inspector: add inspector.waitForDebugger()

This method blocks current node process until a client sends
Runtime.runifWaitingForDebugger.

It can be useful when we need to report inspector.url() before
waiting for connection:
```
inspector.open(0, undefined, false);
fs.writeFileSync(someFileName, inspector.url());
inspector.waitForDebugger();
```

PR-URL: https://github.com/nodejs/node/pull/28453
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>

2 files changed, 21 insertions, 2 deletions

diff --git a/lib/inspector.js b/lib/inspector.js
index 4bec628b7d..198d87ae44 100644
--- a/lib/inspector.js
+++ b/lib/inspector.js
@@ -8,6 +8,7 @@ const {
   ERR_INSPECTOR_COMMAND,
   ERR_INSPECTOR_NOT_AVAILABLE,
   ERR_INSPECTOR_NOT_CONNECTED,
+  ERR_INSPECTOR_NOT_ACTIVE,
   ERR_INVALID_ARG_TYPE,
   ERR_INVALID_CALLBACK
 } = require('internal/errors').codes;
@@ -19,7 +20,12 @@ if (!hasInspector)
 const EventEmitter = require('events');
 const { validateString } = require('internal/validators');
 const util = require('util');
-const { Connection, open, url } = internalBinding('inspector');
+const {
+  Connection,
+  open,
+  url,
+  waitForDebugger
+} = internalBinding('inspector');
 
 const connectionSymbol = Symbol('connectionProperty');
 const messageCallbacksSymbol = Symbol('messageCallbacks');
@@ -105,10 +111,22 @@ class Session extends EventEmitter {
   }
 }
 
+function inspectorOpen(port, host, wait) {
+  open(port, host);
+  if (wait)
+    waitForDebugger();
+}
+
+function inspectorWaitForDebugger() {
+  if (!waitForDebugger())
+    throw new ERR_INSPECTOR_NOT_ACTIVE();
+}
+
 module.exports = {
-  open: (port, host, wait) => open(port, host, !!wait),
+  open: inspectorOpen,
   close: process._debugEnd,
   url: url,
+  waitForDebugger: inspectorWaitForDebugger,
   // This is dynamically added during bootstrap,
   // where the console from the VM is still available
   console: require('internal/util/inspector').consoleFromVM,
diff --git a/lib/internal/errors.js b/lib/internal/errors.js
index 873523f64d..c36f34eff4 100644
--- a/lib/internal/errors.js
+++ b/lib/internal/errors.js
@@ -887,6 +887,7 @@ E('ERR_INPUT_TYPE_NOT_ALLOWED', '--input-type can only be used with string ' +
 E('ERR_INSPECTOR_ALREADY_CONNECTED', '%s is already connected', Error);
 E('ERR_INSPECTOR_CLOSED', 'Session was closed', Error);
 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_INTERNAL_ASSERTION', (message) => {