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traceroute.c
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traceroute.c
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#include <assert.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/time.h>
#include <inttypes.h>
#include <math.h>
#define TRUE 1
#define FALSE 0
#define NO_CODE 0
/* Program flags */
#define TTL_THRESHOLD 30 // Max TTL for sent packet
#define MAX_SECS_TO_WAIT 1 // Max seconds to wait for incoming packet
#define PACKETS_PER_TTL 3 // How many packets are sent for each TTL
#define DEBUG 0
static int sequence_counter;
void handle_error(char *err_msg) {
const int BUFF_SIZE = 50;
char err_str[BUFF_SIZE];
strerror_r(errno, err_str, BUFF_SIZE);
printf("Error occured. msg: %s, error: %s\n", err_str, err_msg);
exit(EXIT_FAILURE);
}
uint16_t compute_icmp_checksum (const void *buff, int length) {
uint32_t sum;
const uint16_t* ptr = buff;
assert (length % 2 == 0);
for (sum = 0; length > 0; length -= 2)
sum += *ptr++;
sum = (sum >> 16) + (sum & 0xffff);
return (uint16_t)(~(sum + (sum >> 16)));
}
void print_as_bytes(unsigned char* buff, ssize_t length) {
for (ssize_t i = 0; i < length; i++, buff++)
printf("%.2x ", *buff);
}
void send_icmp_request(int sockfd, int ttl, const char *ip_addr) {
struct icmphdr icmp_header;
icmp_header.type = ICMP_ECHO;
icmp_header.code = NO_CODE;
icmp_header.un.echo.id = getpid();
icmp_header.un.echo.sequence = sequence_counter++;
icmp_header.checksum = 0;
icmp_header.checksum = compute_icmp_checksum((u_int16_t*) &icmp_header,
sizeof(icmp_header));
struct sockaddr_in recipient;
bzero(&recipient, sizeof(recipient));
recipient.sin_family = AF_INET;
inet_pton(AF_INET, ip_addr, &recipient.sin_addr);
setsockopt(sockfd, IPPROTO_IP, IP_TTL, &ttl, sizeof(int));
ssize_t bytes_sent = sendto(
sockfd, &icmp_header,
sizeof(icmp_header), 0,
(struct sockaddr*) &recipient,
sizeof(recipient)
);
if (DEBUG) printf("Sent %ld bytes to %s\n", bytes_sent, ip_addr);
}
ssize_t receive_icmp_packet(int sockfd, u_int8_t *buffer, struct sockaddr_in *sender) {
socklen_t sender_len = sizeof(sender);
ssize_t packet_len = recvfrom(
sockfd, buffer,
IP_MAXPACKET,
MSG_DONTWAIT,
/* 0, */
(struct sockaddr*) sender,
&sender_len
);
if (packet_len < 0 && errno != EWOULDBLOCK)
handle_error("recvfrom error");
return packet_len;
}
int select_socket(int sockfd) {
/* Wait up to MAX_SECS_TO_WAIT for data arriving into socket
* */
fd_set descriptors;
FD_ZERO(&descriptors);
FD_SET(sockfd, &descriptors);
struct timeval tv;
tv.tv_sec = MAX_SECS_TO_WAIT;
tv.tv_usec = 0;
return select(sockfd+1, &descriptors, NULL, NULL, &tv);
}
void extract_sender_ip_str(struct sockaddr_in *sender, char *ip_str_buff, ssize_t buff_size) {
inet_ntop(AF_INET, &(sender->sin_addr), ip_str_buff, buff_size);
}
int is_ip_addr_valid(const char *ip_addr) {
// TODO
if (!ip_addr[0]) return FALSE;
return TRUE;
}
int packet_reached_destination(struct icmphdr *icmp_header) {
return icmp_header->type == ICMP_ECHOREPLY && \
icmp_header->code == NO_CODE && \
icmp_header->un.echo.id == getpid();
}
uint64_t timeval_us(struct timeval *tv) {
return (tv->tv_sec * (uint64_t)1000 * (uint64_t)1000 ) + (tv->tv_usec);
}
void output_icmp_packet(u_int8_t *buffer, struct icmphdr *icmp_header,
ssize_t ip_header_len, ssize_t packet_len) {
printf ("IP header: ");
print_as_bytes(buffer, ip_header_len);
printf("\n");
printf ("IP data: ");
print_as_bytes(buffer + ip_header_len, packet_len - ip_header_len);
printf("\n");
printf("ICMP header: type=%d, code=%d, id=%d %d\n",
icmp_header->type,
icmp_header->code,
icmp_header->un.echo.id,
icmp_header->un.echo.sequence);
printf("ICMP data: ");
printf("\n\n");
}
void help() {
printf("usage: ./traceroute <ip-address>\n");
exit(EXIT_FAILURE);
}
int process_icmp_hop(int sockfd, int TTL, const char *ip_addr) {
u_int8_t final_dest = FALSE;
u_int8_t buffer[IP_MAXPACKET];
struct timeval tv_start[3];
struct timeval tv_end[3];
ssize_t *packet_len = malloc(sizeof(int) * PACKETS_PER_TTL);
char sender_ip_str[20];
struct sockaddr_in sender;
uint64_t valid_packets = 0;
int packets_not_ready = 0;
int pid = getpid();
for (int i=0; i<PACKETS_PER_TTL; i++) {
// Send out 3 packets with same TTL
gettimeofday(&tv_start[i], NULL);
send_icmp_request(sockfd, TTL, ip_addr);
}
if (TTL < 10) printf(" ");
printf(" %d ", TTL);
for (int i=0; i < PACKETS_PER_TTL; i++) {
// Try to receive 3 packets
int is_socket_ready = select_socket(sockfd);
if (is_socket_ready == -1)
handle_error("select_socket");
if (is_socket_ready == 0) {
packets_not_ready++;
continue;
}
packet_len[i] = receive_icmp_packet(sockfd, buffer, &sender);
gettimeofday(&tv_end[i], NULL);
struct ip *ip = (struct ip *) buffer;
int ip_header_len = ip->ip_hl << 2;
struct icmphdr *icmp_header = (struct icmphdr *) (buffer + ip_header_len);
u_int16_t icmp_pid;
u_int16_t icmp_sequence;
if (icmp_header->type == ICMP_TIME_EXCEEDED) {
struct iphdr* inside_ip_header = (struct iphdr*) ((u_int8_t*)icmp_header + 8);
u_int8_t * inside_icmp_packet = (u_int8_t*)inside_ip_header + 4 * inside_ip_header->ihl;
struct icmphdr* inside_icmp_header = (struct icmphdr*) inside_icmp_packet;
icmp_pid = inside_icmp_header->un.echo.id;
icmp_sequence = inside_icmp_header->un.echo.sequence;
}
if (icmp_header->type == ICMP_ECHOREPLY) {
icmp_pid = icmp_header->un.echo.id;
icmp_sequence = icmp_header->un.echo.sequence;
}
if (DEBUG)
output_icmp_packet(buffer, icmp_header, ip_header_len, packet_len[i]);
if (packet_reached_destination(icmp_header))
final_dest = TRUE;
if (packet_len[i] != -1) {
if (pid == icmp_pid && icmp_sequence >= sequence_counter - PACKETS_PER_TTL) {
valid_packets++;
extract_sender_ip_str(&sender, sender_ip_str, 20);
printf("%s ", sender_ip_str);
} else {
i--;
continue;
}
}
}
if (packets_not_ready == 3)
printf("*");
uint64_t sum_latency = 0;
for (int i=0; i<PACKETS_PER_TTL; i++)
if (packet_len[i] != -1)
sum_latency += timeval_us(&tv_end[i]) - timeval_us(&tv_start[i]);
if (valid_packets) {
double avg_latency_us = sum_latency / valid_packets;
printf(" %.3lf ms", avg_latency_us / 1000);
}
printf("\n");
return final_dest;
}
int main(int argc, char *argv[]) {
if (argc != 2)
help();
// TODO: accept domain name and run `host` on the argument
const char *ip_addr = argv[1];
if (!is_ip_addr_valid(ip_addr))
handle_error("Invalid ip address");
int sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (sockfd < 0)
handle_error("socket");
for (int TTL = 1; TTL <= TTL_THRESHOLD; TTL++)
if (process_icmp_hop(sockfd, TTL, ip_addr))
break;
return EXIT_SUCCESS;
}