ASP.NET Core 9 and IAsyncEnumerable - Async Streaming JSON and NDJSON From Blazor WebAssembly

I've been exploring working with asynchronous streaming data sources over HTTP for quite some time on this blog. I've been playing with async streamed JSON and NDJSON. I've been streaming and receiving streams in ASP.NET Core and console applications. But there is one scenario I haven't touched yet - streaming from Blazor WebAssembly. Why? Simply it wasn't possible.

Streaming objects from Blazor WebAssembly requires two things. First is the support for streaming upload in browsers Fetch API. The Fetch API did support streams for response bodies for quite some time (my first post using it is from 2019) but non-experimental support for streams as request bodies come to Chrome, Edge, and Safari in 2022 (and it is yet to come to Firefox as far as I can tell). Still, it's been available for two years and I haven't explored it yet? Well, I did, more than a year ago, with NDJSON and pure Javascript, where I used the ASP.NET Core endpoint I created long ago. But here we are talking about Blazor WebAssembly, which brings us to the second requirement - the browser API needs to be surfaced in Blazor. This is finally happening with .NET 9 and now I can fully explore it.

Async Streaming NDJSON From Blazor WebAssembly

I've decided to start with NDJSON because I already have my own building blocks for it (that mentioned ASP.NET Core endpoint, and NdjsonAsyncEnumerableContent coming from one of my packages). If things wouldn't work I would be able to easily debug them.

I've quickly put together a typical code using HttpClient. I just had to make sure I've en