Basic example udp server and client

IPv4 AF_INET 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: udp single server and single client : single data transfer

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

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

Topics in this section,

• IPV4 AF_INET 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 : udp single server and single client : multiple data transfer

Topics in this section,

• IPV4 AF_INET 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

IPV4 AF_INET UDP SOCKET : FAQs

Let us answer few basic questions in this socket

What does socket(AF_INET SOCK_DGRAM,IPPROTO_UDP) create?

See Answer

A UDP socket

What does AF_INET signify in socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)?

See Answer

IPv4 address family

Why might you choose SOCK_DGRAM when creating a socket?

See Answer

For connectionless communication

What is the purpose of IPPROTO_UDP in socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)?

See Answer

It is optional and can be omitted.

How does a UDP socket differ from a TCP socket created using socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)?

See Answer

UDP is connectionless, while TCP is connection-oriented,

What is the typical use case for a UDP socket created with socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)?

See Answer

DNS resolution

How would you bind a specific IP address and port to a UDP socket created using socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)?

See Answer

Use the bind() function after creating the socket.

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_INET, SOCK_DGRAM, IPPROTO_UDP);

• 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,

len = 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 <arpa/inet.h>

#define BUFFER_SIZE 1024

void validate_convert_port(
char *port_str,
struct sockaddr_in *sock_addr)
{
  int port;

  if (port_str == NULL) {
     perror("Invalid port_str\n");
     exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
     perror("Invalid sock_addr\n");
     exit(EXIT_FAILURE);
 }

 port = atoi(port_str);

 if (port == 0) {
   perror("Invalid port\n");
   exit(EXIT_FAILURE);
 }

 sock_addr->sin_port = htons(
 (uint16_t)port);
 printf("Port: %d\n",
 ntohs(sock_addr->sin_port));
}

int main(int argc, char *argv[]) 
{
  int server_socket;
  int ret;
  struct sockaddr_in 
  server_addr, 
  client_addr;
  socklen_t addr_size = sizeof(
  client_addr);
  char buffer[BUFFER_SIZE];

  if (argc != 2) {
    printf("%s <port-number>",
    argv[0]);
    return -1;
  }

  server_socket = socket(AF_INET,
                  SOCK_DGRAM,
                  IPPROTO_UDP);

  if (server_socket < 0) {
    perror("Socketfailed");
    return -2;
  }

  server_addr.sin_family = AF_INET;
  server_addr.sin_addr.s_addr = 
  INADDR_ANY;
  validate_convert_port(argv[1], 
  &server_addr);

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

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

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

  if (ret < 0) {
    perror("recvfrom");
    (void)close(server_socket);
    return -4;
  }

  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 8080

Port: 8080
received: Hello from client!

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_INET, SOCK_DGRAM, IPPROTO_UDP);

• 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>

#define BUFFER_SIZE 1024

void validate_convert_port(
char *port_str,
struct sockaddr_in *sock_addr)
{
  int port;

  if (port_str == NULL) {
     perror("Invalid port_str\n");
     exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
     perror("Invalid sock_addr\n");
     exit(EXIT_FAILURE);
 }

 port = atoi(port_str);

 if (port == 0) {
   perror("Invalid port\n");
   exit(EXIT_FAILURE);
 }

 sock_addr->sin_port = htons(
 (uint16_t)port);
 printf("Port: %d\n",
 ntohs(sock_addr->sin_port));
}

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[]) 
{
  int client_socket;
  int ret;
  struct sockaddr_in 
  server_addr;
  char buffer[BUFFER_SIZE] = "Hello from client!";

  if (argc != 3) {
    printf("%s<port-number><ip-addr>\n",
    argv[0]);
    return -1;
  }

  client_socket = socket(AF_INET,
                  SOCK_DGRAM,
                  IPPROTO_UDP);

  if (client_socket < 0) {
    perror("Socket failed");
    return -2;
  }

  server_addr.sin_family = AF_INET;
  validate_convert_port(argv[1], 
  &server_addr);
  validate_convert_addr(argv[2], 
  &server_addr);

  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("Messagesent: %s\n", 
  buffer);

  (void)close(client_socket);

  return 0;
}

Program1 : Step 6: Compile and Execute Client.c

$ gcc -o client client.c

$ sudo ./client 8080 127.0.0.1

Port: 8080
IP Address: 127.0.0.1
Messagesent: Hello from client!

$ sudo ./server 8080 127.0.0.1

$ sudo ./client 8080 127.0.0.1

program to run with elevated privileges, listen on port 8080, and bind to the loopback address 127.0.0.1.

<port_number> <ip_address> decided by the user based on the connection.

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_INET, SOCK_DGRAM, IPPROTO_UDP);

• 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,

len = 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 <arpa/inet.h>

#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

void validate_convert_port(
char *port_str,
struct sockaddr_in *sock_addr)
{
  int port;

  if (port_str == NULL) {
   perror("Invalid port_str\n");
   exit(EXIT_FAILURE);
  }

  if (sock_addr == NULL) {
   perror("Invalid sock_addr\n");
   exit(EXIT_FAILURE);
  }

  port = atoi(port_str);

  if (port == 0) {
    perror("Invalid port\n");
    exit(EXIT_FAILURE);
  }

  sock_addr->sin_port = htons(
  (uint16_t)port);
  printf("Port: %d\n",
  ntohs(sock_addr->sin_port));
}

int main(int argc, char *argv[]) 
{
  int server_socket;
  int i, ret;
  struct sockaddr_in 
  server_addr, 
  client_addr;
  socklen_t addr_size = sizeof(
  client_addr);
  char buffer[BUFFER_SIZE];

  if (argc != 2) {
    printf("%s <port-number>", 
    argv[0]);
    return -1;
  }

  server_socket = socket(AF_INET,
                  SOCK_DGRAM,
                  IPPROTO_UDP);

  if (server_socket < 0) {
    perror("Socket failed");
    return -2;
  }

  server_addr.sin_family = AF_INET;
  server_addr.sin_addr.s_addr = 
  INADDR_ANY;
  validate_convert_port(argv[1], 
  &server_addr);

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

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

  i = 0;
  while (i < NUM_MESSAGES) { 
    memset(buffer, 0, 
    sizeof(buffer));

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

    if (ret < 0) {
      perror("recvfrom");
      (void)close(server_socket);
      return -4;
    }

    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 8080

Port: 8080
Received: Message 1 from server!
Received: Message 2 from server!
Received: Message 3 from server!
Received: Message 4 from server!
Received: Message 5 from server!
Received: Message 6 from server!
Received: Message 7 from server!
Received: Message 8 from server!
Received: Message 9 from server!
Received: Message 10 from 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_INET, SOCK_DGRAM, IPPROTO_UDP);

• 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>

#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

void validate_convert_port(
char *port_str,
struct sockaddr_in *sock_addr)
{
  int port;

  if (port_str == NULL) {
     perror("Invalid port_str\n");
     exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
     perror("Invalid sock_addr\n");
     exit(EXIT_FAILURE);
 }
  
 port = atoi(port_str);

 if (port == 0) {
   perror("Invalid port\n");
   exit(EXIT_FAILURE);
 }

 sock_addr->sin_port = htons(
 (uint16_t)port);
 printf("Port: %d\n",
 ntohs(sock_addr->sin_port));
}

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[]) 
{
  int client_socket;
  int i, ret;
  struct sockaddr_in 
  server_addr;
  char buffer[BUFFER_SIZE] = "Hello from client!";
  socklen_t addr_size = sizeof(
  server_addr);

  if (argc != 3) {
    printf("%s<port-number><ip-addr>\n",
    argv[0]);
    return -1;
  }

  client_socket = socket(AF_INET,
                  SOCK_DGRAM,
                  IPPROTO_UDP);

  if (client_socket < 0) {
    perror("Socket failed");
    return -2;
  }

  server_addr.sin_family = AF_INET;
  validate_convert_port(argv[1], 
  &server_addr);
  validate_convert_addr(argv[2], 
  &server_addr);

  i = 0;
  while (i < NUM_MESSAGES) {  
   snprintf(buffer, sizeof(buffer),
        "Message %d from server!",
        i + 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("Message %d sent: %s\n",
   i + 1, buffer);
   ++i;
  }

  (void)close(client_socket);

  return 0;
}

Program2 : Step 6: Compile and Execute Client.c

$ gcc -o client client.c

$ sudo ./client 8080 127.0.0.1

Port: 8088
IP Address: 127.0.0.1
Message 1 sent: Message 1 from server!
Message 2 sent: Message 2 from server!
Message 3 sent: Message 3 from server!
Message 4 sent: Message 4 from server!
Message 5 sent: Message 5 from server!
Message 6 sent: Message 6 from server!
Message 7 sent: Message 7 from server!
Message 8 sent: Message 8 from server!
Message 9 sent: Message 9 from server!
Message 10 sent: Message 10 from server!

$ sudo ./server 8080 127.0.0.1

$ sudo ./client 8080 127.0.0.1

program to run with elevated privileges, listen on port 8080, and bind to the loopback address 127.0.0.1.

<port_number> <ip_address> decided by the user based on the connection.

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_DGRAM, 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
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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• Current topic

  • Basic example udp server and client

• Next topic

  • IPV4 UDP server client program with Select system call

• Other sockets

  • af_unix_tcp

  • af_unix_udp

  • ipv4_raw_af_inet_icmp

  • ipv4_raw_af_inet_raw

  • ipv4_raw_af_inet_tcp

  • ipv4_raw_af_inet_udp

  • 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