inspector: new API - Session.connectToMainThread

This API is designed to enable worker threads use Inspector protocol
on main thread (and other workers through NodeWorker domain).

Note that worker can cause dead lock by suspending itself. I will
work on a new API that will allow workers to be hidden from the
inspector.

Fixes: #28828
PR-URL: #28870
Reviewed-By: Aleksei Koziatinskii <ak239spb@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

doc/api/errors.md

@@ -1213,6 +1213,12 @@ The `inspector` module is not available for use.
 While using the `inspector` module, an attempt was made to use the inspector
 before it was connected.
 
+<a id="ERR_INSPECTOR_NOT_WORKER"></a>
+### ERR_INSPECTOR_NOT_WORKER
+
+An API was called on the main thread that can only be used from
+the worker thread.
+
 <a id="ERR_INVALID_ADDRESS_FAMILY"></a>
 ### ERR_INVALID_ADDRESS_FAMILY
 

doc/api/inspector.md

@@ -121,9 +121,15 @@ session.on('Debugger.paused', ({ params }) => {
 added: v8.0.0
 -->
 
-Connects a session to the inspector back-end. An exception will be thrown
-if there is already a connected session established either through the API or by
-a front-end connected to the Inspector WebSocket port.
+Connects a session to the inspector back-end.
+
+### session.connectToMainThread()
+<!-- YAML
+added: REPLACEME
+-->
+
+Connects a session to the main thread inspector back-end. An exception will
+be thrown if this API was not called on a Worker thread.
 
 ### session.disconnect()
 <!-- YAML

lib/inspector.js

@@ -9,6 +9,7 @@ const {
   ERR_INSPECTOR_NOT_AVAILABLE,
   ERR_INSPECTOR_NOT_CONNECTED,
   ERR_INSPECTOR_NOT_ACTIVE,
+  ERR_INSPECTOR_NOT_WORKER,
   ERR_INVALID_ARG_TYPE,
   ERR_INVALID_CALLBACK
 } = require('internal/errors').codes;
@@ -20,8 +21,11 @@ if (!hasInspector)
 const EventEmitter = require('events');
 const { validateString } = require('internal/validators');
 const util = require('util');
+const { isMainThread } = require('worker_threads');
+
 const {
   Connection,
+  MainThreadConnection,
   open,
   url,
   waitForDebugger
@@ -47,6 +51,16 @@ class Session extends EventEmitter {
       new Connection((message) => this[onMessageSymbol](message));
   }
 
+  connectToMainThread() {
+    if (isMainThread)
+      throw new ERR_INSPECTOR_NOT_WORKER();
+    if (this[connectionSymbol])
+      throw new ERR_INSPECTOR_ALREADY_CONNECTED('The inspector session');
+    this[connectionSymbol] =
+      new MainThreadConnection(
+        (message) => queueMicrotask(() => this[onMessageSymbol](message)));
+  }
+
   [onMessageSymbol](message) {
     const parsed = JSON.parse(message);
     try {

lib/internal/errors.js

@@ -888,6 +888,7 @@ E('ERR_INSPECTOR_COMMAND', 'Inspector error %d: %s', Error);
 E('ERR_INSPECTOR_NOT_ACTIVE', 'Inspector is not active', Error);
 E('ERR_INSPECTOR_NOT_AVAILABLE', 'Inspector is not available', Error);
 E('ERR_INSPECTOR_NOT_CONNECTED', 'Session is not connected', Error);
+E('ERR_INSPECTOR_NOT_WORKER', 'Current thread is not a worker', Error);
 E('ERR_INTERNAL_ASSERTION', (message) => {
   const suffix = 'This is caused by either a bug in Node.js ' +
     'or incorrect usage of Node.js internals.\n' +

src/inspector/worker_inspector.cc

@@ -72,6 +72,12 @@ void ParentInspectorHandle::WorkerStarted(
   parent_thread_->Post(std::move(request));
 }
 
+std::unique_ptr<inspector::InspectorSession> ParentInspectorHandle::Connect(
+    std::unique_ptr<inspector::InspectorSessionDelegate> delegate,
+    bool prevent_shutdown) {
+  return parent_thread_->Connect(std::move(delegate), prevent_shutdown);
+}
+
 void WorkerManager::WorkerFinished(int session_id) {
   children_.erase(session_id);
 }

src/inspector/worker_inspector.h

@@ -12,6 +12,8 @@
 
 namespace node {
 namespace inspector {
+class InspectorSession;
+class InspectorSessionDelegate;
 class MainThreadHandle;
 class WorkerManager;
 
@@ -68,6 +70,9 @@ class ParentInspectorHandle {
     return wait_;
   }
   const std::string& url() const { return url_; }
+  std::unique_ptr<inspector::InspectorSession> Connect(
+      std::unique_ptr<inspector::InspectorSessionDelegate> delegate,
+      bool prevent_shutdown);
 
  private:
   int id_;

src/inspector_agent.cc

@@ -828,6 +828,17 @@ std::unique_ptr<InspectorSession> Agent::Connect(
       new SameThreadInspectorSession(session_id, client_));
 }
 
+std::unique_ptr<InspectorSession> Agent::ConnectToMainThread(
+    std::unique_ptr<InspectorSessionDelegate> delegate,
+    bool prevent_shutdown) {
+  CHECK_NOT_NULL(parent_handle_);
+  CHECK_NOT_NULL(client_);
+  auto thread_safe_delegate =
+      client_->getThreadHandle()->MakeDelegateThreadSafe(std::move(delegate));
+  return parent_handle_->Connect(std::move(thread_safe_delegate),
+                                 prevent_shutdown);
+}
+
 void Agent::WaitForDisconnect() {
   CHECK_NOT_NULL(client_);
   bool is_worker = parent_handle_ != nullptr;

src/inspector_agent.h

@@ -86,12 +86,19 @@ class Agent {
   std::unique_ptr<ParentInspectorHandle> GetParentHandle(
       int thread_id, const std::string& url);
 
-  // Called to create inspector sessions that can be used from the main thread.
+  // Called to create inspector sessions that can be used from the same thread.
   // The inspector responds by using the delegate to send messages back.
   std::unique_ptr<InspectorSession> Connect(
       std::unique_ptr<InspectorSessionDelegate> delegate,
       bool prevent_shutdown);
 
+  // Called from the worker to create inspector sessions that is connected
+  // to the main thread.
+  // The inspector responds by using the delegate to send messages back.
+  std::unique_ptr<InspectorSession> ConnectToMainThread(
+      std::unique_ptr<InspectorSessionDelegate> delegate,
+      bool prevent_shutdown);
+
   void PauseOnNextJavascriptStatement(const std::string& reason);
 
   std::string GetWsUrl() const;

src/inspector_js_api.cc

@@ -37,6 +37,29 @@ std::unique_ptr<StringBuffer> ToProtocolString(Isolate* isolate,
   return StringBuffer::create(StringView(*buffer, buffer.length()));
 }
 
+struct LocalConnection {
+  static std::unique_ptr<InspectorSession> Connect(
+      Agent* inspector, std::unique_ptr<InspectorSessionDelegate> delegate) {
+    return inspector->Connect(std::move(delegate), false);
+  }
+
+  static Local<String> GetClassName(Environment* env) {
+    return FIXED_ONE_BYTE_STRING(env->isolate(), "Connection");
+  }
+};
+
+struct MainThreadConnection {
+  static std::unique_ptr<InspectorSession> Connect(
+      Agent* inspector, std::unique_ptr<InspectorSessionDelegate> delegate) {
+    return inspector->ConnectToMainThread(std::move(delegate), true);
+  }
+
+  static Local<String> GetClassName(Environment* env) {
+    return FIXED_ONE_BYTE_STRING(env->isolate(), "MainThreadConnection");
+  }
+};
+
+template <typename ConnectionType>
 class JSBindingsConnection : public AsyncWrap {
  public:
   class JSBindingsSessionDelegate : public InspectorSessionDelegate {
@@ -70,14 +93,29 @@ class JSBindingsConnection : public AsyncWrap {
                        : AsyncWrap(env, wrap, PROVIDER_INSPECTORJSBINDING),
                          callback_(env->isolate(), callback) {
     Agent* inspector = env->inspector_agent();
-    session_ = inspector->Connect(std::make_unique<JSBindingsSessionDelegate>(
-        env, this), false);
+    session_ = ConnectionType::Connect(
+        inspector, std::make_unique<JSBindingsSessionDelegate>(env, this));
   }
 
   void OnMessage(Local<Value> value) {
     MakeCallback(callback_.Get(env()->isolate()), 1, &value);
   }
 
+  static void Bind(Environment* env, Local<Object> target) {
+    Local<String> class_name = ConnectionType::GetClassName(env);
+    Local<FunctionTemplate> tmpl =
+        env->NewFunctionTemplate(JSBindingsConnection::New);
+    tmpl->InstanceTemplate()->SetInternalFieldCount(1);
+    tmpl->SetClassName(class_name);
+    tmpl->Inherit(AsyncWrap::GetConstructorTemplate(env));
+    env->SetProtoMethod(tmpl, "dispatch", JSBindingsConnection::Dispatch);
+    env->SetProtoMethod(tmpl, "disconnect", JSBindingsConnection::Disconnect);
+    target->Set(env->context(),
+                class_name,
+                tmpl->GetFunction(env->context()).ToLocalChecked())
+        .ToChecked();
+  }
+
   static void New(const FunctionCallbackInfo<Value>& info) {
     Environment* env = Environment::GetCurrent(info);
     CHECK(info[0]->IsFunction());
@@ -300,18 +338,8 @@ void Initialize(Local<Object> target, Local<Value> unused,
   env->SetMethod(target, "registerAsyncHook", RegisterAsyncHookWrapper);
   env->SetMethodNoSideEffect(target, "isEnabled", IsEnabled);
 
-  auto conn_str = FIXED_ONE_BYTE_STRING(env->isolate(), "Connection");
-  Local<FunctionTemplate> tmpl =
-      env->NewFunctionTemplate(JSBindingsConnection::New);
-  tmpl->InstanceTemplate()->SetInternalFieldCount(1);
-  tmpl->SetClassName(conn_str);
-  tmpl->Inherit(AsyncWrap::GetConstructorTemplate(env));
-  env->SetProtoMethod(tmpl, "dispatch", JSBindingsConnection::Dispatch);
-  env->SetProtoMethod(tmpl, "disconnect", JSBindingsConnection::Disconnect);
-  target
-      ->Set(env->context(), conn_str,
-            tmpl->GetFunction(env->context()).ToLocalChecked())
-      .ToChecked();
+  JSBindingsConnection<LocalConnection>::Bind(env, target);
+  JSBindingsConnection<MainThreadConnection>::Bind(env, target);
 }
 
 }  // namespace

test/sequential/test-inspector-bindings.js → test/parallel/test-inspector-bindings.js

@@ -1,4 +1,3 @@
-// Flags: --expose-internals
 'use strict';
 const common = require('../common');
 common.skipIfInspectorDisabled();
@@ -86,7 +85,7 @@ function testSampleDebugSession() {
   }, TypeError);
   session.post('Debugger.enable', () => cbAsSecondArgCalled = true);
   session.post('Debugger.setBreakpointByUrl', {
-    'lineNumber': 14,
+    'lineNumber': 13,
     'url': pathToFileURL(path.resolve(__dirname, __filename)).toString(),
     'columnNumber': 0,
     'condition': ''