Hi ASP.NET Core team,

Scenario:

I need to accept very large JSON arrays. To avoid buffering the whole payload I read HttpRequest.Body directly and stream‐deserialize with JsonSerializer.DeserializeAsyncEnumerable<Data>().

That (hopefully) keeps memory usage low, but because the action has no [FromBody] parameter, the OpenAPI shows an empty request body.

 [HttpPost]
 [EndpointSummary("...")]
 [EndpointDescription("...")]
 [ProducesResponseType(StatusCodes.Status200OK, Type = typeof(int))]
 [ProducesResponseType(StatusCodes.Status401Unauthorized, Type = typeof(string))]
 [ProducesResponseType(StatusCodes.Status400BadRequest, Type = typeof(string))]
 public async Task<ActionResult<int>> Post(CancellationToken cancellationToken)
 {
 var processedCount = 0;
 var jsonOptions = new JsonSerializerOptions
 {
 PropertyNameCaseInsensitive = true,
 };
 try
 {
 // The array can be a VERY LARGE array.
 await foreach (var data in JsonSerializer.DeserializeAsyncEnumerable<Data>(Request.Body, jsonOptions, cancellationToken))
 {
 if (data == null)
 {
 continue;
 }
 // send data to SQS / background worker here
 processedCount++;
 }
 return processedCount;
 }
 catch
 {
 return BadRequest("Invalid request body");
 }
 }

Questions

1. How do I decorate the action so that OpenAPI documentation shows "array of Data in the request body" even though I’m reading Request.Body myself? (Is there an side-effect free attribute that you recommend? As far as my understanding if I use [FromBody] it will buffer and deserialize the content of the JSON into memory)

2. Is manual streaming still the right approach, or can MVC now bind directly to IAsyncEnumerable?

public async Task<ActionResult<int>> Post([FromBody] IAsyncEnumerable<Data> items, CancellationToken ct)

If this is (or will soon be) supported?

3. Any gotchas when using the manual Request.Body approach?

Related issues:

• Make SystemTextJsonInputFormatter IAsyncEnumerable aware #43489
• Support binding request body as Stream in Controller Actions #41540
• https://learn.microsoft.com/en-us/dotnet/core/compatibility/aspnet-core/6.0/iasyncenumerable-not-buffered-by-mvc (but for output, not input)

Any guidance or pointers to docs would be greatly appreciated.

Thanks for your time and for all the great work on ASP.NET Core!