Add support for generating OpenAPI request bodies

src/OpenApi/sample/Program.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.AspNetCore.Mvc;
 using Microsoft.OpenApi.Models;
 using Sample.Transformers;
 
@@ -21,6 +22,7 @@
     });
 });
 builder.Services.AddOpenApi("responses");
+builder.Services.AddOpenApi("forms");
 
 var app = builder.Build();
 
@@ -30,6 +32,18 @@
     app.MapSwaggerUi();
 }
 
+var forms = app.MapGroup("forms")
+    .WithGroupName("forms");
+
+if (app.Environment.IsDevelopment())
+{
+    forms.DisableAntiforgery();
+}
+
+forms.MapPost("/form-file", (IFormFile resume) => Results.Ok(resume.FileName));
+forms.MapPost("/form-files", (IFormFileCollection files) => Results.Ok(files.Count));
+forms.MapPost("/form-todo", ([FromForm] Todo todo) => Results.Ok(todo));
+
 var v1 = app.MapGroup("v1")
     .WithGroupName("v1");
 var v2 = app.MapGroup("v2")

src/OpenApi/src/Extensions/ApiDescriptionExtensions.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using System.Text;
 using Microsoft.AspNetCore.Mvc.ApiExplorer;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
@@ -81,4 +83,34 @@ public static bool IsRequestBodyParameter(this ApiParameterDescription apiParame
         apiParameterDescription.Source == BindingSource.Body ||
         apiParameterDescription.Source == BindingSource.FormFile ||
         apiParameterDescription.Source == BindingSource.Form;
+
+    /// <summary>
+    /// Retrieves the form parameters from the ApiDescription, if they exist.
+    /// </summary>
+    /// <param name="apiDescription">The ApiDescription to resolve form parameters from.</param>
+    /// <param name="formParameters">A list of <see cref="ApiParameterDescription"/> associated with the form parameters.</param>
+    /// <returns><see langword="true"/> if form parameters were found, <see langword="false"/> otherwise.</returns>
+    public static bool TryGetFormParameters(this ApiDescription apiDescription, out IEnumerable<ApiParameterDescription> formParameters)
+    {
+        formParameters = apiDescription.ParameterDescriptions.Where(parameter => parameter.Source == BindingSource.Form || parameter.Source == BindingSource.FormFile);
+        return formParameters.Any();
+    }
+
+    /// <summary>
+    /// Retrieves the body parameter from the ApiDescription, if it exists.
+    /// </summary>
+    /// <param name="apiDescription">The ApiDescription to resolve the body parameter from.</param>
+    /// <param name="bodyParameter">The <see cref="ApiParameterDescription"/> associated with the body parameter.</param>
+    /// <returns><see langword="true"/> if a single body parameter was found, <see langword="false"/> otherwise.</returns>
+    public static bool TryGetBodyParameter(this ApiDescription apiDescription, [NotNullWhen(true)] out ApiParameterDescription? bodyParameter)
+    {
+        bodyParameter = null;
+        var bodyParameters = apiDescription.ParameterDescriptions.Where(parameter => parameter.Source == BindingSource.Body);
+        if (bodyParameters.Count() == 1)
+        {
+            bodyParameter = bodyParameters.Single();
+            return true;
+        }
+        return false;
+    }
 }

src/OpenApi/src/Services/OpenApiComponentService.cs

@@ -1,6 +1,10 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Collections.Concurrent;
+using Microsoft.AspNetCore.Http;
+using Microsoft.OpenApi.Models;
+
 namespace Microsoft.AspNetCore.OpenApi;
 
 /// <summary>
@@ -10,4 +14,25 @@ namespace Microsoft.AspNetCore.OpenApi;
 /// </summary>
 internal sealed class OpenApiComponentService
 {
+    private readonly ConcurrentDictionary<Type, OpenApiSchema> _schemas = new()
+    {
+        // Pre-populate OpenAPI schemas for well-defined types in ASP.NET Core.
+        [typeof(IFormFile)] = new OpenApiSchema { Type = "string", Format = "binary" },
+        [typeof(IFormFileCollection)] = new OpenApiSchema
+        {
+            Type = "array",
+            Items = new OpenApiSchema { Type = "string", Format = "binary" }
+        },
+    };
+
+    internal OpenApiSchema GetOrCreateSchema(Type type)
+    {
+        return _schemas.GetOrAdd(type, _ => CreateSchema());
+    }
+
+    // TODO: Implement this method to create a schema for a given type.
+    private static OpenApiSchema CreateSchema()
+    {
+        return new OpenApiSchema { Type = "string" };
+    }
 }

src/OpenApi/src/Services/OpenApiDocumentService.cs

@@ -28,6 +28,9 @@ internal sealed class OpenApiDocumentService(
     IServiceProvider serviceProvider)
 {
     private readonly OpenApiOptions _options = optionsMonitor.Get(documentName);
+    private readonly OpenApiComponentService _componentService = serviceProvider.GetRequiredKeyedService<OpenApiComponentService>(documentName);
+
+    private static readonly OpenApiEncoding _defaultFormEncoding = new OpenApiEncoding { Style = ParameterStyle.Form, Explode = true };
 
     /// <summary>
     /// Cache of <see cref="OpenApiOperationTransformerContext"/> instances keyed by the
@@ -124,7 +127,7 @@ private Dictionary<OperationType, OpenApiOperation> GetOperations(IGrouping<stri
         return operations;
     }
 
-    private static OpenApiOperation GetOperation(ApiDescription description, HashSet<OpenApiTag> capturedTags)
+    private OpenApiOperation GetOperation(ApiDescription description, HashSet<OpenApiTag> capturedTags)
     {
         var tags = GetTags(description);
         if (tags != null)
@@ -140,6 +143,7 @@ private static OpenApiOperation GetOperation(ApiDescription description, HashSet
             Description = GetDescription(description),
             Responses = GetResponses(description),
             Parameters = GetParameters(description),
+            RequestBody = GetRequestBody(description),
             Tags = tags,
         };
         return operation;
@@ -256,4 +260,78 @@ private static OpenApiResponse GetResponse(ApiDescription apiDescription, int st
         }
         return parameters;
     }
+
+    private OpenApiRequestBody? GetRequestBody(ApiDescription description)
+    {
+        // Only one parameter can be bound from the body in each request.
+        if (description.TryGetBodyParameter(out var bodyParameter))
+        {
+            return GetJsonRequestBody(description.SupportedRequestFormats, bodyParameter);
+        }
+        // If there are no body parameters, check for form parameters.
+        // Note: Form parameters and body parameters cannot exist simultaneously
+        // in the same endpoint.
+        if (description.TryGetFormParameters(out var formParameters))
+        {
+            return GetFormRequestBody(description.SupportedRequestFormats, formParameters);
+        }
+        return null;
+    }
+
+    private OpenApiRequestBody GetFormRequestBody(IList<ApiRequestFormat> supportedRequestFormats, IEnumerable<ApiParameterDescription> formParameters)
+    {
+        if (supportedRequestFormats.Count == 0)
+        {
+            // Assume "application/x-www-form-urlencoded" as the default media type
+            // to match the default assumed in IFormFeature.
+            supportedRequestFormats = [new ApiRequestFormat { MediaType = "application/x-www-form-urlencoded" }];
+        }
+
+        var requestBody = new OpenApiRequestBody
+        {
+            Required = formParameters.Any(parameter => parameter.IsRequired),
+            Content = new Dictionary<string, OpenApiMediaType>()
+        };
+
+        // Forms are represented as objects with properties for each form field.
+        var schema = new OpenApiSchema { Type = "object", Properties = new Dictionary<string, OpenApiSchema>() };
+        foreach (var parameter in formParameters)
+        {
+            schema.Properties[parameter.Name] = _componentService.GetOrCreateSchema(parameter.Type);
+        }
+
+        foreach (var requestFormat in supportedRequestFormats)
+        {
+            var contentType = requestFormat.MediaType;
+            requestBody.Content[contentType] = new OpenApiMediaType
+            {
+                Schema = schema,
+                Encoding = new Dictionary<string, OpenApiEncoding>() { [contentType] = _defaultFormEncoding }
+            };
+        }
+
+        return requestBody;
+    }
+
+    private static OpenApiRequestBody GetJsonRequestBody(IList<ApiRequestFormat> supportedRequestFormats, ApiParameterDescription bodyParameter)
+    {
+        if (supportedRequestFormats.Count == 0)
+        {
+            supportedRequestFormats = [new ApiRequestFormat { MediaType = "application/json" }];
+        }
+
+        var requestBody = new OpenApiRequestBody
+        {
+            Required = bodyParameter.IsRequired,
+            Content = new Dictionary<string, OpenApiMediaType>()
+        };
+
+        foreach (var requestForm in supportedRequestFormats)
+        {
+            var contentType = requestForm.MediaType;
+            requestBody.Content[contentType] = new OpenApiMediaType();
+        }
+
+        return requestBody;
+    }
 }

src/OpenApi/test/Services/OpenApiDocumentServiceTests.Info.cs

@@ -23,7 +23,7 @@ public void GetOpenApiInfo_RespectsHostEnvironmentName()
             new Mock<IApiDescriptionGroupCollectionProvider>().Object,
             hostEnvironment,
             new Mock<IOptionsMonitor<OpenApiOptions>>().Object,
-            new Mock<IServiceProvider>().Object);
+            new Mock<IKeyedServiceProvider>().Object);
 
         // Act
         var info = docService.GetOpenApiInfo();
@@ -45,7 +45,7 @@ public void GetOpenApiInfo_RespectsDocumentName()
             new Mock<IApiDescriptionGroupCollectionProvider>().Object,
             hostEnvironment,
             new Mock<IOptionsMonitor<OpenApiOptions>>().Object,
-            new Mock<IServiceProvider>().Object);
+            new Mock<IKeyedServiceProvider>().Object);
 
         // Act
         var info = docService.GetOpenApiInfo();