[browser][coreCLR] host cleanup by pavelsavara · Pull Request #126103 · dotnet/runtime

pavelsavara · 2026-03-25T16:25:34Z

Fixes #120226

- add viewOrCopy

Copilot

Pull request overview

Cleans up the Browser/CoreCLR JS host surface by consolidating string/UTF-8 helpers into BrowserUtilsExports, updating interop call sites accordingly, and improving failure handling during WASM instantiation.

Changes:

Move utf8ToStringRelaxed usage from JS interop local utilities to dotnetBrowserUtilsExports and add viewOrCopy/utf8ToStringRelaxed to the BrowserUtils exports table.
Add ReceiverShouldFree handling in resolveOrRejectPromise and update websocket send buffering to avoid SharedArrayBuffer usage.
Improve host/loader error handling by calling exit(1, err) when WASM instantiation fails; remove/refresh a few stale WASM-TODO comments.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/web-socket.ts	Switch to BrowserUtilsExports for UTF-8 decoding and SAB-safe copying when sending.
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/utils.ts	Remove local `utf8ToStringRelaxed` helper and unused Module dependency.
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/types.ts	Trim perf-measure enum and rename prefixes from `mono.` to `clr.`.
src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshal-to-js.ts	Add `ReceiverShouldFree` handling and free posted argument buffers.
src/native/libs/System.Native.Browser/utils/strings.ts	Centralize relaxed UTF-8 decoding and patch Emscripten UTF8Decoder for SAB.
src/native/libs/System.Native.Browser/utils/index.ts	Initialize strings + export `utf8ToStringRelaxed` and `viewOrCopy` via BrowserUtilsExportsTable.
src/native/libs/System.Native.Browser/diagnostics/types.ts	Remove duplicate type definitions; re-export shared types.
src/native/libs/Common/JavaScript/types/exchange.ts	Extend BrowserUtilsExports types to include new exports.
src/native/libs/Common/JavaScript/types/ems-ambient.ts	Add typings for `UTF8ArrayToString` and `UTF8Decoder`.
src/native/libs/Common/JavaScript/loader/run.ts	Update a WASM-TODO comment with an issue link.
src/native/libs/Common/JavaScript/loader/polyfills.ts	Remove a stale WASM-TODO comment.
src/native/libs/Common/JavaScript/loader/assets.ts	Call `dotnetApi.exit(1, err)` on instantiate failures.
src/native/libs/Common/JavaScript/host/assets.ts	Use `UTF8ArrayToString` for probing; call `exit(1, err)` on instantiate failures.
src/native/libs/Common/JavaScript/cross-module/index.ts	Update BrowserUtilsExports table mapping indices for new exports.
src/native/corehost/browserhost/CMakeLists.txt	Update comment to reference tracking issue.

src/native/libs/Common/JavaScript/types/exchange.ts

src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshal-to-js.ts

Copilot

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Copilot · 2026-03-25T21:02:42Z

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

        module = result.module;
+    } catch (err) {
+        dotnetApi.exit(1, err);
+        throw err;


dotnetApi.exit(...) always throws (see Common/JavaScript/loader/exit.ts), so the subsequent throw err; is dead code and can be removed to avoid confusion about which error is propagated.

Suggested change

throw err;

Copilot · 2026-03-25T21:02:42Z

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

+        return { instance, module };
+    } catch (err) {
+        _ems_.dotnetApi.exit(1, err);
+        throw err;


_ems_.dotnetApi.exit(...) throws, so the throw err; immediately after is unreachable and can be removed to make the control flow clearer.

Suggested change

throw err;

Copilot · 2026-03-25T21:02:43Z

...eropServices.JavaScript/src/System/Runtime/InteropServices/JavaScript/JSMarshalerArgument.cs

        public void Initialize()
        {
            slot.Type = MarshalerType.None;
 #if FEATURE_WASM_MANAGED_THREADS
            // we know that this is at the start of some JSImport call, but we don't know yet what would be the target thread
            // also this is called multiple times
            JSProxyContext.JSImportWithUnknownContext();
            slot.ContextHandle = IntPtr.Zero;
-            slot.ReceiverShouldFree = false;
 #endif
+            slot.ReceiverShouldFree = false;
        }


slot.ReceiverShouldFree is only defined under #if FEATURE_WASM_MANAGED_THREADS, but Initialize() now assigns it unconditionally. This will fail to compile when FEATURE_WASM_MANAGED_THREADS is not defined. Move the assignment back under the same #if (or add a non-threading field/alternative).

Copilot · 2026-03-25T21:02:43Z

src/native/libs/System.Native.Browser/utils/strings.ts

+            const originalUTF8DecoderDecode = _ems_.UTF8Decoder.decode;
+            _ems_.UTF8Decoder.decode = function (input: Uint8Array): string {
+                const view = isSharedArrayBuffer(input.buffer) ? input.slice() : input;
+                return originalUTF8DecoderDecode.call(this, view);


With tsconfig.json using "strict": true, the _ems_.UTF8Decoder nullability and method override here won’t type-check: (1) _ems_.UTF8Decoder is typed as TextDecoder | null, so accessing .decode is "possibly null"; and (2) assigning a wrapper with signature (input: Uint8Array) => string is not assignable to TextDecoder.decode which accepts input?: BufferSource plus optional options. Capture a non-null local decoder variable (or use a non-null assertion) and make the wrapper accept the full decode signature (including undefined/options) and forward them after applying the SAB copy when input is a Uint8Array.

Suggested change

const originalUTF8DecoderDecode = _ems_.UTF8Decoder.decode;

_ems_.UTF8Decoder.decode = function (input: Uint8Array): string {

const view = isSharedArrayBuffer(input.buffer) ? input.slice() : input;

return originalUTF8DecoderDecode.call(this, view);

const utf8Decoder = _ems_.UTF8Decoder!;

const originalUTF8DecoderDecode = utf8Decoder.decode;

utf8Decoder.decode = function (input?: BufferSource, options?: TextDecodeOptions): string {

let actualInput = input;

if (input instanceof Uint8Array && isSharedArrayBuffer(input.buffer)) {

actualInput = input.slice();

}

return originalUTF8DecoderDecode.call(this, actualInput, options);

Copilot

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Copilot · 2026-03-26T08:47:45Z

src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/web-socket.ts

        if (length !== 0) {
-            // TODO-WASM: copy, because the provided ArrayBufferView value must not be shared in MT.
-            buffer = bufferView;
+            // the provided ArrayBufferView value must not be SAB.


The comment says the provided view “must not be SAB”, but the code is explicitly handling SharedArrayBuffer-backed views by copying via viewOrCopy. Consider rewording the comment to reflect the behavior (copying only when needed) to avoid confusion for future maintainers.

Suggested change

// the provided ArrayBufferView value must not be SAB.

// the provided ArrayBufferView may be backed by SharedArrayBuffer; viewOrCopy will copy when needed.

Copilot · 2026-03-26T08:47:45Z

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

+        return { instance, module };
+    } catch (err) {
+        _ems_.dotnetApi.exit(1, err);
+        throw err;


_ems_.dotnetApi.exit() throws (and marks the runtime as exited), so throw err; is unreachable here and will never run. Remove the redundant rethrow to avoid dead code and make it clearer that exit() is the terminal path.

Suggested change

throw err;

pavelsavara added 5 commits March 25, 2026 15:06

MeasuredBlock

2b6d9de

- move utf8ToStringRelaxed

0fc202a

- add viewOrCopy

receiverShouldFree

e39b6fa

instantiateWasm fail fast

e7bfcbf

links

e793b32

pavelsavara added this to the 11.0.0 milestone Mar 25, 2026

pavelsavara self-assigned this Mar 25, 2026

Copilot AI review requested due to automatic review settings March 25, 2026 16:25

pavelsavara added arch-wasm WebAssembly architecture area-System.Runtime.InteropServices.JavaScript os-browser Browser variant of arch-wasm labels Mar 25, 2026

Copilot started reviewing on behalf of pavelsavara March 25, 2026 16:26 View session

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src/native/libs/Common/JavaScript/types/exchange.ts Outdated Show resolved Hide resolved

src/native/libs/System.Runtime.InteropServices.JavaScript.Native/interop/marshal-to-js.ts Show resolved Hide resolved

pavelsavara and others added 2 commits March 25, 2026 21:54

fix

393efa3

Merge branch 'main' into browser_cleanup

cd08d6a

Copilot AI review requested due to automatic review settings March 25, 2026 20:54

Copilot started reviewing on behalf of pavelsavara March 25, 2026 20:56 View session

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build-analysis bot mentioned this pull request Mar 26, 2026

tracing/runtimeeventsource/nativeruntimeeventsource/nativeruntimeeventsource failing in CI #90605

Open

pavelsavara and others added 2 commits March 26, 2026 09:39

fix

d7aad93

Merge branch 'main' into browser_cleanup

fe2ddba

Copilot AI review requested due to automatic review settings March 26, 2026 08:41

Copilot started reviewing on behalf of pavelsavara March 26, 2026 08:42 View session

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[browser][coreCLR] host cleanup#126103

[browser][coreCLR] host cleanup#126103
pavelsavara wants to merge 9 commits intodotnet:mainfrom
pavelsavara:browser_cleanup

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-            const originalUTF8DecoderDecode = _ems_.UTF8Decoder.decode;
-            _ems_.UTF8Decoder.decode = function (input: Uint8Array): string {
-                const view = isSharedArrayBuffer(input.buffer) ? input.slice() : input;
-                return originalUTF8DecoderDecode.call(this, view);
+            const utf8Decoder = _ems_.UTF8Decoder!;
+            const originalUTF8DecoderDecode = utf8Decoder.decode;
+            utf8Decoder.decode = function (input?: BufferSource, options?: TextDecodeOptions): string {
+                let actualInput = input;
+                if (input instanceof Uint8Array && isSharedArrayBuffer(input.buffer)) {
+                    actualInput = input.slice();
+                }
+                return originalUTF8DecoderDecode.call(this, actualInput, options);

	// the provided ArrayBufferView value must not be SAB.
	// the provided ArrayBufferView may be backed by SharedArrayBuffer; viewOrCopy will copy when needed.

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