Extract date time from UUID V7

[yashh]

Is there a way to extract date time from the UUID v7 generator?

[pw-lehre]

@yashh It is generally discouraged to do so, e.g. https://datatracker.ietf.org/doc/html/draft-ietf-uuidrev-rfc4122bis#name-opacity

That being said, since the time stamp is defined as 48 bits (cf. https://datatracker.ietf.org/doc/html/draft-ietf-uuidrev-rfc4122bis#name-uuid-version-7), you can extract it with:

long timestamp = uuid.getMostSignificantBits() >>> (Long.SIZE - 48);

[yashh]

Thank you @pw-lehre . My only motive was to make sure the library is taking the current timestamp and which timezone. Thank you for pointer.

[cowtowncoder]

@yashh FWTW, timezone is not relevant; timestamps do not use or have it (generally it's offset from UTC but no timezone info is included).

[yashh]

@cowtowncoder Yup. I was using https://github.com/stevesimmons/uuid7 library to verify that timestamp and all checks out. But there is something wrong with that library. The timestamp its generating is around year 1983. I tried https://github.com/oittaa/uuid6-python and everything checks out.

[fabiolimace]

Some implementations are based on old drafts. That's why https://github.com/stevesimmons/uuid7 is different.

In 2021, UUIDv7 reserved 36 bits for seconds (not milliseconds). To extract the timestamp from this particular implementation, you must extract the initial 36 bits.

	UUID uuid = UUID.fromString("061cb26a-54b8-7a52-8000-2124e7041024");
	long seconds = uuid.getMostSignificantBits() >>> (Long.SIZE - 36);
	Instant instant = Instant.ofEpochSecond(seconds);
	System.out.println(instant); // prints 2021-12-28T15:00:53Z

[yashh]

Makes sense. Thank you @fabiolimace

[cowtowncoder]

Good point: timestamps used are indeed different: original UUID versions (v1 - v4) used higher-granularity ones with 100 ns resolution -- these take lots of space (bits). So v7 trades in smaller size for lower granularity.