% sntp(1) | A bare-bones SNTP client

SNTP - A bare-bones SNTP client

sntp server port?

• Project: A simple SNTP client
• Author: Richard James Howe
• License: The Unlicense
• Email: [email protected]
• Repository: https://github.com/howerj/sntp

Super bare bones SNTP client. Implementing a full NTP client is quite complex, just getting the time from an NTP server is not, most applications do not need sub second accuracy, or even second accuracy. This program should be fine for those use cases.

Most of the complexity of this solution is in dealing with the IPv4/IPv6 connection. They really did make it ugly.

To build and run you will require two things make and a C compiler. Type 'make' to build the example program called 'sntp' and type 'make run' to build and run the 'sntp' program. It will attempt to connect to a NTP pool specified in the makefile.

Building the program also produces a library, 'libsntp.a', the SNTP library is incredibly simple, much like the program, containing just one function:

int sntp(const char *server, unsigned port, unsigned long *seconds, unsigned long *fractional);

This function returns zero on success, and negative on failure. You must provide a SNTP server to connect to (either a hostname, an IPv4, or an IPv6 address), a port (the default port for NTP is port 123, set the port to zero to auto select this) and two variables into which the time will placed on success, on failure both values will be set to zero. This function will block until the client either returns success or failure.

A non-blocking version of the 'sntp' function would be trivial to make, it would require only a file descriptor and a single variable describing the program position to be stored and passed into the 'sntp' function between calls.

References:

• NTPv4 https://tools.ietf.org/html/rfc5905
• NTPv3 https://tools.ietf.org/html/rfc1305
• https://en.wikipedia.org/wiki/Network_Time_Protocol

All code and documentation is released into the public domain where this is allowed, do what thou wilt.

The 'sntp' program returns '1' on failure and '0' on success.