Explores support for idempotency

JsonApiDotNetCore.sln.DotSettings

@@ -633,6 +633,7 @@ $left$ = $right$;</s:String>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=appsettings/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Assignee/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Contoso/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/UserDictionary/Words/=idempotency/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=Injectables/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=jsonapi/@EntryIndexedValue">True</s:Boolean>
 	<s:Boolean x:Key="/Default/UserDictionary/Words/=linebreaks/@EntryIndexedValue">True</s:Boolean>

src/JsonApiDotNetCore/AtomicOperations/EntityFrameworkCoreTransaction.cs

@@ -13,17 +13,19 @@ public sealed class EntityFrameworkCoreTransaction : IOperationsTransaction
 {
     private readonly IDbContextTransaction _transaction;
     private readonly DbContext _dbContext;
+    private readonly bool _ownsTransaction;
 
     /// <inheritdoc />
     public string TransactionId => _transaction.TransactionId.ToString();
 
-    public EntityFrameworkCoreTransaction(IDbContextTransaction transaction, DbContext dbContext)
+    public EntityFrameworkCoreTransaction(IDbContextTransaction transaction, DbContext dbContext, bool ownsTransaction)
     {
         ArgumentGuard.NotNull(transaction, nameof(transaction));
         ArgumentGuard.NotNull(dbContext, nameof(dbContext));
 
         _transaction = transaction;
         _dbContext = dbContext;
+        _ownsTransaction = ownsTransaction;
     }
 
     /// <summary>
@@ -44,14 +46,20 @@ public Task AfterProcessOperationAsync(CancellationToken cancellationToken)
     }
 
     /// <inheritdoc />
-    public Task CommitAsync(CancellationToken cancellationToken)
+    public async Task CommitAsync(CancellationToken cancellationToken)
     {
-        return _transaction.CommitAsync(cancellationToken);
+        if (_ownsTransaction)
+        {
+            await _transaction.CommitAsync(cancellationToken);
+        }
     }
 
     /// <inheritdoc />
-    public ValueTask DisposeAsync()
+    public async ValueTask DisposeAsync()
     {
-        return _transaction.DisposeAsync();
+        if (_ownsTransaction)
+        {
+            await _transaction.DisposeAsync();
+        }
     }
 }

src/JsonApiDotNetCore/AtomicOperations/EntityFrameworkCoreTransactionFactory.cs

@@ -27,10 +27,17 @@ public async Task<IOperationsTransaction> BeginTransactionAsync(CancellationToke
     {
         DbContext dbContext = _dbContextResolver.GetContext();
 
-        IDbContextTransaction transaction = _options.TransactionIsolationLevel != null
+        IDbContextTransaction? existingTransaction = dbContext.Database.CurrentTransaction;
+
+        if (existingTransaction != null)
+        {
+            return new EntityFrameworkCoreTransaction(existingTransaction, dbContext, false);
+        }
+
+        IDbContextTransaction newTransaction = _options.TransactionIsolationLevel != null
             ? await dbContext.Database.BeginTransactionAsync(_options.TransactionIsolationLevel.Value, cancellationToken)
             : await dbContext.Database.BeginTransactionAsync(cancellationToken);
 
-        return new EntityFrameworkCoreTransaction(transaction, dbContext);
+        return new EntityFrameworkCoreTransaction(newTransaction, dbContext, true);
     }
 }

src/JsonApiDotNetCore/Configuration/ApplicationBuilderExtensions.cs

@@ -44,6 +44,7 @@ public static void UseJsonApi(this IApplicationBuilder builder)
             options.Conventions.Insert(0, routingConvention);
         };
 
+        builder.UseMiddleware<IdempotencyMiddleware>();
         builder.UseMiddleware<JsonApiMiddleware>();
     }
 }

src/JsonApiDotNetCore/Configuration/JsonApiApplicationBuilder.cs

@@ -178,6 +178,7 @@ private void AddMiddlewareLayer()
         _services.AddScoped<IJsonApiWriter, JsonApiWriter>();
         _services.AddScoped<IJsonApiReader, JsonApiReader>();
         _services.AddScoped<ITargetedFields, TargetedFields>();
+        _services.AddScoped<IIdempotencyProvider, NoIdempotencyProvider>();
     }
 
     private void AddResourceLayer()

src/JsonApiDotNetCore/JsonApiDotNetCore.csproj

@@ -41,6 +41,7 @@
     <PackageReference Include="Humanizer.Core" Version="$(HumanizerVersion)" />
     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="6.0.0" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="6.0.0" />
+    <PackageReference Include="Microsoft.IO.RecyclableMemoryStream" Version="2.2.0" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
     <PackageReference Include="SauceControl.InheritDoc" Version="1.3.0" PrivateAssets="All" />
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />

src/JsonApiDotNetCore/Middleware/HeaderConstants.cs

@@ -9,4 +9,5 @@ public static class HeaderConstants
 {
     public const string MediaType = "application/vnd.api+json";
     public const string AtomicOperationsMediaType = MediaType + "; ext=\"https://jsonapi.org/ext/atomic\"";
+    public const string IdempotencyKey = "Idempotency-Key";
 }

src/JsonApiDotNetCore/Middleware/IIdempotencyProvider.cs

@@ -0,0 +1,30 @@
+using JetBrains.Annotations;
+using JsonApiDotNetCore.AtomicOperations;
+using Microsoft.AspNetCore.Http;
+
+namespace JsonApiDotNetCore.Middleware;
+
+[PublicAPI]
+public interface IIdempotencyProvider
+{
+    /// <summary>
+    /// Indicates whether the current request supports idempotency.
+    /// </summary>
+    bool IsSupported(HttpRequest request);
+
+    /// <summary>
+    /// Looks for a matching response in the idempotency cache for the specified idempotency key.
+    /// </summary>
+    Task<IdempotentResponse?> GetResponseFromCacheAsync(string idempotencyKey, CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Creates a new cache entry inside a transaction, so that concurrent requests with the same idempotency key will block or fail while the transaction
+    /// hasn't been committed.
+    /// </summary>
+    Task<IOperationsTransaction> BeginRequestAsync(string idempotencyKey, string requestFingerprint, CancellationToken cancellationToken);
+
+    /// <summary>
+    /// Saves the produced response in the cache and commits its transaction.
+    /// </summary>
+    Task CompleteRequestAsync(string idempotencyKey, IdempotentResponse response, IOperationsTransaction transaction, CancellationToken cancellationToken);
+}

src/JsonApiDotNetCore/Middleware/IdempotencyMiddleware.cs

@@ -0,0 +1,249 @@
+using System.Net;
+using System.Text;
+using System.Text.Json;
+using JetBrains.Annotations;
+using JsonApiDotNetCore.AtomicOperations;
+using JsonApiDotNetCore.Configuration;
+using JsonApiDotNetCore.Errors;
+using JsonApiDotNetCore.Serialization.Objects;
+using JsonApiDotNetCore.Serialization.Response;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Extensions;
+using Microsoft.AspNetCore.WebUtilities;
+using Microsoft.IO;
+using Microsoft.Net.Http.Headers;
+using SysNotNull = System.Diagnostics.CodeAnalysis.NotNullAttribute;
+
+namespace JsonApiDotNetCore.Middleware;
+
+// IMPORTANT: In your Program.cs, make sure app.UseDeveloperExceptionPage() is called BEFORE this!
+
+public sealed class IdempotencyMiddleware
+{
+    private static readonly RecyclableMemoryStreamManager MemoryStreamManager = new();
+
+    private readonly IJsonApiOptions _options;
+    private readonly IFingerprintGenerator _fingerprintGenerator;
+    private readonly RequestDelegate _next;
+
+    public IdempotencyMiddleware(IJsonApiOptions options, IFingerprintGenerator fingerprintGenerator, RequestDelegate next)
+    {
+        ArgumentGuard.NotNull(options, nameof(options));
+        ArgumentGuard.NotNull(fingerprintGenerator, nameof(fingerprintGenerator));
+
+        _options = options;
+        _fingerprintGenerator = fingerprintGenerator;
+        _next = next;
+    }
+
+    public async Task InvokeAsync(HttpContext httpContext, IIdempotencyProvider idempotencyProvider)
+    {
+        try
+        {
+            await InnerInvokeAsync(httpContext, idempotencyProvider);
+        }
+        catch (JsonApiException exception)
+        {
+            await FlushResponseAsync(httpContext.Response, _options.SerializerWriteOptions, exception.Errors.Single());
+        }
+    }
+
+    public async Task InnerInvokeAsync(HttpContext httpContext, IIdempotencyProvider idempotencyProvider)
+    {
+        string? idempotencyKey = GetIdempotencyKey(httpContext.Request.Headers);
+
+        if (idempotencyKey != null && idempotencyProvider is NoIdempotencyProvider)
+        {
+            throw new JsonApiException(new ErrorObject(HttpStatusCode.BadRequest)
+            {
+                Title = $"Invalid '{HeaderConstants.IdempotencyKey}' HTTP header.",
+                Detail = "Idempotency is currently disabled.",
+                Source = new ErrorSource
+                {
+                    Header = HeaderConstants.IdempotencyKey
+                }
+            });
+        }
+
+        if (!idempotencyProvider.IsSupported(httpContext.Request))
+        {
+            await _next(httpContext);
+            return;
+        }
+
+        AssertIdempotencyKeyIsValid(idempotencyKey);
+
+        await BufferRequestBodyAsync(httpContext);
+
+        string requestFingerprint = await GetRequestFingerprintAsync(httpContext);
+        IdempotentResponse? idempotentResponse = await idempotencyProvider.GetResponseFromCacheAsync(idempotencyKey, httpContext.RequestAborted);
+
+        if (idempotentResponse != null)
+        {
+            if (idempotentResponse.RequestFingerprint != requestFingerprint)
+            {
+                throw new JsonApiException(new ErrorObject(HttpStatusCode.UnprocessableEntity)
+                {
+                    Title = $"Invalid '{HeaderConstants.IdempotencyKey}' HTTP header.",
+                    Detail = $"The provided idempotency key '{idempotencyKey}' is in use for another request.",
+                    Source = new ErrorSource
+                    {
+                        Header = HeaderConstants.IdempotencyKey
+                    }
+                });
+            }
+
+            httpContext.Response.StatusCode = (int)idempotentResponse.ResponseStatusCode;
+            httpContext.Response.Headers[HeaderConstants.IdempotencyKey] = $"\"{idempotencyKey}\"";
+            httpContext.Response.Headers[HeaderNames.Location] = idempotentResponse.ResponseLocationHeader;
+
+            if (idempotentResponse.ResponseContentTypeHeader != null)
+            {
+                // Workaround for invalid nullability annotation in HttpResponse.ContentType
+                // Fixed after ASP.NET 6 release, see https://github.com/dotnet/aspnetcore/commit/8bb128185b58a26065d0f29e695a2410cf0a3c68#diff-bbfd771a8ef013a9921bff36df0d69f424910e079945992f1dccb24de54ca717
+                httpContext.Response.ContentType = idempotentResponse.ResponseContentTypeHeader;
+            }
+
+            await using TextWriter writer = new HttpResponseStreamWriter(httpContext.Response.Body, Encoding.UTF8);
+            await writer.WriteAsync(idempotentResponse.ResponseBody);
+            await writer.FlushAsync();
+
+            return;
+        }
+
+        await using IOperationsTransaction transaction =
+            await idempotencyProvider.BeginRequestAsync(idempotencyKey, requestFingerprint, httpContext.RequestAborted);
+
+        string responseBody = await CaptureResponseBodyAsync(httpContext, _next);
+
+        idempotentResponse = new IdempotentResponse(requestFingerprint, (HttpStatusCode)httpContext.Response.StatusCode,
+            httpContext.Response.Headers[HeaderNames.Location], httpContext.Response.ContentType, responseBody);
+
+        await idempotencyProvider.CompleteRequestAsync(idempotencyKey, idempotentResponse, transaction, httpContext.RequestAborted);
+    }
+
+    private static string? GetIdempotencyKey(IHeaderDictionary requestHeaders)
+    {
+        if (!requestHeaders.ContainsKey(HeaderConstants.IdempotencyKey))
+        {
+            return null;
+        }
+
+        string headerValue = requestHeaders[HeaderConstants.IdempotencyKey];
+
+        if (headerValue.Length >= 2 && headerValue[0] == '\"' && headerValue[^1] == '\"')
+        {
+            return headerValue[1..^1];
+        }
+
+        return string.Empty;
+    }
+
+    [AssertionMethod]
+    private static void AssertIdempotencyKeyIsValid([SysNotNull] string? idempotencyKey)
+    {
+        if (idempotencyKey == null)
+        {
+            throw new JsonApiException(new ErrorObject(HttpStatusCode.BadRequest)
+            {
+                Title = $"Missing '{HeaderConstants.IdempotencyKey}' HTTP header.",
+                Detail = "An idempotency key is a unique value generated by the client, which the server uses to recognize subsequent retries " +
+                    "of the same request. This should be a random string with enough entropy to avoid collisions."
+            });
+        }
+
+        if (idempotencyKey == string.Empty)
+        {
+            throw new JsonApiException(new ErrorObject(HttpStatusCode.BadRequest)
+            {
+                Title = $"Invalid '{HeaderConstants.IdempotencyKey}' HTTP header.",
+                Detail = "Expected non-empty value surrounded by double quotes.",
+                Source = new ErrorSource
+                {
+                    Header = HeaderConstants.IdempotencyKey
+                }
+            });
+        }
+    }
+
+    /// <summary>
+    /// Enables to read the HTTP request stream multiple times, without risking GC Gen2/LOH promotion.
+    /// </summary>
+    private static async Task BufferRequestBodyAsync(HttpContext httpContext)
+    {
+        // Above this threshold, EnableBuffering() switches to a temporary file on disk.
+        // Source: Microsoft.AspNetCore.Http.BufferingHelper.DefaultBufferThreshold
+        const int enableBufferingThreshold = 1024 * 30;
+
+        if (httpContext.Request.ContentLength > enableBufferingThreshold)
+        {
+            httpContext.Request.EnableBuffering(enableBufferingThreshold);
+        }
+        else
+        {
+            MemoryStream memoryRequestBodyStream = MemoryStreamManager.GetStream();
+            await httpContext.Request.Body.CopyToAsync(memoryRequestBodyStream, httpContext.RequestAborted);
+            memoryRequestBodyStream.Seek(0, SeekOrigin.Begin);
+
+            httpContext.Request.Body = memoryRequestBodyStream;
+            httpContext.Response.RegisterForDispose(memoryRequestBodyStream);
+        }
+    }
+
+    private async Task<string> GetRequestFingerprintAsync(HttpContext httpContext)
+    {
+        using var reader = new StreamReader(httpContext.Request.Body, leaveOpen: true);
+        string requestBody = await reader.ReadToEndAsync();
+        httpContext.Request.Body.Seek(0, SeekOrigin.Begin);
+
+        return _fingerprintGenerator.Generate(ArrayFactory.Create(httpContext.Request.GetEncodedUrl(), requestBody));
+    }
+
+    /// <summary>
+    /// Executes the specified action and returns what it wrote to the HTTP response stream.
+    /// </summary>
+    private static async Task<string> CaptureResponseBodyAsync(HttpContext httpContext, RequestDelegate nextAction)
+    {
+        // Loosely based on https://elanderson.net/2019/12/log-requests-and-responses-in-asp-net-core-3/.
+
+        Stream previousResponseBodyStream = httpContext.Response.Body;
+
+        try
+        {
+            await using MemoryStream memoryResponseBodyStream = MemoryStreamManager.GetStream();
+            httpContext.Response.Body = memoryResponseBodyStream;
+
+            try
+            {
+                await nextAction(httpContext);
+            }
+            finally
+            {
+                memoryResponseBodyStream.Seek(0, SeekOrigin.Begin);
+                await memoryResponseBodyStream.CopyToAsync(previousResponseBodyStream);
+            }
+
+            memoryResponseBodyStream.Seek(0, SeekOrigin.Begin);
+            using var streamReader = new StreamReader(memoryResponseBodyStream, leaveOpen: true);
+            return await streamReader.ReadToEndAsync();
+        }
+        finally
+        {
+            httpContext.Response.Body = previousResponseBodyStream;
+        }
+    }
+
+    private static async Task FlushResponseAsync(HttpResponse httpResponse, JsonSerializerOptions serializerOptions, ErrorObject error)
+    {
+        httpResponse.ContentType = HeaderConstants.MediaType;
+        httpResponse.StatusCode = (int)error.StatusCode;
+
+        var errorDocument = new Document
+        {
+            Errors = error.AsList()
+        };
+
+        await JsonSerializer.SerializeAsync(httpResponse.Body, errorDocument, serializerOptions);
+        await httpResponse.Body.FlushAsync();
+    }
+}