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#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/ip_icmp.h>
#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
uint16_t internet_checksum(const void* ptr, size_t count)
{
uint32_t checksum = 0;
auto* w = (const uint16_t*)ptr;
while (count > 1) {
checksum += ntohs(*w++);
if (checksum & 0x80000000)
checksum = (checksum & 0xffff) | (checksum >> 16);
count -= 2;
}
while (checksum >> 16)
checksum = (checksum & 0xffff) + (checksum >> 16);
return htons(~checksum);
}
int main(int argc, char** argv)
{
if (argc != 2) {
printf("usage: ping <host>\n");
return 0;
}
int fd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (fd < 0) {
perror("socket");
return 1;
}
if (setgid(getgid()) || setuid(getuid())) {
fprintf(stderr, "Failed to drop privileges.\n");
return 1;
}
struct timeval timeout {
1, 0
};
int rc = setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeout, sizeof(timeout));
if (rc < 0) {
perror("setsockopt");
return 1;
}
auto* hostent = gethostbyname(argv[1]);
if (!hostent) {
printf("Lookup failed for '%s'\n", argv[1]);
return 1;
}
pid_t pid = getpid();
sockaddr_in peer_address;
memset(&peer_address, 0, sizeof(peer_address));
peer_address.sin_family = AF_INET;
peer_address.sin_port = 0;
peer_address.sin_addr.s_addr = *(const in_addr_t*)hostent->h_addr_list[0];
struct PingPacket {
struct icmphdr header;
char msg[64 - sizeof(struct icmphdr)];
};
uint16_t seq = 1;
for (;;) {
PingPacket ping_packet;
PingPacket pong_packet;
memset(&ping_packet, 0, sizeof(PingPacket));
ping_packet.header.type = 8; // Echo request
ping_packet.header.code = 0;
ping_packet.header.un.echo.id = htons(pid);
ping_packet.header.un.echo.sequence = htons(seq++);
strcpy(ping_packet.msg, "Hello there!\n");
ping_packet.header.checksum = internet_checksum(&ping_packet, sizeof(PingPacket));
struct timeval tv_send;
gettimeofday(&tv_send, nullptr);
rc = sendto(fd, &ping_packet, sizeof(PingPacket), 0, (const struct sockaddr*)&peer_address, sizeof(sockaddr_in));
if (rc < 0) {
perror("sendto");
return 1;
}
for (;;) {
socklen_t peer_address_size = sizeof(peer_address);
rc = recvfrom(fd, &pong_packet, sizeof(PingPacket), 0, (struct sockaddr*)&peer_address, &peer_address_size);
if (rc < 0) {
if (errno == EAGAIN) {
printf("Request (seq=%u) timed out.\n", ntohs(ping_packet.header.un.echo.sequence));
break;
}
perror("recvfrom");
return 1;
}
if (pong_packet.header.type != 0)
continue;
if (pong_packet.header.code != 0)
continue;
if (ntohs(pong_packet.header.un.echo.id) != pid)
continue;
struct timeval tv_receive;
gettimeofday(&tv_receive, nullptr);
struct timeval tv_diff;
timersub(&tv_receive, &tv_send, &tv_diff);
int ms = tv_diff.tv_sec * 1000 + tv_diff.tv_usec / 1000;
char addr_buf[64];
printf("Pong from %s: id=%u, seq=%u%s, time=%dms\n",
inet_ntop(AF_INET, &peer_address.sin_addr, addr_buf, sizeof(addr_buf)),
ntohs(pong_packet.header.un.echo.id),
ntohs(pong_packet.header.un.echo.sequence),
pong_packet.header.un.echo.sequence != ping_packet.header.un.echo.sequence ? "(!)" : "",
ms);
// If this was a response to an earlier packet, we still need to wait for the current one.
if (pong_packet.header.un.echo.sequence != ping_packet.header.un.echo.sequence)
continue;
break;
}
sleep(1);
}
return 0;
}
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