MultipartReader failed with IOException

[kchan-hdr]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

MultipartReader failed with IOException from a Controller Action with DI

Expected Behavior

Expect MultipartReader to be successful irrespective of the enclosing Controller or Endpoint. Or warnings in documentation.

Steps To Reproduce

https://github.com/dotnet/AspNetCore.Docs/tree/main/aspnetcore/mvc/models/file-uploads/samples/9.x

We cloned the file-uploads sample. And updated the FileController. The original UploadMultipartReader works perfectly. However, failed with the IOException when an additional service. The ILogger is only an example here (any service would trip it.) We could switch to constructor injection and that works fine.

    [HttpPost]
    [Route("multipart_bad")]
    public async Task<IActionResult> UploadMultipartReader_Bad([FromServices] ILogger<FileController> lx)
    {
        lx.LogCritical("in multipart bad");

        if (!Request.ContentType?.StartsWith("multipart/form-data") ?? true)
        {
            return BadRequest("The request does not contain valid multipart form data.");
        }

        var boundary = HeaderUtilities.RemoveQuotes(MediaTypeHeaderValue.Parse(Request.ContentType).Boundary).Value;
        if (string.IsNullOrWhiteSpace(boundary))
        {
            return BadRequest("Missing boundary in multipart form data.");
        }

        var cancellationToken = HttpContext.RequestAborted;
        var filePath = await _fileManager.SaveViaMultipartReaderAsync(boundary, Request.Body, cancellationToken);
        return Ok("Saved file at " + filePath);
    }

Exceptions (if any)

FileManagerSample.Controllers.FileController[0]
in multipart bad
fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
System.IO.IOException: Unexpected end of Stream, the content may have already been read by another component.

.NET Version

9.0.304

Anything else?

No response

[BrennanConroy]

The docs could probably be more explicit here. If you read the upload section, where I assume you got the sample code, the second half talks about disabling MVCs model binding for form data. Specifically, the DisableFormValueModelBindingAttribute part.

This is because as soon as an MVC action has a parameter, model binding kicks in and MVC auto-reads/parses the form data. Then when your app code tries to also read the form, there is no more data because MVC already consumed it.

[danmoseley]

Closing as answered,