Socket send functions only allow you to send strings?

Ruby
1

I am writing a small TimeP (RFC 868) server to sync time with some
networking equipment. The equipment that shall go nameless requires the
use of UDP.

As far as I can tell, my only option to write to a UDPSocket is to use
the send method, which takes a string. I need to send a 32bit integer
representing the date in a UDP packet and I’d love to use something
like:

myUDPsocket.send( Time.now.to_i, 0, host, port)

In my situation I can’t change the receiving program to accept a string
or I could do it that way. I can’t convert the integer to a string
either because that would blow my 32 bit requirement. Does anyone have
any idea?

~Parkingmeter

2

On 9/4/07, Ryan P. [email protected] wrote:

Try

ri Array#pack

[number].pack(‘i’)

should do the trick.
pth

3

Ryan P. wrote:

In my situation I can’t change the receiving program to accept a string
or I could do it that way. I can’t convert the integer to a string
either because that would blow my 32 bit requirement. Does anyone have
any idea?

Strings are just blobs of binary data, when they go through #send. The
receiver doesn’t know it started life as a ruby string.

If you want structure, use #pack. You’ll need to know what byte-order
the client and server should use to communicate. Assuming big-endian:

myUDPsocket.send([Time.now.to_i].pack(“N”), 0, host, port)

4

On Wed, 5 Sep 2007, Ryan P. wrote:

any idea?
A string is just a sequence of bytes. It can be anything.

In your case, you need to encode a decimal number as returned by
Time.now.to_i into 32 bits.

myUDPsocket.send( [Time.now.to_i].pack(‘i’) )

That may be what you need.

http://ruby-doc.org/core/classes/Array.html#M002245

For more information.

Kirk H.

5

On 9/4/07, [email protected] [email protected] wrote:

In my situation I can’t change the receiving program to accept a string

Actually, to support RFC-868, you have to use the same epoch that NTP
uses,
rather than the Unix epoch.

The current time in raw form would be Time.now.to_i + 0x83aa7e80. Pack
into
32 bits (taking care to keep the conversion unsigned), convert to
network-order as necessary, write a four-byte UDP datagram, and away you
go.

6

In article [email protected],
Ryan P. [email protected] writes:

In my situation I can’t change the receiving program to accept a string
or I could do it that way. I can’t convert the integer to a string
either because that would blow my 32 bit requirement. Does anyone have
any idea?

~Parkingmeter

Here, I had this script lying about from one of my earlier experiments
with Ruby sockets:

  • dmw

------ start of code -------
#! /usr/bin/env ruby

nettimesvr.rb - implement Time Server for RFC 868

PROGNAME = ‘nettimesvr.rb’
timeport = Socket.getservbyname(‘time’, ‘udp’) # port 37

timeport = 50037 # for testing

RFC868_POSIX_ADJMENT = 2_208_988_800 # diff between RFC 868 and POSIX
POSIX_EPOCH_ADJMENT = Time.gm(1970, ‘Jan’, 1).to_i

require ‘socket’

def curnettime()
return Time.new.to_i + (RFC868_POSIX_ADJMENT -
POSIX_EPOCH_ADJMENT)
end

port = timeport
begin
case ARGV.size
when 1: port = Integer(ARGV[0])
when 0: nil
else; abort “Usage: #{PROGNAME} [ port ]”
end
rescue ArgumentError => badarg
abort “Argument conversion error: #{badarg}”
end

puts “Listening on port #{port}\n”

UDPSocket.open { |sock|
sock.bind(Socket::INADDR_ANY, port)
loop do
# if we try to receive zero bytes, we get an
error
rmthost = sock.recvfrom(1) [1] # no body
expected
puts “Accepted request from #{rmthost [2]}”

            nettime = [ curnettime() ].pack('N')
            sock.send(nettime, 0, rmthost[2], rmthost[1])
    end

}

------ end of code -------