Fix $ref serialization errors for requestBodies and responses

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -160,7 +160,7 @@ public void SerializeAsV2(IOpenApiWriter writer)
             // paths
             writer.WriteRequiredObject(OpenApiConstants.Paths, Paths, (w, p) => p.SerializeAsV2(w));
 
-            // If references have been inlined we don't need the to render the components section
+            // If references have been inlined we don't need to render the components section
             // however if they have cycles, then we will need a component rendered
             if (writer.GetSettings().InlineLocalReferences)
             {
@@ -208,9 +208,20 @@ public void SerializeAsV2(IOpenApiWriter writer)
                     });
             }
             // parameters
+            var parameters = Components?.Parameters != null 
+                ? new Dictionary<string, OpenApiParameter>(Components.Parameters) 
+                : new Dictionary<string, OpenApiParameter>();
+
+            if (Components?.RequestBodies != null)
+            {
+                foreach (var requestBody in Components.RequestBodies.Where(b => !parameters.ContainsKey(b.Key)))
+                {
+                    parameters.Add(requestBody.Key, requestBody.Value.ConvertToBodyParameter());
+                }
+            }
             writer.WriteOptionalMap(
                 OpenApiConstants.Parameters,
-                Components?.Parameters,
+                parameters,
                 (w, key, component) =>
                 {
                     if (component.Reference != null &&

src/Microsoft.OpenApi/Models/OpenApiOperation.cs

@@ -224,7 +224,7 @@ public void SerializeAsV2(IOpenApiWriter writer)
             // operationId
             writer.WriteProperty(OpenApiConstants.OperationId, OperationId);
 
-            IList<OpenApiParameter> parameters;
+            List<OpenApiParameter> parameters;
             if (Parameters == null)
             {
                 parameters = new List<OpenApiParameter>();
@@ -237,70 +237,58 @@ public void SerializeAsV2(IOpenApiWriter writer)
             if (RequestBody != null)
             {
                 // consumes
-                writer.WritePropertyName(OpenApiConstants.Consumes);
-                writer.WriteStartArray();
                 var consumes = RequestBody.Content.Keys.Distinct().ToList();
-                foreach (var mediaType in consumes)
+                if (consumes.Any())
                 {
-                    writer.WriteValue(mediaType);
-                }
-
-                writer.WriteEndArray();
-
-                // This is form data. We need to split the request body into multiple parameters.
-                if (consumes.Contains("application/x-www-form-urlencoded") ||
-                    consumes.Contains("multipart/form-data"))
-                {
-                    foreach (var property in RequestBody.Content.First().Value.Schema.Properties)
+                    // This is form data. We need to split the request body into multiple parameters.
+                    if (consumes.Contains("application/x-www-form-urlencoded") ||
+                        consumes.Contains("multipart/form-data"))
                     {
-                        var paramSchema = property.Value;
-                        if ("string".Equals(paramSchema.Type, StringComparison.OrdinalIgnoreCase) 
-                            && ("binary".Equals(paramSchema.Format, StringComparison.OrdinalIgnoreCase) 
-                            || "base64".Equals(paramSchema.Format, StringComparison.OrdinalIgnoreCase)))
-                        {
-                            paramSchema.Type = "file";
-                            paramSchema.Format = null;
-                        }
-                        parameters.Add(
-                            new OpenApiFormDataParameter
-                            {
-                                Description = property.Value.Description,
-                                Name = property.Key,
-                                Schema = property.Value,
-                                Required = RequestBody.Content.First().Value.Schema.Required.Contains(property.Key)
-
-                            });
+                        parameters.AddRange(RequestBody.ConvertToFormDataParameters());
+                    }
+                    else
+                    {
+                        parameters.Add(RequestBody.ConvertToBodyParameter());
                     }
                 }
-                else
+                else if (RequestBody.Reference != null)
                 {
-                    var content = RequestBody.Content.Values.FirstOrDefault();
+                    parameters.Add(
+                        new OpenApiParameter
+                        {
+                            UnresolvedReference = true,
+                            Reference = RequestBody.Reference
+                        });
 
-                    var bodyParameter = new OpenApiBodyParameter
+                    if (RequestBody.Reference.HostDocument != null)
                     {
-                        Description = RequestBody.Description,
-                        // V2 spec actually allows the body to have custom name.
-                        // To allow round-tripping we use an extension to hold the name
-                        Name = "body",
-                        Schema = content?.Schema ?? new OpenApiSchema(),
-                        Required = RequestBody.Required,
-                        Extensions = RequestBody.Extensions.ToDictionary(k => k.Key, v => v.Value)  // Clone extensions so we can remove the x-bodyName extensions from the output V2 model.
-                    };
-
-                    if (bodyParameter.Extensions.ContainsKey(OpenApiConstants.BodyName))
+                        var effectiveRequestBody = RequestBody.GetEffective(RequestBody.Reference.HostDocument);
+                        if (effectiveRequestBody != null)
+                            consumes = effectiveRequestBody.Content.Keys.Distinct().ToList();
+                    }
+                }
+
+                if (consumes.Any())
+                {
+                    writer.WritePropertyName(OpenApiConstants.Consumes);
+                    writer.WriteStartArray();
+                    foreach (var mediaType in consumes)
                     {
-                        bodyParameter.Name = (RequestBody.Extensions[OpenApiConstants.BodyName] as OpenApiString)?.Value ?? "body";
-                        bodyParameter.Extensions.Remove(OpenApiConstants.BodyName);
+                        writer.WriteValue(mediaType);
                     }
-
-                    parameters.Add(bodyParameter);
+                    writer.WriteEndArray();
                 }
             }
 
             if (Responses != null)
             {
-                var produces = Responses.Where(r => r.Value.Content != null)
-                    .SelectMany(r => r.Value.Content?.Keys)
+                var produces = Responses
+                    .Where(static r => r.Value.Content != null)
+                    .SelectMany(static r => r.Value.Content?.Keys)
+                    .Concat(
+                        Responses
+                        .Where(static r => r.Value.Reference != null && r.Value.Reference.HostDocument != null)
+                        .SelectMany(static r => r.Value.GetEffective(r.Value.Reference.HostDocument)?.Content?.Keys))
                     .Distinct()
                     .ToList();
 

src/Microsoft.OpenApi/Models/OpenApiReference.cs

@@ -214,31 +214,17 @@ private string GetExternalReferenceV2()
 
         private string GetReferenceTypeNameAsV2(ReferenceType type)
         {
-            switch (type)
+            return type switch
             {
-                case ReferenceType.Schema:
-                    return OpenApiConstants.Definitions;
-
-                case ReferenceType.Parameter:
-                    return OpenApiConstants.Parameters;
-
-                case ReferenceType.Response:
-                    return OpenApiConstants.Responses;
-
-                case ReferenceType.Header:
-                    return OpenApiConstants.Headers;
-
-                case ReferenceType.Tag:
-                    return OpenApiConstants.Tags;
-
-                case ReferenceType.SecurityScheme:
-                    return OpenApiConstants.SecurityDefinitions;
-
-                default:
-                    // If the reference type is not supported in V2, simply return null
-                    // to indicate that the reference is not pointing to any object.
-                    return null;
-            }
+                ReferenceType.Schema => OpenApiConstants.Definitions,
+                ReferenceType.Parameter or ReferenceType.RequestBody => OpenApiConstants.Parameters,
+                ReferenceType.Response => OpenApiConstants.Responses,
+                ReferenceType.Header => OpenApiConstants.Headers,
+                ReferenceType.Tag => OpenApiConstants.Tags,
+                ReferenceType.SecurityScheme => OpenApiConstants.SecurityDefinitions,
+                _ => null,// If the reference type is not supported in V2, simply return null
+                          // to indicate that the reference is not pointing to any object.
+            };
         }
     }
 }

src/Microsoft.OpenApi/Models/OpenApiRequestBody.cs

@@ -1,7 +1,9 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. 
 
+using System;
 using System.Collections.Generic;
+using System.Linq;
 using Microsoft.OpenApi.Any;
 using Microsoft.OpenApi.Interfaces;
 using Microsoft.OpenApi.Writers;
@@ -144,5 +146,50 @@ public void SerializeAsV2WithoutReference(IOpenApiWriter writer)
         {
             // RequestBody object does not exist in V2.
         }
+
+        internal OpenApiBodyParameter ConvertToBodyParameter()
+        {
+            var bodyParameter = new OpenApiBodyParameter
+            {
+                Description = Description,
+                // V2 spec actually allows the body to have custom name.
+                // To allow round-tripping we use an extension to hold the name
+                Name = "body",
+                Schema = Content.Values.FirstOrDefault()?.Schema ?? new OpenApiSchema(),
+                Required = Required,
+                Extensions = Extensions.ToDictionary(static k => k.Key, static v => v.Value)  // Clone extensions so we can remove the x-bodyName extensions from the output V2 model.
+            };
+            if (bodyParameter.Extensions.ContainsKey(OpenApiConstants.BodyName))
+            {
+                bodyParameter.Name = (Extensions[OpenApiConstants.BodyName] as OpenApiString)?.Value ?? "body";
+                bodyParameter.Extensions.Remove(OpenApiConstants.BodyName);
+            }
+            return bodyParameter;
+        }
+
+        internal IEnumerable<OpenApiFormDataParameter> ConvertToFormDataParameters()
+        {
+            if (Content == null || !Content.Any())
+                yield break;
+
+            foreach (var property in Content.First().Value.Schema.Properties)
+            {
+                var paramSchema = property.Value;
+                if ("string".Equals(paramSchema.Type, StringComparison.OrdinalIgnoreCase)
+                    && ("binary".Equals(paramSchema.Format, StringComparison.OrdinalIgnoreCase)
+                    || "base64".Equals(paramSchema.Format, StringComparison.OrdinalIgnoreCase)))
+                {
+                    paramSchema.Type = "file";
+                    paramSchema.Format = null;
+                }
+                yield return new OpenApiFormDataParameter
+                {
+                    Description = property.Value.Description,
+                    Name = property.Key,
+                    Schema = property.Value,
+                    Required = Content.First().Value.Schema.Required.Contains(property.Key) 
+                };
+            }
+        }
     }
 }