feat: add WithBody(req => dostuff) style callback (#102)

src/WireMock.Net/ResponseBuilders/IBodyResponseBuilder.cs

@@ -18,6 +18,17 @@ namespace WireMock.ResponseBuilders
         /// <returns>A <see cref="IResponseBuilder"/>.</returns>
         IResponseBuilder WithBody([NotNull] string body, [CanBeNull] string destination = BodyDestinationFormat.SameAsSource, [CanBeNull] Encoding encoding = null);
 
+
+        /// <summary>
+        /// WithBody : Create a ... response based on a callback function.
+        /// </summary>
+        /// <param name="bodyFactory">The delegate to build the body.</param>
+        /// <param name="destination">The Body Destination format (SameAsSource, String or Bytes).</param>
+        /// <param name="encoding">The body encoding.</param>
+        /// <returns>A <see cref="IResponseBuilder"/>.</returns>
+        IResponseBuilder WithBody([NotNull] Func<RequestMessage,string> bodyFactory, [CanBeNull] string destination = BodyDestinationFormat.SameAsSource, [CanBeNull] Encoding encoding = null);
+
+
         /// <summary>
         /// WithBody : Create a ... response based on a bytearray.
         /// </summary>

src/WireMock.Net/ResponseBuilders/Response.cs

@@ -167,6 +167,13 @@ namespace WireMock.ResponseBuilders
             return this;
         }
 
+        /// <inheritdoc cref="IBodyResponseBuilder.WithBody(Func{RequestMessage, string}, string, Encoding)"/>
+        public IResponseBuilder WithBody(Func<RequestMessage, string> bodyFactory, string destination = BodyDestinationFormat.SameAsSource,
+            Encoding encoding = null)
+        {
+            return WithCallback(req => new ResponseMessage {Body = bodyFactory(req)});
+        }
+
         /// <inheritdoc cref="IBodyResponseBuilder.WithBody(byte[], string, Encoding)"/>
         public IResponseBuilder WithBody(byte[] body, string destination, Encoding encoding = null)
         {

test/WireMock.Net.Tests/FluentMockServerTests.cs

@@ -232,6 +232,27 @@ namespace WireMock.Net.Tests
             Check.That(response).IsEqualTo("Hello world!");
         }
 
+        [Fact]
+        public async Task FluentMockServer_Should_respond_to_request_bodyAsCallback()
+        {
+            // given
+            _server = FluentMockServer.Start();
+
+            _server
+                .Given(Request.Create()
+                    .WithPath("/foo")
+                    .UsingGet())
+                .RespondWith(Response.Create()
+                    .WithStatusCode(200)
+                    .WithBody(req => $"{{ path: '{req.Path}' }}"));
+
+            // when
+            var response = await new HttpClient().GetStringAsync("http://localhost:" + _server.Ports[0] + "/foo");
+
+            // then
+            Check.That(response).IsEqualTo("{ path: '/foo' }");
+        }
+
         [Fact]
         public async Task FluentMockServer_Should_respond_to_request_bodyAsBase64()
         {