Feature/xpath transformer (#398)

* XPath transformer, added handlerbars helper to select nodes using xpath and setting the outerxml value in response

* Added test to select attribute value and node text

* Removed extra empty lines

src/WireMock.Net/Transformers/HandleBarsHelpers.cs

@@ -17,6 +17,8 @@ namespace WireMock.Transformers
 
             HandleBarsXeger.Register(handlebarsContext);
 
+            HandleBarsXPath.Register(handlebarsContext);
+
             HandleBarsFile.Register(handlebarsContext, fileSystemHandler);
         }
     }

src/WireMock.Net/Transformers/HandleBarsXPath.cs

@@ -0,0 +1,102 @@
+using HandlebarsDotNet;
+using System;
+using System.Text;
+using System.Xml;
+using System.Xml.XPath;
+using WireMock.Validation;
+#if !NETSTANDARD1_3
+using Wmhelp.XPath2;
+#endif
+
+namespace WireMock.Transformers
+{
+    internal static class HandleBarsXPath
+    {
+        public static void Register(IHandlebars handlebarsContext)
+        {
+            handlebarsContext.RegisterHelper("XPath.SelectSingleNode", (writer, context, arguments) =>
+            {
+                (XPathNavigator nav, string xpath) = ParseArguments(arguments);
+
+                try
+                {
+#if NETSTANDARD1_3
+                    var result = nav.SelectSingleNode(xpath);
+#else
+                    var result = nav.XPath2SelectSingleNode(xpath);
+#endif
+                    writer.WriteSafeString(result.OuterXml);
+                }
+                catch (Exception)
+                {
+                    // Ignore Exception
+                }
+            });
+
+            handlebarsContext.RegisterHelper("XPath.SelectNodes", (writer, context, arguments) =>
+            {
+                (XPathNavigator nav, string xpath) = ParseArguments(arguments);
+
+                try
+                {
+#if NETSTANDARD1_3
+                    var result = nav.Select(xpath);
+#else
+                    var result = nav.XPath2SelectNodes(xpath);
+#endif
+                    var resultXml = new StringBuilder();
+                    foreach (XPathNavigator node in result)
+                    {
+                        resultXml.Append(node.OuterXml);
+                    }
+
+                    writer.WriteSafeString(resultXml);
+                }
+                catch (Exception)
+                {
+                    // Ignore Exception
+                }
+            });
+
+            handlebarsContext.RegisterHelper("XPath.Evaluate", (writer, context, arguments) =>
+            {
+                (XPathNavigator nav, string xpath) = ParseArguments(arguments);
+
+                try
+                {
+#if NETSTANDARD1_3
+                    var result = nav.Evaluate(xpath);
+#else
+                    var result = nav.XPath2Evaluate(xpath);
+#endif
+                    writer.WriteSafeString(result);
+                }
+                catch (Exception)
+                {
+                    // Ignore Exception
+                }
+            });
+        }
+
+        private static (XPathNavigator nav, string xpath) ParseArguments(object[] arguments)
+        {
+            Check.Condition(arguments, args => args.Length == 2, nameof(arguments));
+            Check.NotNull(arguments[0], "arguments[0]");
+            Check.NotNullOrEmpty(arguments[1] as string, "arguments[1]");
+
+            XPathNavigator nav;
+
+            switch (arguments[0])
+            {
+                case string stringValue:
+                    nav = new XmlDocument { InnerXml = stringValue }.CreateNavigator();
+                    break;
+
+                default:
+                    throw new NotSupportedException($"The value '{arguments[0]}' with type '{arguments[0]?.GetType()}' cannot be used in Handlebars XPath.");
+            }
+
+            return (nav, (string)arguments[1]);
+        }
+    }
+}

test/WireMock.Net.Tests/ResponseBuilders/ResponseWithHandlebarsXPathTests.cs

@@ -0,0 +1,166 @@
+using System.Threading.Tasks;
+using System.Xml;
+using NFluent;
+using WireMock.Models;
+using WireMock.ResponseBuilders;
+using WireMock.Settings;
+using WireMock.Types;
+using WireMock.Util;
+using Xunit;
+#if !NETSTANDARD1_3
+using Wmhelp.XPath2;
+#endif
+
+namespace WireMock.Net.Tests.ResponseBuilders
+{
+    public class ResponseWithHandlebarsXPathTests
+    {
+        private readonly WireMockServerSettings _settings = new WireMockServerSettings();
+        private const string ClientIp = "::1";
+
+        [Fact]
+        public async Task Response_ProvideResponse_Handlebars_XPath_SelectSingleNode_Request_BodyAsString()
+        {
+            // Assign
+            var body = new BodyData
+            {
+                BodyAsString = @"<todo-list>
+                                   <todo-item id='a1'>abc</todo-item>
+                                   <todo-item id='a2'>def</todo-item>
+                                   <todo-item id='a3'>xyz</todo-item>
+                                 </todo-list>",
+                DetectedBodyType = BodyType.String
+            };
+
+            var request = new RequestMessage(new UrlDetails("http://localhost:1234"), "POST", ClientIp, body);
+
+            var response = Response.Create()
+                .WithHeader("Content-Type", "application/xml")
+                .WithBody("<response>{{XPath.SelectSingleNode request.body \"/todo-list/todo-item[1]\"}}</response>")
+                .WithTransformer();
+
+            // Act
+            var responseMessage = await response.ProvideResponseAsync(request, _settings);
+
+            // Assert
+            var nav = new XmlDocument { InnerXml = responseMessage.BodyData.BodyAsString }.CreateNavigator();
+            var node = nav.XPath2SelectSingleNode("/response/todo-item");
+            Check.That(node.Value).Equals("abc");
+            Check.That(node.GetAttribute("id", "")).Equals("a1");
+        }
+
+        [Fact]
+        public async Task Response_ProvideResponse_Handlebars_XPath_SelectSingleNode_Text_Request_BodyAsString()
+        {
+            // Assign
+            var body = new BodyData
+            {
+                BodyAsString = @"<todo-list>
+                                   <todo-item id='a1'>abc</todo-item>
+                                   <todo-item id='a2'>def</todo-item>
+                                   <todo-item id='a3'>xyz</todo-item>
+                                 </todo-list>",
+                DetectedBodyType = BodyType.String
+            };
+
+            var request = new RequestMessage(new UrlDetails("http://localhost:1234"), "POST", ClientIp, body);
+
+            var response = Response.Create()
+                .WithHeader("Content-Type", "application/xml")
+                .WithBody("{{XPath.SelectSingleNode request.body \"/todo-list/todo-item[1]/text()\"}}")
+                .WithTransformer();
+
+            // Act
+            var responseMessage = await response.ProvideResponseAsync(request, _settings);
+
+            // Assert
+            Check.That(responseMessage.BodyData.BodyAsString).IsEqualTo("abc");
+        }
+
+        [Fact]
+        public async Task Response_ProvideResponse_Handlebars_XPath_SelectNodes_Request_BodyAsString()
+        {
+            // Assign
+            var body = new BodyData
+            {
+                BodyAsString = @"<todo-list>
+                                   <todo-item id='a1'>abc</todo-item>
+                                   <todo-item id='a2'>def</todo-item>
+                                   <todo-item id='a3'>xyz</todo-item>
+                                 </todo-list>",
+                DetectedBodyType = BodyType.String
+            };
+
+            var request = new RequestMessage(new UrlDetails("http://localhost:1234"), "POST", ClientIp, body);
+
+            var response = Response.Create()
+                .WithHeader("Content-Type", "application/xml")
+                .WithBody("<response>{{XPath.SelectNodes request.body \"/todo-list/todo-item\"}}</response>")
+                .WithTransformer();
+
+            // Act
+            var responseMessage = await response.ProvideResponseAsync(request, _settings);
+
+            // Assert
+            var nav = new XmlDocument { InnerXml = responseMessage.BodyData.BodyAsString }.CreateNavigator();
+            var nodes = nav.XPath2SelectNodes("/response/todo-item");
+            Check.That(nodes.Count + 1).IsEqualTo(3);
+        }
+
+        [Fact]
+        public async Task Response_ProvideResponse_Handlebars_XPath_Evaluate_Request_BodyAsString()
+        {
+            // Assign
+            var body = new BodyData
+            {
+                BodyAsString = @"<todo-list>
+                                   <todo-item id='a1'>abc</todo-item>
+                                   <todo-item id='a2'>def</todo-item>
+                                   <todo-item id='a3'>xyz</todo-item>
+                                 </todo-list>",
+                DetectedBodyType = BodyType.String
+            };
+
+            var request = new RequestMessage(new UrlDetails("http://localhost:1234"), "POST", ClientIp, body);
+
+            var response = Response.Create()
+                .WithHeader("Content-Type", "application/xml")
+                .WithBody("{{XPath.Evaluate request.body \"boolean(/todo-list[count(todo-item) = 3])\"}}")
+                .WithTransformer();
+
+            // Act
+            var responseMessage = await response.ProvideResponseAsync(request, _settings);
+
+            // Assert
+            Check.That(responseMessage.BodyData.BodyAsString).IsEqualIgnoringCase("True");
+        }
+
+        [Fact]
+        public async Task Response_ProvideResponse_Handlebars_XPath_Evaluate_Attribute_Request_BodyAsString()
+        {
+            // Assign
+            var body = new BodyData
+            {
+                BodyAsString = @"<todo-list>
+                                   <todo-item id='a1'>abc</todo-item>
+                                   <todo-item id='a2'>def</todo-item>
+                                   <todo-item id='a3'>xyz</todo-item>
+                                 </todo-list>",
+                DetectedBodyType = BodyType.String
+            };
+
+            var request = new RequestMessage(new UrlDetails("http://localhost:1234"), "POST", ClientIp, body);
+
+            var response = Response.Create()
+                .WithHeader("Content-Type", "application/xml")
+                .WithBody("{{XPath.Evaluate request.body \"string(/todo-list/todo-item[1]/@id)\"}}")
+                .WithTransformer();
+
+            // Act
+            var responseMessage = await response.ProvideResponseAsync(request, _settings);
+
+            // Assert
+            Check.That(responseMessage.BodyData.BodyAsString).IsEqualTo("a1");
+        }
+    }
+}