debugger: wait for target startup

The inspector can accept a connection before an --inspect-brk target
enters its frontend wait. Runtime.runIfWaitingForDebugger can then be
handled too early, allowing the target to subsequently block forever.

Wait for NodeRuntime.waitingForDebugger before initializing and
releasing launched targets. Race the handshake against disconnects and
apply it to both interactive and probe startup.

Refs: #64116
Assisted-by: codex:gpt-5.6-sol
Co-authored-by: Archkon <180910180+Archkon@users.noreply.github.com>
Signed-off-by: Archkon <180910180+Archkon@users.noreply.github.com>
Signed-off-by: Filip Skokan <panva.ip@gmail.com>
PR-URL: #65194
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: panva

lib/internal/debugger/inspect_helpers.js

@@ -1,11 +1,20 @@
 'use strict';
 
 const {
+  ArrayPrototypePop,
+  ArrayPrototypePush,
   ArrayPrototypePushApply,
+  MapPrototypeGet,
   Number,
   Promise,
+  PromiseWithResolvers,
   RegExpPrototypeExec,
+  RegExpPrototypeSymbolReplace,
+  SafePromiseRace,
   StringPrototypeEndsWith,
+  StringPrototypeIndexOf,
+  StringPrototypeSlice,
+  StringPrototypeStartsWith,
 } = primordials;
 
 const { spawn } = require('child_process');
@@ -18,12 +27,24 @@ const {
   AbortController,
 } = require('internal/abort_controller');
 
-const { ERR_DEBUGGER_STARTUP_ERROR } = require('internal/errors').codes;
+const {
+  ERR_DEBUGGER_ERROR,
+  ERR_DEBUGGER_STARTUP_ERROR,
+} = require('internal/errors').codes;
 const {
   exitCodes: {
     kInvalidCommandLineArgument,
   },
 } = internalBinding('errors');
+const {
+  types: {
+    kBoolean,
+    kNoOp,
+    kV8Option,
+  },
+} = internalBinding('options');
+
+const { getCLIOptionsInfo } = require('internal/options');
 
 const debugRegex = /Debugger listening on ws:\/\/\[?(.+?)\]?:(\d+)\//;
 
@@ -61,6 +82,176 @@ function ensureTrailingNewline(text) {
   return StringPrototypeEndsWith(text, '\n') ? text : `${text}\n`;
 }
 
+// Mirror OptionsParser::Parse() far enough to find the child script. Options
+// before it must not undo the inspector setup added by launchChildProcess().
+function validateChildArgs(childArgs) {
+  const { options, aliases } = getCLIOptionsInfo();
+  const syntheticArgs = [];
+  let breakFirstLine = true;
+  let childArgIndex = 0;
+  let inspectorEnabled = true;
+
+  function peekArg() {
+    return syntheticArgs.length > 0 ?
+      syntheticArgs[syntheticArgs.length - 1] :
+      childArgs[childArgIndex];
+  }
+
+  function shiftArg() {
+    return syntheticArgs.length > 0 ?
+      ArrayPrototypePop(syntheticArgs) :
+      childArgs[childArgIndex++];
+  }
+
+  while (true) {
+    const nextArg = peekArg();
+    if (nextArg === undefined || nextArg.length <= 1 || nextArg[0] !== '-') {
+      break;
+    }
+
+    const isSynthetic = syntheticArgs.length > 0;
+    const arg = shiftArg();
+    if (arg === '--') { break; }
+    if (!isSynthetic &&
+        (arg === '--experimental-config-file' ||
+         arg === '--experimental-default-config-file')) {
+      // ConfigReader rewrites these to an inline default path before parsing.
+      continue;
+    }
+    if (!isSynthetic &&
+        StringPrototypeStartsWith(
+          arg, '--experimental-default-config-file=')) {
+      // ConfigReader rejects this form before parsing the remaining options.
+      return;
+    }
+
+    const equalsIndex = arg[1] === '-' ? StringPrototypeIndexOf(arg, '=') : -1;
+    let name = equalsIndex === -1 ? arg : StringPrototypeSlice(arg, 0, equalsIndex);
+    if (name.length > 2) {
+      name = `${StringPrototypeSlice(name, 0, 2)}${
+        RegExpPrototypeSymbolReplace(/_/g, StringPrototypeSlice(name, 2), '-')}`;
+    }
+
+    let isNegation = false;
+    if (StringPrototypeStartsWith(name, '--no-')) {
+      name = `--${StringPrototypeSlice(name, 5)}`;
+      isNegation = true;
+    }
+
+    while (true) {
+      let expansion = MapPrototypeGet(aliases, name);
+      if (expansion === undefined && equalsIndex !== -1) {
+        expansion = MapPrototypeGet(aliases, `${name}=`);
+      }
+      const aliasArg = peekArg();
+      if (expansion === undefined &&
+          aliasArg !== undefined &&
+          aliasArg.length > 0 &&
+          aliasArg[0] !== '-') {
+        expansion = MapPrototypeGet(aliases, `${name} <arg>`);
+      }
+      if (expansion === undefined) { break; }
+
+      const previousName = name;
+      // process.allowedNodeEnvironmentFlags may remove a self-recursive
+      // first entry from the cached alias metadata. Preserve the native
+      // parser's synthetic option terminator in that case.
+      if (expansion[0] === '--') {
+        for (let i = expansion.length - 1; i >= 0; i--) {
+          ArrayPrototypePush(syntheticArgs, expansion[i]);
+        }
+        break;
+      }
+      name = expansion[0];
+      for (let i = expansion.length - 1; i > 0; i--) {
+        ArrayPrototypePush(syntheticArgs, expansion[i]);
+      }
+      if (name === previousName) { break; }
+    }
+
+    const info = MapPrototypeGet(options, name);
+    if (info === undefined) { continue; }
+    if (isNegation && info.type !== kBoolean && info.type !== kV8Option) {
+      return;
+    }
+    if (info.type === kBoolean || info.type === kNoOp || info.type === kV8Option) {
+      if (name === '--inspect') {
+        inspectorEnabled = !isNegation;
+      } else if (name === '--inspect-brk') {
+        breakFirstLine = !isNegation;
+        if (!isNegation) { inspectorEnabled = true; }
+      } else if (!isNegation &&
+                 (name === '--inspect-wait' ||
+                  name === '--inspect-brk-node')) {
+        inspectorEnabled = true;
+      }
+      continue;
+    }
+
+    if (equalsIndex !== -1) {
+      if (equalsIndex === arg.length - 1) { return; }
+      continue;
+    }
+
+    const value = peekArg();
+    if (value === undefined || (value.length > 0 && value[0] === '-')) {
+      return;
+    }
+    shiftArg();
+  }
+
+  if (!inspectorEnabled) {
+    throw new ERR_DEBUGGER_STARTUP_ERROR(
+      '--no-inspect is incompatible with node inspect before the child script');
+  }
+  if (!breakFirstLine) {
+    throw new ERR_DEBUGGER_STARTUP_ERROR(
+      '--no-inspect-brk is incompatible with node inspect before the child script');
+  }
+}
+
+async function waitForDebugger(
+  client,
+  callMethod = (method) => client.callMethod(method),
+) {
+  const {
+    promise: waitingPromise,
+    resolve: resolveWaiting,
+  } = PromiseWithResolvers();
+  const {
+    promise: closedPromise,
+    reject: rejectClosed,
+  } = PromiseWithResolvers();
+  const onWaiting = () => resolveWaiting();
+  const onClose = () => {
+    rejectClosed(new ERR_DEBUGGER_ERROR(
+      'Debugger session ended while waiting for target startup'));
+  };
+
+  // The inspector can accept a connection before the target reaches its
+  // startup wait. Enabling NodeRuntime makes that state observable whether
+  // the target was already waiting or starts waiting later.
+  client.once('NodeRuntime.waitingForDebugger', onWaiting);
+  client.once('close', onClose);
+  try {
+    await SafePromiseRace([
+      callMethod('NodeRuntime.enable'),
+      closedPromise,
+    ]);
+    await SafePromiseRace([
+      waitingPromise,
+      closedPromise,
+    ]);
+    await SafePromiseRace([
+      callMethod('NodeRuntime.disable'),
+      closedPromise,
+    ]);
+  } finally {
+    client.removeListener('NodeRuntime.waitingForDebugger', onWaiting);
+    client.removeListener('close', onClose);
+  }
+}
+
 function writeInspectUsageAndExit(invokedAs, message, exitCode) {
   const code = exitCode ?? (message ? kInvalidCommandLineArgument : 0);
   const out = code === 0 ? process.stdout : process.stderr;
@@ -141,6 +332,8 @@ probe output schema.
 
 async function launchChildProcess(childArgs, inspectHost, inspectPort,
                                   childOutput, options = { __proto__: null }) {
+  validateChildArgs(childArgs);
+
   if (!options.skipPortPreflight) {
     await portIsFree(inspectHost, inspectPort);
   }
@@ -189,5 +382,6 @@ async function launchChildProcess(childArgs, inspectHost, inspectPort,
 module.exports = {
   ensureTrailingNewline,
   launchChildProcess,
+  waitForDebugger,
   writeInspectUsageAndExit,
 };

lib/internal/debugger/inspect_probe.js

@@ -33,6 +33,7 @@ const InspectClient = require('internal/debugger/inspect_client');
 const {
   ensureTrailingNewline,
   launchChildProcess,
+  waitForDebugger,
 } = require('internal/debugger/inspect_helpers');
 
 const { ERR_DEBUGGER_STARTUP_ERROR } = require('internal/errors').codes;
@@ -1044,6 +1045,17 @@ class ProbeInspectorSession {
       this.connected = true;
 
       try {
+        try {
+          await waitForDebugger(
+            this.client,
+            (method) => this.callCdp(method),
+          );
+        } catch (err) {
+          // A close event may have completed the structured report while the
+          // readiness helper was rejecting its disconnect race.
+          if (this.finished) { throw kInspectorFailedSentinel; }
+          throw err;
+        }
         await this.callCdp('Runtime.enable');
         await this.callCdp('Debugger.enable');
         await this.bindBreakpoints();

lib/internal/debugger/inspect_repl.js

@@ -60,6 +60,7 @@ const { fileURLToPath } = require('internal/url');
 const { customInspectSymbol, SideEffectFreeRegExpPrototypeSymbolReplace } = require('internal/util');
 const { inspect: utilInspect } = require('internal/util/inspect');
 const { isObjectLiteral } = require('internal/repl/utils');
+const { waitForDebugger } = require('internal/debugger/inspect_helpers');
 const debuglog = require('internal/util/debuglog').debuglog('inspect');
 
 const SHORTCUTS = {
@@ -1204,9 +1205,13 @@ function createRepl(inspector) {
   }
 
   async function initAfterStart() {
+    const waitForDebuggerOnStart = !!inspector.options?.script;
     waitForInitialBreakRender =
-      !!inspector.options?.script &&
+      waitForDebuggerOnStart &&
       process.env.NODE_INSPECT_RESUME_ON_START !== '1';
+    if (waitForDebuggerOnStart) {
+      await waitForDebugger(inspector.client);
+    }
     await Runtime.enable();
     await Profiler.enable();
     await Profiler.setSamplingInterval({ interval: 100 });