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

IPv4 RAW_AF_INET RAW

• 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 RAW 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 RAW SOCKET : FAQs

Let us answer few basic questions in this socket

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

See Answer

This call creates a raw socket in the IPv4 address family (AF_INET) that allows applications to send raw IP packets.

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 header.

Why specify IPPROTO_RAW as the protocol?

See Answer

It indicates that the socket will be used to send raw IP packets without any specific transport layer protocol.

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

See Answer

Unlike UDP or TCP sockets, a raw socket with IPPROTO_RAW is intended specifically for sending raw IP packets.

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 IP?

See Answer

No, IPPROTO_RAW specifies that the socket is exclusively for sending raw IP packets.

How is the destination IP address specified for the packet?

See Answer

The destination IP address is set in the IP header of the packet created by the application.

How is the source IP address handled in the packet?

See Answer

The source IP address needs to be set in the IP header by the application.

Can this socket type be used with IPv6?

See Answer

For IPv6, the equivalent would be AF_INET6 with SOCK_RAW and IPPROTO_RAW.

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

  • Bind Socket

  • Poll

  • Recvfrom data_packet

  • Sendto data_packet

  • Close socket

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

sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);

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

ret = poll(fds, 1, 1000);

• 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(sockfd, buffer, sizeof(buffer), 0, (struct sockaddr*)&server_addr, &addr_len));

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

ret = sendto(sockfd, buffer, len, 0, (struct sockaddr*)&server_addr, addr_len);

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

(void)close(sockfd);

• See the full program below,

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

#define BUFFER_SIZE 1024

int sockfd = -1;

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

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

int main(void) 
{
    int len, ret, i;
    struct sockaddr_in 
    server_addr;
    struct timeval timeout;
    socklen_t addr_len = 
    sizeof(struct sockaddr_in);
    char buffer[BUFFER_SIZE];
    struct pollfd fds[1];
    
    register_signal_handler(SIGINT,
    sigint_handler);

    memset(&server_addr, 0,
    sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    server_addr.sin_addr.s_addr = 
    INADDR_ANY;

    sockfd = socket(AF_INET, 
             SOCK_RAW, 
             IPPROTO_RAW);

    if (sockfd < 0) {
        perror("socket");
        return -1;
    }

    ret = bind(sockfd, 
    (struct sockaddr *)&server_addr, 
    sizeof(server_addr));
    
    if (ret < 0) {
        perror("bind");
        (void)close(sockfd);
        return -2;
    }

    printf("Server is waiting\n");

    memset(fds, 0, sizeof(fds));
    fds[0].fd = sockfd;
    fds[0].events = POLLIN;
    
    while (1) { 
      ret = poll(fds, 1, 1000);
      
      if (ret < 0) {
        perror("poll");
        break;   
      }

      if (fds[0].revents & POLLIN) {
         len = recvfrom(sockfd, buffer, 
         sizeof(buffer), 0, 
         (struct sockaddr *)&server_addr, 
         &addr_len);

      if (len < 0) {
         perror("recvfrom");
         break;
      }

      printf("Received raw packet:\n");
    
      for (i = 0; i < len; i++) {
        printf("%02X ", 
        (unsigned char)buffer[i]);
      }

      (void)printf("\n");

      ret = sendto(sockfd, buffer, 
      len, 0, 
      (struct sockaddr *)&server_addr, 
      addr_len);
    
      if (ret < 0) {
        perror("send");
        break;
     }
   }
 }
  
 (void)close(sockfd);
    
  return 0;
}

Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server

Server is waiting
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Received raw packet:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01

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,

sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW);

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

ret = poll(fds, 2, 1000);

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

ret = sendto(sockfd, buffer, IP_HEADER_SIZE, 0, (struct sockaddr*)&server_addr, sizeof(server_addr));

• 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(sockfd, buffer, sizeof(buffer), 0, NULL, NULL);

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

(void)close(sockfd);

• See the full program below,

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

#define IP_HEADER_SIZE sizeof(struct iphdr)
#define BUFFER_SIZE 1024

int sockfd = -1;

static void sigint_handler(
int signo)
{
  (void)close(sockfd);
  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 recv_data(char *buffer)
{
  int ret, len, i;

  len = recvfrom(sockfd, 
  buffer, IP_HEADER_SIZE, 
  0, NULL, NULL);

  if (len < 0) {
     perror("recvfrom");
     (void)close(sockfd);
     exit(0);
  }

  (void)printf("Received:\n");
  
  for (i = 0; i < len; i++) {
      printf("%02X ", 
      (unsigned char)buffer[i]);
  }
  
  (void)printf("\n");
}

int main(int argc, char *argv[]) 
{
    int ret;
    int len, i;
    struct timeval timeout;
    struct sockaddr_in 
    server_addr;
    struct iphdr *ip_header;
    char buffer[BUFFER_SIZE];
    struct pollfd fds[1];
    
    register_signal_handler(SIGINT,
    sigint_handler);
   
    if (argc != 2) {
      printf("%s<ip-addr>\n",
      argv[0]);
      exit(EXIT_FAILURE);
    }

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

    sockfd = socket(AF_INET, 
             SOCK_RAW, 
             IPPROTO_RAW);

    if (sockfd < 0) {
        perror("socket");
        return -1;
    }

    ip_header = (struct iphdr *)buffer;
    ip_header->ihl = 5;
    ip_header->version = 4;
    ip_header->tos = 0;
    ip_header->tot_len = IP_HEADER_SIZE;
    ip_header->id = htons(12345);
    ip_header->frag_off = 0;
    ip_header->ttl = 255;
    ip_header->protocol = IPPROTO_RAW;
    ip_header->check = 0;
    ip_header->saddr = inet_addr(argv[1]);
    ip_header->daddr = inet_addr(argv[1]);

    while (1) {
      printf("Client is sending\n");

      ret = sendto(sockfd, buffer, 
      IP_HEADER_SIZE, 0, 
      (struct sockaddr *)&server_addr, 
      sizeof(server_addr));

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

      fds[0].fd = sockfd;
      fds[0].events = POLLIN;
	
      ret = poll(fds, 2, 1000);

      if (ret < 0) {
       perror("poll");
       (void)close(sockfd);
       break;
      }

      if (fds[0].revents & POLLIN) {
         recv_data(buffer);
      }
    }

    (void)close(sockfd);
   
    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
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01
Client is sending
Received:
45 00 00 14 30 39 00 00 FF FF 8C AF 7F 00 00 01 7F 00 00 01

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_RAW).

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

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