MapStaticAssets returns incorrect Content-Length for custom Range

[Kanawanagasaki]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

In Blazor projects, MapStaticAssets returns the full file size in the Content-Length header when a custom Range is requested, causing a mismatch between the Content-Length and Content-Range headers

Expected Behavior

Content-Length is equals to end - start + 1 where start and end are ranges from Content-Range response header

Steps To Reproduce

1. Create an empty blazor project

dotnet new blazor --empty

2. Add video file to wwwroot folder
3. Run application

dotnet run

4. Run curl command to fetch 100 bytes from application

curl -v -H "Range: bytes=0-99" http://localhost:5253/video.mp4 -o NIL

5. Observe a mismatch between Content-Length and Content-Range

* Host localhost:5253 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying [::1]:5253...
* Connected to localhost (::1) port 5253
* using HTTP/1.x
> GET /video.mp4 HTTP/1.1
> Host: localhost:5253
> User-Agent: curl/8.14.1
> Accept: */*
> Range: bytes=0-99
>
* Request completely sent off
< HTTP/1.1 206 Partial Content
< Content-Length: 95507362
< Content-Type: video/mp4
< Date: Mon, 18 Aug 2025 19:39:00 GMT
< Server: Kestrel
< Accept-Ranges: bytes
< Accept-Ranges: bytes
< Cache-Control: no-cache
< Content-Range: bytes 0-99/95507362
< ETag: "Ohy6wB7zeYQVaLxVqXJBsAx5fNPo8NWfrXhRmX8qH1M="
< Last-Modified: Mon, 26 Jun 2023 21:12:26 GMT
<
{ [16384 bytes data]
100 91.0M  100 91.0M    0     0   122M      0 --:--:-- --:--:-- --:--:--  123M
* Connection #0 to host localhost left intact

6. Stop application, open Components\Pages\Home.razor and add following text:

<video controls>
    <source src="/video.mp4" type="video/mp4">
</video>

7. Run application again

dotnet run

8. Open Home page in firefox and observe "No video with supported format and MIME type found." or in chrome and observe that the video does not load

Exceptions (if any)

No response

.NET Version

9.0.302

Anything else?

.NET SDK:
Version: 9.0.302
Commit: bb2550b9af
Workload version: 9.0.300-manifests.88387b28
MSBuild version: 17.14.13+65391c53b

Runtime Environment:
OS Name: Windows
OS Version: 10.0.26100
OS Platform: Windows
RID: win-x64
Base Path: C:\Program Files\dotnet\sdk\9.0.302\

.NET workloads installed:
[maccatalyst]
Installation Source: VS 17.14.36327.8
Manifest Version: 18.5.9214/9.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.maccatalyst\18.5.9214\WorkloadManifest.json
Install Type: Msi

[aspire]
Installation Source: VS 17.14.36327.8
Manifest Version: 8.2.2/8.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.aspire\8.2.2\WorkloadManifest.json
Install Type: Msi

[ios]
Installation Source: VS 17.14.36327.8
Manifest Version: 18.5.9214/9.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.ios\18.5.9214\WorkloadManifest.json
Install Type: Msi

[android]
Installation Source: VS 17.14.36327.8
Manifest Version: 35.0.78/9.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.android\35.0.78\WorkloadManifest.json
Install Type: Msi

[maui-windows]
Installation Source: VS 17.14.36327.8
Manifest Version: 9.0.51/9.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.maui\9.0.51\WorkloadManifest.json
Install Type: Msi

[wasm-tools]
Installation Source: VS 17.14.36327.8
Manifest Version: 9.0.7/9.0.100
Manifest Path: C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.workload.mono.toolchain.current\9.0.7\WorkloadManifest.json
Install Type: Msi

Configured to use loose manifests when installing new manifests.

Host:
Version: 9.0.7
Architecture: x64
Commit: 3c298d9f00

.NET SDKs installed:
8.0.119 [C:\Program Files\dotnet\sdk]
8.0.413 [C:\Program Files\dotnet\sdk]
9.0.302 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 3.1.27 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.32 [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 6.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.23 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.26 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.0-rc.1.22427.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.0-preview.7.23375.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.18 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.23 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.27 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.32 [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 6.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.5 [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 6.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.23 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.26 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.27 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.0-rc.1.22426.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.0-preview.7.23375.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.18 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.23 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.27 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.32 [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 6.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.5 [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 6.0.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.23 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.26 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.27 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.0-rc.1.22427.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.0-preview.7.23376.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.18 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 8.0.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 9.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
x86 [C:\Program Files (x86)\dotnet]
registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download

[MihuBot]

I'm a bot. Here is a possible related and/or duplicate issue (I may be wrong):

• Loading an mp4 video static asset in Blazor returns http 416 error #58829

[javiercn]

* IPv6: ::1
* IPv4: 127.0.0.1
*   Trying [::1]:5259...
* Connected to localhost (::1) port 5259
* using HTTP/1.x
> GET /lib/bootstrap/dist/css/bootstrap.min.46ein0sx1k.css HTTP/1.1
> Host: localhost:5259
> User-Agent: curl/8.14.1
> Accept: */*
> Range: bytes=0-99
>
< HTTP/1.1 206 Partial Content
< Content-Length: 100
< Content-Type: text/css
< Date: Fri, 05 Sep 2025 17:06:29 GMT
< Server: Kestrel
< Accept-Ranges: bytes
< Cache-Control: max-age=31536000, immutable
< Content-Range: bytes 0-99/232803
< ETag: "PI8n5gCcz9cQqQXm3PEtDuPG8qx9oFsFctPg0S5zb8g="
< Last-Modified: Fri, 05 Sep 2025 16:42:14 GMT
< Vary: Accept-Encoding
<
@charset "UTF-8";/*!
 * Bootstrap  v5.3.3 (https://getbootstrap.com/)
 * Copyright 2011-2024 The Boo* Connection #0 to host localhost left intact

This is caused by the RuntimeHandler https://github.com/dotnet/aspnetcore/blob/main/src/StaticAssets/src/Development/StaticAssetDevelopmentRuntimeHandler.cs#L159 which incorrectly reacts to Range Requests.

I validated that this is not a problem in non-development scenarios.

In development, ReloadStaticAssetsAtRuntime: false can be used to avoid in appSettings.json to disable hot reloading files at runtime, which is what is causing the problem.