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ntpquery: Compute and print delay and offset

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Nico Weber 2020-09-06 19:55:01 -04:00 • committed by Andreas Kling
parent 39d14c22d1
commit 4ac5cc2461
1 changed files with 22 additions and 0 deletions
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22
Userland/ntpquery.cpp
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@ -28,6 +28,7 @@
#include <LibCore/ArgsParser.h> #include <LibCore/ArgsParser.h>
#include <arpa/inet.h> #include <arpa/inet.h>
#include <endian.h> #include <endian.h>
#include <math.h>
#include <netdb.h> #include <netdb.h>
#include <netinet/in.h> #include <netinet/in.h>
#include <stdio.h> #include <stdio.h>
@ -213,4 +214,25 @@ int main(int argc, char** argv)
printf("Receive timestamp: %#016llx (%s)\n", receive_timestamp, format_ntp_timestamp(receive_timestamp).characters()); printf("Receive timestamp: %#016llx (%s)\n", receive_timestamp, format_ntp_timestamp(receive_timestamp).characters());
printf("Transmit timestamp: %#016llx (%s)\n", transmit_timestamp, format_ntp_timestamp(transmit_timestamp).characters()); printf("Transmit timestamp: %#016llx (%s)\n", transmit_timestamp, format_ntp_timestamp(transmit_timestamp).characters());
printf("Destination timestamp: %#016llx (%s)\n", destination_timestamp, format_ntp_timestamp(destination_timestamp).characters()); printf("Destination timestamp: %#016llx (%s)\n", destination_timestamp, format_ntp_timestamp(destination_timestamp).characters());
// Parts of the "Clock Filter" computations, https://tools.ietf.org/html/rfc5905#section-10
NtpTimestamp T1 = origin_timestamp;
NtpTimestamp T2 = receive_timestamp;
NtpTimestamp T3 = transmit_timestamp;
NtpTimestamp T4 = destination_timestamp;
auto timestamp_difference_in_seconds = [](NtpTimestamp from, NtpTimestamp to) {
return static_cast<int64_t>(to - from) / pow(2.0, 32);
};
// The network round-trip time of the request.
// T4-T1 is the wall clock roundtrip time, in local ticks.
// T3-T2 is the server side processing time, in server ticks.
double delay_s = timestamp_difference_in_seconds(T1, T4) - timestamp_difference_in_seconds(T2, T3);
// The offset from local time to server time, ignoring network delay.
// Both T2-T1 and T3-T4 estimate this; this takes the average of both.
// Or, equivalently, (T1+T4)/2 estimates local time, (T2+T3)/2 estimate server time, this is the difference.
double offset_s = 0.5 * (timestamp_difference_in_seconds(T1, T2) + timestamp_difference_in_seconds(T4, T3));
printf("Delay: %f\n", delay_s);
printf("Offset: %f\n", offset_s);
} }