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

IPv4 RAW_AF_INET UDP

• 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 UDP 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 UDP SOCKET : FAQs

Let us answer few basic questions in this socket

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

See Answer

This call creates a raw socket in the AF_INET address family for direct access to UDP packets.

When would I use SOCK_RAW sockets with IPPROTO_UDP?

See Answer

This combination is used for tasks like packet sniffing, crafting custom protocols, or low-level UDP packet manipulation.

Can SOCK_RAW sockets be used for regular UDP communication?

See Answer

While technically possible, it’s not recommended. Higher-level APIs are more suitable for standard UDP communication.

What is the difference between IPPROTO_UDP and SOCK_RAW for UDP communication?

See Answer

IPPROTO_UDP specifies the transport protocol (UDP), while SOCK_RAW indicates a raw socket, providing more control over UDP packet content.

What are common issues when working with raw UDP sockets?

See Answer

Common issues include permission errors, endianness mismatches, and improper packet handling.

How do I handle errors when using raw UDP sockets?

See Answer

Use error codes returned by system calls like socket and sendto for error handling. Log and handle errors gracefully.

Can raw UDP sockets be used for both sending and receiving data?

See Answer

Yes, raw UDP sockets can be used for both sending and receiving UDP packets.

Why is it important to check the return value of sendto() and recvfrom() in socket programming?

See Answer

It detects issues such as network errors or closed connections.

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,

sock_fd = socket(AF_INET, SOCK_RAW, IPPROTO_UDP);

• 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,

ret = recvfrom(sock_fd, recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, &length);

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

ret = sendto(sock_fd, buffer, (sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in));

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

(void)close(sock_fd);

• See the full program below,

#include <stdio.h>
#include <string.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <linux/udp.h> /* UDP Header */
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>
#include <linux/ip.h>
#include <poll.h>

struct sockaddr_in 
*clientaddr = NULL;
int sock_fd;
int SERVPORT=20000;
int DESTPORT=20001;

struct pseudo_iphdr {
  unsigned int source_ip_addr;
  unsigned int dest_ip_addr;
  unsigned char fixed;
  unsigned char protocol;
  unsigned short udp_len;
};

unsigned short in_cksum (
uint16_t * addr, int len)
{
  int nleft = len;
  unsigned int sum = 0;
  unsigned short *w = addr;
  unsigned short answer = 0;

  while (nleft > 1) {
    sum += *w++;
    nleft -= 2;
  }

  if (nleft == 1) {
    *(unsigned char *) (&answer) = 
    * (unsigned char *) w;
    sum += answer;
  }

  sum = (sum >> 16) + 
  (sum & 0xffff); 
  sum += (sum >> 16); 
  answer = (unsigned short) ~sum; 
  return (answer);
}

void interrupt_handler (
int signum)
{
  (void)close(sock_fd);
  free(clientaddr);
  exit(0);
}

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 main (int argc, char *argv[]) 
{
  socklen_t length;
  char buffer[1024] = {0};
  unsigned char 
  recvbuffer[1024] = {0};
  char *string = 
  "Hello client\n";
  struct udphdr *udp_hdr = NULL;
  char *string_data = NULL;
  char *recv_string_data = NULL;
  char *csum_buffer = NULL;
  struct pseudo_iphdr 
  csum_hdr;
  int ret;
  struct pollfd fds[1];
 
  signal (SIGINT, 
  interrupt_handler);
  signal (SIGTERM, 
  interrupt_handler);

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

  sock_fd = socket(AF_INET, 
               SOCK_RAW, 
               IPPROTO_UDP);
  
  if (sock_fd < 0) {
    printf("create a socket\n");
    exit(0);
  }

  clientaddr = (struct sockaddr_in *)malloc(
  sizeof(struct sockaddr_in));

  if (clientaddr == NULL) {
    printf("allocate memory\n");
    goto end;
  }

  clientaddr->sin_family = AF_INET;
  clientaddr->sin_port = 
  htons(DESTPORT);
  validate_convert_addr(argv[1],
  clientaddr);

  memset(buffer, 0, 
  sizeof(buffer));

  string_data = (char *)
  (buffer + sizeof(struct udphdr));
  strncpy(string_data, 
  string, strlen(string));

  udp_hdr = (struct udphdr *)buffer;

  udp_hdr->source = htons(SERVPORT);
  udp_hdr->dest = htons(DESTPORT);
  udp_hdr->len = htons(
  sizeof(struct udphdr));

  csum_buffer = (char *)calloc((
  sizeof(struct pseudo_iphdr) + 
  sizeof(struct udphdr) + 
  strlen(string_data)), sizeof(char));
  
 if (csum_buffer == NULL) {
    printf("allocate csum buffer\n");
    goto end1;
  }

  csum_hdr.source_ip_addr = 
  inet_addr("127.0.0.1");
  csum_hdr.dest_ip_addr = 
  inet_addr("127.0.0.1");
  csum_hdr.fixed = 0;
  csum_hdr.protocol = IPPROTO_UDP; 
  csum_hdr.udp_len = htons(
  sizeof(struct udphdr) + 
  strlen(string_data) + 1);

  memcpy(csum_buffer, 
  (char *)&csum_hdr, 
  sizeof(struct pseudo_iphdr));
  memcpy(csum_buffer + 
  sizeof(struct pseudo_iphdr), buffer, 
  (sizeof(struct udphdr) + 
  strlen(string_data) + 1));

  udp_hdr->check = (in_cksum(
  (unsigned short *) csum_buffer,
  (sizeof(struct pseudo_iphdr)+ 
  sizeof(struct udphdr) + 
  strlen(string_data) + 1)));

  printf("checksum is %x\n", 
  udp_hdr->check);
  free (csum_buffer);

  memset(fds, 0, sizeof(fds));
  fds[0].fd = sock_fd;
  fds[0].events = POLLIN;

  while (1) {
    ret = poll(fds, 1, 1000);

    if (ret < 0) {
       perror("poll");
       exit(EXIT_FAILURE);
    }

    if (fds[0].revents & POLLIN) {
     memset(recvbuffer, 0, 
     sizeof(recvbuffer));

     ret = recvfrom(sock_fd, recvbuffer,
     (sizeof(struct iphdr) + 
     sizeof(struct udphdr)+
     strlen(string_data)+1), 0,
     (struct sockaddr *)clientaddr, 
     &length);

     if (ret < 0) {
        printf("recv Message\n");
	goto end1;
     }
		  
     udp_hdr = (struct udphdr *)
     (recvbuffer + sizeof (struct iphdr));
		  
     recv_string_data = (char *) 
     (recvbuffer + 
     sizeof (struct iphdr) + 
     sizeof (struct udphdr));
		  
     if (SERVPORT == 
     ntohs(udp_hdr->source)) {
       printf("Received :%s\n", 
       recv_string_data);
     }
	
     ret = sendto(sock_fd, buffer,
     (sizeof(struct udphdr)+
     strlen(string_data)+1), 0,
     (struct sockaddr *)clientaddr, 
     sizeof(struct sockaddr_in));
		  
     if (ret < 0) {
	printf("send Message\n");
	goto end1;
     }
    }
  }
end1:
  free (clientaddr);
end:
  (void)close(sock_fd);
  return;
}

Step 3: Compile and Execute server.c

$ gcc -o server server.c

$ sudo ./server 127.0.0.1

IP Address: 127.0.0.1
checksum is 53fc
Received :Hello server

Received :Hello server

Received :Hello server

Received :Hello server

Received :Hello server

Received :Hello client

Received :Hello server

Received :Hello server

Received :Hello client

Received :Hello server

Received :Hello server

Received :Hello client
^C

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_UDP);

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

ret = poll(fds, 1, 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, (sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, sizeof(struct sockaddr_in));

• 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,

ret = recvfrom(sockfd, recvbuffer, (sizeof(struct iphdr) + sizeof(struct udphdr)+ strlen(string_data)+1), 0, (struct sockaddr*)clientaddr, &length);

• 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 <string.h>
#include <sys/socket.h>
#include <stdlib.h>
#include <linux/udp.h> /* UDP Header */
#include <arpa/inet.h>
#include <unistd.h>
#include <signal.h>
#include <linux/ip.h>
#include <poll.h>

struct sockaddr_in 
*clientaddr = NULL;
int sockfd;
int SERVPORT=20000;
int DESTPORT=20001;

struct pseudo_iphdr {
  unsigned int source_ip_addr;
  unsigned int dest_ip_addr;
  unsigned char fixed;
  unsigned char protocol;
  unsigned short udp_len;
};

unsigned short in_cksum (
uint16_t * addr, int len)
{
  int nleft = len;
  unsigned int sum = 0;
  unsigned short *w = addr;
  unsigned short answer = 0;

  while (nleft > 1) {
    sum += *w++;
    nleft -= 2;
  }

  if (nleft == 1) {
    *(unsigned char *) (&answer) = * 
    (unsigned char *) w;
    sum += answer;
  }

  sum = (sum >> 16) + 
  (sum & 0xffff); 
  sum += (sum >> 16); 
  answer = (unsigned short) ~sum; 
  return (answer);
}

void interrupt_handler (
int signum)
{
  (void)close(sockfd);
  free(clientaddr);
  exit(0);
}

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);
  }
}

int main(int argc, char *argv[])
{
   socklen_t length; 
   char buffer[1024] = {0};
   unsigned char recvbuffer[1024] = 
   {0};
   char *string = 
   "Hello server\n";
   struct udphdr *udp_hdr = NULL;
   char *string_data = NULL;
   char *recv_string_data = NULL;
   char *csum_buffer = NULL;
   struct pseudo_iphdr csum_hdr;
   int ret;
   struct pollfd fds[1];

   signal (SIGINT, 
   interrupt_handler);
   signal (SIGTERM, 
   interrupt_handler);

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

   sockfd = socket(AF_INET, 
            SOCK_RAW, 
            IPPROTO_UDP);

   if (sockfd < 0) {
      printf("create a socket\n");
      exit(0);
   }

   clientaddr = (struct sockaddr_in *)
   malloc(sizeof(struct sockaddr_in));

   if (clientaddr == NULL) {
      printf("allocate memory\n");
      goto end;
   }

   clientaddr->sin_family = AF_INET;
   clientaddr->sin_port = 
   htons(DESTPORT);
   validate_convert_addr(argv[1],
   clientaddr);

   memset(buffer, 0, 
   sizeof(buffer));

   string_data = (char *) 
   (buffer + sizeof(struct udphdr));
   strncpy(string_data, 
   string, strlen(string));

   udp_hdr = (struct udphdr *)buffer;

   udp_hdr->source = htons(SERVPORT);
   udp_hdr->dest = htons(DESTPORT);
   udp_hdr->len = htons(
   sizeof(struct udphdr));

   csum_buffer = (char *)calloc(
   (sizeof(struct pseudo_iphdr) + 
   sizeof(struct udphdr) + 
   strlen(string_data)), sizeof(char));
      
   if (csum_buffer == NULL) {
       printf("allocate csum buffer\n");
       goto end1;
   }

   csum_hdr.source_ip_addr = 
   inet_addr("127.0.0.1");
   csum_hdr.dest_ip_addr = 
   inet_addr("127.0.0.1");
   csum_hdr.fixed = 0;
   csum_hdr.protocol = IPPROTO_UDP; /* UDP protocol */
   csum_hdr.udp_len = htons(
   sizeof(struct udphdr) + 
   strlen(string_data) + 1);

   memcpy(csum_buffer, 
   (char *)&csum_hdr, 
   sizeof(struct pseudo_iphdr));
   memcpy(csum_buffer + 
   sizeof(struct pseudo_iphdr), 
   buffer, (sizeof(struct udphdr) + 
   strlen(string_data) + 1));

   udp_hdr->check = (in_cksum(
   (unsigned short *) csum_buffer,
   (sizeof(struct pseudo_iphdr)+ 
   sizeof(struct udphdr) + 
   strlen(string_data) + 1)));

   printf("checksum is %x\n",
   udp_hdr->check);
   free (csum_buffer);

   memset(fds, 0, sizeof(fds));
   fds[0].fd = sockfd;
   fds[0].events = POLLIN;

   while (1) {
      ret = sendto(sockfd, buffer,
      (sizeof(struct udphdr)+
      strlen(string_data)+1), 0,
      (struct sockaddr *)clientaddr, 
      sizeof(struct sockaddr_in));
        
      if (ret == -1) {
          printf("send Message\n");
          goto end1;
      }

      ret = poll(fds, 1, 1000);

      if (ret < 0) {
	 perror("poll");
	 exit(EXIT_FAILURE);
      }
	
      if (fds[0].revents & POLLIN) {
	memset(recvbuffer, 0, 
	sizeof(recvbuffer));
	
	ret = recvfrom(sockfd, recvbuffer,
     	(sizeof(struct iphdr) +
     	sizeof(struct udphdr)+
     	strlen(string_data)+1), 0,
     	(struct sockaddr *)clientaddr, 
	&length);

     	if (ret < 0) {
          printf("recv Message\n");
          goto end1;
        }

        udp_hdr = (struct udphdr *)
        (recvbuffer + 
	sizeof (struct iphdr));

        recv_string_data = (char *)
        (recvbuffer +
        sizeof (struct iphdr) +
        sizeof (struct udphdr));

        if (SERVPORT ==
        ntohs(udp_hdr->source)) {
           printf("Received :%s\n",
           recv_string_data);
        }
      }
   }

end1:
    free (clientaddr);
end:
    (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
checksum is 4bec
Received :Hello server

Received :Hello server

Received :Hello server

Received :Hello server

Received :Hello server

Received :Hello client

Received :Hello server

Received :Hello server

Received :Hello client

Received :Hello server

Received :Hello server

Received :Hello client
^C

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_UDP).

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 UDP server client program with Select system call

• current topic

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

• Next topic

  • IPV4 RAW AF INET UDP server client program with Epoll system call

• Other sockets

  • ipv6_af_inet6_tcp

  • ipv6_af_inet6_udp

  • //TODO ipv6_raw_af_inet6_icmp

  • //TODO ipv6_raw_af_inet6_tcp

  • //TODO ipv6_raw_af_inet6_udp

  • // TODO ipv6_raw_af_inet6_raw

  • raw_af_packet_raw_htons_ETH_P_ALL

  • raw_af_packet_tcp_htons_ETH_P_ALL

  • raw_af_packet_udp_htons_ETH_P_ALL

• Other IPCs

  • Message_queues

  • NamedPipes

  • Netlink

  • Shared_Memory

  • Shared_Memory_2_FDS

  • SocketPair

  • Timerfd