C# Client Generation Fails to Use Multipart for File Uploads from python fastapi

What are you generating using Kiota, clients or plugins?

API Client/SDK

In what context or format are you using Kiota?

Windows executable

Client library/SDK language

Csharp .net8

Describe the bug

I am facing an issue while generating a C# client for my FastAPI application using Kiota. The API has an endpoint for file uploads, but the generated client does not utilize multipart/form-data, which is required for this operation.

The generated Client's method:

public async Task<UntypedNode?> PostAsync(Body_upload_file_uploadfile__post body, Action<RequestConfiguration<DefaultQueryParameters>>? requestConfiguration = default, CancellationToken cancellationToken = default)
{
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable restore
#else
    public async Task<UntypedNode> PostAsync(Body_upload_file_uploadfile__post body, Action<RequestConfiguration<DefaultQueryParameters>> requestConfiguration = default, CancellationToken cancellationToken = default)
    {
#endif
    _ = body ?? throw new ArgumentNullException(nameof(body));
    var requestInfo = ToPostRequestInformation(body, requestConfiguration);
    var errorMapping = new Dictionary<string, ParsableFactory<IParsable>>
    {
        { "422", HTTPValidationError.CreateFromDiscriminatorValue },
    };
    return await RequestAdapter.SendAsync<UntypedNode>(requestInfo, UntypedNode.CreateFromDiscriminatorValue, errorMapping, cancellationToken).ConfigureAwait(false);
}

/// <summary>
/// Upload File
/// </summary>
/// <returns>A <see cref="RequestInformation"/></returns>
/// <param name="body">The request body</param>
/// <param name="requestConfiguration">Configuration for the request such as headers, query parameters, and middleware options.</param>
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable enable
public RequestInformation ToPostRequestInformation(Body_upload_file_uploadfile__post body, Action<RequestConfiguration<DefaultQueryParameters>>? requestConfiguration = default)
{
#nullable restore
#else
public RequestInformation ToPostRequestInformation(Body_upload_file_uploadfile__post body, Action<RequestConfiguration<DefaultQueryParameters>> requestConfiguration = default)
{
#endif
    _ = body ?? throw new ArgumentNullException(nameof(body));
    var requestInfo = new RequestInformation(Method.POST, UrlTemplate, PathParameters);
    requestInfo.Configure(requestConfiguration);
    requestInfo.Headers.TryAdd("Accept", "application/json");
    requestInfo.SetContentFromParsable(RequestAdapter, "multipart/form-data", body);
    return requestInfo;
}

Generated model Body_upload_file_uploadfile__post.cs:

// <auto-generated/>
#pragma warning disable CS0618
using Microsoft.Kiota.Abstractions.Extensions;
using Microsoft.Kiota.Abstractions.Serialization;
using System.Collections.Generic;
using System;

[global::System.CodeDom.Compiler.GeneratedCode("Kiota", "1.18.0")]
#pragma warning disable CS1591
public partial class Body_upload_file_uploadfile__post : IAdditionalDataHolder, IParsable
#pragma warning restore CS1591
{
    /// <summary>Stores additional data not described in the OpenAPI description found when deserializing. Can be used for serialization as well.</summary>
    public IDictionary<string, object> AdditionalData { get; set; }

    /// <summary>The file property</summary>
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable enable
    public string? File { get; set; }
#nullable restore
#else
    public string File { get; set; }
#endif

    /// <summary>The language property</summary>
#if NETSTANDARD2_1_OR_GREATER || NETCOREAPP3_1_OR_GREATER
#nullable enable
    public string? Language { get; set; }
#nullable restore
#else
    public string Language { get; set; }
#endif

    /// <summary>
    /// Instantiates a new <see cref="Body_upload_file_uploadfile__post"/> and sets the default values.
    /// </summary>
    public Body_upload_file_uploadfile__post()
    {
        AdditionalData = new Dictionary<string, object>();
        Language = "En";
    }

    /// <summary>
    /// Creates a new instance of the appropriate class based on discriminator value
    /// </summary>
    /// <returns>A <see cref="Body_upload_file_uploadfile__post"/></returns>
    /// <param name="parseNode">The parse node to use to read the discriminator value and create the object</param>
    public static Body_upload_file_uploadfile__post CreateFromDiscriminatorValue(IParseNode parseNode)
    {
        _ = parseNode ?? throw new ArgumentNullException(nameof(parseNode));
        return new Body_upload_file_uploadfile__post();
    }

    /// <summary>
    /// The deserialization information for the current model
    /// </summary>
    /// <returns>A IDictionary&lt;string, Action&lt;IParseNode&gt;&gt;</returns>
    public virtual IDictionary<string, Action<IParseNode>> GetFieldDeserializers()
    {
        return new Dictionary<string, Action<IParseNode>>
        {
            { "file", n => { File = n.GetStringValue(); } },
            { "language", n => { Language = n.GetStringValue(); } },
        };
    }

    /// <summary>
    /// Serializes information the current object
    /// </summary>
    /// <param name="writer">Serialization writer to use to serialize this model</param>
    public virtual void Serialize(ISerializationWriter writer)
    {
        _ = writer ?? throw new ArgumentNullException(nameof(writer));
        writer.WriteStringValue("file", File);
        writer.WriteStringValue("language", Language);
        writer.WriteAdditionalData(AdditionalData);
    }
}
#pragma warning restore CS0618

Expected behavior

The generated client should properly handle multipart/form-data for file uploads in accordance with the OpenAPI specification. Kiota should generate a method with MultipartBody like this:

public async Task<?> PostAsync(MultipartBody body, Action<RequestBuilderPostRequestConfiguration>? requestConfiguration = default, CancellationToken cancellationToken = default)

How to reproduce

Here’s the relevant code snippet for my FastAPI application:

main.py :

from fastapi import FastAPI, File, UploadFile, Form
from fastapi.responses import HTMLResponse

app = FastAPI()
app.openapi_version = "3.0.2"
@app.get("/", response_class=HTMLResponse)
async def main():
    content = """
    <form action="/uploadfile/" enctype="multipart/form-data" method="post">
    <input name="file" type="file">
    <button type="submit">Upload</button>
    </form>
    """
    return HTMLResponse(content=content)

@app.post("/uploadfile/")
async def upload_file(
    file: UploadFile = File(...),
    language: str = Form(default="En")
):
    return {"filename": file.filename}

requirements.txt

fastapi==0.112.4
python-multipart==0.0.12
uvicorn==0.30.6

Open API description file

{
    "openapi": "3.0.2",
    "info": {
        "title": "FastAPI",
        "version": "0.1.0"
    },
    "paths": {
        "/": {
            "get": {
                "summary": "Main",
                "operationId": "main__get",
                "responses": {
                    "200": {
                        "description": "Successful Response",
                        "content": {
                            "text/html": {
                                "schema": {
                                    "type": "string"
                                }
                            }
                        }
                    }
                }
            }
        },
        "/uploadfile/": {
            "post": {
                "summary": "Upload File",
                "operationId": "upload_file_uploadfile__post",
                "requestBody": {
                    "content": {
                        "multipart/form-data": {
                            "schema": {
                                "$ref": "#/components/schemas/Body_upload_file_uploadfile__post"
                            }
                        }
                    },
                    "required": true
                },
                "responses": {
                    "200": {
                        "description": "Successful Response",
                        "content": {
                            "application/json": {
                                "schema": {}
                            }
                        }
                    },
                    "422": {
                        "description": "Validation Error",
                        "content": {
                            "application/json": {
                                "schema": {
                                    "$ref": "#/components/schemas/HTTPValidationError"
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "components": {
        "schemas": {
            "Body_upload_file_uploadfile__post": {
                "properties": {
                    "file": {
                        "type": "string",
                        "format": "binary",
                        "title": "File"
                    },
                    "language": {
                        "type": "string",
                        "title": "Language",
                        "default": "En"
                    }
                },
                "type": "object",
                "required": [
                    "file"
                ],
                "title": "Body_upload_file_uploadfile__post"
            },
            "HTTPValidationError": {
                "properties": {
                    "detail": {
                        "items": {
                            "$ref": "#/components/schemas/ValidationError"
                        },
                        "type": "array",
                        "title": "Detail"
                    }
                },
                "type": "object",
                "title": "HTTPValidationError"
            },
            "ValidationError": {
                "properties": {
                    "loc": {
                        "items": {
                            "anyOf": [
                                {
                                    "type": "string"
                                },
                                {
                                    "type": "integer"
                                }
                            ]
                        },
                        "type": "array",
                        "title": "Location"
                    },
                    "msg": {
                        "type": "string",
                        "title": "Message"
                    },
                    "type": {
                        "type": "string",
                        "title": "Error Type"
                    }
                },
                "type": "object",
                "required": [
                    "loc",
                    "msg",
                    "type"
                ],
                "title": "ValidationError"
            }
        }
    }
}

Kiota Version

1.18.0+5c6b5d0ef23865ba2f9d9f0b9fe4b944cf26b1ec

Latest Kiota version known to work for scenario above?(Not required)

No response

Known Workarounds

No response

Configuration

No response

Debug output

Click to expand log

``` ```

Other information

No response

microsoft / kiota