[browser][CoreCLR] lazy and satelite assemblies by pavelsavara · Pull Request #124853 · dotnet/runtime

pavelsavara · 2026-02-25T12:04:11Z

Contributes to #120226

dotnet-policy-service · 2026-02-25T12:05:05Z

Tagging subscribers to this area: @agocke, @jeffschwMSFT, @elinor-fung
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Copilot

Pull request overview

This PR implements support for loading satellite assemblies (localization resources) and lazy-loaded assemblies in the browser/CoreCLR JavaScript loader by wiring new loader export functions end-to-end (loader → cross-module table → interop INTERNAL.* APIs).

Changes:

Implemented loadSatelliteAssemblies / loadLazyAssembly by delegating to loader-side asset fetchers.
Added new loader exports (fetchSatelliteAssemblies, fetchLazyAssembly) to the cross-module exchange table and exposed them via dotnetLoaderExports.
Added support code for downloading/registration of satellite resources and lazy assemblies, plus PDB registration in the host FS.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/lazy.ts	Implements interop entrypoints by delegating to loader exports.
src/native/libs/Common/JavaScript/types/exchange.ts	Extends `LoaderExports` / `LoaderExportsTable` with new asset-fetching APIs.
src/native/libs/Common/JavaScript/loader/run.ts	Optionally preloads all satellite resources during startup.
src/native/libs/Common/JavaScript/loader/index.ts	Publishes the new loader functions into the cross-module table.
src/native/libs/Common/JavaScript/loader/config.ts	Updates resource merging to include satellite resource keys (but currently duplicates data).
src/native/libs/Common/JavaScript/loader/assets.ts	Adds `fetchSatelliteAssemblies`/`fetchLazyAssembly` and culture-aware assembly fetching.
src/native/libs/Common/JavaScript/host/assets.ts	Updates assembly name aliasing and implements PDB registration into the VFS.
src/native/libs/Common/JavaScript/cross-module/index.ts	Extends loader exports reconstruction from the exchange table.

src/native/libs/Common/JavaScript/loader/config.ts

src/native/libs/Common/JavaScript/loader/assets.ts

Copilot · 2026-02-25T12:11:37Z

src/native/libs/Common/JavaScript/loader/assets.ts

+export async function fetchLazyAssembly(assemblyNameToLoad: string): Promise<boolean> {
+    const lazyAssemblies = loaderConfig.resources?.lazyAssembly;
+    if (!lazyAssemblies) {
+        throw new Error("No assemblies have been marked as lazy-loadable. Use the 'BlazorWebAssemblyLazyLoad' item group in your project file to enable lazy loading an assembly.");
+    }
+
+    let assemblyNameWithoutExtension = assemblyNameToLoad;
+    if (assemblyNameToLoad.endsWith(".dll"))
+        assemblyNameWithoutExtension = assemblyNameToLoad.substring(0, assemblyNameToLoad.length - 4);
+    else if (assemblyNameToLoad.endsWith(".wasm"))
+        assemblyNameWithoutExtension = assemblyNameToLoad.substring(0, assemblyNameToLoad.length - 5);
+
+    const assemblyNameToLoadDll = assemblyNameWithoutExtension + ".dll";
+    const assemblyNameToLoadWasm = assemblyNameWithoutExtension + ".wasm";
+
+    let dllAsset: AssemblyAsset | null = null;
+    for (const asset of lazyAssemblies) {
+        if (asset.virtualPath === assemblyNameToLoadDll || asset.virtualPath === assemblyNameToLoadWasm) {
+            dllAsset = asset;
+            break;
+        }
+    }
+
+    if (!dllAsset) {
+        throw new Error(`${assemblyNameToLoad} must be marked with 'BlazorWebAssemblyLazyLoad' item group in your project file to allow lazy-loading.`);
+    }
+
+    await fetchDll(dllAsset);
+
+    if (loaderConfig.debugLevel != 0) {
+        const pdbNameToLoad = assemblyNameWithoutExtension + ".pdb";
+        const pdbAssets = loaderConfig.resources?.pdb;
+        if (pdbAssets) {
+            for (const pdbAsset of pdbAssets) {
+                if (pdbAsset.virtualPath === pdbNameToLoad) {
+                    await fetchPdb(pdbAsset);
+                    break;
+                }
+            }
+        }
+    }
+
+    return true;
+}


fetchLazyAssembly always returns true and re-registers the assembly even if it was already loaded previously. The existing WASM loader API returns false when the assembly is already loaded (see src/mono/browser/runtime/lazyLoading.ts) and avoids redundant downloads/allocations; the current behavior can leak memory because registerDllBytes allocates unmanaged memory each time. Track loaded assemblies (e.g., by asset name) and return false when already loaded.

src/native/libs/Common/JavaScript/loader/assets.ts

src/native/libs/Common/JavaScript/host/assets.ts

src/native/libs/Common/JavaScript/loader/config.ts

src/native/libs/Common/JavaScript/loader/assets.ts

ilonatommy

Apart from automated review (lazy loading / unexpected result of multiple calls of fetchDll) it loos good to me.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 7 comments.

src/native/libs/Common/JavaScript/loader/assets.ts

src/native/libs/Common/JavaScript/host/assets.ts

src/native/libs/Common/JavaScript/loader/assets.ts

src/native/libs/Common/JavaScript/loader/config.ts

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated no new comments.

pavelsavara added 2 commits February 25, 2026 13:01

lazy and satelite assemblies

e71fa62

cleanup

116d374

pavelsavara added this to the 11.0.0 milestone Feb 25, 2026

pavelsavara self-assigned this Feb 25, 2026

pavelsavara added the arch-wasm WebAssembly architecture label Feb 25, 2026

Copilot AI review requested due to automatic review settings February 25, 2026 12:04

pavelsavara added area-Host os-browser Browser variant of arch-wasm labels Feb 25, 2026

pavelsavara requested review from ilonatommy and radekdoulik February 25, 2026 12:04

pavelsavara marked this pull request as ready for review February 25, 2026 12:05

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ilonatommy reviewed Feb 25, 2026

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feedback

92f78c7

ilonatommy reviewed Feb 25, 2026

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Update src/native/libs/Common/JavaScript/loader/assets.ts

8cfa998

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings February 25, 2026 14:50

Copilot started reviewing on behalf of pavelsavara February 25, 2026 14:51 View session

Update src/native/libs/Common/JavaScript/loader/assets.ts

ef58abf

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot AI reviewed Feb 25, 2026

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Update src/native/libs/Common/JavaScript/loader/assets.ts

03efb1e

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings February 25, 2026 15:00

Copilot started reviewing on behalf of pavelsavara February 25, 2026 15:01 View session

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feedback

ecdb42c

ilonatommy approved these changes Feb 25, 2026

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build-analysis bot mentioned this pull request Feb 25, 2026

[android][clr] No peer certificates when executing System.Net.Http.Functional.Tests on Android emulator #124526

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pavelsavara commented Feb 25, 2026 •

edited

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