IPV4 RAW AF INET RAW server client program with Epoll 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

  • epoll_create1

  • epoll_ctl

  • epoll_wait

  • 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 primary purpose of the epoll system call?

See Answer

To efficiently monitor multiple file descriptors for I/O events

What types of file descriptors can be monitored using epoll?

See Answer

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

What data structure is used by epoll to store events?

See Answer

Hash table

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

See Answer

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

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

See Answer

Create the epoll Instance:

Before monitoring file descriptors, the application creates an epoll instance using the epoll_create system call.

int epoll_fd = epoll_create1(0);

Register File Discriptors:

The application registers file descriptors with the epoll instance using the epoll_ctl system call. It specifies the file descriptor, the events it is interested in (EPOLLIN for readability, EPOLLOUT for writability, etc.), and a user-defined data associated with the file descriptor.

struct epoll_event event;
event.events = EPOLLIN | EPOLLOUT;  // Interested in readability and writability
event.data.fd = my_file_descriptor; // File descriptor to monitor

epoll_ctl(epoll_fd, EPOLL_CTL_ADD, my_file_descriptor, &event);

Wait for Events:

The application enters a loop where it calls epoll_wait to wait for events. This call blocks until one or more registered file descriptors become ready or until a timeout occurs.

#define MAX_EVENTS 10
struct epoll_event events[MAX_EVENTS];

int num_events = epoll_wait(epoll_fd, events, MAX_EVENTS, timeout_ms);

Modify or Remove File Descriptors:

The application can dynamically modify or remove file descriptors from the epoll set using the epoll_ctl system call. For example, to modify events for an existing file descriptor:

struct epoll_event new_event;
new_event.events = EPOLLOUT;  // Modify to be interested in writability

epoll_ctl(epoll_fd, EPOLL_CTL_MOD, my_file_descriptor, &new_event);

To remove a file descriptor from the epoll set:

epoll_ctl(epoll_fd, EPOLL_CTL_DEL, my_file_descriptor, NULL);

How does epoll Checking Ready File Descriptors?

See Answer

After epoll_wait returns, the application iterates through the returned events to identify which file descriptors are ready and for what types of events.

for (int i = 0; i < num_events; ++i) {
        if (events[i].events & EPOLLIN) {
                // File descriptor i is ready for reading
        }

        if (events[i].events & EPOLLOUT) {
                // File descriptor i is ready for writing
        }
        // Check other events if needed (e.g., EPOLLERR, EPOLLHUP)
}

What does it mean if epoll 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

  • Epoll create1

  • Epoll_ctl

  • Epoll_wait

  • 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);

• epoll_create1() creating an epoll instance using epoll_create1, The size parameter is an advisory hint for the kernel regarding the number of file descriptors expected to be monitored, For example,

epoll_fd = epoll_create1(0);

• epoll_ctl() After creating an epoll instance, file descriptors are added to it using epoll_ctl, For example,

ret = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, sockfd, &event);

• epoll_wait() The application then enters a loop where it waits for events using epoll_wait, For example,

ready_fds = epoll_wait(epoll_fd, events, MAX_EVENTS, -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(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 <sys/epoll.h>

#define BUFFER_SIZE 1024
#define MAX_EVENTS 2

int sockfd = -1;
int epoll_fd = -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);
  (void)close(epoll_fd);
  sleep(2);
  (void)printf("Caught sigINT!\n");
  exit(EXIT_SUCCESS);
}

int main(void) 
{
    int len, ret, i;
    int ready_fds;
    struct sockaddr_in 
    server_addr;
    struct timeval timeout;
    socklen_t addr_len = 
    sizeof(struct sockaddr_in);
    char buffer[BUFFER_SIZE];
    struct epoll_event 
    events[MAX_EVENTS];
    struct epoll_event event;
    
    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");

    epoll_fd = epoll_create1(0);
 
    if (epoll_fd < 0) {
      perror("Epoll creation failed");
      exit(EXIT_FAILURE);
    }
	
    event.events = EPOLLIN;
    event.data.fd = sockfd;
  
    ret = epoll_ctl(epoll_fd, 
    EPOLL_CTL_ADD, sockfd, 
    &event);
 
    if (ret < 0) {
      perror("Epoll_ctl failed");
      (void)close(epoll_fd);
      (void)close(sockfd);
      return -3;
    }


    while (1) { 
     ready_fds = epoll_wait(epoll_fd, 
     events, MAX_EVENTS, -1);

     if (ready_fds < 0) {
        perror("epoll_wait() failed");
        break;   
      }

     if (events[0].data.fd == 
        sockfd) {
         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(epoll_fd); 
 (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

  • Epoll create1

  • Epoll_ctl

  • Epoll_wait

  • 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);

• epoll_create1() creating an epoll instance using epoll_create1, The size parameter is an advisory hint for the kernel regarding the number of file descriptors expected to be monitored, For example,

epoll_fd = epoll_create1(0);

• epoll_ctl() After creating an epoll instance, file descriptors are added to it using epoll_ctl, For example,

ret = epoll_ctl(epoll_fd, EPOLL_CTL_ADD, sockfd, &event);

• epoll_wait() The application then enters a loop where it waits for events using epoll_wait, For example,

ready_fds = epoll_wait(epoll_fd, events, MAX_EVENTS, -1);

• 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 <sys/epoll.h>

#define IP_HEADER_SIZE sizeof(struct iphdr)
#define BUFFER_SIZE 1024
#define MAX_EVENTS 2

int sockfd = -1;
int epoll_fd = -1;

static void sigint_handler(
int signo)
{
  (void)close(sockfd);
  (void)close(epoll_fd);
  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;
    int ready_fds;
    struct epoll_event
    events[MAX_EVENTS];
    struct epoll_event event;
    struct timeval timeout;
    struct sockaddr_in 
    server_addr;
    struct iphdr *ip_header;
    char buffer[BUFFER_SIZE];
    
    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]);

    epoll_fd = epoll_create1(0);

    if (epoll_fd < 0) {
       perror("Epoll creation failed");
       (void)close(sockfd);
       return -2;
    }

    event.events = EPOLLIN;
    event.data.fd = sockfd;

    ret = epoll_ctl(epoll_fd, EPOLL_CTL_ADD,
    sockfd, &event);

    if (ret < 0) {
	perror("Epoll_ctl failed");
        (void)close(sockfd);
	return -3;
    }

    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;
      }

      ready_fds = epoll_wait(epoll_fd,
      events,
      MAX_EVENTS, -1);

      if (ready_fds < 0) {
       perror("epoll wait failed");
       (void)close(sockfd);
       break;
      }

      if (events[0].data.fd ==
          sockfd) {
         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
epoll	handles a set of file descriptors with different states, such as reading, writing, and exceptions, by using the struct epoll_event structure and the associated event flags..
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

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• Current topic

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• Next topic

  • ipv4_raw_af_inet_tcp

• Other sockets

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  • 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