src: add public API for linked bindings

(Re-?)add a public API for creating linked bindings (access to
`NM_F_LINKED` as a constant was previously removed in
d6ac8a4), and add a test for
the functionality.

PR-URL: nodejs#26457
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: addaleax

node.gyp

@@ -1038,6 +1038,7 @@
         'test/cctest/test_base64.cc',
         'test/cctest/test_node_postmortem_metadata.cc',
         'test/cctest/test_environment.cc',
+        'test/cctest/test_linked_binding.cc',
         'test/cctest/test_platform.cc',
         'test/cctest/test_report_util.cc',
         'test/cctest/test_traced_value.cc',

src/node.h

@@ -445,6 +445,10 @@ typedef void (*addon_context_register_func)(
     v8::Local<v8::Context> context,
     void* priv);
 
+enum ModuleFlags {
+  kLinked = 0x02
+};
+
 struct node_module {
   int nm_version;
   unsigned int nm_flags;
@@ -532,6 +536,14 @@ extern "C" NODE_EXTERN void node_module_register(void* mod);
   /* NOLINTNEXTLINE (readability/null_usage) */                       \
   NODE_MODULE_CONTEXT_AWARE_X(modname, regfunc, NULL, 0)
 
+// Embedders can use this type of binding for statically linked native bindings.
+// It is used the same way addon bindings are used, except that linked bindings
+// can be accessed through `process._linkedBinding(modname)`.
+#define NODE_MODULE_LINKED(modname, regfunc)                               \
+  /* NOLINTNEXTLINE (readability/null_usage) */                            \
+  NODE_MODULE_CONTEXT_AWARE_X(modname, regfunc, NULL,                      \
+                              node::ModuleFlags::kLinked)
+
 /*
  * For backward compatibility in add-on modules.
  */

src/node_binding.h

@@ -21,6 +21,11 @@ enum {
   NM_F_DELETEME = 1 << 3,
 };
 
+// Make sure our internal values match the public API's values.
+static_assert(static_cast<int>(NM_F_LINKED) ==
+              static_cast<int>(node::ModuleFlags::kLinked),
+              "NM_F_LINKED != node::ModuleFlags::kLinked");
+
 #define NODE_MODULE_CONTEXT_AWARE_CPP(modname, regfunc, priv, flags)           \
   static node::node_module _module = {                                         \
       NODE_MODULE_VERSION,                                                     \

test/cctest/test_linked_binding.cc

@@ -0,0 +1,42 @@
+#include "node_test_fixture.h"
+#include "node_internals.h"  // RunBootstrapping()
+
+void InitializeBinding(v8::Local<v8::Object> exports,
+                       v8::Local<v8::Value> module,
+                       v8::Local<v8::Context> context) {
+  v8::Isolate* isolate = context->GetIsolate();
+  exports->Set(
+      context,
+      v8::String::NewFromOneByte(isolate,
+                                 reinterpret_cast<const uint8_t*>("key"),
+                                 v8::NewStringType::kNormal).ToLocalChecked(),
+      v8::String::NewFromOneByte(isolate,
+                                 reinterpret_cast<const uint8_t*>("value"),
+                                 v8::NewStringType::kNormal).ToLocalChecked())
+      .FromJust();
+}
+
+NODE_MODULE_LINKED(cctest_linkedbinding, InitializeBinding);
+
+class LinkedBindingTest : public EnvironmentTestFixture {};
+
+TEST_F(LinkedBindingTest, SimpleTest) {
+  const v8::HandleScope handle_scope(isolate_);
+  const Argv argv;
+  Env test_env {handle_scope, argv};
+
+  v8::Local<v8::Context> context = isolate_->GetCurrentContext();
+
+  const char* run_script =
+      "process._linkedBinding('cctest_linkedbinding').key";
+  v8::Local<v8::Script> script = v8::Script::Compile(
+      context,
+      v8::String::NewFromOneByte(isolate_,
+                                 reinterpret_cast<const uint8_t*>(run_script),
+                                 v8::NewStringType::kNormal).ToLocalChecked())
+      .ToLocalChecked();
+  v8::Local<v8::Value> completion_value = script->Run(context).ToLocalChecked();
+  v8::String::Utf8Value utf8val(isolate_, completion_value);
+  CHECK_NOT_NULL(*utf8val);
+  CHECK_EQ(strcmp(*utf8val, "value"), 0);
+}