Add per-mock rate to MockResponsePlugin

DevProxy.Abstractions/DevProxy.Abstractions.csproj

@@ -5,7 +5,7 @@
     <RootNamespace>DevProxy.Abstractions</RootNamespace>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-    <Version>4.0.0</Version>
+    <Version>4.1.0</Version>
     <IncludeSourceRevisionInInformationalVersion>false</IncludeSourceRevisionInInformationalVersion>
     <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>

DevProxy.Abstractions/Models/MockResponse.cs

@@ -12,6 +12,12 @@ public class MockResponse : ICloneable
 {
     public MockResponseRequest? Request { get; set; }
     public MockResponseResponse? Response { get; set; }
+    /// <summary>
+    /// Probability (0-100) that the mock is applied when it matches a request.
+    /// When not set, the mock is always applied. When the mock isn't applied,
+    /// the request falls through to the next matching mock or the real API.
+    /// </summary>
+    public int? Rate { get; set; }
 
     public object Clone()
     {

DevProxy.Integration.Tests/ManipulationAndMockingIntegrationTests.cs

@@ -452,6 +452,171 @@ public async Task MockResponse_Nth_DistinctMatchersHaveIndependentCounts(
         Assert.Equal(HttpStatusCode.Accepted, third.StatusCode);
     }
 
+    [Theory]
+    [InlineData(null)]
+    [InlineData("100")]
+    [InlineData("-5")]
+    [InlineData("150")]
+    public async Task MockResponse_Rate_AlwaysAppliesWhenAbsentFullOrInvalid(string? rate)
+    {
+        await using var origin = await FakeOrigin.StartAsync();
+        var urls = KestrelProxyHarness.BuildUrlsToWatch(origin.Host);
+        var config = PluginConfig.FromJson($$"""
+            {
+              "mocks": [
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 201 },
+                  "rate": {{rate ?? "null"}}
+                }
+              ]
+            }
+            """);
+        using var plugin = new MockResponsePlugin(
+            SharedHttpClient, NullLogger<MockResponsePlugin>.Instance, urls, ProxyConfig, config);
+        await using var proxy = await KestrelProxyHarness.StartAsync(origin.Host, [plugin]);
+        using var client = proxy.CreateHttpClient();
+        var uri = new Uri($"http://{origin.Host}/get");
+
+        for (var i = 0; i < 10; i++)
+        {
+            using var response = await client.GetAsync(uri);
+            Assert.Equal(HttpStatusCode.Created, response.StatusCode);
+        }
+    }
+
+    [Fact]
+    public async Task MockResponse_Rate0_PassesThroughToOrigin()
+    {
+        await using var origin = await FakeOrigin.StartAsync();
+        var urls = KestrelProxyHarness.BuildUrlsToWatch(origin.Host);
+        var config = PluginConfig.FromJson($$"""
+            {
+              "mocks": [
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 503 },
+                  "rate": 0
+                }
+              ]
+            }
+            """);
+        using var plugin = new MockResponsePlugin(
+            SharedHttpClient, NullLogger<MockResponsePlugin>.Instance, urls, ProxyConfig, config);
+        await using var proxy = await KestrelProxyHarness.StartAsync(origin.Host, [plugin]);
+        using var client = proxy.CreateHttpClient();
+        var uri = new Uri($"http://{origin.Host}/get");
+
+        for (var i = 0; i < 10; i++)
+        {
+            using var response = await client.GetAsync(uri);
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+        }
+    }
+
+    [Fact]
+    public async Task MockResponse_Rate0_FallsThroughToNextMatchingMock()
+    {
+        await using var origin = await FakeOrigin.StartAsync();
+        var urls = KestrelProxyHarness.BuildUrlsToWatch(origin.Host);
+        var config = PluginConfig.FromJson($$"""
+            {
+              "mocks": [
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 503 },
+                  "rate": 0
+                },
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 202 }
+                }
+              ]
+            }
+            """);
+        using var plugin = new MockResponsePlugin(
+            SharedHttpClient, NullLogger<MockResponsePlugin>.Instance, urls, ProxyConfig, config);
+        await using var proxy = await KestrelProxyHarness.StartAsync(origin.Host, [plugin]);
+        using var client = proxy.CreateHttpClient();
+        var uri = new Uri($"http://{origin.Host}/get");
+
+        for (var i = 0; i < 10; i++)
+        {
+            using var response = await client.GetAsync(uri);
+            Assert.Equal(HttpStatusCode.Accepted, response.StatusCode);
+        }
+    }
+
+    [Fact]
+    public async Task MockResponse_Rate0_WithNth_IsNeverApplied()
+    {
+        await using var origin = await FakeOrigin.StartAsync();
+        var urls = KestrelProxyHarness.BuildUrlsToWatch(origin.Host);
+        var config = PluginConfig.FromJson($$"""
+            {
+              "mocks": [
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET", "nth": 2 },
+                  "response": { "statusCode": 201 },
+                  "rate": 0
+                },
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 202 }
+                }
+              ]
+            }
+            """);
+        using var plugin = new MockResponsePlugin(
+            SharedHttpClient, NullLogger<MockResponsePlugin>.Instance, urls, ProxyConfig, config);
+        await using var proxy = await KestrelProxyHarness.StartAsync(origin.Host, [plugin]);
+        using var client = proxy.CreateHttpClient();
+        var uri = new Uri($"http://{origin.Host}/get");
+
+        for (var i = 0; i < 3; i++)
+        {
+            using var response = await client.GetAsync(uri);
+            Assert.Equal(HttpStatusCode.Accepted, response.StatusCode);
+        }
+    }
+
+    [Fact]
+    public async Task MockResponse_PartialRate_AppliesSomeOfTheTime()
+    {
+        await using var origin = await FakeOrigin.StartAsync();
+        var urls = KestrelProxyHarness.BuildUrlsToWatch(origin.Host);
+        var config = PluginConfig.FromJson($$"""
+            {
+              "mocks": [
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 503 },
+                  "rate": 50
+                },
+                {
+                  "request": { "url": "http://{{origin.Host}}/get", "method": "GET" },
+                  "response": { "statusCode": 202 }
+                }
+              ]
+            }
+            """);
+        using var plugin = new MockResponsePlugin(
+            SharedHttpClient, NullLogger<MockResponsePlugin>.Instance, urls, ProxyConfig, config);
+        await using var proxy = await KestrelProxyHarness.StartAsync(origin.Host, [plugin]);
+        using var client = proxy.CreateHttpClient();
+        var uri = new Uri($"http://{origin.Host}/get");
+
+        var statusCodes = new HashSet<HttpStatusCode>();
+        // the chance of 100 rolls at 50% landing on the same side is ~2^-99
+        for (var i = 0; i < 100; i++)
+        {
+            using var response = await client.GetAsync(uri);
+            _ = statusCodes.Add(response.StatusCode);
+        }
+
+        Assert.Equal([HttpStatusCode.Accepted, HttpStatusCode.ServiceUnavailable], statusCodes.Order());
+    }
+
     [Theory]
     [InlineData("/Get")]
     [InlineData("/Ge*")]

DevProxy.Plugins/DevProxy.Plugins.csproj

@@ -6,7 +6,7 @@
     <Nullable>enable</Nullable>
     <EnableDynamicLoading>true</EnableDynamicLoading>
     <RunPostBuildEvent>OnOutputUpdated</RunPostBuildEvent>
-    <Version>4.0.0</Version>
+    <Version>4.1.0</Version>
     <IncludeSourceRevisionInInformationalVersion>false</IncludeSourceRevisionInInformationalVersion>
     <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>

DevProxy.Plugins/Mocking/MockResponsePlugin.cs

@@ -35,7 +35,7 @@ public sealed class MockResponseConfiguration
     [JsonIgnore]
     public bool NoMocks { get; set; }
     [JsonPropertyName("$schema")]
-    public string Schema { get; set; } = "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/mockresponseplugin.mocksfile.schema.json";
+    public string Schema { get; set; } = "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/mockresponseplugin.mocksfile.schema.json";
 }
 
 public class MockResponsePlugin(
@@ -308,8 +308,32 @@ Configuration.Mocks is null ||
         }
 
         return matchingMocks.FirstOrDefault(mockResponse =>
-            mockResponse.Request!.Nth is null ||
-            mockResponse.Request.Nth == requestCounts[GetMockKey(mockResponse)]);
+            (mockResponse.Request!.Nth is null ||
+            mockResponse.Request.Nth == requestCounts[GetMockKey(mockResponse)]) &&
+            ShouldApplyMock(mockResponse));
+    }
+
+    internal static bool IsValidRate(int rate) => rate is >= 0 and <= 100;
+
+    private bool ShouldApplyMock(MockResponse mockResponse)
+    {
+        if (mockResponse.Rate is not { } rate || !IsValidRate(rate))
+        {
+            return true;
+        }
+
+        var roll = Random.Shared.Next(1, 101);
+        if (roll <= rate)
+        {
+            return true;
+        }
+
+        Logger.LogDebug(
+            "Skipping mock for {Method} {Url} based on its rate of {Rate}%",
+            mockResponse.Request!.Method,
+            mockResponse.Request.Url,
+            rate);
+        return false;
     }
 
     private static MockRequestKey GetMockKey(MockResponse mockResponse)

DevProxy.Plugins/Mocking/MockResponsesLoader.cs

@@ -34,6 +34,15 @@ protected override void LoadData(string fileContents)
                 {
                     Logger.LogInformation("Mock responses for {ConfigResponseCount} url patterns loaded from {MockFile}", configResponses.Count(), _configuration.MocksFile);
                 }
+
+                foreach (var mock in configResponses.Where(m => m.Rate is not null && !MockResponsePlugin.IsValidRate(m.Rate.Value)))
+                {
+                    Logger.LogWarning(
+                        "Mock for {Method} {Url} has an invalid rate {Rate}. Rate must be between 0 and 100. Ignoring rate and always applying the mock",
+                        mock.Request?.Method,
+                        mock.Request?.Url,
+                        mock.Rate);
+                }
             }
         }
         catch (Exception ex)

DevProxy.Plugins/Mocking/MockStdioResponsePlugin.cs

@@ -32,7 +32,7 @@ public sealed class MockStdioResponseConfiguration
     public bool NoMocks { get; set; }
 
     [JsonPropertyName("$schema")]
-    public string Schema { get; set; } = "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/mockstdioresponseplugin.mocksfile.schema.json";
+    public string Schema { get; set; } = "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/mockstdioresponseplugin.mocksfile.schema.json";
 }
 
 public class MockStdioResponsePlugin(

DevProxy.Plugins/Mocking/WebSocketMockResponsePlugin.cs

@@ -28,7 +28,7 @@ public sealed class WebSocketMockResponseConfiguration
     public bool NoMocks { get; set; }
 
     [JsonPropertyName("$schema")]
-    public string Schema { get; set; } = "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/websocketmockresponseplugin.mocksfile.schema.json";
+    public string Schema { get; set; } = "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/websocketmockresponseplugin.mocksfile.schema.json";
 }
 
 /// <summary>

DevProxy.Proxy.Kestrel/DevProxy.Proxy.Kestrel.csproj

@@ -5,7 +5,7 @@
     <RootNamespace>DevProxy.Proxy.Kestrel</RootNamespace>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-    <Version>4.0.0</Version>
+    <Version>4.1.0</Version>
     <IncludeSourceRevisionInInformationalVersion>false</IncludeSourceRevisionInInformationalVersion>
     <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>

DevProxy/DevProxy.csproj

@@ -8,7 +8,7 @@
     <Nullable>enable</Nullable>
     <PackageLicenseFile>LICENSE</PackageLicenseFile>
     <Title>Dev Proxy</Title>
-    <Version>4.0.0</Version>
+    <Version>4.1.0</Version>
     <Company>.NET Foundation</Company>
     <Product>Dev Proxy</Product>
     <AssemblyName>devproxy</AssemblyName>

DevProxy/config-templates/devproxyrc.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/rc.schema.json",
+  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/rc.schema.json",
   "plugins": [
   ],
   "urlsToWatch": [

DevProxy/config-templates/devproxyrc.yaml

@@ -1,4 +1,4 @@
-# yaml-language-server: $schema=https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/rc.schema.json
+# yaml-language-server: $schema=https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/rc.schema.json
 plugins:
   -
 urlsToWatch:

DevProxy/config/m365-mocks.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/mockresponseplugin.mocksfile.schema.json",
+  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/mockresponseplugin.mocksfile.schema.json",
   "mocks": [
     {
       "request": {

DevProxy/config/m365.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/rc.schema.json",
+  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/rc.schema.json",
   "plugins": [
     {
       "name": "DevToolsPlugin",
@@ -173,11 +173,11 @@
     "https://*.sharepoint-df.*/*_vti_bin/*"
   ],
   "mocksPlugin": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/mockresponseplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/mockresponseplugin.schema.json",
     "mocksFile": "m365-mocks.json"
   },
   "graphRandomErrorsPlugin": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/graphrandomerrorplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/graphrandomerrorplugin.schema.json",
     "allowedErrors": [
       429,
       500,
@@ -189,28 +189,28 @@
     "rate": 50
   },
   "executionSummaryPlugin": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/executionsummaryplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/executionsummaryplugin.schema.json",
     "groupBy": "url"
   },
   "graphMinimalPermissionsPlugin": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/graphminimalpermissionsplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/graphminimalpermissionsplugin.schema.json",
     "type": "delegated"
   },
   "cachingGuidance": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/cachingguidanceplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/cachingguidanceplugin.schema.json",
     "cacheThresholdSeconds": 5
   },
   "latencyPlugin": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/latencyplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/latencyplugin.schema.json",
     "minMs": 200,
     "maxMs": 10000
   },
   "devTools": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/devtoolsplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/devtoolsplugin.schema.json",
     "preferredBrowser": "Edge"
   },
   "rateLimiting": {
-    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/ratelimitingplugin.schema.json",
+    "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/ratelimitingplugin.schema.json",
     "costPerRequest": 2,
     "rateLimit": 120,
     "resetTimeWindowSeconds": 5

DevProxy/config/microsoft-graph-rate-limiting.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.0.0/rc.schema.json",
+  "$schema": "https://raw.githubusercontent.com/dotnet/dev-proxy/main/schemas/v4.1.0/rc.schema.json",
   "plugins": [
     {
       "name": "RateLimitingPlugin",