readline has incorrect cursor with ANSI escape codes

[indexzero]

A simple code example:

var readline = require('readline');

var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: process.stdout.isTTY
});

rl.setPrompt('\u001b[90musername: \u001b[39m');
rl.prompt();

Yields the output:

username:           Cursor-Here

Without ANSI escape codes:

var readline = require('readline');

var rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  terminal: process.stdout.isTTY
});

rl.setPrompt('username: ');
rl.prompt();

Yields the expected output:

username: Cursor-Here

The bug appears to be in Interface.prototype.setPrompt:

Interface.prototype.setPrompt = function(prompt, length) {
  this._prompt = prompt;
  if (length) {
    this._promptLength = length;
  } else {
    var lines = prompt.split(/[\r\n]/);
    var lastLine = lines[lines.length - 1];
    this._promptLength = lastLine.length;
  }
};

Changing:

  this._promptLength = lastLine.length;

To:

  this._promptLength = lastLine.replace(/\u001b\[(\d+(;\d+)*)?m/g, '').length;

Should do the trick.

[isaacs]

Care to rephrase that suggestion in the form of a pull req? ;)

[bnoordhuis]

@indexzero That regex won't handle all cases. Have a look at emitKey() in lib/readline.js, it should be decomposed so the ANSI parser can be reused.

[piscisaureus]

@bnoordhuis EmitKey also won't handle all cases, unfortunately...

[Mithgol]

If that regex won't handle all cases, then what are the unhandled cases and how that regex could be improved to handle them?

[piscisaureus]

A more complete parser is here: https://github.com/joyent/libuv/blob/938a30589cd72f482b15df7290101ffc6e226e05/src/win/tty.c#L1336-1612. Now rewrite as a regex :-)

[rlidwka]

We could try to partially implement that parser in plain javascript. It would be useful for readline testing anyway, I thought about it some time ago.

The question is: doesn't such thing feel too heavy there?

[tmpfs]

This fix is available in >0.11.3 but for those of us using the stable 0.10.x series this is still an issue.

The workaround is to calculate the prompt length without any ANSI escape sequences and pass the length as the second argument to setPrompt(), something like:

var rl = ... // create readline interface
var prompt = '>';
var len = prompt.length;
var colorized = colorize(prompt) // add ANSI sequences
rl.setPrompt(colorized, len);