Basic example af_packet udp server and client

AF_PACKET UDP

• In this program, you are going to learn

• How to create a Socket ?

• How to bind a socket ?

• How to send a data ?

• How to recv a data ?

• How to use socket APIs ?

  • socket

  • bind

  • sendto

  • recvfrom

Topics in this section,

• program 1: af_packet udp single server and single client : single data transfer

• program 2: af_packet udp single server and single client : multiple data transfer

program 1 : af_packet udp single server and single client : single data transfer

Topics in this section,

• AF_PACKET UDP SOCKET FAQs

• Program1 : Step 1: Sequence Diagram for SERVER.c

• Program1 : Step 2: Program for Server.c

• Program1 : Step 3: Compile and Execute Server.c

• Program1 : Step 4: Sequence Diagram for CLIENT.c

• Program1 : Step 5: Program for Client.c

• Program1 : Step 6: Compile and Execute Client.c

• Summary

program 2 : af_packet udp multiple server and single client : multiple data transfer

Topics in this section,

• AF_PACKET UDP SOCKET FAQs

• Program2 : Step 1: Sequence Diagram for SERVER.c

• Program2 : Step 2: Program for Server.c

• Program2 : Step 3: Compile and Execute Server.c

• Program2 : Step 4: Sequence Diagram for CLIENT.c

• Program2 : Step 5: Program for Client.c

• Program2 : Step 6: Compile and Execute Client.c

• Summary

AF_PACKET UDP SOCKET : FAQs

Let us answer few basic questions in this socket

What does socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL)) do?

See Answer

This call creates a packet socket that allows receiving all Ethernet frames, regardless of destination address, using the recvfrom function.

How can I handle errors when creating a packet socket for receiving all data?

See Answer

Check the return value of the socket function. If it returns -1, use perror to print a descriptive error message.

What kind of errors can occur when using a packet socket for receiving data?

See Answer

Common errors include permission-related errors (EACCES), socket creation failures (ENOMEM), or invalid arguments (EINVAL).

How do I handle errors when binding a packet socket for receiving data?

See Answer

Check the return value of the bind function. If it returns -1, handle the error by printing a message or taking appropriate corrective action based on the error code.

What is the significance of error code EPERM when dealing with packet sockets?

See Answer

EPERM (Operation not permitted) typically indicates insufficient privileges. Ensure the program has the necessary permissions to create packet sockets.

How do I handle errors when using recvfrom to receive data with a packet socket?

See Answer

Check the return value of recvfrom. If it returns -1, handle the error by printing a message or taking appropriate corrective action.

Is it important to close the packet socket on error?

See Answer

Yes, closing the socket is crucial to release system resources. Always follow error-handling best practices and close sockets on error.

Is it possible to receive packets only from a specific network interface with a packet socket?

See Answer

Yes, use the bind function to associate the packet socket with a specific network interface.

How do I handle errors related to socket file descriptor management?

See Answer

When closing sockets, check for errors using close. Handle errors by printing messages or taking corrective actions.

Program1 : Step 1: Sequence Diagram for SERVER.c

Program1 : 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

  • Recvfrom data_packet

  • Close socket

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

server_socket = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

• bind() is used to associate the socket with a specific address and port. For example,

ret = bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

• recvfrom is commonly used with UDP 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(server_socket, buffer, BUFFER_SIZE, 0, (struct sockaddr*)&client_addr, &client_addr_len);

• 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 <signal.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>

#define BUFFER_SIZE 1024

int server_socket;

int main() 
{
  int ret;
  struct sockaddr_ll 
  server_addr, 
  client_addr;
  char buffer[BUFFER_SIZE];

  server_socket = socket(AF_PACKET, 
                  SOCK_DGRAM, 
                  htons(ETH_P_ALL));

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

  memset(&server_addr, 0, 
  sizeof(server_addr));
  server_addr.sll_family = AF_PACKET;
  server_addr.sll_protocol = 
  htons(ETH_P_ALL);
  server_addr.sll_ifindex = 
  if_nametoindex("lo");

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

  printf("UDP is listening\n");

  socklen_t client_addr_len = 
  sizeof(client_addr);

  memset(buffer, 0, 
  sizeof(buffer));
  ret = recvfrom(server_socket, 
  buffer, BUFFER_SIZE, 0, 
  (struct sockaddr*)&client_addr, 
  &client_addr_len);

  if (ret > 0) {
    buffer[ret] = '\0';
    printf("Received: %s\n", 
    buffer);
  } else {
    perror("recvfrom error");
    return - 3;
  }

  (void)close(server_socket);

  return 0;
}

Program1 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server

Received: hello server!

Program1 : Step 4: Sequence Diagram for CLIENT.c

Program1 : Step 5: Program for Client.c

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

  • Create Socket

  • Sendto data_packet

  • Close socket

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

client_socket = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

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

ret = sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_addr, sizeof(server_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 <signal.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>

#define BUFFER_SIZE 1024

int client_socket;

int main(void)
{
  int ret;
  struct sockaddr_ll 
  server_addr;
  char buffer[BUFFER_SIZE];

  client_socket = socket(AF_PACKET, 
                  SOCK_DGRAM, 
                  htons(ETH_P_ALL));

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

  memset(&server_addr, 0, 
  sizeof(server_addr));
  server_addr.sll_family = AF_PACKET;
  server_addr.sll_protocol = 
  htons(ETH_P_ALL);
  server_addr.sll_ifindex = 
  if_nametoindex("lo");

  sprintf(buffer, "%s", "hello server!");
  ret = sendto(client_socket, buffer, 
  strlen(buffer), 0, 
  (struct sockaddr*)&server_addr, 
  sizeof(server_addr));
  
  if (ret == -1) {
    perror("sendto");
    return -2;
  }
  
  printf("Sentbuffer : %s\n",
  buffer);

  (void)close(client_socket);

  return 0;
}

Program1 : Step 6: Compile and Execute Client.c

$ gcc -o client client.c

$ sudo ./client

Sentbuffer : hello server!

Program2 : Step 1: Sequence Diagram for SERVER.c

Program2 : 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

  • Recvfrom data_packet

  • Close socket

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

server_socket = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

• bind() is used to associate the socket with a specific address and port. For example,

ret = bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

• recvfrom is commonly used with UDP 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(server_socket, buffer, BUFFER_SIZE, 0, (struct sockaddr*)&client_addr, &client_addr_len);

• 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 <signal.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>

#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

int server_socket;

int main(void) 
{
  int ret, i;
  struct sockaddr_ll 
  server_addr, 
  client_addr;
  char buffer[BUFFER_SIZE];

  server_socket = socket(AF_PACKET, 
                  SOCK_DGRAM, 
                  htons(ETH_P_ALL));

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

  memset(&server_addr, 0, 
  sizeof(server_addr));
  server_addr.sll_family = AF_PACKET;
  server_addr.sll_protocol = 
  htons(ETH_P_ALL);
  server_addr.sll_ifindex = 
  if_nametoindex("lo");

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

  printf("UDP is listening\n");

  socklen_t client_addr_len = 
  sizeof(client_addr);

  i = 0;
  while (i < NUM_MESSAGES) {
    memset(buffer, 0, 
    sizeof(buffer));
    ret = recvfrom(server_socket, 
    buffer, BUFFER_SIZE, 0, 
    (struct sockaddr*)&client_addr, 
    &client_addr_len);

    if (ret > 0) {
      buffer[ret] = '\0';
      printf("Received: %s\n", 
      buffer);
    } else if (ret < 0) {
      perror("recvfrom error");
      break;
    }
    ++i;
  }

  (void)close(server_socket);

  return 0;
}

Program2 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server

UDP is listening
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!
Received: hello server!

Program2 : Step 4: Sequence Diagram for CLIENT.c

Program2 : Step 5: Program for Client.c

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

  • Create Socket

  • Sendto data_packet

  • Close socket

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

client_socket = socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL));

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

ret = sendto(client_socket, buffer, strlen(buffer), 0, (struct sockaddr*)&server_addr, sizeof(server_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 <signal.h>
#include <netpacket/packet.h>
#include <net/ethernet.h>
#include <net/if.h>

#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

int client_socket;

int main(void)
{
  int ret, i;
  struct sockaddr_ll 
  server_addr;
  char buffer[BUFFER_SIZE];

  client_socket = socket(AF_PACKET, 
                  SOCK_DGRAM, 
                  htons(ETH_P_ALL));

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

  memset(&server_addr, 0, 
  sizeof(server_addr));
  server_addr.sll_family = AF_PACKET;
  server_addr.sll_protocol = 
  htons(ETH_P_ALL);
  server_addr.sll_ifindex = 
  if_nametoindex("lo");

  i = 0;
  while (i < NUM_MESSAGES) {
    sprintf(buffer, "%s", "hello server!");
    ret = sendto(client_socket, buffer, 
    strlen(buffer), 0, 
    (struct sockaddr*)&server_addr, 
    sizeof(server_addr));
  
    if (ret < 0) {
      perror("sendto");
      break;
    }
  
    printf("Sentbuffer : %s\n",
    buffer);
    ++i;
  }

  (void)close(client_socket);

  return 0;
}

Program2 : Step 6: Compile and Execute Client.c

$ gcc -o client client.c

$ sudo ./client

Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!
Sentbuffer : hello server!

Enhanced Socket Flexibility with AF_PACKET and PF_PACKET Domains

Default Domain:

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

Additional Domain Support:

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

Socket Creation:

We set up a network connection point known as a socket using socket(PF_PACKET, SOCK_DGRAM, IPPROTO_UDP).

Working Scenario:

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

Enhanced Protocol Flexibility in Socket Configuration

Default Protocol Support:

By default, the socket is configured to support the capture of all Ethernet frames (ETH_P_ALL protocol).

Additional Protocol:

The socket is designed to seamlessly support an additional protocol, namely ETH_P_PAE.

Socket Creation:

A socket is created using the socket(AF_PACKET, SOCK_DGRAM, htons(ETH_P_PAE)) call.

Working Scenario:

Despite the change in protocol to ETH_P_PAE, the overall working scenario of the socket remains consistent.

Summary

Socket API	Learning
socket	Create a new socket
bind	Associate the socket with a specific address and port
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 UDP socket.

See Also

• Previous topic

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• Other sockets

  • raw_af_packet_tcp_htons_ETH_P_ALL

• Other IPCs

  • Message_queues

  • NamedPipes

  • Netlink

  • Shared_Memory

  • Shared_Memory_2_FDS

  • SocketPair

  • Timerfd