This struct wraps up a UUID that encodes a timestamp measured as seconds from the epoch (0001-01-01 00:00:00.0 UTC) observed at the location where the timestamp was generated, plus nanoseconds in the current second, plus 6 bytes for unique identification of the source -- this could be an IPV4 address with two null bytes, a MAC address, or some other sequence that will fit in 6 bytes.
Nanoseconds will fit in an Int32 (4 bytes), but seconds since the epoch will not. The current number of seconds leaks a short distance into a 5th byte, meaning that in this class, it has to be represented by an Int64. This is problematic because a UID allows for 16 bytes, so the use of 8 for seconds and 4 for nanoseconds leaves only 4 bytes for system identification. It also leaves three bytes in the UUID as zeros because 8 bytes for seconds is a lot of seconds.
One solution is to combine the seconds and the nanoseconds into a single Int64 number. This requires math operations to do efficiently:
(seconds * 1000000000) + nanoseconds
and then more math to extract the original numbers in order to reconstruct the original timestamp. This leaves 8 bytes for identification or other uniqueness information, which is lovely, but the math requirement is less lovely.
The other options is to truncate 2 bytes off of the seconds, storing 6 bytes of seconds data. This leaves 6 bytes for identification.
The current implementation chose option #2, as it is less work to generate a UUID if math is not involved.
The byte structure of the CSUUID is:
+-------------+-----------------+------------+
| nanoseconds | seconds | identifier |
| 0..3 | 4..10 | 11..15 |
+-------------+-----------------+------------+
The representational structure of the CSUUID, however, is itself sortable, as are the objects themselves.
.00.0e.d9.eb.-.7e.05.-.08.ae.-.f2.9c.-.df.18.10.1c.4a.dc.
^ seconds ^ nanoseconds ^identifier/entropy^
-
Add the dependency to your
shard.yml:dependencies: csuuid: github: wyhaines/csuuid.cr
-
Run
shards install
require "csuuid"
uuid = CSUUID.new
uuid = CSUUID.new(seconds: 9223372036, nanoseconds: 729262400)
uuid = CSUUID.new(identifier: Random.new.random_bytes(6))
dt = ParseDate.parse("2020/07/29 09:15:37")
uuid = CSUUID.new(dt)https://wyhaines.github.io/csuuid.cr/
- Fork it (https://github.com/wyhaines/csuuid.cr/fork)
- Create your feature branch (
git checkout -b my-new-feature) - Commit your changes (
git commit -am 'Add some feature') - Push to the branch (
git push origin my-new-feature) - Create a new Pull Request
- Kirk Haines - creator and maintainer
