Sending multiple pings in c - ping

Question

I wrote a code in C that pings a host every second (e.g: ./ping 8.8.8.8). The program sends an ICMP ECHO REQUEST to the host, and when receiving ICMP-ECHO- REPLY, the program will send the next ICMP ECHO REQUEST (no need to stop).
But it only pings once, then gets stuck when I try to receive the reply after the second ping.
Ping Code
#include <arpa/inet.h>
#include <errno.h>
#include <netinet/in.h>
#include <resolv.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/time.h> // gettimeofday()
#include <sys/types.h>
#include <unistd.h>
// IPv4 header len without options
#define IP4_HDRLEN 20
// ICMP header len for echo req
#define ICMP_HDRLEN 8
// Checksum algo
unsigned short calculate_checksum(unsigned short *paddress, int len);
#define SOURCE_IP "127.0.0.1"
int main(int count, char *argv[])
{
int seq = 1;
struct icmp icmphdr; // ICMP-header
char data[IP_MAXPACKET] = "This is the ping.\n";
int datalen = strlen(data) + 1;
//===================
// ICMP header
//===================
// Message Type (8 bits): ICMP_ECHO_REQUEST
icmphdr.icmp_type = ICMP_ECHO;
// Message Code (8 bits): echo request
icmphdr.icmp_code = 0;
// Identifier (16 bits): some number to trace the response.
// It will be copied to the response packet and used to map response to the request sent earlier.
// Thus, it serves as a Transaction-ID when we need to make "ping"
icmphdr.icmp_id = 18;
// Sequence Number (16 bits): starts at 0
icmphdr.icmp_seq = 0;
// ICMP header checksum (16 bits): set to 0 not to include into checksum calculation
icmphdr.icmp_cksum = 0;
// Combine the packet
char packet[IP_MAXPACKET];
// Next, ICMP header
memcpy((packet), &icmphdr, ICMP_HDRLEN);
// After ICMP header, add the ICMP data.
memcpy(packet + ICMP_HDRLEN, data, datalen);
// Calculate the ICMP header checksum
icmphdr.icmp_cksum = calculate_checksum((unsigned short *)(packet), ICMP_HDRLEN + datalen);
memcpy((packet), &icmphdr, ICMP_HDRLEN);
struct sockaddr_in dest_in;
memset(&dest_in, 0, sizeof(struct sockaddr_in));
dest_in.sin_family = AF_INET;
// The port is irrelant for Networking and therefore was zeroed.
dest_in.sin_addr.s_addr = inet_addr(argv[1]);
// Create raw socket for IP-RAW (make IP-header by yourself)
int sock = -1;
if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
{
fprintf(stderr, "socket() failed with error: %d", errno);
fprintf(stderr, "To create a raw socket, the process needs to be run by Admin/root user.\n\n");
return -1;
}
struct timeval start, end;
while (1)
{
gettimeofday(&start, 0);
// Send the packet using sendto() for sending datagrams.
int bytes_sent = sendto(sock, packet, ICMP_HDRLEN + datalen, 0, (struct sockaddr *)&dest_in, sizeof(dest_in));
if (bytes_sent == -1)
{
fprintf(stderr, "sendto() failed with error: %d", errno);
return -1;
}
bzero(packet, IP_MAXPACKET);
socklen_t len = sizeof(dest_in);
ssize_t bytes_received = -1;
while ((bytes_received = recvfrom(sock, packet, sizeof(packet), 0, (struct sockaddr *)&dest_in, &len)))
{
printf("recv: %ld\n", bytes_received);
if (bytes_received > 0)
{
// Check the IP header
struct iphdr *iphdr = (struct iphdr *)packet;
struct icmphdr *icmphdr = (struct icmphdr *)(packet + (iphdr->ihl * 4));
// printf("%ld bytes from %s\n", bytes_received, inet_ntoa(dest_in.sin_addr));
// icmphdr->type
gettimeofday(&end, 0);
unsigned long microseconds = (end.tv_sec - start.tv_sec) * 1000.0f + (end.tv_usec - start.tv_usec);
printf("Successfuly received one packet: IP: %s, Packet seq number: %d , Time that the ping took: %ld microseconds\n", SOURCE_IP, seq++, microseconds);
break;
}
}
sleep(1);
}
// Close the raw socket descriptor.
close(sock);
return 0;
}
// Compute checksum (RFC 1071).
unsigned short calculate_checksum(unsigned short *paddress, int len)
{
int nleft = len;
int sum = 0;
unsigned short *w = paddress;
unsigned short answer = 0;
while (nleft > 1)
{
sum += *w++;
nleft -= 2;
}
if (nleft == 1)
{
*((unsigned char *)&answer) = *((unsigned char *)w);
sum += answer;
}
// add back carry outs from top 16 bits to low 16 bits
sum = (sum >> 16) + (sum & 0xffff); // add hi 16 to low 16
sum += (sum >> 16); // add carry
answer = ~sum; // truncate to 16 bits
return answer;
}

Answer 1

There are few silly mistakes in the code:
bzero(packet, IP_MAXPACKET); at line 83
bytes_received = recvfrom(sock, packet, sizeof(packet), 0, (struct sockaddr *)&dest_in, &len))) overwriting the same buffer char packet[IP_MAXPACKET]; which is being used in
sendto(sock, packet, ICMP_HDRLEN + datalen, 0, (struct sockaddr *)&dest_in, sizeof(dest_in));
Solution:
Remove bzero(packet, IP_MAXPACKET);
You can use char data[IP_MAXPACKET] buffer in recvfrom(sock, data, sizeof(data), 0, (struct sockaddr *)&dest_in, &len)))
Here is slightly modified version of your original code:
#include <arpa/inet.h>
#include <errno.h>
#include <netinet/in.h>
#include <resolv.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/time.h> // gettimeofday()
#include <sys/types.h>
#include <unistd.h>
// IPv4 header len without options
#define IP4_HDRLEN 20
// ICMP header len for echo req
#define ICMP_HDRLEN 8
// Checksum algo
unsigned short calculate_checksum(unsigned short *paddress, int len);
#define SOURCE_IP "127.0.0.1"
int main(int count, char *argv[])
{
int seq = 1;
struct icmp icmphdr; // ICMP-header
char data[IP_MAXPACKET] = "This is the ping.\n";
int datalen = strlen(data) + 1;
//===================
// ICMP header
//===================
// Message Type (8 bits): ICMP_ECHO_REQUEST
icmphdr.icmp_type = ICMP_ECHO;
// Message Code (8 bits): echo request
icmphdr.icmp_code = 0;
// Identifier (16 bits): some number to trace the response.
// It will be copied to the response packet and used to map response to the request sent earlier.
// Thus, it serves as a Transaction-ID when we need to make "ping"
icmphdr.icmp_id = 18;
// Sequence Number (16 bits): starts at 0
icmphdr.icmp_seq = 0;
// ICMP header checksum (16 bits): set to 0 not to include into checksum calculation
icmphdr.icmp_cksum = 0;
// Combine the packet
char packet[IP_MAXPACKET];
// Next, ICMP header
memcpy((packet), &icmphdr, ICMP_HDRLEN);
// After ICMP header, add the ICMP data.
memcpy(packet + ICMP_HDRLEN, data, datalen);
// Calculate the ICMP header checksum
icmphdr.icmp_cksum = calculate_checksum((unsigned short *)(packet), ICMP_HDRLEN + datalen);
memcpy((packet), &icmphdr, ICMP_HDRLEN);
struct sockaddr_in dest_in;
memset(&dest_in, 0, sizeof(struct sockaddr_in));
dest_in.sin_family = AF_INET;
// The port is irrelant for Networking and therefore was zeroed.
dest_in.sin_addr.s_addr = inet_addr(argv[1]);
// Create raw socket for IP-RAW (make IP-header by yourself)
int sock = -1;
if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1)
{
fprintf(stderr, "socket() failed with error: %d", errno);
fprintf(stderr, "To create a raw socket, the process needs to be run by Admin/root user.\n\n");
return -1;
}
struct timeval start, end;
while (1)
{
gettimeofday(&start, 0);
// Send the packet using sendto() for sending datagrams.
int bytes_sent = sendto(sock, packet, ICMP_HDRLEN + datalen, 0, (struct sockaddr *)&dest_in, sizeof(dest_in));
if (bytes_sent == -1)
{
fprintf(stderr, "sendto() failed with error: %d", errno);
return -1;
}
//bzero(packet, IP_MAXPACKET); //Commented this zeroing of transmit buffer
socklen_t len = sizeof(dest_in);
ssize_t bytes_received = -1;
//using different buffer for receiving the response
while ((bytes_received = recvfrom(sock, data, sizeof(data), 0, (struct sockaddr *)&dest_in, &len)))
{
printf("recv: %ld\n", bytes_received);
if (bytes_received > 0)
{
// Check the IP header
struct iphdr *iphdr = (struct iphdr *)data;
struct icmphdr *icmphdr = (struct icmphdr *)(data + (iphdr->ihl * 4));
// printf("%ld bytes from %s\n", bytes_received, inet_ntoa(dest_in.sin_addr));
// icmphdr->type
gettimeofday(&end, 0);
unsigned long microseconds = (end.tv_sec - start.tv_sec) * 1000.0f + (end.tv_usec - start.tv_usec);
printf("Successfuly received one packet: IP: %s, Packet seq number: %d , Time that the ping took: %ld microseconds\n", SOURCE_IP, seq++, microseconds);
break;
}
}
sleep(1);
}
// Close the raw socket descriptor.
close(sock);
return 0;
}
// Compute checksum (RFC 1071).
unsigned short calculate_checksum(unsigned short *paddress, int len)
{
int nleft = len;
int sum = 0;
unsigned short *w = paddress;
unsigned short answer = 0;
while (nleft > 1)
{
sum += *w++;
nleft -= 2;
}
if (nleft == 1)
{
*((unsigned char *)&answer) = *((unsigned char *)w);
sum += answer;
}
// add back carry outs from top 16 bits to low 16 bits
sum = (sum >> 16) + (sum & 0xffff); // add hi 16 to low 16
sum += (sum >> 16); // add carry
answer = ~sum; // truncate to 16 bits
return answer;
}