From: Colin Bartlett <colinb2r@...>
Date: 2010-01-23T02:12:09+09:00
Subject: Re: Get time object from the web?

On Fri, Jan 22, 2010 at 11:43 AM, Ralph Shnelvar <ralphs@dos32.com> wrote:
> SK> another way:
> SK> http://juretta.com/log/2006/08/26/ruby_contacting_a_timeserver/
>
> In that URL cited, there is a comment that reads
>  # you might want to cache the Cache result... it won't change ;-)
>
> What does this mean?

The code (full code is below for ease of reference) says that
the time server returns the number of seconds from 1900-01-01.
The Ruby Time class works with the number of seconds
from 1970-01-01, so to use the seconds to create a Time object
we need to adjust the seconds returned from the time server
by the number of seconds from 1900-01-01 to 1970-01-01.
That number of adjustment seconds won't change,
so once it has been calculated using get_seconds_diff_1970_1900
that adjustment can be stored for future use.

So you could do something like:
  adjustment_secs_1900_to_1970 = get_seconds_diff_1970_1900
and then
  seconds = Net::Telnet.new(options).recv(4).unpack('N').first
  remote_time = Time.at( seconds - adjustment_secs_1900_to_1970 )

Does that explain what you were asking about?


## code at http://juretta.com/log/2006/08/26/ruby_contacting_a_timeserver/
require 'net/telnet'
TIME_SERVER = 'ntp2.fau.de'

options = {
  "Host" => TIME_SERVER,
  "Telnetmode" => false,
  "Timeout" => 30,
  "Port" => "time"
}

# The time is the number of seconds since 00:00 (midnight) 1 January 1900
# GMT, such that the time 1 is 12:00:01 am on 1 January 1900 GMT; this
# base will serve until the year 2036.
seconds = Net::Telnet.new(options).recv(4).unpack('N').first

# The Ruby Time class handles dates with an epoch
# starting at midnight january 1 1970
# We have to use the Date class to work with pre-epoch dates.
require 'date'
def get_seconds_diff_1970_1900
  # you might want to cache the Cache result... it won't change ;-)
  (DateTime.new(1970, 1, 1) - DateTime.new(1900, 1, 1)).to_i * 24 * 60 * 60
end

# Convert seconds to a Time object
remote_time = Time.at(seconds - \
  get_seconds_diff_1970_1900).strftime("%Y-%m-%d %H:%M:%S")

print "Time from #{TIME_SERVER} -> #{remote_time}"