[Blazor] HttpPost with StreamContent reads whole file into memory

[mrpmorris]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When using StreamContent with HttpClient.PostAsync in Blazor WASM, the whole file is loaded into memory before initiating the HTTP call

Expected Behavior

The HTTP call should be made immediately, and the data in the stream should be read in chunks.

Steps To Reproduce

1: Create a hosted Blazor WASM app
2: Add the following to WeatherForecast controller

        [HttpPost]
        [RequestFormLimits(MultipartBodyLengthLimit = long.MaxValue)]
        [RequestSizeLimit(long.MaxValue)]
        public IActionResult Upload()
        {
            Console.Beep();
            IFormFile file = Request.Form.Files[0];
            if (file.Length == 0)
                return BadRequest();
            Console.Beep();
            return Ok();
        }

Now try running the following code in both a console app with FileStream as the source for StreamContent, and then inside a Blazor WASM app with IBrowserFile.Open.OpenReadStream as the source

// Console
// using var theSourceStream = new FileStream("c:\\temp\\500MB.zip", FileMode.Open);

// WASM
// var theSourceStream = SomeIBrowserFile.OpenReadStream(long.MaxValue);

var streamContent = new StreamContent(theSourceStream, 4069);
httpContent.Add(streamContent, name: "file", fileName: "somefile.bin");

HttpResponseMessage response = await httpClient.PostAsync("https://localhost:7057/weatherforecast", httpContent);
response.EnsureSuccessStatusCode();

Results

Console app

1. HttpClient.PostAsync is called
2. Transfer starts
3. Server beeps to indicate start of controller code
4. Data continues to transfer until end (e.g. 10 seconds)
5. Server beeps to indicate end of controller code
6. The end

Blazor WASM

1. HttpClient.PoastAsync is called
2. Whole file contents are (very slowly) loaded into memory
3. Transfer starts
4. Server beeps to indicate start of controller code
5. Data continues to transfer until end (e.g. 10 seconds)
6. Server beeps to indicate end of controller code
7. The end

Exceptions (if any)

No response

.NET Version

6.0.303

Anything else?

WASM

dotnet --info

.NET SDK (reflecting any global.json):
Version: 6.0.303
Commit: 7494fee64a

Runtime Environment:
OS Name: Windows
OS Version: 10.0.19044
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\6.0.303\

global.json file:
Not found

Host:
Version: 6.0.8
Architecture: x64
Commit: 55fb7ef977

.NET SDKs installed:
3.1.422 [C:\Program Files\dotnet\sdk]
6.0.202 [C:\Program Files\dotnet\sdk]
6.0.303 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.All 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.28 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[campersau]

Related: dotnet/runtime#36634

[javiercn]

@mrpmorris thanks for contacting us.

Unfortunately, fetch does not support HTTP request body streaming (only supported in Chrome for the time being) so the client needs to buffer. Lets use dotnet/runtime#36634 to track it.

[davidfowl]

Fetch sucks 😢. I've been lobbying the w3c to add this for ages (for different reasons).

[mrpmorris]

Fetch sucks 😢. I've been lobbying the w3c to add this for ages (for different reasons).

Is there a good reason to use fetch instead of XMLHttpRequest?

[javiercn]

@mrpmorris you can't stream the request with XMLHttpRequest either. It's not a problem with the API but a missing capability in the browser.

[davidfowl]

whatwg/fetch#1438

[mrpmorris]

@javiercn XMLHttpRequest does stream it. I just uploaded a 1GB file without the memory usage going through the roof.

https://twitter.com/MrPeterLMorris/status/1561650669584621568?s=20&t=svki19salJp9qnOvc_So9A