Basic example af unix udp server and client

AF_UNIX 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 unix udp single server and single client : single data transfer

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

program 1 : af unix udp single server and single client : single data transfer

Topics in this section,

• AF_UNIX 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 unix udp single server and single client : multiple data transfer

Topics in this section,

• AF_UNIX 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_UNIX UDP SOCKET : FAQs

Let us answer few basic questions in this socket

What does socket(AF_UNIX, SOCK_DGRAM, 0) do?

See Answer

Creates a Unix domain socket for datagram communication.

How does AF_UNIX differ from AF_INET in sockets?

See Answer

AF_UNIX is for local communication using file system paths, while AF_INET is for network communication using IP addresses.

Why choose SOCK_DGRAM as the socket type?

See Answer

It enables connectionless, datagram-oriented communication.

What does the third parameter (0) indicate in socket(AF_UNIX, SOCK_DGRAM, 0)?

See Answer

The system chooses the default protocol for the specified domain and type.

What role does the file system path play in AF_UNIX datagram sockets?

See Answer

Serves as the address for Unix domain datagram sockets.

How does error handling work with the socket call?

See Answer

Check the return value; if it’s -1, an error occurred. Use appropriate error-handling mechanisms.

How is data flow managed in AF_UNIX datagram sockets?

See Answer

Data is sent and received in discrete, independent units known as datagrams.

Can a Unix domain datagram socket connect to multiple servers?

See Answer

Yes, each datagram is independent, allowing communication with multiple servers.

What happens if the specified file system path in AF_UNIX datagram sockets doesn’t exist?

See Answer

Typically results in an error; the path should exist or be creatable.

Are AF_UNIX datagram sockets suitable for bi-directional communication?

See Answer

Yes, they can handle both sending and receiving data independently.

Program1 : 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

  • Recvfrom data_packet

  • Close socket

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

server_socket = socket(AF_UNIX, SOCK_DGRAM, 0);

• 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, &addr_size);

• 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 <sys/socket.h>
#include <sys/un.h>

#define SOCKET_PATH "/tmp/my_unix_socket"
#define BUFFER_SIZE 1024

int main(void) 
{
  int server_socket;
  int client_socket;
  int ret;
  struct sockaddr_un 
  server_addr, 
  client_addr;
  socklen_t addr_size = sizeof(
  client_addr);
  char buffer[BUFFER_SIZE] 
  = "Hello from server!";

  server_addr.sun_family = AF_UNIX;
  strncpy(server_addr.sun_path, 
  SOCKET_PATH, 
  sizeof(server_addr.sun_path) - 1);
  unlink(SOCKET_PATH);

  server_socket = socket(AF_UNIX, 
                  SOCK_DGRAM, 
                  0);

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

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

  if (ret < 0) {
    perror("Bind failed");
    (void)close(server_socket);
    return -2;
  }

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

  if (ret < 0) {
    perror("recvfrom");
    (void)close(server_socket);
    return -3;
  }

  printf("Received: %s\n", 
  buffer);

  (void)close(server_socket);

  return 0;
}

Program1 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server

Received: Hello from client!

Program1 : 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

  • Sendto data_packet

  • Close socket

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

client_socket = socket(AF_UNIX, SOCK_DGRAM, 0);

• 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 <sys/socket.h>
#include <sys/un.h>

#define SOCKET_PATH "/tmp/my_unix_socket"
#define BUFFER_SIZE 1024

int main(void) 
{
  int client_socket;
  int ret;
  struct sockaddr_un 
  server_addr;
  char buffer[BUFFER_SIZE] 
  = "Hello from client!";

  server_addr.sun_family = AF_UNIX;
  strncpy(server_addr.sun_path, 
  SOCKET_PATH, 
  sizeof(server_addr.sun_path) - 1);

  client_socket = socket(AF_UNIX, 
                  SOCK_DGRAM, 0);

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

  ret = sendto(client_socket, 
  buffer, strlen(buffer), 0, 
  (struct sockaddr *)&server_addr, 
  sizeof(server_addr));

  if (ret < 0) {
    perror("sendto");
    (void)close(client_socket);
    return -3;
  } 

  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 from client!

Program2 : 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

  • Recvfrom data_packet

  • Close socket

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

server_socket = socket(AF_UNIX, SOCK_DGRAM, 0);

• 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, &addr_size);

• 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 <sys/socket.h>
#include <sys/un.h>

#define SOCKET_PATH "/tmp/my_unix_socket"
#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

int main(void) 
{
  int server_socket; 
  int client_socket;
  int ret, i;
  struct sockaddr_un 
  server_addr, 
  client_addr;
  socklen_t addr_size = sizeof(
  client_addr);
  char buffer[BUFFER_SIZE];

  server_addr.sun_family = AF_UNIX;
  strncpy(server_addr.sun_path, 
  SOCKET_PATH, 
  sizeof(server_addr.sun_path) - 1);
  unlink(SOCKET_PATH);

  server_socket = socket(AF_UNIX, 
                  SOCK_DGRAM, 0);

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

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

  if (ret < 0) {
    perror("Bind failed");
    (void)close(server_socket);
    return -2;
  }

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

    if (ret < 0) {
      perror("recvfrom");
      break;
    }
    
    printf("received: %s\n", buffer);
    ++i;
  }

  (void)close(server_socket);

  return 0;
}

Program2 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./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!
received: Hello Server!

Program2 : 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

  • Sendto data_packet

  • Close socket

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

client_socket = socket(AF_UNIX, SOCK_DGRAM, 0);

• 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 <sys/socket.h>
#include <sys/un.h>

#define SOCKET_PATH "/tmp/my_unix_socket"
#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

int main(void) 
{
  int client_socket;
  int ret, i;
  struct sockaddr_un 
  server_addr;
  char buffer[BUFFER_SIZE]
  = "Hello Server!";

  server_addr.sun_family = AF_UNIX;
  strncpy(server_addr.sun_path, 
  SOCKET_PATH,
  sizeof(server_addr.sun_path) - 1);
  
 client_socket = socket(AF_UNIX, 
                 SOCK_DGRAM, 0);

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

  i = 0;
  while (i < NUM_MESSAGES) {
    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!

Summary

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

See Also

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