simple socket example in C

simple_socket_example.c

/* --- Usage --- */
g++ server.c -o server
g++ client.c -o client
./server
./client 127.0.0.1

/* --- server.c --- */
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <time.h>

int main(int argc, char *argv[])
{
	int listenfd = 0, connfd = 0;
	struct sockaddr_in serv_addr;

	char sendBuff[1025];
	time_t ticks;

	/* creates an UN-named socket inside the kernel and returns
	 * an integer known as socket descriptor
	 * This function takes domain/family as its first argument.
	 * For Internet family of IPv4 addresses we use AF_INET
	 */
	listenfd = socket(AF_INET, SOCK_STREAM, 0);
	memset(&serv_addr, '0', sizeof(serv_addr));
	memset(sendBuff, '0', sizeof(sendBuff));

	serv_addr.sin_family = AF_INET;
	serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	serv_addr.sin_port = htons(5000);

	/* The call to the function "bind()" assigns the details specified
	 * in the structure 『serv_addr' to the socket created in the step above
	 */
	bind(listenfd, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

	/* The call to the function "listen()" with second argument as 10 specifies
	 * maximum number of client connections that server will queue for this listening
	 * socket.
	 */
	listen(listenfd, 10);

	while(1)
	{
		/* In the call to accept(), the server is put to sleep and when for an incoming
		 * client request, the three way TCP handshake* is complete, the function accept()
		 * wakes up and returns the socket descriptor representing the client socket.
		 */
		connfd = accept(listenfd, (struct sockaddr*)NULL, NULL);

		/* As soon as server gets a request from client, it prepares the date and time and
		 * writes on the client socket through the descriptor returned by accept()
		 */
		ticks = time(NULL);
		snprintf(sendBuff, sizeof(sendBuff), "%.24s\r\n", ctime(&ticks));
		write(connfd, sendBuff, strlen(sendBuff));

		close(connfd);
		sleep(1);
	}
}

/* --- client.c --- */
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
	int sockfd = 0, n = 0;
	char recvBuff[1024];
	struct sockaddr_in serv_addr;

	if(argc != 2)
	{
		printf("\n Usage: %s <ip of server> \n",argv[0]);
		return 1;
	}

	memset(recvBuff, '0',sizeof(recvBuff));

	/* a socket is created through call to socket() function */
	if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
	{
		printf("\n Error : Could not create socket \n");
		return 1;
	}

	memset(&serv_addr, '0', sizeof(serv_addr));

	serv_addr.sin_family = AF_INET;
	serv_addr.sin_port = htons(5000);

	if(inet_pton(AF_INET, argv[1], &serv_addr.sin_addr)<=0)
	{
		printf("\n inet_pton error occured\n");
		return 1;
	}

	/* Information like IP address of the remote host and its port is
	 * bundled up in a structure and a call to function connect() is made
	 * which tries to connect this socket with the socket (IP address and port)
	 * of the remote host
	 */
	if( connect(sockfd, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) < 0)
	{
		printf("\n Error : Connect Failed \n");
		return 1;
	}

	/* Once the sockets are connected, the server sends the data (date+time)
	 * on clients socket through clients socket descriptor and client can read it
	 * through normal read call on the its socket descriptor.
	 */
	while ( (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) > 0)
	{
		recvBuff[n] = 0;
		if(fputs(recvBuff, stdout) == EOF)
		{
			printf("\n Error : Fputs error\n");
		}
	}

	if(n < 0)
	{
		printf("\n Read error \n");
	}

	return 0;
}