From c34940cd0354a0d2c6b32878e9958cb600fc0d42 Mon Sep 17 00:00:00 2001
From: Shelley Vohr <shelley.vohr@gmail.com>
Date: Tue, 1 Sep 2026 00:58:56 +0000
Subject: [PATCH] src: add a flag to keep the embedder's wasm streaming
 callback

`SetIsolateMiscHandlers()` always installs Node.js's
`WebAssembly.compileStreaming()` implementation, which is backed by the
Environment's fetch-based handler. An embedder that provides its own
streaming callback (for example one wired to its own network stack) has
to re-install it after every `SetIsolateUpForNode()` or `NewIsolate()`
call. Add `SHOULD_NOT_SET_WASM_STREAMING_CALLBACK` next to the existing
`SHOULD_NOT_SET_PROMISE_REJECTION_CALLBACK` and
`SHOULD_NOT_SET_PREPARE_STACK_TRACE_CALLBACK` flags so it can opt out
the same way.

Refs: https://github.com/nodejs/node/pull/36447
Signed-off-by: Shelley Vohr <shelley.vohr@gmail.com>
---
 src/api/environment.cc          |  4 +++-
 src/node.h                      |  1 +
 test/cctest/test_environment.cc | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/src/api/environment.cc b/src/api/environment.cc
index 459830a2af80..316da3741785 100644
--- a/src/api/environment.cc
+++ b/src/api/environment.cc
@@ -269,7 +269,9 @@ void SetIsolateMiscHandlers(v8::Isolate* isolate, const IsolateSettings& s) {
   isolate->SetModifyCodeGenerationFromStringsCallback(
       modify_code_generation_from_strings_callback);
 
-  isolate->SetWasmStreamingCallback(wasm_web_api::StartStreamingCompilation);
+  if ((s.flags & SHOULD_NOT_SET_WASM_STREAMING_CALLBACK) == 0) {
+    isolate->SetWasmStreamingCallback(wasm_web_api::StartStreamingCompilation);
+  }
 
   Mutex::ScopedLock lock(node::per_process::cli_options_mutex);
   if (per_process::cli_options->get_per_isolate_options()
diff --git a/src/node.h b/src/node.h
index e827a46e14dd..61c85884521f 100644
--- a/src/node.h
+++ b/src/node.h
@@ -420,6 +420,7 @@ enum IsolateSettingsFlags {
   DETAILED_SOURCE_POSITIONS_FOR_PROFILING = 1 << 1,
   SHOULD_NOT_SET_PROMISE_REJECTION_CALLBACK = 1 << 2,
   SHOULD_NOT_SET_PREPARE_STACK_TRACE_CALLBACK = 1 << 3,
+  SHOULD_NOT_SET_WASM_STREAMING_CALLBACK = 1 << 4,
   ALLOW_MODIFY_CODE_GENERATION_FROM_STRINGS_CALLBACK = 0, /* legacy no-op */
 };
 
diff --git a/test/cctest/test_environment.cc b/test/cctest/test_environment.cc
index 109e224f788d..e84a6d9c1f97 100644
--- a/test/cctest/test_environment.cc
+++ b/test/cctest/test_environment.cc
@@ -60,6 +60,39 @@ TEST_F(EnvironmentTest, ManagedBufferCache) {
   (*env)->release_managed_buffer(buffer);
 }
 
+static int embedder_wasm_streaming_calls = 0;
+static void EmbedderWasmStreaming(const v8::FunctionCallbackInfo<v8::Value>&) {
+  embedder_wasm_streaming_calls++;
+}
+
+TEST_F(EnvironmentTest, KeepsEmbedderWasmStreamingCallbackWhenAsked) {
+  const v8::HandleScope handle_scope(isolate_);
+  const Argv argv;
+  Env env{handle_scope, argv};
+
+  auto compile_streaming = [&]() {
+    v8::Local<v8::Context> context = isolate_->GetCurrentContext();
+    v8::Script::Compile(context,
+                        v8::String::NewFromUtf8Literal(
+                            isolate_, "WebAssembly.compileStreaming(0); 0"))
+        .ToLocalChecked()
+        ->Run(context)
+        .ToLocalChecked();
+    isolate_->PerformMicrotaskCheckpoint();
+  };
+
+  node::IsolateSettings settings;
+  settings.flags |= node::SHOULD_NOT_SET_WASM_STREAMING_CALLBACK;
+  isolate_->SetWasmStreamingCallback(EmbedderWasmStreaming);
+  node::SetIsolateUpForNode(isolate_, settings);
+  compile_streaming();
+  EXPECT_EQ(embedder_wasm_streaming_calls, 1);
+
+  node::SetIsolateUpForNode(isolate_);
+  compile_streaming();
+  EXPECT_EQ(embedder_wasm_streaming_calls, 1);
+}
+
 TEST_F(EnvironmentTest, EnvironmentWithoutBrowserGlobals) {
   const v8::HandleScope handle_scope(isolate_);
   Argv argv;