The Console That Thought 2010 Was a Leap Year — JavaScript Bug Hunt

Briefing

Modelled on ApocalyPS3 (1 March 2010): the PlayStation 3's clock firmware treated 2010 as a leap year. On 1 March the hardware reported a 29 February that did not exist, date validation failed everywhere, and older consoles worldwide could not sign in, play games or use trophies.

clock.js has the same faulty leap-year rule.

Fix isLeapYear so it follows the Gregorian rule.

Bug report

BUG-8001050F · Priority: Critical · Reported by: platform

isLeapYear(year) must implement the Gregorian rule:

• divisible by 4 -> leap
• unless divisible by 100 -> not leap
• unless divisible by 400 -> leap

Observed: 2010 is reported as a leap year, and so is every year ending in 0. 1900 is also wrong in the other direction.

Logs

[rtc] date rolled to 2010-02-29
[rtc] trophy sync failed: invalid timestamp

The code as shipped

src/clock/clock.js (editable)

// Gregorian leap-year test.
exports.isLeapYear = function (year) {
  // "Every fourth year, and also the round ones" — as shipped.
  if (year % 10 === 0) return true;
  return year % 4 === 0;
};

exports.daysInFebruary = function (year) {
  return exports.isLeapYear(year) ? 29 : 28;
};