readline: key interval delay for \r & \n

Emit two line events when there is a delay between
CR('\r') and LF('\n').

Introduced a new option `crlfDelay`. If the delay between \r and \n
exceeds `crlfDelay` milliseconds, both \r and \n will be treated as
separate end-of-line input. Default to 100 milliseconds.
`crlfDelay` will be coerced to [100, 2000] range.

PR-URL: https://github.com/nodejs/node/pull/8109
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

doc/api/readline.md

@@ -361,6 +361,10 @@ added: v0.1.98
     only if `terminal` is set to `true` by the user or by an internal `output`
     check, otherwise the history caching mechanism is not initialized at all.
   * `prompt` - the prompt string to use. Default: `'> '`
+  * `crlfDelay` {number} If the delay between `\r` and `\n` exceeds
+    `crlfDelay` milliseconds, both `\r` and `\n` will be treated as separate
+    end-of-line input. Default to `100` milliseconds.
+    `crlfDelay` will be coerced to `[100, 2000]` range.
 
 The `readline.createInterface()` method creates a new `readline.Interface`
 instance.

lib/readline.js

@@ -7,6 +7,8 @@
 'use strict';
 
 const kHistorySize = 30;
+const kMincrlfDelay = 100;
+const kMaxcrlfDelay = 2000;
 
 const util = require('util');
 const debug = util.debuglog('readline');
@@ -39,13 +41,14 @@ function Interface(input, output, completer, terminal) {
     return self;
   }
 
-  this._sawReturn = false;
+  this._sawReturnAt = 0;
   this.isCompletionEnabled = true;
   this._sawKeyPress = false;
   this._previousKey = null;
 
   EventEmitter.call(this);
   var historySize;
+  let crlfDelay;
   let prompt = '> ';
 
   if (arguments.length === 1) {
@@ -57,6 +60,7 @@ function Interface(input, output, completer, terminal) {
     if (input.prompt !== undefined) {
       prompt = input.prompt;
     }
+    crlfDelay = input.crlfDelay;
     input = input.input;
   }
 
@@ -85,6 +89,8 @@ function Interface(input, output, completer, terminal) {
   this.output = output;
   this.input = input;
   this.historySize = historySize;
+  this.crlfDelay = Math.max(kMincrlfDelay,
+                            Math.min(kMaxcrlfDelay, crlfDelay >>> 0));
 
   // Check arity, 2 - for async, 1 for sync
   if (typeof completer === 'function') {
@@ -345,9 +351,10 @@ Interface.prototype._normalWrite = function(b) {
     return;
   }
   var string = this._decoder.write(b);
-  if (this._sawReturn) {
+  if (this._sawReturnAt &&
+      Date.now() - this._sawReturnAt <= this.crlfDelay) {
     string = string.replace(/^\n/, '');
-    this._sawReturn = false;
+    this._sawReturnAt = 0;
   }
 
   // Run test() on the new string chunk, not on the entire line buffer.
@@ -358,7 +365,7 @@ Interface.prototype._normalWrite = function(b) {
     this._line_buffer = null;
   }
   if (newPartContainsEnding) {
-    this._sawReturn = string.endsWith('\r');
+    this._sawReturnAt = string.endsWith('\r') ? Date.now() : 0;
 
     // got one or more newlines; process into "line" events
     var lines = string.split(lineEnding);
@@ -846,20 +853,22 @@ Interface.prototype._ttyWrite = function(s, key) {
     /* No modifier keys used */
 
     // \r bookkeeping is only relevant if a \n comes right after.
-    if (this._sawReturn && key.name !== 'enter')
-      this._sawReturn = false;
+    if (this._sawReturnAt && key.name !== 'enter')
+      this._sawReturnAt = 0;
 
     switch (key.name) {
       case 'return':  // carriage return, i.e. \r
-        this._sawReturn = true;
+        this._sawReturnAt = Date.now();
         this._line();
         break;
 
       case 'enter':
-        if (this._sawReturn)
-          this._sawReturn = false;
-        else
+        // When key interval > crlfDelay
+        if (this._sawReturnAt === 0 ||
+            Date.now() - this._sawReturnAt > this.crlfDelay) {
           this._line();
+        }
+        this._sawReturnAt = 0;
         break;
 
       case 'backspace':

test/parallel/test-readline-interface.js

@@ -26,6 +26,34 @@ function isWarned(emitter) {
   return false;
 }
 
+{
+  // Default crlfDelay is 100ms
+  const fi = new FakeInput();
+  const rli = new readline.Interface({ input: fi, output: fi });
+  assert.strictEqual(rli.crlfDelay, 100);
+  rli.close();
+}
+
+{
+  // Minimum crlfDelay is 100ms
+  const fi = new FakeInput();
+  const rli = new readline.Interface({ input: fi, output: fi, crlfDelay: 0});
+  assert.strictEqual(rli.crlfDelay, 100);
+  rli.close();
+}
+
+{
+  // Maximum crlfDelay is 2000ms
+  const fi = new FakeInput();
+  const rli = new readline.Interface({
+    input: fi,
+    output: fi,
+    crlfDelay: 1 << 30
+  });
+  assert.strictEqual(rli.crlfDelay, 2000);
+  rli.close();
+}
+
 [ true, false ].forEach(function(terminal) {
   var fi;
   var rli;
@@ -199,6 +227,29 @@ function isWarned(emitter) {
   assert.equal(callCount, expectedLines.length);
   rli.close();
 
+  // Emit two line events when the delay
+  //   between \r and \n exceeds crlfDelay
+  {
+    const fi = new FakeInput();
+    const delay = 200;
+    const rli = new readline.Interface({
+      input: fi,
+      output: fi,
+      terminal: terminal,
+      crlfDelay: delay
+    });
+    let callCount = 0;
+    rli.on('line', function(line) {
+      callCount++;
+    });
+    fi.emit('data', '\r');
+    setTimeout(common.mustCall(() => {
+      fi.emit('data', '\n');
+      assert.equal(callCount, 2);
+      rli.close();
+    }), delay * 2);
+  }
+
   // \t when there is no completer function should behave like an ordinary
   //   character
   fi = new FakeInput();