├── README
├── ntp.c
└── rfc.txt


/README:
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1 | ntp - Network Time Protocol client
2 | author: Eugene Ma (edma2)
3 | 


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/ntp.c:
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  1 | /* ntp.c - Network Time Protocol client
  2 |  * author: Eugene Ma (edma)
  3 |  */
  4 | 
  5 | #include <stdio.h>
  6 | #include <stdlib.h>
  7 | #include <stdint.h>
  8 | #include <string.h>
  9 | #include <sys/types.h>
 10 | #include <sys/socket.h>
 11 | #include <netdb.h>
 12 | #include <arpa/inet.h>
 13 | #include <time.h>
 14 | 
 15 | #define NTP_VERSION 		0xe3
 16 | #define NTP_DEFAULT_PORT	"123"
 17 | #define SEC_IN_YEAR 		31556926
 18 | #define UNIX_OFFSET 		2208988800L
 19 | #define VN_BITMASK(byte) 	((byte & 0x3f) >> 3)
 20 | #define LI_BITMASK(byte) 	(byte >> 6)
 21 | #define MODE_BITMASK(byte) 	(byte & 0x7)
 22 | #define ENDIAN_SWAP32(data)  	((data >> 24) | /* right shift 3 bytes */ \
 23 | 				((data & 0x00ff0000) >> 8) | /* right shift 1 byte */ \
 24 | 			        ((data & 0x0000ff00) << 8) | /* left shift 1 byte */ \
 25 | 				((data & 0x000000ff) << 24)) /* left shift 3 bytes */
 26 | 
 27 | struct ntpPacket {
 28 | 	uint8_t flags;
 29 | 	uint8_t stratum;
 30 | 	uint8_t poll;
 31 | 	uint8_t precision;
 32 | 	uint32_t root_delay;
 33 | 	uint32_t root_dispersion;
 34 | 	uint8_t referenceID[4];
 35 | 	uint32_t ref_ts_sec;
 36 | 	uint32_t ref_ts_frac;
 37 | 	uint32_t origin_ts_sec;
 38 | 	uint32_t origin_ts_frac;
 39 | 	uint32_t recv_ts_sec;
 40 | 	uint32_t recv_ts_frac;
 41 | 	uint32_t trans_ts_sec;
 42 | 	uint32_t trans_ts_frac;
 43 | } __attribute__((__packed__)); /* this is not strictly necessary,
 44 | 				* structure follows alignment rules */
 45 | 
 46 | int main(int argc, char *argv[]) {
 47 | 	char *server; /* no default server */
 48 | 	char *port = NTP_DEFAULT_PORT;
 49 | 	struct addrinfo hints, *res, *ap; /* address info structs */
 50 | 	socklen_t addrlen = sizeof(struct sockaddr_storage);
 51 | 
 52 | 	struct ntpPacket packet;
 53 | 	uint8_t *ptr = (uint8_t *)(&packet); /* to read raw bytes */
 54 | 
 55 | 	int server_sock; /* send through this socket */
 56 | 	int error; /* error checking */
 57 | 	int i;
 58 | 	unsigned int recv_secs;
 59 | 
 60 | 	time_t total_secs;
 61 | 	struct tm *now;
 62 | 
 63 | 	/* server is required, port is optional */
 64 | 	if (argc < 2) {
 65 | 		fprintf(stderr, "Usage: %s <server> [port]\n", argv[0]);
 66 | 		exit(1);
 67 | 	}
 68 | 	server = argv[1];
 69 | 	if (argc > 2)
 70 | 		port = argv[2];
 71 | 
 72 | 	memset(&packet, 0, sizeof(struct ntpPacket));
 73 | 	packet.flags = NTP_VERSION;
 74 | 	
 75 | 	memset(&hints, 0, sizeof(hints));
 76 | 	hints.ai_socktype = SOCK_DGRAM;
 77 | 
 78 | 	/* fill our address structs for ntp server */
 79 | 	error = getaddrinfo(server, port, &hints, &res);
 80 | 	/* error checking */
 81 | 	if (error != 0) {
 82 | 		fprintf(stderr, "getaddrinfo() error: %s", gai_strerror(error));
 83 | 		exit(1);
 84 | 	}
 85 | 	/* loop through results */
 86 | 	for (ap = res; ap != NULL; ap = ap->ai_next) {
 87 | 		server_sock = socket(ap->ai_family, ap->ai_socktype, ap->ai_protocol);
 88 | 		if (server_sock == -1)
 89 | 			continue;
 90 | 		break;
 91 | 	}
 92 | 	if (ap == NULL) {
 93 | 		fprintf(stderr, "socket() error\n");
 94 | 		exit(2);
 95 | 	}
 96 | 
 97 | 	error = sendto(server_sock, &packet, sizeof(struct ntpPacket), 0, ap->ai_addr, addrlen);
 98 | 	if (error == -1) {
 99 | 		fprintf(stderr, "sendto() error\n");
100 | 		exit(2);
101 | 	}
102 | 	error = recvfrom(server_sock, &packet, sizeof(struct ntpPacket), 0, ap->ai_addr, &addrlen);
103 | 	if (error == -1) {
104 | 		fprintf(stderr, "recvfrom() error\n");
105 | 		exit(2);
106 | 	}
107 | 	
108 | 	freeaddrinfo(res); /* all done */
109 | 
110 | 	/* print raw bytes */
111 | 	for (i = 0; i < sizeof(struct ntpPacket); i++) {
112 | 		if (i != 0 && i % 8 == 0)
113 | 			printf("\n");
114 | 		printf("0x%2x ", ptr[i]);
115 | 	}
116 | 	printf("\n");
117 | 
118 | 	/* correct for right endianess */
119 | 	packet.root_delay = ENDIAN_SWAP32(packet.root_delay);
120 | 	packet.root_dispersion = ENDIAN_SWAP32(packet.root_dispersion);
121 | 	packet.ref_ts_sec = ENDIAN_SWAP32(packet.ref_ts_sec);
122 | 	packet.ref_ts_frac = ENDIAN_SWAP32(packet.ref_ts_frac);
123 | 	packet.origin_ts_sec = ENDIAN_SWAP32(packet.origin_ts_sec);
124 | 	packet.origin_ts_frac = ENDIAN_SWAP32(packet.origin_ts_frac);
125 | 	packet.recv_ts_sec = ENDIAN_SWAP32(packet.recv_ts_sec);
126 | 	packet.recv_ts_frac = ENDIAN_SWAP32(packet.recv_ts_frac);
127 | 	packet.trans_ts_sec = ENDIAN_SWAP32(packet.trans_ts_sec);
128 | 	packet.trans_ts_frac = ENDIAN_SWAP32(packet.trans_ts_frac);
129 | 
130 | 	/* print raw data */
131 | 	printf("LI: %u\n", LI_BITMASK(packet.flags));
132 | 	printf("VN: %u\n", VN_BITMASK(packet.flags));
133 | 	printf("Mode: %u\n", MODE_BITMASK(packet.flags));
134 | 	printf("stratum: %u\n", packet.stratum);
135 | 	printf("poll: %u\n", packet.poll);
136 | 	printf("precision: %u\n", packet.precision);
137 | 	printf("root delay: %u\n", packet.root_delay);
138 | 	printf("root dispersion: %u\n", packet.root_dispersion);
139 | 	printf("reference ID: %u.", packet.referenceID[0]);
140 | 	printf("%u.", packet.referenceID[1]);
141 | 	printf("%u.", packet.referenceID[2]);
142 | 	printf("%u\n", packet.referenceID[3]);
143 | 	printf("reference timestamp: %u.", packet.ref_ts_sec);
144 | 	printf("%u\n", packet.ref_ts_frac);
145 | 	printf("origin timestamp: %u.", packet.origin_ts_sec);
146 | 	printf("%u\n", packet.origin_ts_frac);
147 | 	printf("receive timestamp: %u.", packet.recv_ts_sec);
148 | 	printf("%u\n", packet.recv_ts_frac);
149 | 	printf("transmit timestamp: %u.", packet.trans_ts_sec);
150 | 	printf("%u\n", packet.trans_ts_frac);
151 | 
152 | 	/* print date with receive timestamp */
153 | 	recv_secs = packet.recv_ts_sec - UNIX_OFFSET; /* convert to unix time */
154 | 	total_secs = recv_secs;
155 | 	printf("Unix time: %u\n", (unsigned int)total_secs);
156 | 	now = localtime(&total_secs);
157 | 	printf("%02d/%02d/%d %02d:%02d:%02d\n", now->tm_mday, now->tm_mon+1, \
158 | 		       	now->tm_year+1900, now->tm_hour, now->tm_min, now->tm_sec);
159 | 
160 | 	return 0;
161 | }
162 | 


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