Basic example tcp server and client

IPv4 AF_INET TCP

• In this program, you are going to learn

• How to create a Socket ?

• How to bind a socket ?

• How to listen a socket ?

• How to connect a socket ?

• How to accept a socket ?

• How to send a data ?

• How to recv a data ?

• How to use socket APIs ?

  • socket

  • bind

  • listen

  • connect

  • accept

  • send

  • recv

Topics in this section,

• program 1: tcp single server and single client : single data transfer

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

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

Topics in this section,

• IPV4 AF_INET TCP 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 : tcp single server and single client : multiple data transfer

Topics in this section,

• IPV4 AF_INET TCP 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 TCP SOCKET : FAQs

Let us answer few basic questions in this socket

What does the AF_INET parameter represent in the socket() function call?

See Answer

Address Family for IPv4

Why is SOCK_STREAM used as the second parameter in the socket() function call?

See Answer

It indicates that the socket will use a reliable, connection-oriented communication (TCP).

What is the default protocol for a TCP socket created with socket(AF_INET, SOCK_STREAM, ?? )?

See Answer

IPPROTO_TCP

What is the primary characteristic of TCP communication?

See Answer

Connection-oriented and reliable

What does a return value of -1 indicate in socket functions?

See Answer

In many socket programming APIs, a return value of -1 usually indicates an error. Functions often set an error code that can be retrieved using perror (or an equivalent mechanism) to determine the specific nature of the error.

Why might bind() or listen() fail in socket programming?

See Answer

bind() might fail if the specified address is already in use, or if the process lacks the necessary permissions. listen() might fail if the socket is not bound, or the operating system limit for pending connections is reached.

How should you handle errors when using accept() in socket programming?

See Answer

Check the return value and handle errors appropriately

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

See Answer

It detects issues such as network errors or closed connections.

Can you use a TCP socket (SOCK_STREAM) for sending and receiving data concurrently between a client and server?

See Answer

Yes, TCP sockets support bidirectional communication.

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

  • Listen Socket

  • Accept Socket

  • Send data_packet

  • Close socket

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

server_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

• 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));

• listen() is used to set up a socket to accept incoming connections. For example,

ret = listen(server_socket, 5);

• accept() is used in network programming on the server side to accept a connection request from a client. For example,

client_socket = accept(server_socket, (struct sockaddr*)&client_addr, &addr_size);

• send is used in network programming to send data over a connected socket. For example,

ret = send(client_socket, buffer, strlen(buffer), 0);

• 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));
}

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

    if (argc != 2) {
       printf("%s <port-number>", 
       argv[0]);
       return -1;
   }
    
   server_addr.sin_family = AF_INET;
   server_addr.sin_addr.s_addr = 
   INADDR_ANY;
   validate_convert_port(argv[1], 
   &server_addr);

   server_socket = socket(AF_INET, 
		   SOCK_STREAM, 
                   IPPROTO_TCP);

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

   ret = bind(server_socket, 
   (struct sockaddr *)&server_addr, 
   sizeof(server_addr));
   
   if (ret < 0) {
      perror("Bind failed");
      (void)close(server_socket);
      return -3;
   }

   ret = listen(server_socket, 5);
   
   if (ret < 0) {
      perror("Listen failed");
      (void)close(server_socket);
      return -4;
   }

   client_socket = accept(server_socket, 
   (struct sockaddr *)&client_addr, 
   &addr_size);
    
   if (client_socket < 0) {
        perror("Accept failed");
        (void)close(server_socket);
        return -5;
   }

   ret = send(client_socket, buffer, 
   strlen(buffer), 0);

   if (ret < 0) {
       perror("send");
       (void)close(server_socket);
       (void)close(client_socket);
       return -6;
   }

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

   (void)close(client_socket);
   (void)close(server_socket);

   return 0;
}

Program1 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server 8080

Port: 8080
Message sent: Hello from 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

  • Connect Socket

  • Recv data_packet

  • Close socket

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

client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

• connect is used in network programming to establish a connection from a client to a server. For example,

ret = connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

• recv is used in network programming to receive data from a connected socket. For example,

ret = recv(client_socket, buffer, BUFFER_SIZE, 0);

• 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];

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

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

  client_socket = socket(AF_INET, 
                  SOCK_STREAM, 
                  IPPROTO_TCP);

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

  ret = connect(client_socket, 
  (struct sockaddr *)&server_addr, 
  sizeof(server_addr));
  
  if (ret < 0) {
     perror("Connection failed");
     (void)close(client_socket);
     return -3;
  }
    
  ret = recv(client_socket, 
  buffer, BUFFER_SIZE, 0);
  
  if (ret < 0) {
     perror("recv");
     (void)close(client_socket);
     return -4;
  }  

  printf("received = %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
received = Hello 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.

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

  • Listen Socket

  • Accept Socket

  • Send data_packet

  • Recv data_packet

  • Close socket

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

server_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

• 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));

• listen() is used to set up a socket to accept incoming connections. For example,

ret = listen(server_socket, 5);

• accept() is used in network programming on the server side to accept a connection request from a client. For example,

client_socket = accept(server_socket, (struct sockaddr*)&client_addr, &addr_size);

• send is used in network programming to send data over a connected socket. For example,

ret = send(client_socket, buffer, strlen(buffer), 0);

• recv is used in network programming to receive data from a connected socket. For example,

ret = recv(client_socket, buffer, sizeof(buffer), 0);

• 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));
}

int main(int argc, char *argv[]) 
{
  int server_socket; 
  int client_socket;
  int i = 0, ret;
  struct sockaddr_in 
  server_addr, 
  client_addr;
  socklen_t addr_size = sizeof(
  client_addr);
  char buffer[BUFFER_SIZE] = "Hello from server!";

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

  server_socket = socket(AF_INET, 
                  SOCK_STREAM, 
                  IPPROTO_TCP);

  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;
  }

  ret = listen(server_socket, 5);

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

  client_socket = accept(server_socket, 
  (struct sockaddr *)&client_addr, 
  &addr_size);

  if (client_socket < 0) {
     perror("Accept failed");
     (void)close(server_socket);
     return -5;
  }
   
  while (i < NUM_MESSAGES) {
   snprintf(buffer, sizeof(buffer), 
   "Message %d from server!",
   i + 1);

   ret = send(client_socket, buffer, 
   strlen(buffer), 0);

   if (ret < 0) {
      perror("send");
      (void)close(server_socket);
      (void)close(client_socket);
      return -6;
   }

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

   ret = recv(client_socket, buffer, 
   sizeof(buffer), 0);

   if (ret < 0) {
      perror("recv");
      (void)close(server_socket);
      (void)close(client_socket);
      return -7;
   }

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

  (void)close(client_socket);
  (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 client!
Received: Message 2 from client!
Received: Message 3 from client!
Received: Message 4 from client!
Received: Message 5 from client!
Received: Message 6 from client!
Received: Message 7 from client!
Received: Message 8 from client!
Received: Message 9 from client!
Received: Message 10 from client!

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

  • Connect Socket

  • Recv data_packet

  • Send data_packet

  • Close socket

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

client_socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

• connect is used in network programming to establish a connection from a client to a server. For example,

ret = connect(client_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

• recv is used in network programming to receive data from a connected socket. For example,

ret = recv(client_socket, buffer, BUFFER_SIZE, 0);

• send is used in network programming to send data over a connected socket. For example,

ret = send(client_socket, buffer, strlen(buffer), 0);

• 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 = 0, ret;
 struct sockaddr_in 
 server_addr;
 char buffer[BUFFER_SIZE];

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

 client_socket = socket(AF_INET, 
                 SOCK_STREAM, 
                 IPPROTO_TCP);

 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 = connect(client_socket, 
 (struct sockaddr *)&server_addr, 
 sizeof(server_addr));

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

 while (i < NUM_MESSAGES) {
   ret = recv(client_socket, buffer, 
   BUFFER_SIZE, 0);

   if (ret < 0) {
      perror("recv");
      (void)close(client_socket);
      return -6;
   }

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

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

   snprintf(buffer, sizeof(buffer), 
   "Message %d from client!", i + 1);

   ret = send(client_socket, buffer, 
   strlen(buffer), 0);

   if (ret < 0) {
      perror("send");
      (void)close(client_socket);
      return -7;
   }

   ++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: 8080
IP Address: 127.0.0.1
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!

$ 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_STREAM, IPPROTO_TCP).

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
listen	Set up a socket to accept incoming connections.
connect	Establish a connection from a client to a server.
accept	Server side to accept a connection request from a client.
recv	Receive data from a connected socket.
send	Send data over a connected socket.

See Also

• Current topic

  • Basic example tcp server and client

• Next topic

  • IPV4 TCP server client program with Select system call

• Other sockets

  • ipv4_af_inet_udp

  • 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