IPV4 RAW AF INET ICMP server client program with Poll system call

IPv4 RAW_AF_INET ICMP

• In this program, you are going to learn

• How to create a Socket ?

• How to send a data ?

• How to recv a data ?

• How to use socket APIs ?

  • socket

  • sendto

  • recvfrom

Topics in this section,

• IPV4 RAW_AF_INET ICMP SOCKET FAQs

• Step 1: Sequence Diagram for SERVER.c

• Step 2: Program for Server.c

• Step 3: Compile and Execute Server.c

• Step 4:Sequence Diagram for CLIENT.c

• Step 5: Program for Client.c

• Step 6: Compile and Execute Client.c

• Summary

IPV4 RAW_AF_INET ICMP SOCKET : FAQs

Let us answer few basic questions in this socket

What does socket(AF_INET, SOCK_RAW, IPPROTO_ICMP) do?

See Answer

This call creates a raw socket in the IPv4 address family (AF_INET) that can receive ICMP (Internet Control Message Protocol) packets directly.

Why use AF_INET as the address family?

See Answer

AF_INET specifies that the socket will work with IPv4 addresses.

What is the purpose of SOCK_RAW in the socket type?

See Answer

SOCK_RAW allows the socket to operate at a lower level by providing direct access to the packet, including the IP and transport layer headers.

Why specify IPPROTO_ICMP as the protocol?

See Answer

It filters the socket to receive only ICMP packets, allowing applications to handle ICMP messages directly.

Can this socket send ICMP packets as well?

See Answer

Yes, the same socket can be used to send and receive ICMP packets.

How does this socket differ from a standard UDP or TCP socket?

See Answer

Unlike UDP or TCP sockets, a raw socket provides direct access to the IP and ICMP headers, making it suitable for low-level packet handling.

Is error checking needed after creating the socket?

See Answer

Yes, checking for errors ensures that the socket is created successfully before proceeding with further operations.

Can this socket be used for other protocols besides ICMP?

See Answer

While created specifically for ICMP, the socket can be adapted for handling other IP protocols by changing the IPPROTO parameter.

Why close the socket after processing?

See Answer

Closing the socket ensures proper resource cleanup and releases the associated system resources.

How is the source IP address extracted from the received packet?

See Answer

The source IP address can be extracted by parsing the IP header within the received packet.

Can this socket receive ICMP messages from any source?

See Answer

Yes, the socket can receive ICMP packets from any source as it operates at the network layer.

Why cast to struct iphdr and struct icmphdr in packet processing?

See Answer

Casting allows the code to interpret the received buffer as IP and ICMP headers, facilitating packet analysis.

What is the purpose of the poll system call?

See Answer

To block and wait for activity on one or more file descriptors.

How does poll differ from poll in terms of usability?

See Answer

poll is more efficient than poll for monitoring multiple file descriptors.

What types of file descriptors can be monitored using poll?

See Answer

sockets, files, timerfd, socketpair, message_queue, Namedpipes and shared_memory.

How does poll handle a set of file descriptors with different states (e.g., reading, writing, exception)?

See Answer

It uses different structures for each state in the pollfd array.

How do you handle errors when using the poll system call?

See Answer

Check the return value for -1 to detect errors, Use perror to print error messages.

How does poll handle a set of file descriptors with different states (e.g., reading, writing, exception)?

See Answer

Array of pollfd Structures:

Before calling poll, you need to create an array of pollfd structures, where each structure represents a file descriptor and its associated events.

struct pollfd fds[NUM_FDS];

NUM_FDS is the number of file descriptors you want to monitor.

Initialize pollfd Structures:

For each file descriptor you want to monitor, initialize the corresponding pollfd structure with the following information:

fd: The file descriptor to monitor. events: The events of interest (e.g., POLLIN for readability, POLLOUT for writability). revents: Initially set to zero. After the poll call, this field is updated to indicate the events that occurred.

fds[0].fd = fd1;

fds[0].events = POLLIN;

fds[0].revents = 0;

fds[1].fd = fd2;

fds[1].events = POLLIN;

fds[1].revents = 0;

Call poll:

After initializing the pollfd array, call the poll function, providing the array, the number of file descriptors, and a timeout

int ready_fds = poll(fds, NUM_FDS, timeout_ms);

ready_fds will contain the number of file descriptors that are ready.

How does poll Checking Ready File Descriptors?

See Answer

After the poll call, loop through the pollfd array and check the revents field for each file descriptor to determine which events occurred.

for (int i = 0; i < NUM_FDS; ++i) {
        if (fds[i].revents & POLLIN) {
                // File descriptor i is ready for reading
        }

        if (fds[i].revents & POLLOUT) {
                // File descriptor i is ready for writing
        }
        // Check other events if needed (e.g., POLLERR, POLLHUP)
}

What does it mean if poll returns 0?

See Answer

No file descriptors are ready within the specified timeout.

Step 1: Sequence Diagram for SERVER.c

Step 2: Program for Server.c

• There are many functions used in socket. We can classify those functions based on functionalities.

  • Create Socket

  • Poll

  • Recvfrom data_packet

  • Sendto data_packet

  • Close socket

• socket() is used to create a new socket. For example,

server_socket = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);

• poll() is used for monitoring multiple file descriptors to see if I/O is possible on any of them.

ret = poll(fds, 1, -1);

• recvfrom is commonly used with sockets, where communication is connectionless. it provides information about the source (sender) of the data, including the sender’s IP address and port number. For example,

len = recvfrom(server_socket, buffer, sizeof(buffer), 0, NULL, NULL);

• sendto is used to send the encoded message to the specified server address and port using a socket. For example,

ret = sendto(server_socket, buffer, sizeof(struct icmphdr) + strlen(data), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr));

• close is used to close the socket To free up system resources associated with the socket. For example,

(void)close(server_socket);

• See the full program below,

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <fcntl.h>
#include <signal.h>
#include <poll.h>

#define BUFFER_SIZE 1024

int server_socket = -1;

static void sigint_handler(int signo)
{
  (void)close(server_socket);
  sleep(2);
  (void)printf("Caught sigINT!\n");
  exit(EXIT_SUCCESS);
}

void register_signal_handler(
int signum,
void (*handler)(int))
{
  if (signal(signum, handler) ==
  SIG_ERR) {
     printf("Cannot handle signal\n");
     exit(EXIT_FAILURE);
  }
}

void send_icmp_message(
int client_socket, 
const char *data) 
{
  char buffer[BUFFER_SIZE];
  struct sockaddr_in 
  dest_addr;
  int ret;
  struct icmphdr 
  *icmp_header;

  snprintf(buffer + 
  sizeof(struct icmphdr), 
  sizeof(buffer) - 
  sizeof(struct icmphdr), "%s",
  data);
      
  icmp_header = 
  (struct icmphdr *)buffer;
  icmp_header->type = ICMP_ECHO;
  icmp_header->code = 0;
  icmp_header->checksum = 0;
  icmp_header->un.echo.id = 0;
  icmp_header->un.echo.sequence = 0;

  ret = sendto(client_socket, 
  buffer, sizeof(struct icmphdr) + 
  strlen(data), 0,
  (struct sockaddr *)&dest_addr, 
  sizeof(dest_addr));
        
  if (ret < 0) {
     perror("sendto");
     (void)close(client_socket);
     exit(EXIT_FAILURE);
   }
}

void process_icmp_message(
char *buffer, 
ssize_t length) 
{
    struct iphdr 
    *ip_header;    
    struct icmphdr 
    *icmp_header;
    char *original_data;

    icmp_header = (struct icmphdr *)
    (buffer + sizeof(struct iphdr));
    ip_header = (struct iphdr *)buffer;

    printf("Received ICMP message:\n");
    printf("Source IP: %s\n", 
    inet_ntoa(*(struct in_addr *)&
    (ip_header->saddr)));
    printf("Type: %d\n", icmp_header->type);
    printf("Code: %d\n", icmp_header->code);
    
    original_data = buffer + 
    sizeof(struct iphdr) + 
    sizeof(struct icmphdr);
    printf("Original Data: %s\n", 
    original_data);

}

int main() 
{
  int  ret;
  char buffer[BUFFER_SIZE];
  struct pollfd fds[1];

  register_signal_handler(SIGINT,
  sigint_handler);
    
  server_socket = socket(AF_INET, 
                  SOCK_RAW, 
                  IPPROTO_ICMP);

  if (server_socket < 0) {
        perror("Socket failed");
        exit(EXIT_FAILURE);
  }

  fcntl(server_socket, 
  F_SETFL, 
  O_NONBLOCK);

  memset(fds, 0, sizeof(fds));

  fds[0].fd = server_socket;
  fds[0].events = POLLIN;

  while (1) {
   ret = poll(fds, 1, -1); 

   if (ret < 0) {
      perror("select");
      break;     
   }
   if (fds[0].revents & POLLIN) {
     ret = recvfrom(server_socket, 
     buffer, sizeof(buffer), 0, NULL, NULL);
        
     if (ret < 0) {
       perror("recv");
       break;
     }

     process_icmp_message(buffer, ret);
     send_icmp_message(server_socket, 
     "Hello from server!");
     sleep(2);
   }
  }

  (void)close(server_socket);

  return 0;
}

Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server

Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from client!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from server!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from client!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from server!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from client!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from server!
^CCaught sigINT!

Step 4 : Sequence Diagram for CLIENT.c

Step 5: program for client.c

• There are many functions used in socket. We can classify those functions based on functionalities.

  • Create Socket

  • Poll

  • Sendto data_packet

  • Recvfrom data_packet

  • Close socket

• socket is used to create a new socket. For example,

client_socket = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);

• poll() is used for monitoring multiple file descriptors to see if I/O is possible on any of them.

ret = poll(fds, 1, -1);

• recvfrom is commonly used with sockets, where communication is connectionless. it provides information about the source (sender) of the data, including the sender’s IP address and port number. For example,

len = recvfrom(client_socket, buffer, sizeof(buffer), 0, NULL, NULL);

• sendto is used to send the encoded message to the specified server address and port using a socket. For example,

ret = sendto(client_socket, buffer, sizeof(struct icmphdr) + strlen(data), 0, (struct sockaddr*)&dest_addr, sizeof(dest_addr));

• close is used to close the socket To free up system resources associated with the socket. For example,

(void)close(client_socket);

• See the full program below,

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip.h>
#include <sys/socket.h>
#include <sys/select.h>
#include <fcntl.h>
#include <signal.h>
#include <poll.h>

#define BUFFER_SIZE 1024

struct sockaddr_in 
dest_addr;
int client_socket = -1;

static void sigint_handler(int signo)
{
  (void)close(client_socket);
  sleep(2);
  (void)printf("Caught sigINT!\n");
  exit(EXIT_SUCCESS);
}

void register_signal_handler(
int signum,
void (*handler)(int))
{
  if (signal(signum, handler) ==
  SIG_ERR) {
     printf("Cannot handle signal\n");
     exit(EXIT_FAILURE);
  }
}

void validate_convert_addr(
char *ip_str,
struct sockaddr_in *sock_addr)
{
  if (ip_str == NULL) {
   perror("Invalid ip_str\n");
   exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
   perror("Invalid sock_addr\n");
   exit(EXIT_FAILURE);
 }

 printf("IP Address: %s\n", ip_str);

 if (inet_pton(AF_INET, ip_str,
 &(sock_addr->sin_addr)) <= 0) {
    perror("Invalid address\n");
    exit(EXIT_FAILURE);
  }
}

void send_icmp_message(
int client_socket, 
const char *data) 
{
  int ret;
  char buffer[BUFFER_SIZE];
  struct icmphdr *icmp_header;

  snprintf(buffer + 
  sizeof(struct icmphdr), sizeof(buffer) - 
  sizeof(struct icmphdr), "%s", data);

  icmp_header = (struct icmphdr *)buffer;
  icmp_header->type = ICMP_ECHO;
  icmp_header->code = 0;
  icmp_header->checksum = 0;
  icmp_header->un.echo.id = 0;
  icmp_header->un.echo.sequence = 0;

  ret = sendto(client_socket, 
  buffer, sizeof(struct icmphdr) + 
  strlen(data), 0,
  (struct sockaddr *)&dest_addr, 
  sizeof(dest_addr));
  
  if (ret < 0) {
    perror("sendto");
    (void)close(client_socket);
    exit(EXIT_FAILURE);
  }
}

void process_icmp_message(
char *buffer, 
ssize_t length)
{
  struct iphdr *ip_header;
  struct icmphdr *icmp_header; 
  char *original_data;  

  ip_header = (struct iphdr *)buffer;
  icmp_header = (struct icmphdr *)
  (buffer + sizeof(struct iphdr));

  printf("Received ICMP message:\n");
  printf("Source IP: %s\n", 
  inet_ntoa(*(struct in_addr *)&
  (ip_header->saddr)));
  printf("Type: %d\n", icmp_header->type);
  printf("Code: %d\n", icmp_header->code);

  original_data = buffer + 
  sizeof(struct iphdr) + 
  sizeof(struct icmphdr);
  printf("Original Data: %s\n", 
  original_data);
}

int main(int argc, char *argv[]) 
{
  int ret;
  char buffer[BUFFER_SIZE];
  struct pollfd fds[1];

  register_signal_handler(SIGINT,
  sigint_handler);

  if (argc != 2) {
    printf("%s <ip-addr>",
    argv[0]);
    exit(EXIT_FAILURE);
  }

  memset(&dest_addr, 0, 
  sizeof(dest_addr));
  dest_addr.sin_family = AF_INET;
  validate_convert_addr(argv[1],
  &dest_addr);

  client_socket = socket(AF_INET, 
                  SOCK_RAW, 
                  IPPROTO_ICMP);
  
  if (client_socket < 0) {
    perror("Socket failed");
    exit(EXIT_FAILURE);
  }

  fcntl(client_socket, 
  F_SETFL, O_NONBLOCK);

  while (1) {
    send_icmp_message(client_socket, 
    "Hello from client!");

    sleep(2);

    memset(fds, 0, sizeof(fds));

    fds[0].fd = client_socket;
    fds[0].events = POLLIN;

    ret = poll(fds, 1, -1);

    if (ret < 0) {
      perror("select");
      break;
    }

    if (fds[0].revents & POLLIN) {
      ret = recvfrom(client_socket, 
      buffer, sizeof(buffer), 0, NULL, NULL);
    
      if (ret < 0) {
        perror("recv");
        break;
      } else {
         process_icmp_message(buffer, ret);
      }
    }
  }

  (void)close(client_socket);

  return 0;
}

Step 6: Compile and Execute client.c

$ gcc -o client client.c

$ sudo ./client 127.0.0.1

IP Address: 127.0.0.1
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from client!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from server!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from client!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from server!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from client!
Received ICMP message:
Source IP: 127.0.0.1
Type: 8
Code: 0
Original Data: Hello from server!
^CCaught sigINT!

Enhanced Socket Flexibility with AF_INET and PF_INET Domains

Default Domain:

By default, the socket is configured to work in the AF_INET domain, handling all types of network data.

Additional Domain Support:

We expand the socket’s capabilities to also function in the PF_INET domain, allowing it to operate similarly to AF_INET.

Socket Creation:

We set up a network connection point known as a socket using socket(PF_INET, SOCK_RAW, IPPROTO_ICMP).

Working Scenario:

Despite the change in domain to PF_INET, the socket continues to operate the same way, handling general network data.

Summary

Socket API	Learning
socket	Create a new socket
poll	Monitor multiple file descriptors (usually sockets) for read, write, or error conditions.
recvfrom	It provides information about the source (sender) of the data, including the sender’s IP address and port number.
sendto	Send the encoded message to the specified server address and port using a socket.

See Also

• previous topic

  • IPV4 RAW AF INET ICMP server client program with Select system call

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  • //TODO ipv6_raw_af_inet6_icmp

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