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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: NTP
Date: Sat, 16 Sep 2017 11:29:09 +0200
Organization: Aioe.org NNTP Server
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Xref: news.eternal-september.org comp.lang.ada:48143
Date: 2017-09-16T11:29:09+02:00
List-Id: <comp.lang.ada>

On 2017-09-16 08:40, Anatoly Chernyshev wrote:

> Is there a way to get time via the Network Time Protocol in Ada? It
> doesn't look like AWS has it (or I've missed something).
> 
> Currently I'm getting around spawning the Cygwin "nc" command, but it hurts my feelings.

Do you mean send a single UDP request to an NTP server and convert the 
response to Ada time?

You can try this:
----------------------------------------------------------------------
with Ada.Text_IO;              use Ada.Text_IO;
with Ada.Calendar;             use Ada.Calendar;
with Ada.Calendar.Formatting;  use Ada.Calendar.Formatting;
with Ada.Exceptions;           use Ada.Exceptions;
with Ada.Streams;              use Ada.Streams;
with GNAT.Sockets;             use GNAT.Sockets;
with Interfaces;               use Interfaces;

procedure Test is

    function Get_NTP_Time
             (  Server  : String;
                Timeout : Timeval_Duration := 10.0
             )  return Time is
       NTP_Packet_Size : constant := 48;
          -- RFC 5905: Official NTP era begins at 1 Jan 1900. We cannot
          -- have it in Ada.Calendar.Time, so taking a later time. Note
          -- Time_Zone = 0 in order to have it UTC
       Era : constant Time := Time_Of (1999, 12, 31, Time_Zone => 0);
          -- RFC 5905: seconds since 1 Jan 1900 to 31 Dec 1999
       Era_Offset : constant := 3_155_587_200;

       Socket   : Socket_Type;
       Address  : Sock_Addr_Type;
       Seconds  : Unsigned_32;
       Fraction : Unsigned_32;
       Last     : Stream_Element_Offset;
       Data     : Stream_Element_Array (1..NTP_Packet_Size) :=
                     (  1  => 2#1110_0011#, -- LI, Version, Mode
                        2  => 0,            -- Stratum, or type of clock
                        3  => 0,            -- Polling Interval
                        4  => 16#EC#,       -- Peer Clock Precision
                        13 => 49,
                        14 => 16#4E#,
                        15 => 49,
                        16 => 52,
                        others => 0
                     );
    begin
       Address.Addr := Addresses (Get_Host_By_Name (Server), 1);
       Address.Port := 123; -- NTP port
       Create_Socket (Socket, Family_Inet, Socket_Datagram);
       Set_Socket_Option
       (  Socket,
          Socket_Level,
          (Receive_Timeout, Timeout)
       );
       Send_Socket (Socket, Data, Last, Address);
       Receive_Socket (Socket, Data, Last, Address);
       if Last /= Data'Last then
          Raise_Exception (Data_Error'Identity, "Mangled response");
       end if;
       Seconds := (  Unsigned_32 (Data (41)) * 2**24
                  +  Unsigned_32 (Data (42)) * 2**16
                  +  Unsigned_32 (Data (43)) * 2**8
                  +  Unsigned_32 (Data (44))
                  -  Era_OFfset
                  );
       Fraction := (  Unsigned_32 (Data (45)) * 2**24
                   +  Unsigned_32 (Data (46)) * 2**16
                   +  Unsigned_32 (Data (47)) * 2**8
                   +  Unsigned_32 (Data (48))
                   );
       return (  Era
              +  Duration (Seconds)
         --     +  Duration (Long_Float (Fraction) / 2.0**32)
              );
    end Get_NTP_Time;

    Stamp : Time;
begin
    Stamp := Get_NTP_Time ("time.nist.gov");
    Put_Line ("NTP time " & Image (Stamp));
exception
    when Error : others =>
       Put_Line ("Error: " & Exception_Information (Error));
end Test;
-------------------------------------------------------------------

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de