Some errors "Failed to load resource: the server responded with a status of 404 (Not Found)" appear in the browser console panel when updating the Counter file of 11.0 Blazor Web for WASM App and then run without build

[EmilyFeng97]

REGRESSION INFO Works well on 10.0 and previous build 11.0.100-preview.1.26071.101

INSTALL STEPS

1. Clean Win11 x64 23h2 ENU
2. Install the .NET 11.0 preview 1 SDK from corohot build
3. Add feed

Platform

• Windows
• macOS
• Linux

Repro Steps

1. Open a normal Command Prompt
2. Create a Blazor Web App for WASM project

   dotnet new blazor -int WebAssembly -o MyBlazorWASMApp
   cd MyBlazorWASMApp
   

3. Build the project using dotnet build
4. Open MyBlazorWASMApp.Client\Pages\Counter.razor in notepad and update with following content:

   @code {
       int currentCount = 0;
   
       [Parameter]
       public int IncrementAmount { get; set; } = 1;
   
       void IncrementCount()
       {
           currentCount+=IncrementAmount;
       }
   }
   

5. Run the project using dotnet run
6. Navigate to the "Counter" page in the browser

Note:

1. This issue does not repro if I rebuild the project after updating the code in the Counter.razor file.
2. This issue does not repro on Blazor web server project.
3. If I try to add <p>New changes</p> in Counter.razor file, will meet issue https://github.com/dotnet/AspNetCore-ManualTests/issues/3152

Actual Result

Error Log

_framework/BlazorAuto.Client.lwytxz2dwg.pdb:1   Failed to load resource: the server responded with a status of 404 (Not Found)
counter:1  Failed to find a valid digest in the 'integrity' attribute for resource 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' with computed SHA-256 integrity 'gz5sb6R6HVnpwimWUeos+YZtyruSPoW+e1c4HQKQwBs='. The resource has been blocked.
counter:1  Fetch API cannot load http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb. SRI's integrity checks failed.
blazor.web.e6dv2k50rl.js:1  Error in mono_download_assets: Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
No @ blazor.web.e6dv2k50rl.js:1
blazor.web.e6dv2k50rl.js:1  Error in mono_download_assets: Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
No @ blazor.web.e6dv2k50rl.js:1
dotnet.9go4sbqo7h.js:4  Uncaught (in promise) TypeError: Failed to fetch. SRI's integrity checks failed.
    at Object.M [as fetch_like] (dotnet.9go4sbqo7h.js:4:4729)
    at dotnet.9go4sbqo7h.js:4:14189
    at ue (dotnet.9go4sbqo7h.js:4:14205)
    at dotnet.9go4sbqo7h.js:4:12549
    at se (dotnet.9go4sbqo7h.js:4:13021)
    at re (dotnet.9go4sbqo7h.js:4:10941)
    at o (dotnet.9go4sbqo7h.js:4:6964)
    at te (dotnet.9go4sbqo7h.js:4:6990)
    at dotnet.9go4sbqo7h.js:4:31594
dotnet.9go4sbqo7h.js:4  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
dotnet.9go4sbqo7h.js:4  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
counter:1  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
startup.ts:338  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
counter:1  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
blazor.web.e6dv2k50rl.js:1  Uncaught (in promise) Error: Failed to start platform. Reason: Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
    at ri (blazor.web.e6dv2k50rl.js:1:186766)
blazor.web.e6dv2k50rl.js:1  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.lwytxz2dwg.pdb' for BlazorAuto.Client.lwytxz2dwg.pdb failed 0 TypeError: Failed to fetch
_framework/BlazorAuto.Client.y861nlbcob.wasm:1   Failed to load resource: the server responded with a status of 404 (Not Found)
counter:1  Failed to find a valid digest in the 'integrity' attribute for resource 'http://localhost:5018/_framework/BlazorAuto.Client.y861nlbcob.wasm' with computed SHA-256 integrity 'gz5sb6R6HVnpwimWUeos+YZtyruSPoW+e1c4HQKQwBs='. The resource has been blocked.
counter:1  Fetch API cannot load http://localhost:5018/_framework/BlazorAuto.Client.y861nlbcob.wasm. SRI's integrity checks failed.
blazor.web.e6dv2k50rl.js:1  Error in mono_download_assets: Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.y861nlbcob.wasm' for BlazorAuto.Client.y861nlbcob.wasm failed 0 TypeError: Failed to fetch
No @ blazor.web.e6dv2k50rl.js:1
dotnet.9go4sbqo7h.js:4  Uncaught (in promise) TypeError: Failed to fetch. SRI's integrity checks failed.
    at Object.M [as fetch_like] (dotnet.9go4sbqo7h.js:4:4729)
    at dotnet.9go4sbqo7h.js:4:14189
    at ue (dotnet.9go4sbqo7h.js:4:14205)
    at dotnet.9go4sbqo7h.js:4:12549
    at se (dotnet.9go4sbqo7h.js:4:13021)
    at re (dotnet.9go4sbqo7h.js:4:10941)
    at o (dotnet.9go4sbqo7h.js:4:6964)
    at te (dotnet.9go4sbqo7h.js:4:7014)
    at dotnet.9go4sbqo7h.js:4:31594
counter:1  Uncaught (in promise) Error: download 'http://localhost:5018/_framework/BlazorAuto.Client.y861nlbcob.wasm' for BlazorAuto.Client.y861nlbcob.wasm failed 0 TypeError: Failed to fetch
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[oroztocil]

@EmilyFeng97 Thanks for the report. We should investigate this together with https://github.com/dotnet/AspNetCore-ManualTests/issues/3152

[lewing]

Root Cause Analysis

I was able to reproduce this issue with SDK 11.0.100-preview.1.26078.121 using Playwright to verify the browser errors.

Summary

The issue is that dotnet.js contains embedded references to fingerprinted assembly files (e.g., BlazorRepro.Client.l3j91j9hxg.wasm), but when the client assembly is recompiled with a new fingerprint, the dotnet.js fingerprint is not recomputed even though its content changed.

Detailed Flow

1. Initial dotnet build:

   • Client assembly compiled → fingerprint l3j91j9hxg
   • dotnet.js generated with embedded reference: BlazorRepro.Client.l3j91j9hxg.wasm
   • dotnet.js gets fingerprint kebya7y6lx → served as dotnet.kebya7y6lx.js

2. Modify Counter.razor, then dotnet run (implicit build):

   • Client assembly recompiled → NEW fingerprint i46og7bz9c
   • Local dotnet.js file IS regenerated with correct reference: BlazorRepro.Client.i46og7bz9c.wasm ✓
   • BUT the fingerprint for dotnet.js remains kebya7y6lx (stale)
   • Server continues to serve the OLD dotnet.kebya7y6lx.js with stale embedded references

3. At runtime:

   • Browser loads dotnet.kebya7y6lx.js (stale content)
   • Tries to fetch BlazorRepro.Client.l3j91j9hxg.wasm which no longer exists → 404
   • SRI integrity check fails

Evidence

# Actual file on disk (CORRECT):
Local dotnet.js references: BlazorRepro.Client.i46og7bz9c.wasm

# What server serves via fingerprinted URL (STALE):
dotnet.kebya7y6lx.js references: BlazorRepro.Client.l3j91j9hxg.wasm

Likely Location of Bug

The fingerprint for dotnet.js is computed without considering that its content includes references to other fingerprinted files. When those referenced files change fingerprints, dotnet.js content changes, but the static web assets fingerprinting pipeline doesn't detect this as a content change.

This is likely in the WebAssembly SDK targets in dotnet/runtime that generate the boot config and embed asset references into dotnet.js, or in the StaticWebAssets fingerprinting logic in dotnet/sdk.

Potentially related PRs:

• [browser] Bundler friendly output runtime#116300 - Bundler friendly boot config (changed how asset references are embedded)
• [browser] Generate boot config with hash field instead of integrity runtime#122353 - Fix for boot config hash field

[lewing]

Root Cause Found - Target Ordering Issue

After analyzing MSBuild binlogs, I've identified the exact root cause:

The Problem

During incremental builds, there's a target ordering issue where the compression task runs BEFORE the updated dotnet.js is copied to wwwroot:

Target ID	Target Name	What it does
222	_GenerateBuildWasmBootJson	Creates obj\Debug\net11.0\dotnet.js with NEW fingerprints
228	GenerateBuildCompressedStaticWebAssets	Compresses wwwroot_framework\dotnet.js (still OLD)
237	_BuildStaticWebAssetsPreserveNewest	Copies obj\dotnet.js to wwwroot\dotnet.js (too late!)

Result

• dotnet.js (uncompressed) has correct fingerprints ✅
• dotnet.js.gz (compressed) has stale fingerprints from previous build ❌

When browsers request with Accept-Encoding: gzip, they get the stale .gz file which references old fingerprinted assets → 404 errors.

Evidence from binlog

\
Compressing 'C:...\wwwroot_framework\dotnet.js' because compressed file '...\compressed\l3uzavl18l-{0}-nao1fxyr6k-nao1fxyr6k.gz' does not exist.
\\

The compression task reads from wwwroot_framework\dotnet.js, but at that point the file still has old content. The new content is in obj\Debug\net11.0\dotnet.js but hasn't been copied yet.

Likely Fix

The GenerateBuildCompressedStaticWebAssets target should either:

1. Depend on _BuildStaticWebAssetsPreserveNewest to ensure files are copied first, OR
2. Read from obj\ source files instead of wwwroot\ destination files

Repro Details

• SDK: 11.0.100-preview.1.26078.121
• Hot Reload: Disabled (--no-hot-reload)
• Browser cache: Disabled