src: make process.dlopen() load well-known symbol

Look for symbol `node_register_module_v${NODE_MODULE_VERSION}` if the add-on didn't self-register. This can be used to create add-ons that support multiple Node.js versions from a single shared object. PR-URL: #18934 Reviewed-By: Colin Ihrig <[email protected]> Reviewed-By: Daniel Bevenius <[email protected]> Reviewed-By: Franziska Hinkelmann <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Joyee Cheung <[email protected]> Reviewed-By: Matheus Marchini <[email protected]> Reviewed-By: Tobias Nießen <[email protected]>

Author: bnoordhuis

src/node.cc

@@ -2483,6 +2483,7 @@ struct DLib{
 
 inlineboolOpen();
 inlinevoidClose();
+inlinevoid* GetSymbolAddress(constchar* name);
 
 const std::string filename_;
 constint flags_;
@@ -2510,6 +2511,10 @@ void DLib::Close(){
 dlclose(handle_);
  handle_ = nullptr;
 }
+
+void* DLib::GetSymbolAddress(constchar* name){
+returndlsym(handle_, name);
+}
 #else// !__POSIX__
 boolDLib::Open(){
 int ret = uv_dlopen(filename_.c_str(), &lib_);
@@ -2527,8 +2532,23 @@ void DLib::Close(){
 uv_dlclose(&lib_);
  handle_ = nullptr;
 }
+
+void* DLib::GetSymbolAddress(constchar* name){
+void* address;
+if (0 == uv_dlsym(&lib_, name, &address)) return address;
+returnnullptr;
+}
 #endif// !__POSIX__
 
+using InitializerCallback = void (*)(Local<Object> exports,
+ Local<Value> module,
+ Local<Context> context);
+
+inline InitializerCallback GetInitializerCallback(DLib* dlib){
+constchar* name = "node_register_module_v"STRINGIFY(NODE_MODULE_VERSION);
+returnreinterpret_cast<InitializerCallback>(dlib->GetSymbolAddress(name));
+}
+
 // DLOpen is process.dlopen(module, filename, flags).
 // Used to load 'module.node' dynamically shared objects.
 //
@@ -2583,10 +2603,15 @@ static void DLOpen(const FunctionCallbackInfo<Value>& args){
  }
 
 if (mp == nullptr){
- dlib.Close();
- env->ThrowError("Module did not self-register.");
+if (auto callback = GetInitializerCallback(&dlib)){
+callback(exports, module, context);
+ } else{
+ dlib.Close();
+ env->ThrowError("Module did not self-register.");
+ }
 return;
  }
+
 if (mp->nm_version == -1){
 if (env->EmitNapiWarning()){
 if (ProcessEmitWarning(env, "N-API is an experimental feature and could "

src/node.h

@@ -532,6 +532,9 @@ extern "C" NODE_EXTERN void node_module_register(void* mod);
  } \
  }
 
+// Usage: `NODE_MODULE(NODE_GYP_MODULE_NAME, InitializerFunction)`
+// If no NODE_MODULE is declared, Node.js looks for the well-known
+// symbol `node_register_module_v${NODE_MODULE_VERSION}`.
 #defineNODE_MODULE(modname, regfunc) \
 NODE_MODULE_X(modname, regfunc, NULL, 0) // NOLINT (readability/null_usage)
 

test/addons/hello-world/binding.cc

@@ -6,8 +6,12 @@ void Method(const v8::FunctionCallbackInfo<v8::Value>& args){
  args.GetReturnValue().Set(v8::String::NewFromUtf8(isolate, "world"));
 }
 
-voidinit(v8::Local<v8::Object> exports){
+#defineCONCAT(a, b) CONCAT_HELPER(a, b)
+#defineCONCAT_HELPER(a, b) a##b
+#defineINITIALIZERCONCAT(node_register_module_v, NODE_MODULE_VERSION)
+
+extern "C" NODE_MODULE_EXPORT void INITIALIZER(v8::Local<v8::Object> exports,
+ v8::Local<v8::Value> module,
+ v8::Local<v8::Context> context){
 NODE_SET_METHOD(exports, "hello", Method);
 }
-
-NODE_MODULE(NODE_GYP_MODULE_NAME, init)