DefaultApiDescriptionProvider.cs

// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Linq;
using Microsoft.AspNetCore.Http.Metadata;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ActionConstraints;
using Microsoft.AspNetCore.Mvc.Controllers;
using Microsoft.AspNetCore.Mvc.Formatters;
using Microsoft.AspNetCore.Mvc.Infrastructure;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.ModelBinding.Metadata;
using Microsoft.AspNetCore.Routing;
using Microsoft.AspNetCore.Routing.Template;
using Microsoft.Extensions.Options;

namespace Microsoft.AspNetCore.Mvc.ApiExplorer;

/// <summary>
/// Implements a provider of <see cref="ApiDescription"/> for actions represented
/// by <see cref="ControllerActionDescriptor"/>.
/// </summary>
public class DefaultApiDescriptionProvider : IApiDescriptionProvider
{
    private readonly MvcOptions _mvcOptions;
    private readonly ApiResponseTypeProvider _responseTypeProvider;
    private readonly RouteOptions _routeOptions;
    private readonly IInlineConstraintResolver _constraintResolver;
    private readonly IModelMetadataProvider _modelMetadataProvider;

    /// <summary>
    /// Creates a new instance of <see cref="DefaultApiDescriptionProvider"/>.
    /// </summary>
    /// <param name="optionsAccessor">The accessor for <see cref="MvcOptions"/>.</param>
    /// <param name="constraintResolver">The <see cref="IInlineConstraintResolver"/> used for resolving inline
    /// constraints.</param>
    /// <param name="modelMetadataProvider">The <see cref="IModelMetadataProvider"/>.</param>
    /// <param name="mapper">The <see cref="IActionResultTypeMapper"/>.</param>
    /// <param name="routeOptions">The accessor for <see cref="RouteOptions"/>.</param>
    /// <remarks>The <paramref name="mapper"/> parameter is currently ignored.</remarks>
    public DefaultApiDescriptionProvider(
        IOptions<MvcOptions> optionsAccessor,
        IInlineConstraintResolver constraintResolver,
        IModelMetadataProvider modelMetadataProvider,
        IActionResultTypeMapper mapper,
        IOptions<RouteOptions> routeOptions)
    {
        _mvcOptions = optionsAccessor.Value;
        _constraintResolver = constraintResolver;
        _modelMetadataProvider = modelMetadataProvider;
        _responseTypeProvider = new ApiResponseTypeProvider(modelMetadataProvider, mapper, _mvcOptions);
        _routeOptions = routeOptions.Value;
    }

    /// <inheritdoc />
    public int Order => -1000;

    /// <inheritdoc />
    public void OnProvidersExecuting(ApiDescriptionProviderContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        foreach (var action in context.Actions.OfType<ControllerActionDescriptor>())
        {
            if (action.AttributeRouteInfo != null && action.AttributeRouteInfo.SuppressPathMatching)
            {
                continue;
            }

            // ApiDescriptionActionData is only added to the ControllerActionDescriptor if
            // the action is marked as `IsVisible` to the ApiExplorer. This null-check is
            // effectively asserting if the endpoint should be generated into the final
            // OpenAPI metadata.
            var extensionData = action.GetProperty<ApiDescriptionActionData>();
            if (extensionData != null)
            {
                var httpMethods = GetHttpMethods(action);
                foreach (var httpMethod in httpMethods)
                {
                    context.Results.Add(CreateApiDescription(action, httpMethod, GetGroupName(action, extensionData)));
                }
            }
        }
    }

    /// <inheritdoc />
    public void OnProvidersExecuted(ApiDescriptionProviderContext context)
    {
    }

    private ApiDescription CreateApiDescription(
        ControllerActionDescriptor action,
        string? httpMethod,
        string? groupName)
    {
        var parsedTemplate = ParseTemplate(action);

        var apiDescription = new ApiDescription()
        {
            ActionDescriptor = action,
            GroupName = groupName,
            HttpMethod = httpMethod,
            RelativePath = GetRelativePath(parsedTemplate),
        };

        var templateParameters = parsedTemplate?.Parameters?.ToList() ?? new List<TemplatePart>();

        var parameterContext = new ApiParameterContext(_modelMetadataProvider, action, templateParameters);

        foreach (var parameter in GetParameters(parameterContext))
        {
            apiDescription.ParameterDescriptions.Add(parameter);
        }

        var apiResponseTypes = _responseTypeProvider.GetApiResponseTypes(action);
        foreach (var apiResponseType in apiResponseTypes)
        {
            apiDescription.SupportedResponseTypes.Add(apiResponseType);
        }

        // It would be possible here to configure an action with multiple body parameters, in which case you
        // could end up with duplicate data.
        if (apiDescription.ParameterDescriptions.Count > 0)
        {
            // Get the most significant accepts metadata
            var acceptsMetadata = action.EndpointMetadata.OfType<IAcceptsMetadata>().LastOrDefault();
            var requestMetadataAttributes = GetRequestMetadataAttributes(action);

            var contentTypes = GetDeclaredContentTypes(requestMetadataAttributes, acceptsMetadata);
            foreach (var parameter in apiDescription.ParameterDescriptions)
            {
                if (parameter.Source == BindingSource.Body)
                {
                    // For request body bound parameters, determine the content types supported
                    // by input formatters.
                    var requestFormats = GetSupportedFormats(contentTypes, parameter.Type);
                    foreach (var format in requestFormats)
                    {
                        apiDescription.SupportedRequestFormats.Add(format);
                    }
                }
                else if (parameter.Source == BindingSource.FormFile)
                {
                    // Add all declared media types since FormFiles do not get processed by formatters.
                    foreach (var contentType in contentTypes)
                    {
                        apiDescription.SupportedRequestFormats.Add(new ApiRequestFormat
                        {
                            MediaType = contentType,
                        });
                    }
                }
            }
        }

        return apiDescription;
    }

    private IList<ApiParameterDescription> GetParameters(ApiParameterContext context)
    {
        // First, get parameters from the model-binding/parameter-binding side of the world.
        if (context.ActionDescriptor.Parameters != null)
        {
            foreach (var actionParameter in context.ActionDescriptor.Parameters)
            {
                var visitor = new PseudoModelBindingVisitor(context, actionParameter);

                ModelMetadata metadata;
                if (actionParameter is ControllerParameterDescriptor controllerParameterDescriptor &&
                    _modelMetadataProvider is ModelMetadataProvider provider)
                {
                    // The default model metadata provider derives from ModelMetadataProvider
                    // and can therefore supply information about attributes applied to parameters.
                    metadata = provider.GetMetadataForParameter(controllerParameterDescriptor.ParameterInfo);
                }
                else
                {
                    // For backward compatibility, if there's a custom model metadata provider that
                    // only implements the older IModelMetadataProvider interface, access the more
                    // limited metadata information it supplies. In this scenario, validation attributes
                    // are not supported on parameters.
                    metadata = _modelMetadataProvider.GetMetadataForType(actionParameter.ParameterType);
                }

                var bindingContext = new ApiParameterDescriptionContext(
                    metadata,
                    actionParameter.BindingInfo,
                    propertyName: actionParameter.Name);
                visitor.WalkParameter(bindingContext);
            }
        }

        if (context.ActionDescriptor.BoundProperties != null)
        {
            foreach (var actionParameter in context.ActionDescriptor.BoundProperties)
            {
                var visitor = new PseudoModelBindingVisitor(context, actionParameter);
                var modelMetadata = context.MetadataProvider.GetMetadataForProperty(
                    containerType: context.ActionDescriptor.ControllerTypeInfo.AsType(),
                    propertyName: actionParameter.Name);

                var bindingContext = new ApiParameterDescriptionContext(
                    modelMetadata,
                    actionParameter.BindingInfo,
                    propertyName: actionParameter.Name);

                visitor.WalkParameter(bindingContext);
            }
        }

        for (var i = context.Results.Count - 1; i >= 0; i--)
        {
            // Remove any 'hidden' parameters. These are things that can't come from user input,
            // so they aren't worth showing.
            if (!context.Results[i].Source.IsFromRequest)
            {
                context.Results.RemoveAt(i);
            }
        }

        // Next, we want to join up any route parameters with those discovered from the action's parameters.
        // This will result us in creating a parameter representation for each route parameter that does not
        // have a mapping parameter or bound property.
        ProcessRouteParameters(context);

        // Set IsRequired=true
        ProcessIsRequired(context, _mvcOptions);

        // Set DefaultValue
        ProcessParameterDefaultValue(context);

        return context.Results;
    }

    private void ProcessRouteParameters(ApiParameterContext context)
    {
        var routeParameters = new Dictionary<string, ApiParameterRouteInfo>(StringComparer.OrdinalIgnoreCase);
        foreach (var routeParameter in context.RouteParameters)
        {
            routeParameters.Add(routeParameter.Name!, CreateRouteInfo(routeParameter));
        }

        for (var i = context.Results.Count - 1; i >= 0; i--)
        {
            var parameter = context.Results[i];

            if (parameter.Source == BindingSource.Path ||
               parameter.Source == BindingSource.ModelBinding ||
               parameter.Source == BindingSource.Custom)
            {
                if (routeParameters.TryGetValue(parameter.Name, out var routeInfo))
                {
                    parameter.RouteInfo = routeInfo;
                    routeParameters.Remove(parameter.Name);

                    if (parameter.Source == BindingSource.ModelBinding &&
                        !parameter.RouteInfo.IsOptional)
                    {
                        // If we didn't see any information about the parameter, but we have
                        // a route parameter that matches, let's switch it to path.
                        parameter.Source = BindingSource.Path;
                    }
                }
                else
                {
                    if (parameter.Source == BindingSource.Path &&
                        parameter.ModelMetadata is DefaultModelMetadata defaultModelMetadata &&
                        !defaultModelMetadata.Attributes.Attributes.OfType<IFromRouteMetadata>().Any())
                    {
                        // If we didn't see the parameter in the route and no FromRoute metadata is set, it probably means
                        // the parameter binding source was inferred (InferParameterBindingInfoConvention)  
                        // probably because another route to this action contains it as route parameter and
                        // will be removed from the API description
                        // https://github.com/dotnet/aspnetcore/issues/26234
                        context.Results.RemoveAt(i);
                    }
                }
            }
        }

        // Lastly, create a parameter representation for each route parameter that did not find
        // a partner.
        foreach (var routeParameter in routeParameters)
        {
            context.Results.Add(new ApiParameterDescription()
            {
                Name = routeParameter.Key,
                RouteInfo = routeParameter.Value,
                Source = BindingSource.Path,
            });
        }
    }

    internal static void ProcessIsRequired(ApiParameterContext context, MvcOptions mvcOptions)
    {
        foreach (var parameter in context.Results)
        {
            if (parameter.Source == BindingSource.Body)
            {
                if (parameter.BindingInfo == null || parameter.BindingInfo.EmptyBodyBehavior == EmptyBodyBehavior.Default)
                {
                    parameter.IsRequired = !mvcOptions.AllowEmptyInputInBodyModelBinding;
                }
                else
                {
                    parameter.IsRequired = !(parameter.BindingInfo.EmptyBodyBehavior == EmptyBodyBehavior.Allow);
                }
            }

            if (parameter.ModelMetadata != null && parameter.ModelMetadata.IsBindingRequired)
            {
                parameter.IsRequired = true;
            }

            if (parameter.Source == BindingSource.Path && parameter.RouteInfo != null && !parameter.RouteInfo.IsOptional)
            {
                parameter.IsRequired = true;
            }
        }
    }

    internal static void ProcessParameterDefaultValue(ApiParameterContext context)
    {
        foreach (var parameter in context.Results)
        {
            if (parameter.Source == BindingSource.Path)
            {
                parameter.DefaultValue = parameter.RouteInfo?.DefaultValue;
            }
            else
            {
                if (parameter.ParameterDescriptor is ControllerParameterDescriptor controllerParameter &&
                    ParameterDefaultValues.TryGetDeclaredParameterDefaultValue(controllerParameter.ParameterInfo, out var defaultValue))
                {
                    parameter.DefaultValue = defaultValue;
                }
            }
        }
    }

    private ApiParameterRouteInfo CreateRouteInfo(TemplatePart routeParameter)
    {
        var constraints = new List<IRouteConstraint>();
        if (routeParameter.InlineConstraints != null)
        {
            foreach (var constraint in routeParameter.InlineConstraints)
            {
                constraints.Add(_constraintResolver.ResolveConstraint(constraint.Constraint)!);
            }
        }

        return new ApiParameterRouteInfo()
        {
            Constraints = constraints,
            DefaultValue = routeParameter.DefaultValue,
            IsOptional = routeParameter.IsOptional || routeParameter.DefaultValue != null,
        };
    }

    private static IEnumerable<string?> GetHttpMethods(ControllerActionDescriptor action)
    {
        if (action.ActionConstraints != null && action.ActionConstraints.Count > 0)
        {
            return action.ActionConstraints.OfType<HttpMethodActionConstraint>().SelectMany(c => c.HttpMethods);
        }
        else
        {
            return new string?[] { null };
        }
    }

    private static RouteTemplate? ParseTemplate(ControllerActionDescriptor action)
    {
        if (action.AttributeRouteInfo?.Template != null)
        {
            return TemplateParser.Parse(action.AttributeRouteInfo.Template);
        }

        return null;
    }

    private string? GetRelativePath(RouteTemplate? parsedTemplate)
    {
        if (parsedTemplate == null)
        {
            return null;
        }

        var segments = new List<string>();

        foreach (var segment in parsedTemplate.Segments)
        {
            var currentSegment = string.Empty;
            foreach (var part in segment.Parts)
            {
                if (part.IsLiteral)
                {
                    currentSegment += _routeOptions.LowercaseUrls ?
                        part.Text!.ToLowerInvariant() :
                        part.Text;
                }
                else if (part.IsParameter)
                {
                    currentSegment += "{" + part.Name + "}";
                }
            }

            segments.Add(currentSegment);
        }

        return string.Join("/", segments);
    }

    private IReadOnlyList<ApiRequestFormat> GetSupportedFormats(MediaTypeCollection contentTypes, Type type)
    {
        if (contentTypes.Count == 0)
        {
            contentTypes = new MediaTypeCollection
                {
                    (string)null!,
                };
        }

        var results = new List<ApiRequestFormat>();
        foreach (var contentType in contentTypes)
        {
            foreach (var formatter in _mvcOptions.InputFormatters)
            {
                if (formatter is IApiRequestFormatMetadataProvider requestFormatMetadataProvider)
                {
                    var supportedTypes = requestFormatMetadataProvider.GetSupportedContentTypes(contentType, type);

                    if (supportedTypes != null)
                    {
                        foreach (var supportedType in supportedTypes)
                        {
                            results.Add(new ApiRequestFormat()
                            {
                                Formatter = formatter,
                                MediaType = supportedType,
                            });
                        }
                    }
                }
            }
        }

        return results;
    }

    internal static MediaTypeCollection GetDeclaredContentTypes(IReadOnlyList<IApiRequestMetadataProvider>? requestMetadataAttributes, IAcceptsMetadata? acceptsMetadata)
    {
        var contentTypes = new MediaTypeCollection();

        // Walking the content types from the accepts metadata first
        // to allow any RequestMetadataProvider to see or override any accepts metadata
        // keeping the current behavior.
        if (acceptsMetadata != null)
        {
            foreach (var contentType in acceptsMetadata.ContentTypes)
            {
                contentTypes.Add(contentType);
            }
        }

        // Walk through all 'filter' attributes in order, and allow each one to see or override
        // the results of the previous ones. This is similar to the execution path for content-negotiation.
        if (requestMetadataAttributes != null)
        {
            foreach (var metadataAttribute in requestMetadataAttributes)
            {
                metadataAttribute.SetContentTypes(contentTypes);
            }
        }

        return contentTypes;
    }

    private static IApiRequestMetadataProvider[]? GetRequestMetadataAttributes(ControllerActionDescriptor action)
    {
        if (action.FilterDescriptors == null)
        {
            return null;
        }

        // This technique for enumerating filters will intentionally ignore any filter that is an IFilterFactory
        // while searching for a filter that implements IApiRequestMetadataProvider.
        //
        // The workaround for that is to implement the metadata interface on the IFilterFactory.
        return action.FilterDescriptors
            .Select(fd => fd.Filter)
            .OfType<IApiRequestMetadataProvider>()
            .ToArray();
    }

    private static string? GetGroupName(ControllerActionDescriptor action, ApiDescriptionActionData extensionData)
    {
        // The `GroupName` set in the `ApiDescriptionActionData` is either the
        // group name set via [ApiExplorerSettings(GroupName = "foo")] on the
        // action or controller. So, this lookup favors the following sequence:
        // - EndpointGroupName on the action, if it is set
        // - EndpointGroupName on the controller, if it is set
        // - ApiExplorerSettings.GroupName on the action, if it is set
        // - ApiExplorerSettings.GroupName on the controller, if it is set
        var endpointGroupName = action.EndpointMetadata.OfType<IEndpointGroupNameMetadata>().LastOrDefault();
        return endpointGroupName?.EndpointGroupName ?? extensionData.GroupName;
    }

    private sealed class ApiParameterDescriptionContext
    {
        public ModelMetadata ModelMetadata { get; }

        public string? BinderModelName { get; }

        public BindingSource? BindingSource { get; }

        public string? PropertyName { get; }

        public BindingInfo? BindingInfo { get; }

        public ApiParameterDescriptionContext(
            ModelMetadata metadata,
            BindingInfo? bindingInfo,
            string? propertyName)
        {
            // BindingMetadata can be null if the metadata represents properties.
            ModelMetadata = metadata;
            BinderModelName = bindingInfo?.BinderModelName;
            BindingSource = bindingInfo?.BindingSource;
            PropertyName = propertyName ?? metadata.Name;
            BindingInfo = bindingInfo;
        }
    }

    private sealed class PseudoModelBindingVisitor
    {
        public PseudoModelBindingVisitor(ApiParameterContext context, ParameterDescriptor parameter)
        {
            Context = context;
            Parameter = parameter;

            Visited = new HashSet<PropertyKey>(new PropertyKeyEqualityComparer());
        }

        public ApiParameterContext Context { get; }

        public ParameterDescriptor Parameter { get; }

        // Avoid infinite recursion by tracking properties.
        private HashSet<PropertyKey> Visited { get; }

        public void WalkParameter(ApiParameterDescriptionContext context)
        {
            // Attempt to find a binding source for the parameter
            //
            // The default is ModelBinding (aka all default value providers)
            var source = BindingSource.ModelBinding;
            Visit(context, source, containerName: string.Empty);
        }

        private void Visit(
            ApiParameterDescriptionContext bindingContext,
            BindingSource ambientSource,
            string containerName)
        {
            var source = bindingContext.BindingSource;
            if (source != null && source.IsGreedy)
            {
                // We have a definite answer for this model. This is a greedy source like
                // [FromBody] so there's no need to consider properties.
                Context.Results.Add(CreateResult(bindingContext, source, containerName));
                return;
            }

            var modelMetadata = bindingContext.ModelMetadata;

            // For any property which is a leaf node, we don't want to keep traversing:
            //
            //  1)  Collections - while it's possible to have binder attributes on the inside of a collection,
            //      it hardly seems useful, and would result in some very weird binding.
            //
            //  2)  Simple Types - These are generally part of the .net framework - primitives, or types which have a
            //      type converter from string.
            //
            //  3)  Types with no properties. Obviously nothing to explore there.
            //
            if (modelMetadata.IsEnumerableType ||
                !modelMetadata.IsComplexType ||
                modelMetadata.Properties.Count == 0)
            {
                Context.Results.Add(CreateResult(bindingContext, source ?? ambientSource, containerName));
                return;
            }

            // This will come from composite model binding - so investigate what's going on with each property.
            //
            // Ex:
            //
            //      public IActionResult PlaceOrder(OrderDTO order) {...}
            //
            //      public class OrderDTO
            //      {
            //          public int AccountId { get; set; }
            //
            //          [FromBody]
            //          public Order { get; set; }
            //      }
            //
            // This should result in two parameters:
            //
            //  AccountId - source: Any
            //  Order - source: Body
            //

            // We don't want to append the **parameter** name when building a model name.
            var newContainerName = containerName;
            if (modelMetadata.ContainerType != null)
            {
                newContainerName = GetName(containerName, bindingContext);
            }

            var metadataProperties = modelMetadata.Properties;
            var metadataPropertiesCount = metadataProperties.Count;
            for (var i = 0; i < metadataPropertiesCount; i++)
            {
                var propertyMetadata = metadataProperties[i];
                var key = new PropertyKey(propertyMetadata, source);
                var bindingInfo = BindingInfo.GetBindingInfo(Enumerable.Empty<object>(), propertyMetadata);

                var propertyContext = new ApiParameterDescriptionContext(
                    propertyMetadata,
                    bindingInfo: bindingInfo,
                    propertyName: null);

                if (Visited.Add(key))
                {
                    Visit(propertyContext, source ?? ambientSource, newContainerName);
                    Visited.Remove(key);
                }
                else
                {
                    // This is cycle, so just add a result rather than traversing.
                    Context.Results.Add(CreateResult(propertyContext, source ?? ambientSource, newContainerName));
                }
            }
        }

        private ApiParameterDescription CreateResult(
            ApiParameterDescriptionContext bindingContext,
            BindingSource source,
            string containerName)
        {
            return new ApiParameterDescription()
            {
                ModelMetadata = bindingContext.ModelMetadata,
                Name = GetName(containerName, bindingContext),
                Source = source,
                Type = bindingContext.ModelMetadata.ModelType,
                ParameterDescriptor = Parameter,
                BindingInfo = bindingContext.BindingInfo
            };
        }

        private static string GetName(string containerName, ApiParameterDescriptionContext metadata)
        {
            var propertyName = !string.IsNullOrEmpty(metadata.BinderModelName) ? metadata.BinderModelName : metadata.PropertyName;
            return ModelNames.CreatePropertyModelName(containerName, propertyName);
        }

        private readonly struct PropertyKey
        {
            public readonly Type ContainerType;

            public readonly string PropertyName;

            public readonly BindingSource? Source;

            public PropertyKey(ModelMetadata metadata, BindingSource? source)
            {
                ContainerType = metadata.ContainerType!;
                PropertyName = metadata.PropertyName!;
                Source = source;
            }
        }

        private sealed class PropertyKeyEqualityComparer : IEqualityComparer<PropertyKey>
        {
            public bool Equals(PropertyKey x, PropertyKey y)
            {
                return
                    x.ContainerType == y.ContainerType &&
                    x.PropertyName == y.PropertyName &&
                    x.Source == y.Source;
            }

            public int GetHashCode(PropertyKey obj)
            {
                return HashCode.Combine(obj.ContainerType, obj.PropertyName, obj.Source);
            }
        }
    }
}