Implement Random Delay (#633)

* implement random delays

* fixing CodeFactor issue

* fix code comments

* ...

* UT

Co-authored-by: Michael Yarichuk <michael.yarichuk@gmail.com>

src/WireMock.Net.Abstractions/Admin/Mappings/ResponseModel.cs

@@ -83,6 +83,16 @@ namespace WireMock.Admin.Mappings
         /// </summary>
         public int? Delay { get; set; }
 
+        /// <summary>
+        /// Gets or sets the minimum random delay in milliseconds.
+        /// </summary>
+        public int? MinimumRandomDelay { get; set; }
+
+        /// <summary>
+        /// Gets or sets the maximum random delay in milliseconds.
+        /// </summary>
+        public int? MaximumRandomDelay { get; set; }
+
         /// <summary>
         /// Gets or sets the Proxy URL.
         /// </summary>

src/WireMock.Net/ResponseBuilders/IDelayResponseBuilder.cs

@@ -20,5 +20,13 @@ namespace WireMock.ResponseBuilders
         /// <param name="milliseconds">The milliseconds to delay.</param>
         /// <returns>The <see cref="IResponseBuilder"/>.</returns>
         IResponseBuilder WithDelay(int milliseconds);
+
+        /// <summary>
+        /// Introduce random delay
+        /// </summary>
+        /// <param name="minimumMilliseconds">Minimum milliseconds to delay</param>
+        /// <param name="maximumMilliseconds">Maximum milliseconds to delay</param>
+        /// <returns>The <see cref="IResponseBuilder"/>.</returns>
+        IResponseBuilder WithRandomDelay(int minimumMilliseconds = 0, int maximumMilliseconds = 60_000);
     }
 }

src/WireMock.Net/ResponseBuilders/Response.cs

@@ -5,6 +5,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Net;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using JetBrains.Annotations;
 using WireMock.Proxy;
@@ -24,10 +25,40 @@ namespace WireMock.ResponseBuilders
     /// </summary>
     public partial class Response : IResponseBuilder
     {
+        private static readonly ThreadLocal<Random> Random = new ThreadLocal<Random>(() => new Random(DateTime.UtcNow.Millisecond));
+
+        private TimeSpan? _delay;
+
+        /// <summary>
+        /// The minimum random delay in milliseconds.
+        /// </summary>
+        public int? MinimumDelayMilliseconds { get; private set; }
+
+        /// <summary>
+        /// The maximum random delay in milliseconds.
+        /// </summary>
+        public int? MaximumDelayMilliseconds { get; private set; }
+
         /// <summary>
         /// The delay
         /// </summary>
-        public TimeSpan? Delay { get; private set; }
+        public TimeSpan? Delay
+        {
+            get
+            {
+                if (MinimumDelayMilliseconds != null && MaximumDelayMilliseconds != null)
+                {
+                    return TimeSpan.FromMilliseconds(Random.Value.Next(MinimumDelayMilliseconds.Value, MaximumDelayMilliseconds.Value));
+                }
+
+                return _delay;
+            }
+
+            private set
+            {
+                _delay = value;
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether [use transformer].
@@ -334,6 +365,18 @@ namespace WireMock.ResponseBuilders
             return WithDelay(TimeSpan.FromMilliseconds(milliseconds));
         }
 
+        /// <inheritdoc cref="IDelayResponseBuilder.WithRandomDelay(int, int)"/>
+        public IResponseBuilder WithRandomDelay(int minimumMilliseconds = 0, int maximumMilliseconds = 60_000)
+        {
+            Check.Condition(minimumMilliseconds, min => min >= 0, nameof(minimumMilliseconds));
+            Check.Condition(maximumMilliseconds, max => max > minimumMilliseconds, nameof(maximumMilliseconds));
+
+            MinimumDelayMilliseconds = minimumMilliseconds;
+            MaximumDelayMilliseconds = maximumMilliseconds;
+
+            return this;
+        }
+
         /// <inheritdoc cref="IResponseProvider.ProvideResponseAsync(RequestMessage, IWireMockServerSettings)"/>
         public async Task<(ResponseMessage Message, IMapping Mapping)> ProvideResponseAsync(RequestMessage requestMessage, IWireMockServerSettings settings)
         {

src/WireMock.Net/Serialization/MappingConverter.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using WireMock.Admin.Mappings;
 using WireMock.Matchers.Request;
@@ -6,7 +7,6 @@ using WireMock.RequestBuilders;
 using WireMock.ResponseBuilders;
 using WireMock.Settings;
 using WireMock.Types;
-using WireMock.Validation;
 
 namespace WireMock.Serialization
 {
@@ -16,9 +16,7 @@ namespace WireMock.Serialization
 
         public MappingConverter(MatcherMapper mapper)
         {
-            Check.NotNull(mapper, nameof(mapper));
+            _mapper = mapper ?? throw new ArgumentNullException(nameof(mapper));
-
-            _mapper = mapper;
         }
 
         public MappingModel ToMappingModel(IMapping mapping)
@@ -81,12 +79,19 @@ namespace WireMock.Serialization
                         Matchers = _mapper.Map(pm.Matchers)
                     }).ToList() : null
                 },
-                Response = new ResponseModel
+                Response = new ResponseModel()
-                {
-                    Delay = (int?)response.Delay?.TotalMilliseconds
-                }
             };
 
+            if (response.MinimumDelayMilliseconds >= 0 || response.MaximumDelayMilliseconds > 0)
+            {
+                mappingModel.Response.MinimumRandomDelay = response.MinimumDelayMilliseconds;
+                mappingModel.Response.MaximumRandomDelay = response.MaximumDelayMilliseconds;
+            }
+            else
+            {
+                mappingModel.Response.Delay = (int?)response.Delay?.TotalMilliseconds;
+            }
+
             if (mapping.Webhooks?.Length == 1)
             {
                 mappingModel.Webhook = WebhookMapper.Map(mapping.Webhooks[0]);

src/WireMock.Net/Server/WireMockServer.Admin.cs

@@ -782,6 +782,10 @@ namespace WireMock.Server
             {
                 responseBuilder = responseBuilder.WithDelay(responseModel.Delay.Value);
             }
+            else if (responseModel.MinimumRandomDelay >= 0 || responseModel.MaximumRandomDelay > 0)
+            {
+                responseBuilder = responseBuilder.WithRandomDelay(responseModel.MinimumRandomDelay ?? 0, responseModel.MaximumRandomDelay ?? 60_000);
+            }
 
             if (responseModel.UseTransformer == true)
             {

test/WireMock.Net.Tests/Serialization/MappingConverterTests.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using FluentAssertions;
 using WireMock.Models;
@@ -163,5 +163,61 @@ namespace WireMock.Net.Tests.Serialization
             model.Priority.Should().Be(42);
             model.Response.UseTransformer.Should().BeTrue();
         }
+
+        [Fact]
+        public void ToMappingModel_WithDelay_ReturnsCorrectModel()
+        {
+            // Assign
+            int delay = 1000;
+            var request = Request.Create();
+            var response = Response.Create().WithDelay(delay);
+            var mapping = new Mapping(Guid.NewGuid(), "", null, _settings, request, response, 42, null, null, null, null, null);
+
+            // Act
+            var model = _sut.ToMappingModel(mapping);
+
+            // Assert
+            model.Should().NotBeNull();
+            model.Response.Delay.Should().Be(delay);
+        }
+
+        [Fact]
+        public void ToMappingModel_WithRandomMininumDelay_ReturnsCorrectModel()
+        {
+            // Assign
+            int minimumDelay = 1000;
+            var request = Request.Create();
+            var response = Response.Create().WithRandomDelay(minimumDelay);
+            var mapping = new Mapping(Guid.NewGuid(), "", null, _settings, request, response, 42, null, null, null, null, null);
+
+            // Act
+            var model = _sut.ToMappingModel(mapping);
+
+            // Assert
+            model.Should().NotBeNull();
+            model.Response.Delay.Should().BeNull();
+            model.Response.MinimumRandomDelay.Should().Be(minimumDelay);
+            model.Response.MaximumRandomDelay.Should().Be(60_000);
+        }
+
+        [Fact]
+        public void ToMappingModel_WithRandomDelay_ReturnsCorrectModel()
+        {
+            // Assign
+            int minimumDelay = 1000;
+            int maximumDelay = 2000;
+            var request = Request.Create();
+            var response = Response.Create().WithRandomDelay(minimumDelay, maximumDelay);
+            var mapping = new Mapping(Guid.NewGuid(), "", null, _settings, request, response, 42, null, null, null, null, null);
+
+            // Act
+            var model = _sut.ToMappingModel(mapping);
+
+            // Assert
+            model.Should().NotBeNull();
+            model.Response.Delay.Should().BeNull();
+            model.Response.MinimumRandomDelay.Should().Be(minimumDelay);
+            model.Response.MaximumRandomDelay.Should().Be(maximumDelay);
+        }
     }
 }

test/WireMock.Net.Tests/WireMockServerTests.cs

@@ -115,6 +115,38 @@ namespace WireMock.Net.Tests
             server.Stop();
         }
 
+        [Fact]
+        public async Task WireMockServer_Should_randomly_delay_responses_for_a_given_route()
+        {
+            // Arrange
+            var server = WireMockServer.Start();
+
+            server
+                .Given(Request.Create()
+                    .WithPath("/*"))
+                .RespondWith(Response.Create()
+                    .WithBody(@"{ msg: ""Hello world!""}")
+                    .WithRandomDelay(10, 1000));
+
+            var watch = new Stopwatch();
+            watch.Start();
+
+            var httClient = new HttpClient();
+            async Task<long> ExecuteTimedRequestAsync()
+            {
+                watch.Reset();
+                await httClient.GetStringAsync("http://localhost:" + server.Ports[0] + "/foo");
+                return watch.ElapsedMilliseconds;
+            }
+
+            // Act
+            await ExecuteTimedRequestAsync();
+            await ExecuteTimedRequestAsync();
+            await ExecuteTimedRequestAsync();
+
+            server.Stop();
+        }
+
         [Fact]
         public async Task WireMockServer_Should_delay_responses()
         {