readline: expose stream API in cursorTo()

This commit adds an optional callback to cursorTo(), which is
passed to the stream's write() method. It also exposes the
return value of write().

PR-URL: https://github.com/nodejs/node/pull/28674
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>

doc/api/readline.md

@@ -487,14 +487,22 @@ function completer(linePartial, callback) {
 }
 ```
 
-## readline.cursorTo(stream, x, y)
+## readline.cursorTo(stream, x, y[, callback])
 <!-- YAML
 added: v0.7.7
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/28674
+    description: The stream's write() callback and return value are exposed.
 -->
 
 * `stream` {stream.Writable}
 * `x` {number}
 * `y` {number}
+* `callback` {Function} Invoked once the operation completes.
+* Returns: {boolean} `false` if `stream` wishes for the calling code to wait for
+  the `'drain'` event to be emitted before continuing to write additional data;
+  otherwise `true`.
 
 The `readline.cursorTo()` method moves cursor to the specified position in a
 given [TTY][] `stream`.

lib/readline.js

@@ -1189,21 +1189,21 @@ function emitKeypressEvents(stream, iface) {
  * moves the cursor to the x and y coordinate on the given stream
  */
 
-function cursorTo(stream, x, y) {
+function cursorTo(stream, x, y, callback) {
-  if (stream === null || stream === undefined)
+  if (callback !== undefined && typeof callback !== 'function')
-    return;
+    throw new ERR_INVALID_CALLBACK(callback);
 
-  if (typeof x !== 'number' && typeof y !== 'number')
+  if (stream == null || (typeof x !== 'number' && typeof y !== 'number')) {
-    return;
+    if (typeof callback === 'function')
+      process.nextTick(callback);
+    return true;
+  }
 
   if (typeof x !== 'number')
     throw new ERR_INVALID_CURSOR_POS();
 
-  if (typeof y !== 'number') {
+  const data = typeof y !== 'number' ? CSI`${x + 1}G` : CSI`${y + 1};${x + 1}H`;
-    stream.write(CSI`${x + 1}G`);
+  return stream.write(data, callback);
-  } else {
-    stream.write(CSI`${y + 1};${x + 1}H`);
-  }
 }
 
 /**

test/parallel/test-readline-csi.js

@@ -106,15 +106,17 @@ assert.strictEqual(readline.moveCursor(undefined, 1, 1, common.mustCall()),
                    true);
 
 // Undefined or null as stream should not throw.
-readline.cursorTo(null);
+assert.strictEqual(readline.cursorTo(null), true);
-readline.cursorTo();
+assert.strictEqual(readline.cursorTo(), true);
+assert.strictEqual(readline.cursorTo(null, 1, 1, common.mustCall()), true);
+assert.strictEqual(readline.cursorTo(undefined, 1, 1, common.mustCall()), true);
 
 writable.data = '';
-readline.cursorTo(writable, 'a');
+assert.strictEqual(readline.cursorTo(writable, 'a'), true);
 assert.strictEqual(writable.data, '');
 
 writable.data = '';
-readline.cursorTo(writable, 'a', 'b');
+assert.strictEqual(readline.cursorTo(writable, 'a', 'b'), true);
 assert.strictEqual(writable.data, '');
 
 writable.data = '';
@@ -128,9 +130,18 @@ common.expectsError(
 assert.strictEqual(writable.data, '');
 
 writable.data = '';
-readline.cursorTo(writable, 1, 'a');
+assert.strictEqual(readline.cursorTo(writable, 1, 'a'), true);
 assert.strictEqual(writable.data, '\x1b[2G');
 
 writable.data = '';
-readline.cursorTo(writable, 1, 2);
+assert.strictEqual(readline.cursorTo(writable, 1, 2), true);
 assert.strictEqual(writable.data, '\x1b[3;2H');
+
+writable.data = '';
+assert.strictEqual(readline.cursorTo(writable, 1, 2, common.mustCall()), true);
+assert.strictEqual(writable.data, '\x1b[3;2H');
+
+// Verify that cursorTo() throws on invalid callback.
+assert.throws(() => {
+  readline.cursorTo(writable, 1, 1, null);
+}, /ERR_INVALID_CALLBACK/);