[browser][wasm] Fix buffered symbol asset loading by elringus · Pull Request #127087 · dotnet/runtime

elringus · 2026-04-17T17:42:35Z

This fixes SymbolsAsset.buffer handling in the browser runtime and adds a WBT regression test for buffered runtime assets:

Fixed the browser loader so symbols assets supplied via buffer are handled correctly, instead of effectively requiring pendingDownload
Kept the symbols path working with the existing text-based symbol map loading flow
Added BufferedAssetsTest to WasmBasicTestApp that supplies these runtime assets via buffer:
- dotnetwasm
- assemblies
- pdbs
- symbols
Added a matching ModuleConfigTests.BufferedAssetsTest integration test

The issue was discussed with @pavelsavara on .NET's Discord server.

Note: I was not able to run the browser test end-to-end in the local environment due local WBT/workload packaging setup issues. If anything fails on CI, I’ll follow up and fix the remaining issues there.

Copilot

Pull request overview

Fixes buffered symbols runtime asset loading in the browser WASM loader, and adds a regression scenario in WBT to exercise supplying runtime assets via asset.buffer.

Changes:

Adjusted asset instantiation flow to correctly handle symbols assets when provided via buffer (and enabled buffered-response .text() decoding).
Added a BufferedAssetsTest scenario to WasmBasicTestApp that assigns buffer for wasm/assemblies/pdbs/symbols during onConfigLoaded.
Added a matching ModuleConfigTests.BufferedAssetsTest publish-and-run integration test.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/main.js	Adds the `BufferedAssetsTest` scenario that supplies runtime assets via `asset.buffer`.
src/mono/wasm/Wasm.Build.Tests/ModuleConfigTests.cs	Adds an integration test that publishes and runs the new scenario (with symbol map emission enabled).
src/mono/browser/runtime/loader/assets.ts	Fixes loader handling for buffered `symbols` assets and implements `.text()` for buffered-response shim.

elringus · 2026-04-17T22:50:19Z

It seems the fingerprint stuff doesn't support file names with hashes. Is it somehow possible to generate the symbols file without the hash? Or maybe I should also patch the fingerprint resolver to ignore the hash on symbols?

Found unknown files in C:\helix\work\workitem\e\wbt artifacts\ModuleConfigTests_BufferedAssetsTest_Debug_False_0zxtutco_2je_鿀蜒枛遫䡫煉\App\bin\Debug\net11.0\publish\wwwroot_framework:
dotnet.native.8o3vuf3rfy.js.symbols
Add these to GetAllKnownDotnetFilesToFingerprintMap method

dotnet-policy-service · 2026-04-18T14:55:37Z

Tagging subscribers to 'arch-wasm': @lewing, @pavelsavara
See info in area-owners.md if you want to be subscribed.

pavelsavara · 2026-04-20T06:11:25Z

Log

Wasm.Build.Tests.ModuleConfigTests.BufferedAssetsTest [FAIL]
      Found unknown files in /root/helix/work/workitem/e/wbt artifacts/ModuleConfigTests_BufferedAssetsTest_Debug_False_zwqmgjzy_he5_鿀蜒枛遫䡫煉/App/bin/Debug/net11.0/publish/wwwroot/_framework:
          dotnet.native.gkigrwomkb.js.symbols
      Add these to GetAllKnownDotnetFilesToFingerprintMap method
      Expected dotnet.js
        dotnet.native.js
        dotnet.native.wasm
        dotnet.runtime.js
      Options AssertBundleOptions { Configuration = Debug, BuildOptions = PublishOptions { IsPublish = True, TargetFramework = net11.0, AOT = False, ExpectedFileType = FromRuntimePack, GlobalizationMode = Sharded, CustomIcuFile = , UseCache = True, ExpectSuccess = True, AssertAppBundle = True, Label = , WarnAsError = True, RuntimeType = SingleThreaded, ExtraBuildEnvironmentVariables = System.Collections.Generic.Dictionary`2[System.String,System.String], NonDefaultFrameworkDir = , ExtraMSBuildArgs = -p:CompressionEnabled=false -p:WasmEnableHotReload=false, EnableDiagnostics = False, BuildOnlyAfterPublish = True, ExpectRelinkDirWhenPublishing = False }, ExpectedFileType = FromRuntimePack, BinFrameworkDir = /root/helix/work/workitem/e/wbt artifacts/ModuleConfigTests_BufferedAssetsTest_Debug_False_zwqmgjzy_he5_鿀蜒枛遫䡫煉/App/bin/Debug/net11.0/publish/wwwroot/_framework, ExpectSymbolsFile = True, AssertIcuAssets = True, AssertSymbolsFile = False, ExpectDotnetJsFingerprinting =  } 
      
      Stack Trace:
        /_/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs(165,0): at Wasm.Build.Tests.ProjectProviderBase.FindAndAssertDotnetFiles(String binFrameworkDir, AssertBundleOptions assertOptions, IReadOnlyDictionary`2 superSet, IReadOnlySet`1 expected)
        /_/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs(83,0): at Wasm.Build.Tests.ProjectProviderBase.FindAndAssertDotnetFiles(AssertBundleOptions assertOptions)
        /_/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs(49,0): at Wasm.Build.Tests.ProjectProviderBase.AssertBasicBundle(AssertBundleOptions assertOptions)
        /_/src/mono/wasm/Wasm.Build.Tests/WasmSdkBasedProjectProvider.cs(111,0): at Wasm.Build.Tests.WasmSdkBasedProjectProvider.AssertBundle(AssertBundleOptions assertOptions)
        /_/src/mono/wasm/Wasm.Build.Tests/WasmSdkBasedProjectProvider.cs(97,0): at Wasm.Build.Tests.WasmSdkBasedProjectProvider.AssertBundle(Configuration config, MSBuildOptions buildOptions, Boolean isUsingWorkloads, Nullable`1 isNativeBuild, Nullable`1 wasmFingerprintDotnetJs)
        /_/src/mono/wasm/Wasm.Build.Tests/WasmSdkBasedProjectProvider.cs(181,0): at Wasm.Build.Tests.WasmSdkBasedProjectProvider.AssertWasmSdkBundle(Configuration config, MSBuildOptions buildOptions, Boolean isUsingWorkloads, Nullable`1 isNativeBuild, Nullable`1 wasmFingerprintDotnetJs, String buildOutput)
        /_/src/mono/wasm/Wasm.Build.Tests/Templates/WasmTemplateTestsBase.cs(265,0): at Wasm.Build.Tests.WasmTemplateTestsBase.BuildProjectCore(ProjectInfo info, Configuration configuration, MSBuildOptions buildOptions, Nullable`1 isNativeBuild, Nullable`1 wasmFingerprintDotnetJs)
        /_/src/mono/wasm/Wasm.Build.Tests/Templates/WasmTemplateTestsBase.cs(181,0): at Wasm.Build.Tests.WasmTemplateTestsBase.PublishProject(ProjectInfo info, Configuration configuration, Nullable`1 isNativeBuild, Nullable`1 wasmFingerprintDotnetJs)
        /_/src/mono/wasm/Wasm.Build.Tests/ModuleConfigTests.cs(108,0): at Wasm.Build.Tests.ModuleConfigTests.BufferedAssetsTest()
        --- End of stack trace from previous location ---

Log

 Wasm.Build.Tests.ModuleConfigTests.BufferedAssetsTest [FAIL]
      System.Exception : Expected exit code 0 but got 1.
      consoleOutput=Failed to load resource: the server responded with a status of 404 (Not Found)
      Failed to load resource: the server responded with a status of 404 (Not Found)
      MONO_WASM: onConfigLoaded() failed TypeError: config.resources.corePdb is not iterable
      MONO_WASM: Failed to initialize config TypeError: config.resources.corePdb is not iterable TypeError: config.resources.corePdb is not iterable
          at Object.onConfigLoaded (http://127.0.0.1:41655/main.js:603:21)
          at xe (http://127.0.0.1:41655/main.js:136:20568)
          at async http://127.0.0.1:41655/main.js:136:29683
          at async http://127.0.0.1:41655/main.js:136:34856
          at async Object.create (http://127.0.0.1:41655/main.js:136:34826)
          at async http://127.0.0.1:41655/main.js:616:70
      Error: Failed to initialize config TypeError: config.resources.corePdb is not iterable TypeError: config.resources.corePdb is not iterable
          at Object.onConfigLoaded (http://127.0.0.1:41655/main.js:603:21)
          at xe (http://127.0.0.1:41655/main.js:136:20568)
          at async http://127.0.0.1:41655/main.js:136:29683
          at async http://127.0.0.1:41655/main.js:136:34856
          at async Object.create (http://127.0.0.1:41655/main.js:136:34826)
          at async http://127.0.0.1:41655/main.js:616:70
          at xe (http://127.0.0.1:41655/main.js:136:20880)
          at async http://127.0.0.1:41655/main.js:136:29683
          at async http://127.0.0.1:41655/main.js:136:34856
          at async Object.create (http://127.0.0.1:41655/main.js:136:34826)
          at async http://127.0.0.1:41655/main.js:616:70
      WASM EXIT 1

pavelsavara · 2026-04-21T10:23:45Z

Log

dotnet.runtime.y92zvik3q0.js }
    Wasm.Build.Tests.ModuleConfigTests.BufferedAssetsTest [FAIL]
      Found unknown files in /root/helix/work/workitem/e/wbt artifacts/ModuleConfigTests_BufferedAssetsTest_Debug_False_j4harjjp_1r1_鿀蜒枛遫䡫煉/App/bin/Debug/net11.0/publish/wwwroot/_framework:
          dotnet.native.gkigrwomkb.js.symbols
      Add these to GetAllKnownDotnetFilesToFingerprintMap method
      Expected dotnet.js
        dotnet.native.js
        dotnet.native.wasm
        dotnet.runtime.js

elringus · 2026-04-21T11:09:58Z

dotnet.native.gkigrwomkb.js.symbols

The thing is, dotnet.native.js.symbols already exists under GetAllKnownDotnetFilesToFingerprintMap. But it doesn't seem to support hashes.

runtime/src/mono/wasm/Wasm.Build.Tests/WasmSdkBasedProjectProvider.cs

Lines 28 to 48 in 6f2ad2d

    
           protected override IReadOnlyDictionary<string, bool> GetAllKnownDotnetFilesToFingerprintMap(AssertBundleOptions assertOptions) 
        
           { 
        
               var result = new SortedDictionary<string, bool>() 
        
               { 
        
                   { "dotnet.js", true }, 
        
                   { "dotnet.js.map", false }, 
        
                   { "dotnet.native.js", true }, 
        
                   { "dotnet.native.js.symbols", true }, 
        
                   { "dotnet.native.wasm", true }, 
        
                   { "dotnet.native.worker.mjs", true }, 
        
                   { "dotnet.runtime.js", true }, 
        
                   { "dotnet.runtime.js.map", false }, 
        
                   { "dotnet.diagnostics.js", true }, 
        
                   { "dotnet.diagnostics.js.map", false }, 
        
               }; 
        
               if (assertOptions.ExpectDotnetJsFingerprinting == false) 
        
                   result["dotnet.js"] = false; 
        
               return result; 
        
           }

maraf · 2026-04-22T09:48:07Z

I think the logic that asserts the files incorrectly finds where the fingerprint should be, see https://github.com/elringus/dotnet/blob/fix/symbols-buffer/src/mono/wasm/Wasm.Build.Tests/ProjectProviderBase.cs#L116 (dotnet.native.{FP}.js.symbols vs dotnet.native.js.{FP}.symbols)

elringus · 2026-04-26T19:01:57Z

Would it be ok to add a special case for .js.symbols in FindAndAssertDotnetFiles?

pavelsavara · 2026-05-25T08:31:44Z

Would it be ok to add a special case for .js.symbols in FindAndAssertDotnetFiles?

@maraf is that what you mean ?

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

maraf · 2026-06-08T13:10:50Z

Would it be ok to add a special case for .js.symbols in FindAndAssertDotnetFiles?

@elringus I'm sorry for late reply. Yes, we can add a special case for .js.symbols

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

src/mono/browser/runtime/loader/assets.ts:1

TextDecoder is constructed on every json()/text() call. While likely not hot, it’s avoidable overhead and easy to fix by reusing a single TextDecoder instance within the closure (or higher scope) and calling decoder.decode(buffer) in both methods.

// Licensed to the .NET Foundation under one or more agreements.

elringus · 2026-06-08T13:56:40Z

+        const originalFetch4 = globalThis.fetch.bind(globalThis);
+        dotnet.withModuleConfig({
+            onConfigLoaded: (config) => {
+                const bufferedAssets = [
+                    ...config.resources.wasmNative,
+                    ...config.resources.assembly,
+                    ...config.resources.pdb,
+                    ...config.resources.wasmSymbols,
+                ];


It's controlled by the test fixtures — nothing can be missing here.

elringus · 2026-06-08T13:59:28Z

+                for (const asset of bufferedAssets) {
+                    const url = new URL(`./_framework/${asset.name}`, location.href);
+                    asset.buffer = originalFetch4(url).then(r => r.arrayBuffer());
+                }


elringus · 2026-06-08T13:54:58Z

        dotnet.withApplicationArgumentsFromQuery();
        break;
+    case "BufferedAssetsTest":
+        const originalFetch4 = globalThis.fetch.bind(globalThis);


The name is following the established pattern in the file. Changing the pattern is out of scope of this PR.

elringus · 2026-06-08T13:55:52Z

I've renamed the conflicting fetch variable and added support for fingerprinting the symbols file.

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

elringus · 2026-06-08T14:04:44Z

+                const bufferedAssets = [
+                    ...config.resources.wasmNative,
+                    ...config.resources.assembly,
+                    ...config.resources.pdb,
+                    ...config.resources.wasmSymbols,
+                ];


Already commented above.

elringus · 2026-06-08T14:05:33Z

+            const headersOnly = skipBufferByAssetTypes[asset.behavior];
+
+            if (headersOnly) {
+                if (asset.behavior === "symbols") {
+                    await runtimeHelpers.instantiate_symbols_asset(asset);
+                    cleanupAsset(asset);
+                }
+                ++loaderHelpers.actual_downloaded_assets_count;
+                return;
+            }


Out of scope for this PR.

elringus · 2026-06-08T14:05:36Z

-                text: () => {
-                    throw new Error("NotImplementedException");
-                },
+                text: () => new TextDecoder("utf-8").decode(buffer),


Out of scope for this PR.

fix symbols buffer

f3053fd

elringus requested review from ilonatommy, lewing and maraf as code owners April 17, 2026 17:42

Copilot AI review requested due to automatic review settings April 17, 2026 17:42

elringus requested a review from pavelsavara as a code owner April 17, 2026 17:42

github-actions Bot added the area-Build-mono label Apr 17, 2026

dotnet-policy-service Bot added the community-contribution Indicates that the PR has been added by a community member label Apr 17, 2026

Copilot started reviewing on behalf of elringus April 17, 2026 17:43 View session

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Comment thread src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/main.js

This was referenced Apr 17, 2026

[browser] Wasm.Build.Tests timeout - Timed out after 10s waiting for 'WASM EXIT' #116697

Open

Assertion failed: new_time >= loop->time in Component Governance Detection dotnet/dnceng#6510

Open

pavelsavara self-assigned this Apr 18, 2026

pavelsavara added arch-wasm WebAssembly architecture os-browser Browser variant of arch-wasm labels Apr 18, 2026

pavelsavara assigned maraf Apr 18, 2026

remove missing assets

b0dadf3

build-analysis Bot mentioned this pull request Apr 20, 2026

Unable to pull image from mcr.microsoft.com #117164

Open

Merge branch 'main' into fix/symbols-buffer

9950bf4

Copilot AI review requested due to automatic review settings May 25, 2026 08:31

Copilot started reviewing on behalf of pavelsavara May 25, 2026 08:31 View session

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Comment thread src/mono/wasm/testassets/WasmBasicTestApp/App/wwwroot/main.js

build-analysis Bot mentioned this pull request May 25, 2026

BlazorWasm AOT not requiring trimming #125233

Open

maraf and others added 2 commits June 8, 2026 15:10

Merge branch 'main' into fix/symbols-buffer

1e6b860

fix var name collision

b03afe1

Copilot AI review requested due to automatic review settings June 8, 2026 13:52

support js.symbols fingerprinting

c1f38f7

Copilot AI reviewed Jun 8, 2026

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assert http response ok

fba083c

Copilot AI review requested due to automatic review settings June 8, 2026 13:59

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