcNow, span => TracingSendAsync(span, request, cancellationToken));
         }
 
-        protected virtual async Task<HttpResponseMessage> TracingSendAsync(ISpan span, HttpRequestMessage request, CancellationToken cancellationToken)
+        protected virtual async Task<HttpResponseMessage> TracingSendAsync(
+            ISpan span, 
+            HttpRequestMessage request, 
+            CancellationToken cancellationToken)
         {
             IEnumerable<string> traceIdVals = null;
             if (request.Headers.TryGetValues(prefix_spanId, out traceIdVals))
@@ -33,6 +44,8 @@ namespace Ocelot.Requester
                 request.Headers.TryAddWithoutValidation(prefix_spanId, span.SpanContext.SpanId);
             }
 
+            _repo.Add("TraceId", span.SpanContext.TraceId);
+            
             span.Tags.Client().Component("HttpClient")
                 .HttpMethod(request.Method.Method)
                 .HttpUrl(request.RequestUri.OriginalString)

src/Ocelot/Requester/TracingHandlerFactory.cs

@@ -1,20 +1,25 @@
 using Butterfly.Client.Tracing;
 using Butterfly.OpenTracing;
+using Ocelot.Infrastructure.RequestData;
 
 namespace Ocelot.Requester
 {
     public class TracingHandlerFactory : ITracingHandlerFactory
     {
         private readonly IServiceTracer _tracer;
+        private readonly IRequestScopedDataRepository _repo;
 
-        public TracingHandlerFactory(IServiceTracer tracer)
+        public TracingHandlerFactory(
+            IServiceTracer tracer,
+            IRequestScopedDataRepository repo)
         {
+            _repo = repo;
             _tracer = tracer;
         }
 
         public ITracingHandler Get()
         {
-            return new OcelotHttpTracingHandler(_tracer);
+            return new OcelotHttpTracingHandler(_tracer, _repo);
         }
     }
 

test/Ocelot.AcceptanceTests/ButterflyTracingTests.cs

@@ -70,7 +70,7 @@ namespace Ocelot.AcceptanceTests
                                 new FileHostAndPort
                                 {
                                     Host = "localhost",
-                                    Port = 51888,
+                                    Port = 51388,
                                 }
                             },
                             UpstreamPathTemplate = "/api002/values",
@@ -92,7 +92,7 @@ namespace Ocelot.AcceptanceTests
             var butterflyUrl = "http://localhost:9618";
 
             this.Given(x => GivenServiceOneIsRunning("http://localhost:51887", "/api/values", 200, "Hello from Laura", butterflyUrl))
-                .And(x => GivenServiceTwoIsRunning("http://localhost:51888", "/api/values", 200, "Hello from Tom", butterflyUrl))
+                .And(x => GivenServiceTwoIsRunning("http://localhost:51388", "/api/values", 200, "Hello from Tom", butterflyUrl))
                 .And(x => GivenFakeButterfly(butterflyUrl))
                 .And(x => _steps.GivenThereIsAConfiguration(configuration))
                 .And(x => _steps.GivenOcelotIsRunningUsingButterfly(butterflyUrl))
@@ -109,6 +109,60 @@ namespace Ocelot.AcceptanceTests
             commandOnAllStateMachines.ShouldBeTrue();
         }
 
+        [Fact]
+        public void should_return_tracing_header()
+        {
+            var configuration = new FileConfiguration
+            {
+                ReRoutes = new List<FileReRoute>
+                    {
+                        new FileReRoute
+                        {
+                            DownstreamPathTemplate = "/api/values",
+                            DownstreamScheme = "http",
+                            DownstreamHostAndPorts = new List<FileHostAndPort>
+                            {
+                                new FileHostAndPort
+                                {
+                                    Host = "localhost",
+                                    Port = 51387,
+                                }
+                            },
+                            UpstreamPathTemplate = "/api001/values",
+                            UpstreamHttpMethod = new List<string> { "Get" },
+                            HttpHandlerOptions = new FileHttpHandlerOptions
+                            {
+                                UseTracing = true
+                            },
+                            QoSOptions = new FileQoSOptions
+                            {
+                                ExceptionsAllowedBeforeBreaking = 3,
+                                DurationOfBreak = 10,
+                                TimeoutValue = 5000
+                            },
+                            DownstreamHeaderTransform = new Dictionary<string, string>()
+                            {
+                                {"Trace-Id", "{TraceId}"},
+                                {"Tom", "Laura"}
+                            }
+                        }
+                    }
+            };
+
+            var butterflyUrl = "http://localhost:9618";
+
+            this.Given(x => GivenServiceOneIsRunning("http://localhost:51387", "/api/values", 200, "Hello from Laura", butterflyUrl))
+                .And(x => GivenFakeButterfly(butterflyUrl))
+                .And(x => _steps.GivenThereIsAConfiguration(configuration))
+                .And(x => _steps.GivenOcelotIsRunningUsingButterfly(butterflyUrl))
+                .When(x => _steps.WhenIGetUrlOnTheApiGateway("/api001/values"))
+                .Then(x => _steps.ThenTheStatusCodeShouldBe(HttpStatusCode.OK))
+                .And(x => _steps.ThenTheResponseBodyShouldBe("Hello from Laura"))
+                .And(x => _steps.ThenTheTraceHeaderIsSet("Trace-Id"))
+                .And(x => _steps.ThenTheResponseHeaderIs("Tom", "Laura"))
+                .BDDfy();
+        }
+
         private void GivenServiceOneIsRunning(string baseUrl, string basePath, int statusCode, string responseBody, string butterflyUrl)
         {
             _serviceOneBuilder = new WebHostBuilder()

test/Ocelot.AcceptanceTests/Steps.cs

@@ -318,6 +318,12 @@ namespace Ocelot.AcceptanceTests
             header.First().ShouldBe(value);
         }
 
+        public void ThenTheTraceHeaderIsSet(string key)
+        {
+            var header = _response.Headers.GetValues(key);
+            header.First().ShouldNotBeNullOrEmpty();
+        }
+
         public void GivenOcelotIsRunningUsingJsonSerializedCache()
         {
             _webHostBuilder = new WebHostBuilder();

test/Ocelot.UnitTests/Configuration/ConsulFileConfigurationPollerTests.cs

@@ -34,7 +34,7 @@ namespace Ocelot.UnitTests.Configuration
             _fileConfig = new FileConfiguration();
             _config = new Mock<IConsulPollerConfiguration>();
             _repo.Setup(x => x.Get()).ReturnsAsync(new OkResponse<FileConfiguration>(_fileConfig));
-            _config.Setup(x => x.Delay).Returns(10);
+            _config.Setup(x => x.Delay).Returns(100);
             _poller = new ConsulFileConfigurationPoller(_factory.Object, _repo.Object, _setter.Object, _config.Object);
         }
         

test/Ocelot.UnitTests/Configuration/FileConfigurationCreatorTests.cs

@@ -827,6 +827,7 @@ namespace Ocelot.UnitTests.Configuration
                 result.DownstreamReRoute[0].ClaimsToQueries.Count.ShouldBe(expected.DownstreamReRoute[0].ClaimsToQueries.Count);
                 result.DownstreamReRoute[0].RequestIdKey.ShouldBe(expected.DownstreamReRoute[0].RequestIdKey);   
                 result.DownstreamReRoute[0].DelegatingHandlers.ShouldBe(expected.DownstreamReRoute[0].DelegatingHandlers);      
+                result.DownstreamReRoute[0].AddHeadersToDownstream.ShouldBe(expected.DownstreamReRoute[0].AddHeadersToDownstream);           
             }
         }
 
@@ -909,7 +910,7 @@ namespace Ocelot.UnitTests.Configuration
 
         private void GivenTheHeaderFindAndReplaceCreatorReturns()
         {
-            _headerFindAndReplaceCreator.Setup(x => x.Create(It.IsAny<FileReRoute>())).Returns(new HeaderTransformations(new List<HeaderFindAndReplace>(), new List<HeaderFindAndReplace>()));
+            _headerFindAndReplaceCreator.Setup(x => x.Create(It.IsAny<FileReRoute>())).Returns(new HeaderTransformations(new List<HeaderFindAndReplace>(), new List<HeaderFindAndReplace>(), new List<AddHeader>()));
         }
 
         private void GivenTheFollowingIsReturned(ServiceProviderConfiguration serviceProviderConfiguration)

test/Ocelot.UnitTests/Configuration/HeaderFindAndReplaceCreatorTests.cs

@@ -5,7 +5,11 @@ using Ocelot.Configuration;
 using Ocelot.Configuration.Builder;
 using Ocelot.Configuration.Creator;
 using Ocelot.Configuration.File;
+using Ocelot.Infrastructure;
+using Ocelot.Logging;
 using Ocelot.Middleware;
+using Ocelot.Responses;
+using Ocelot.UnitTests.Responder;
 using Shouldly;
 using TestStack.BDDfy;
 using Xunit;
@@ -17,12 +21,17 @@ namespace Ocelot.UnitTests.Configuration
         private HeaderFindAndReplaceCreator _creator;
         private FileReRoute _reRoute;
         private HeaderTransformations _result;
-        private Mock<IBaseUrlFinder> _finder;
+        private Mock<IPlaceholders> _placeholders;
+        private Mock<IOcelotLoggerFactory> _factory;
+        private Mock<IOcelotLogger> _logger;
 
         public HeaderFindAndReplaceCreatorTests()
         {
-            _finder = new Mock<IBaseUrlFinder>();
-            _creator = new HeaderFindAndReplaceCreator(_finder.Object);
+            _logger = new Mock<IOcelotLogger>();
+            _factory = new Mock<IOcelotLoggerFactory>();
+            _factory.Setup(x => x.CreateLogger<HeaderFindAndReplaceCreator>()).Returns(_logger.Object);
+            _placeholders = new Mock<IPlaceholders>();
+            _creator = new HeaderFindAndReplaceCreator(_placeholders.Object, _factory.Object);
         }
 
         [Fact]
@@ -84,6 +93,40 @@ namespace Ocelot.UnitTests.Configuration
                 .BDDfy();
         }
 
+        [Fact]
+        public void should_log_errors_and_not_add_headers()
+        {
+            var reRoute = new FileReRoute
+            {
+                DownstreamHeaderTransform = new Dictionary<string, string>
+                {
+                    {"Location", "http://www.bbc.co.uk/, {BaseUrl}"},
+                },
+                UpstreamHeaderTransform = new Dictionary<string, string>
+                {
+                    {"Location", "http://www.bbc.co.uk/, {BaseUrl}"},
+                }
+            };
+
+            var expected = new List<HeaderFindAndReplace>
+            {
+            };
+
+            this.Given(x => GivenTheReRoute(reRoute))
+                .And(x => GivenTheBaseUrlErrors())
+                .When(x => WhenICreate())
+                .Then(x => ThenTheFollowingDownstreamIsReturned(expected))
+                .And(x => ThenTheFollowingUpstreamIsReturned(expected))
+                .And(x => ThenTheLoggerIsCalledCorrectly("Unable to add DownstreamHeaderTransform Location: http://www.bbc.co.uk/, {BaseUrl}"))
+                .And(x => ThenTheLoggerIsCalledCorrectly("Unable to add UpstreamHeaderTransform Location: http://www.bbc.co.uk/, {BaseUrl}"))
+                .BDDfy();
+        }
+
+        private void ThenTheLoggerIsCalledCorrectly(string message)
+        {
+            _logger.Verify(x => x.LogError(message), Times.Once);
+        }
+
         [Fact]
         public void should_use_base_url_partial_placeholder()
         {
@@ -107,9 +150,41 @@ namespace Ocelot.UnitTests.Configuration
                 .BDDfy();
         }
 
+        
+        [Fact]
+        public void should_add_trace_id_header()
+        {
+            var reRoute = new FileReRoute
+            {
+                 DownstreamHeaderTransform = new Dictionary<string, string>
+                {
+                    {"Trace-Id", "{TraceId}"},
+                }
+            };
+
+            var expected = new AddHeader("Trace-Id", "{TraceId}");
+
+            this.Given(x => GivenTheReRoute(reRoute))
+                .And(x => GivenTheBaseUrlIs("http://ocelot.com/"))
+                .When(x => WhenICreate())
+                .Then(x => ThenTheFollowingAddHeaderIsReturned(expected))
+                .BDDfy();
+        }
+
         private void GivenTheBaseUrlIs(string baseUrl)
         {
-            _finder.Setup(x => x.Find()).Returns(baseUrl);
+            _placeholders.Setup(x => x.Get(It.IsAny<string>())).Returns(new OkResponse<string>(baseUrl));
+        }
+
+        private void GivenTheBaseUrlErrors()
+        {
+            _placeholders.Setup(x => x.Get(It.IsAny<string>())).Returns(new ErrorResponse<string>(new AnyError()));
+        }
+
+        private void ThenTheFollowingAddHeaderIsReturned(AddHeader addHeader)
+        {
+            _result.AddHeadersToDownstream[0].Key.ShouldBe(addHeader.Key);
+            _result.AddHeadersToDownstream[0].Value.ShouldBe(addHeader.Value);
         }
 
         private void ThenTheFollowingDownstreamIsReturned(List<HeaderFindAndReplace> downstream)

test/Ocelot.UnitTests/Headers/AddHeadersToResponseTests.cs

@@ -0,0 +1,148 @@
+using Xunit;
+using Shouldly;
+using TestStack.BDDfy;
+using Ocelot.Headers;
+using System.Net.Http;
+using System.Collections.Generic;
+using Ocelot.Configuration.Creator;
+using System.Linq;
+using Moq;
+using Ocelot.Infrastructure.RequestData;
+using Ocelot.Responses;
+using Ocelot.Infrastructure;
+using Ocelot.UnitTests.Responder;
+using System;
+using Ocelot.Logging;
+
+namespace Ocelot.UnitTests.Headers
+{
+    public class AddHeadersToResponseTests
+    {
+        private IAddHeadersToResponse _adder;
+        private Mock<IPlaceholders> _placeholders;
+        private HttpResponseMessage _response;
+        private List<AddHeader> _addHeaders;
+        private Mock<IOcelotLoggerFactory> _factory;
+        private Mock<IOcelotLogger> _logger;
+
+        public AddHeadersToResponseTests()
+        {
+            _factory = new Mock<IOcelotLoggerFactory>();
+            _logger = new Mock<IOcelotLogger>();
+            _factory.Setup(x => x.CreateLogger<AddHeadersToResponse>()).Returns(_logger.Object);
+            _placeholders = new Mock<IPlaceholders>();
+            _adder = new AddHeadersToResponse(_placeholders.Object, _factory.Object);
+        }
+
+        [Fact]
+        public void should_add_header()
+        {
+            var addHeaders = new List<AddHeader>
+            {
+                new AddHeader("Laura", "Tom")
+            };
+
+            this.Given(_ => GivenAResponseMessage())
+                .And(_ => GivenTheAddHeaders(addHeaders))
+                .When(_ => WhenIAdd())
+                .And(_ => ThenTheHeaderIsReturned("Laura", "Tom"))
+                .BDDfy();
+        }
+
+        [Fact]
+        public void should_add_trace_id_placeholder()
+        {
+            var addHeaders = new List<AddHeader>
+            {
+                new AddHeader("Trace-Id", "{TraceId}")
+            };
+             
+             var traceId = "123";
+            
+            this.Given(_ => GivenAResponseMessage())
+                .And(_ => GivenTheTraceIdIs(traceId))
+                .And(_ => GivenTheAddHeaders(addHeaders))
+                .When(_ => WhenIAdd())
+                .Then(_ => ThenTheHeaderIsReturned("Trace-Id", traceId))
+                .BDDfy();
+        }
+
+        [Fact]
+        public void should_add_trace_id_placeholder_and_normal()
+        {
+            var addHeaders = new List<AddHeader>
+            {
+                new AddHeader("Trace-Id", "{TraceId}"),
+                new AddHeader("Tom", "Laura")
+            };
+
+            var traceId = "123";
+
+            this.Given(_ => GivenAResponseMessage())
+                .And(_ => GivenTheTraceIdIs(traceId))
+                .And(_ => GivenTheAddHeaders(addHeaders))
+                .When(_ => WhenIAdd())
+                .Then(_ => ThenTheHeaderIsReturned("Trace-Id", traceId))
+                .Then(_ => ThenTheHeaderIsReturned("Tom", "Laura"))
+                .BDDfy();
+        }
+
+        [Fact]
+        public void should_do_nothing_and_log_error()
+        {
+            var addHeaders = new List<AddHeader>
+            {
+                new AddHeader("Trace-Id", "{TraceId}")
+            };
+             
+            this.Given(_ => GivenAResponseMessage())
+                .And(_ => GivenTheTraceIdErrors())
+                .And(_ => GivenTheAddHeaders(addHeaders))
+                .When(_ => WhenIAdd())
+                .Then(_ => ThenTheHeaderIsNotAdded("Trace-Id"))
+                .And(_ => ThenTheErrorIsLogged())
+                .BDDfy();
+        }
+
+        private void ThenTheErrorIsLogged()
+        {
+            _logger.Verify(x => x.LogError("Unable to add header to response Trace-Id: {TraceId}"), Times.Once);
+        }
+
+        private void ThenTheHeaderIsNotAdded(string key)
+        {
+            _response.Headers.TryGetValues(key, out var values).ShouldBeFalse();
+        }
+
+        private void GivenTheTraceIdIs(string traceId)
+        {
+            _placeholders.Setup(x => x.Get("{TraceId}")).Returns(new OkResponse<string>(traceId));
+        }
+
+        private void GivenTheTraceIdErrors()
+        {
+            _placeholders.Setup(x => x.Get("{TraceId}")).Returns(new ErrorResponse<string>(new AnyError()));
+        }
+
+        private void ThenTheHeaderIsReturned(string key, string value)
+        {
+            var values = _response.Headers.GetValues(key);
+            values.First().ShouldBe(value);
+        }
+
+        private void WhenIAdd()
+        {
+            _adder.Add(_addHeaders, _response);
+        }
+
+        private void GivenAResponseMessage()
+        {
+            _response = new HttpResponseMessage();
+        }
+
+        private void GivenTheAddHeaders(List<AddHeader> addHeaders)
+        {
+            _addHeaders = addHeaders;
+        }
+    }
+}

test/Ocelot.UnitTests/Headers/HttpHeadersTransformationMiddlewareTests.cs

@@ -26,6 +26,7 @@ namespace Ocelot.UnitTests.Headers
         private HttpHeadersTransformationMiddleware _middleware;
         private DownstreamContext _downstreamContext;
         private OcelotRequestDelegate _next;
+        private Mock<IAddHeadersToResponse> _addHeaders;
 
         public HttpHeadersTransformationMiddlewareTests()
         {
@@ -36,7 +37,8 @@ namespace Ocelot.UnitTests.Headers
             _logger = new Mock<IOcelotLogger>();
             _loggerFactory.Setup(x => x.CreateLogger<AuthorisationMiddleware>()).Returns(_logger.Object);
             _next = context => Task.CompletedTask;
-            _middleware = new HttpHeadersTransformationMiddleware(_next, _loggerFactory.Object, _preReplacer.Object, _postReplacer.Object);
+            _addHeaders = new Mock<IAddHeadersToResponse>();
+            _middleware = new HttpHeadersTransformationMiddleware(_next, _loggerFactory.Object, _preReplacer.Object, _postReplacer.Object, _addHeaders.Object);
         }
 
         [Fact]
@@ -49,9 +51,16 @@ namespace Ocelot.UnitTests.Headers
                 .When(x => WhenICallTheMiddleware())
                 .Then(x => ThenTheIHttpContextRequestHeaderReplacerIsCalledCorrectly())
                 .And(x => ThenTheIHttpResponseHeaderReplacerIsCalledCorrectly())
+                .And(x => ThenAddHeadersIsCalledCorrectly())
                 .BDDfy();
         }
 
+        private void ThenAddHeadersIsCalledCorrectly()
+        {
+            _addHeaders
+                .Verify(x => x.Add(_downstreamContext.DownstreamReRoute.AddHeadersToDownstream, _downstreamContext.DownstreamResponse), Times.Once);
+        }
+
         private void WhenICallTheMiddleware()
         {
             _middleware.Invoke(_downstreamContext).GetAwaiter().GetResult();

test/Ocelot.UnitTests/Headers/HttpResponseHeaderReplacerTests.cs

@@ -7,20 +7,30 @@ using Ocelot.Configuration;
 using System.Collections.Generic;
 using Ocelot.Responses;
 using System.Linq;
+using Moq;
+using Ocelot.Infrastructure;
+using Ocelot.Middleware;
+using Ocelot.Infrastructure.RequestData;
 
 namespace Ocelot.UnitTests.Headers
 {
     public class HttpResponseHeaderReplacerTests
     {
         private HttpResponseMessage _response;
+        private Placeholders _placeholders;
         private HttpResponseHeaderReplacer _replacer;
         private List<HeaderFindAndReplace> _headerFindAndReplaces;
         private Response _result;
         private HttpRequestMessage _request;
+        private Mock<IBaseUrlFinder> _finder;
+        private Mock<IRequestScopedDataRepository> _repo;
 
         public HttpResponseHeaderReplacerTests()
         {
-            _replacer = new HttpResponseHeaderReplacer();
+            _repo = new Mock<IRequestScopedDataRepository>();
+            _finder = new Mock<IBaseUrlFinder>();
+            _placeholders = new Placeholders(_finder.Object, _repo.Object);
+            _replacer = new HttpResponseHeaderReplacer(_placeholders);
         }
 
         [Fact]

test/Ocelot.UnitTests/Infrastructure/PlaceholdersTests.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Net.Http;
+using Moq;
+using Ocelot.Infrastructure;
+using Ocelot.Infrastructure.RequestData;
+using Ocelot.Middleware;
+using Ocelot.Responses;
+using Shouldly;
+using Xunit;
+
+namespace Ocelot.UnitTests.Infrastructure
+{
+    public class PlaceholdersTests
+    {
+        private IPlaceholders _placeholders;
+        private Mock<IBaseUrlFinder> _finder;
+        private Mock<IRequestScopedDataRepository> _repo;
+        
+        public PlaceholdersTests()
+        {
+            _repo = new Mock<IRequestScopedDataRepository>();
+            _finder = new Mock<IBaseUrlFinder>();
+            _placeholders = new Placeholders(_finder.Object, _repo.Object);
+        }
+
+        [Fact]
+        public void should_return_base_url()
+        {
+            var baseUrl = "http://www.bbc.co.uk";
+            _finder.Setup(x => x.Find()).Returns(baseUrl);
+            var result = _placeholders.Get("{BaseUrl}");
+            result.Data.ShouldBe(baseUrl);
+        }
+
+        [Fact]
+        public void should_return_key_does_not_exist()
+        {
+            var result = _placeholders.Get("{Test}");
+            result.IsError.ShouldBeTrue();
+            result.Errors[0].Message.ShouldBe("Unable to find placeholder called {Test}");
+        }
+
+        [Fact]
+        public void should_return_downstream_base_url_when_port_is_not_80_or_443()
+        {
+            var request = new HttpRequestMessage();
+            request.RequestUri = new Uri("http://www.bbc.co.uk");
+            var result = _placeholders.Get("{DownstreamBaseUrl}", request);
+            result.Data.ShouldBe("http://www.bbc.co.uk/");
+        }
+
+
+        [Fact]
+        public void should_return_downstream_base_url_when_port_is_80_or_443()
+        {
+              var request = new HttpRequestMessage();
+            request.RequestUri = new Uri("http://www.bbc.co.uk:123");
+            var result = _placeholders.Get("{DownstreamBaseUrl}", request);
+            result.Data.ShouldBe("http://www.bbc.co.uk:123/");
+        }
+
+        [Fact]
+        public void should_return_key_does_not_exist_for_http_request_message()
+        {
+            var result = _placeholders.Get("{Test}", new System.Net.Http.HttpRequestMessage());
+            result.IsError.ShouldBeTrue();
+            result.Errors[0].Message.ShouldBe("Unable to find placeholder called {Test}");
+        }
+
+        [Fact]
+        public void should_return_trace_id()
+        {
+            var traceId = "123";
+            _repo.Setup(x => x.Get<string>("TraceId")).Returns(new OkResponse<string>(traceId));
+            var result = _placeholders.Get("{TraceId}");
+            result.Data.ShouldBe(traceId);
+        }
+    }
+}

test/Ocelot.UnitTests/Requester/TracingHandlerFactoryTests.cs

@@ -1,5 +1,6 @@
 using Butterfly.Client.Tracing;
 using Moq;
+using Ocelot.Infrastructure.RequestData;
 using Ocelot.Requester;
 using Shouldly;
 using Xunit;
@@ -10,11 +11,13 @@ namespace Ocelot.UnitTests.Requester
     {
         private TracingHandlerFactory _factory;
         private Mock<IServiceTracer> _tracer;
+        private Mock<IRequestScopedDataRepository> _repo;
 
         public TracingHandlerFactoryTests()
         {
             _tracer = new Mock<IServiceTracer>();
-            _factory = new TracingHandlerFactory(_tracer.Object);
+            _repo = new Mock<IRequestScopedDataRepository>();
+            _factory = new TracingHandlerFactory(_tracer.Object, _repo.Object);
         }
 
         [Fact]

test/Ocelot.UnitTests/Responder/ErrorsToHttpStatusCodeMapperTests.cs

@@ -120,7 +120,7 @@ namespace Ocelot.UnitTests.Responder
             // If this test fails then it's because the number of error codes has changed.
             // You should make the appropriate changes to the test cases here to ensure
             // they cover all the error codes, and then modify this assertion.
-            Enum.GetNames(typeof(OcelotErrorCode)).Length.ShouldBe(33, "Looks like the number of error codes has changed. Do you need to modify ErrorsToHttpStatusCodeMapper?");
+            Enum.GetNames(typeof(OcelotErrorCode)).Length.ShouldBe(34, "Looks like the number of error codes has changed. Do you need to modify ErrorsToHttpStatusCodeMapper?");
         }
 
         private void ShouldMapErrorToStatusCode(OcelotErrorCode errorCode, HttpStatusCode expectedHttpStatusCode)