Add 1 millisecond to a Time/DateTime object

Question

Is there a way to add 1 millisecond to a Time/DateTime object in Ruby?

For an Webservice Request i need a time scoping with milliseconds:

irb(main):034:0> time_start = Date.today.to_time.utc.iso8601(3)
=> "2016-09-27T22:00:00.000Z"

irb(main):035:0> time_end = ((Date.today + 1).to_time).utc.iso8601(3)
=> "2016-09-28T22:00:00.000Z"
-- or --
irb(main):036:0> time_end = ((Date.today + 1).to_time - 1).utc.iso8601(3)
=> "2016-09-28T21:59:59.000Z"

So I'm near my prefered solution, but time_end should be 2016-09-28T21:59:59.999Z.

I didn't find solutions that Ruby can handle calculating with milliseconds. I only did it with strftime, but it would be great if there is a possibility to calculate.

-- This works, but hard coded --
time_end = ((Date.today + 1).to_time - 1).utc.strftime("%Y-%m-%dT%H:%M:%S.999Z")
=> "2016-09-28T21:59:59.999Z"

FYI: I'm on plain Ruby, no Rails.

Answer 1

Ok i found a solution. With real calculation i looks like.

time_end = ((Date.today + 1).to_time - 1/1001).utc.iso8601(3)
=> "2016-09-28T21:59:59.999Z"

EXAMPLE

Formatting in iso8601(3) is only to show behavior.

irb(main):055:0> Date.today.to_time.iso8601(3)
=> "2016-09-28T00:00:00.000+02:00

Adding a millisecond"

irb(main):058:0> (Date.today.to_time + 1/1000.0).iso8601(3)
=> "2016-09-28T00:00:00.001+02:00"

Subtract a millisecond

!DONT USE, see result with subtracted 2 milliseconds!
irb(main):060:0> (Date.today.to_time - 1/1000.0).iso8601(3)
=> "2016-09-27T23:59:59.998+02:00"

USE
irb(main):061:0> (Date.today.to_time - 1/1001.0).iso8601(3)
=> "2016-09-27T23:59:59.999+02:00"