Add support for UUIDs before 1970 #133
Description
The UUID generators do not support generating UUIDs with a timestamp before 1970. Such UUIDs may be of interest for various reasons, such as (1) users wishing to better understand the UUID format, (2) users who want to test whether their application really supports any valid UUID, or (3) users interested in anachronistic video games.
The following snippet shows that this library does not support UUIDs with timestamps before 1970:
private UUIDTimer createFixedTimer(Long milliTimestamp) throws IOException {
return new UUIDTimer(
new Random(),
null,
new UUIDClock() {
@Override
public long currentTimeMillis() {
return milliTimestamp;
}
}
);
}
public void myFunction() throws IOException {
long milliTimestamp = -219292800000L; // Corresponds to 1963-01-19 21:20:00
TimeBasedGenerator generator = Generators.timeBasedGenerator(null, createFixedTimer(milliTimestamp));
UUID uuid = generator.generate();
System.out.println(uuid); // e.g. 138140d9-1dd2-11b2-a49b-43863b6a1ebd, which corresponds to 1970-01-01 00:00:00
}The cause appears to be inside UUIDTimer's getTimestamp function, which implicitly assumes that timestamps are non-negative:
if (systime <= _lastUsedTimestamp) {
if (_clockCounter < kClockMultiplier) {
systime = _lastUsedTimestamp;Since _lastUsedTimestamp defaults to 0, if systime is negative, systime will always be set to _lastUsedTimestamp.