Zig library example

00_zig_library_example

Zig library example

main.c

#include <stdio.h>
#include <time.h>
#include "udp_get_time.h"

int main()
{
	const char *ipaddr = "127.0.0.1";
	time_t t = udp_get_time(ipaddr);
	puts(ctime(&t));
}

Makefile

CC = zig cc

all: main

main: main.o libudp_time_lib.a
	$(CC) -o $@ $^

libudp_time_lib.a: udp_time_lib.zig
	zig build-lib -lc -O ReleaseSmall $<

main.o: main.c udp_get_time.h

clean:
	rm -rf *.o *.a main

udp_get_time.h

#ifndef _UDP_GET_TIME_H
#define _UDP_GET_TIME_H 1
#include <time.h>

extern time_t udp_get_time(const char *ipaddr);

#endif /* _UDP_GET_TIME_H */

udp_time_lib.zig

const std = @import("std");
const os = std.os;
const log = std.log;
const time = std.time;
const c = @cImport(@cInclude("time.h"));

const UDP_PAYLOADSIZE = 65507;
const TIMESERVER_PORT = 37;
const UNIX_TIME_BASE = 2_208_988_800;

fn queryTime(ipaddr: []const u8, verbose:bool) !u32 {
    var buf: [UDP_PAYLOADSIZE]u8 = .{};

    const sockfd = try os.socket(os.AF.INET, os.SOCK.DGRAM | os.SOCK.CLOEXEC, 0);
    defer os.closeSocket(sockfd);

    const addr = try std.net.Address.resolveIp(ipaddr, TIMESERVER_PORT);
    try os.connect(sockfd, &addr.any, addr.getOsSockLen());

    if (0 != try os.send(sockfd, "", 0)) unreachable; // send empty data
    if (4 != try os.recv(sockfd, &buf, 0)) unreachable;
    const t = std.mem.readIntBig(u32, buf[0..4]);
    if (verbose) {
        log.info("{d}: t={d}", .{time.milliTimestamp(), t});
    }
    // timeserver returns the number of seconds since 00:00 (midnight) 1 January 1900 GMT
    return t - UNIX_TIME_BASE;
}

export fn udp_get_time(c_ipaddr: [*c]const u8) c.time_t {
    const ipaddr = std.mem.sliceTo(c_ipaddr, 0);
    return queryTime(ipaddr, false) catch -1;
}