#347 Add support for setting custom idempotency keys

src/Mollie.Api/Client/Abstract/IBaseMollieClient.cs

@@ -0,0 +1,9 @@
+using System;
+
+namespace Mollie.Api.Client.Abstract
+{
+    public interface IBaseMollieClient : IDisposable
+    {
+        IDisposable WithIdempotencyKey(string value);
+    }
+}

src/Mollie.Api/Client/Abstract/IPaymentClient.cs

@@ -1,13 +1,12 @@
-using System;
-using System.Threading.Tasks;
+using System.Threading.Tasks;
 using Mollie.Api.Models;
 using Mollie.Api.Models.List;
 using Mollie.Api.Models.Payment.Request;
 using Mollie.Api.Models.Payment.Response;
 using Mollie.Api.Models.Url;
 
 namespace Mollie.Api.Client.Abstract {
-    public interface IPaymentClient : IDisposable {
+    public interface IPaymentClient : IBaseMollieClient {
         Task<PaymentResponse> CreatePaymentAsync(PaymentRequest paymentRequest, bool includeQrCode = false);
 
         /// <summary>

src/Mollie.Api/Client/BaseMollieClient.cs

@@ -8,6 +8,7 @@
 using System.Threading.Tasks;
 using Mollie.Api.Extensions;
 using Mollie.Api.Framework;
+using Mollie.Api.Framework.Idempotency;
 using Mollie.Api.Models.Url;
 
 namespace Mollie.Api.Client {
@@ -17,6 +18,8 @@ public abstract class BaseMollieClient : IDisposable {
         private readonly string _apiKey;
         private readonly HttpClient _httpClient;
         private readonly JsonConverterService _jsonConverterService;
+
+        private readonly AsyncLocalVariable<string> _idempotencyKey = new AsyncLocalVariable<string>(null);
 
         private readonly bool _createdHttpClient = false;
 
@@ -37,6 +40,11 @@ protected BaseMollieClient(HttpClient httpClient = null, string apiEndpoint = Ap
             this._createdHttpClient = httpClient == null;
             this._httpClient = httpClient ?? new HttpClient();
         }
+
+        public IDisposable WithIdempotencyKey(string value) {
+            _idempotencyKey.Value = value;
+            return _idempotencyKey;
+        }
 
         private async Task<T> SendHttpRequest<T>(HttpMethod httpMethod, string relativeUri, object data = null) {
             HttpRequestMessage httpRequest = this.CreateHttpRequest(httpMethod, relativeUri);
@@ -127,7 +135,8 @@ protected virtual HttpRequestMessage CreateHttpRequest(HttpMethod method, string
             httpRequest.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
             httpRequest.Headers.Authorization = new AuthenticationHeaderValue("Bearer", this._apiKey);
             httpRequest.Headers.Add("User-Agent", this.GetUserAgent());
-            httpRequest.Headers.Add("Idempotency-Key", Guid.NewGuid().ToString());
+            var idemPotencyKey = _idempotencyKey.Value ?? Guid.NewGuid().ToString();
+            httpRequest.Headers.Add("Idempotency-Key", idemPotencyKey);
             httpRequest.Content = content;
 
             return httpRequest;

src/Mollie.Api/Framework/Idempotency/AsyncLocalVariable.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Threading;
+
+namespace Mollie.Api.Framework.Idempotency
+{
+    public class AsyncLocalVariable<T> : IDisposable where T : class
+    {
+        private readonly AsyncLocal<T> _asyncLocal = new AsyncLocal<T>();
+
+        public T Value
+        {
+            get => _asyncLocal.Value;
+            set => _asyncLocal.Value = value;
+        }
+
+        public AsyncLocalVariable(T value)
+        {
+            _asyncLocal.Value = value;
+        }
+
+        public void Dispose()
+        {
+            _asyncLocal.Value = null;
+        }
+    }
+}

tests/Mollie.Tests.Unit/Client/PaymentClientTests.cs

@@ -6,6 +6,7 @@
 using Mollie.Api.Models.Payment.Response;
 using RichardSzalay.MockHttp;
 using System.Collections.Generic;
+using System.Linq;
 using System.Net.Http;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -16,6 +17,32 @@
 namespace Mollie.Tests.Unit.Client;
 
 public class PaymentClientTests : BaseClientTests {
+    [Fact]
+    public async Task CreatePaymentAsync_WithCustomIdempotencyKey_CustomIdemPotencyKeyIsSent()
+    {
+        // Given: We create a payment request with only the required parameters
+        PaymentRequest paymentRequest = new PaymentRequest()
+        {
+            Amount = new Amount(Currency.EUR, "100.00"),
+            Description = "Description",
+            RedirectUrl = "http://www.mollie.com"
+        };
+        const string customIdempotencyKey = "my-idempotency-key";
+        const string jsonToReturnInMockResponse = defaultPaymentJsonResponse;
+        var mockHttp = new MockHttpMessageHandler();
+        mockHttp.When($"{BaseMollieClient.ApiEndPoint}*")
+            .With(request => request.Headers.Contains("Idempotency-Key") && request.Headers.GetValues("Idempotency-Key").Single() == customIdempotencyKey)
+            .Respond("application/json", jsonToReturnInMockResponse);
+        HttpClient httpClient = mockHttp.ToHttpClient();
+        PaymentClient paymentClient = new PaymentClient("abcde", httpClient);
+
+        // Arrange & Act
+        using (paymentClient.WithIdempotencyKey(customIdempotencyKey))
+        {
+            await paymentClient.CreatePaymentAsync(paymentRequest);
+        }
+    }
+
     [Fact]
     public async Task CreatePaymentAsync_PaymentWithRequiredParameters_ResponseIsDeserializedInExpectedFormat() {
         // Given: we create a payment request with only the required parameters