readline: add support for async iteration

Co-authored-by: Ivan Filenko <ivan.filenko@protonmail.com>
Fixes: https://github.com/nodejs/node/issues/18603
Refs: https://github.com/nodejs/node/pull/18904
PR-URL: https://github.com/nodejs/node/pull/23916
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

1 files changed, 43 insertions, 0 deletions

diff --git a/lib/readline.js b/lib/readline.js
index b293292d83..049f5aaecc 100644
--- a/lib/readline.js
+++ b/lib/readline.js
@@ -33,6 +33,7 @@ const {
   ERR_INVALID_OPT_VALUE
 } = require('internal/errors').codes;
 const { debug, inherits } = require('util');
+const { emitExperimentalWarning } = require('internal/util');
 const { Buffer } = require('buffer');
 const EventEmitter = require('events');
 const {
@@ -54,11 +55,16 @@ const {
 // Lazy load StringDecoder for startup performance.
 let StringDecoder;
 
+// Lazy load Readable for startup performance.
+let Readable;
+
 const kHistorySize = 30;
 const kMincrlfDelay = 100;
 // \r\n, \n, or \r followed by something other than \n
 const lineEnding = /\r?\n|\r(?!\n)/;
 
+const kLineObjectStream = Symbol('line object stream');
+
 const KEYPRESS_DECODER = Symbol('keypress-decoder');
 const ESCAPE_DECODER = Symbol('escape-decoder');
 
@@ -190,6 +196,8 @@ function Interface(input, output, completer, terminal) {
     self._refreshLine();
   }
 
+  this[kLineObjectStream] = undefined;
+
   if (!this.terminal) {
     function onSelfCloseWithoutTerminal() {
       input.removeListener('data', ondata);
@@ -1019,6 +1027,41 @@ Interface.prototype._ttyWrite = function(s, key) {
   }
 };
 
+Interface.prototype[Symbol.asyncIterator] = function() {
+  emitExperimentalWarning('readline Interface [Symbol.asyncIterator]');
+
+  if (this[kLineObjectStream] === undefined) {
+    if (Readable === undefined) {
+      Readable = require('stream').Readable;
+    }
+    const readable = new Readable({
+      objectMode: true,
+      read: () => {
+        this.resume();
+      },
+      destroy: (err, cb) => {
+        this.off('line', lineListener);
+        this.off('close', closeListener);
+        this.close();
+        cb(err);
+      }
+    });
+    const lineListener = (input) => {
+      if (!readable.push(input)) {
+        this.pause();
+      }
+    };
+    const closeListener = () => {
+      readable.push(null);
+    };
+    this.on('line', lineListener);
+    this.on('close', closeListener);
+    this[kLineObjectStream] = readable;
+  }
+
+  return this[kLineObjectStream][Symbol.asyncIterator]();
+};
+
 /**
  * accepts a readable Stream instance and makes it emit "keypress" events
  */