TCP Client Server-Socket Programming in C

TCP Client-Server Socket Programming in C

TCP Client Server-Socket Programming | Socket programming is a common way of connecting two nodes on a network to communicate with each other. One node/socket is listening to a particular port at an IP. While another socket reaches out to the other to form a connection. The server forms the listener socket while the client reaches out to the server.

TCP Stands for Transmission Control Protocol. TCP is a communication protocol that was introduced in 1974.

Responsibilities of TPC:

Creating packets from byte stream received from the application layer. Transport Layer uses the port numbers to create a process to process communications. It uses the acknowledgement packet, time out, and retransmission
to achieve error control.

Features:

TCP is a connection-oriented protocol. Before any data transfer activity, TCP established a connection. One entity who is waiting for connection is server and another entity is a client connects to the server. In TCP is connection is full-duplex.

TCP is a reliable transmission protocol. Byte streams are broken into chunks known as segments. The receiver always sends acknowledgements (ACKs) for segments. If a segment not received in time then TCP retransmit. We can say TCP maintains timer as well.

Client-Side Programming:

#include<stdio.h>
#include<sys/socket.h>
#include<string.h>
#include<unistd.h>
#include<stdlib.h>
#include<netinet/in.h>
#include<netdb.h>

int main(int argc, char *argv[])
{
    int sockfd, portno, conn;
    char buffer[256];
    int buf;	
    struct sockaddr_in server;
    struct hostent *server1;

    if(argc<3)
    {
        perror("Not provided all the information.");
        exit(1);
    }

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd<0)
    {
        perror("could not create socket.");
        exit(1);
    
    }

    server1=gethostbyname(argv[1]);
    if(server1==NULL)
    {
        perror("No such host is available");
        exit(1);
    }
    
    
    memset((char *)&server, 0, sizeof(server));
    server.sin_family=AF_INET;
    memcpy((char *)server1->h_addr,(char *)&server.sin_addr.s_addr,server1->h_length);

    
    portno=atoi(argv[2]);
    server.sin_port=htons(portno);
    

    conn=connect(sockfd,(struct sockaddr *)&server,sizeof(server));
    if(conn<0)
    {
        perror("could not connect server.");
        exit(1);
    }
    printf("Please enter the message: ");

    memset(buffer,0,sizeof(buffer));
    fgets(buffer,256,stdin);

    buf=write(sockfd,buffer,strlen(buffer));
    if(buf<0)
    {
        perror("error in writing.");
        exit(1);
    }
    
    memset(buffer,0,sizeof(buffer));
    buf=read(sockfd,buffer,256);
    if(buf<0)
    {
        perror("error in writing.");
        exit(1);
    }
    printf("%s\n",buffer);	
    return 0;
}

Server Side

#include<stdio.h>
#include<sys/socket.h>
#include<string.h>
//#include<sys/types.h>
#include<netinet/in.h>	//...for htons,INADDR_ANY
#include<stdlib.h>
#include<unistd.h>


int main(int argc, char *argv[])
{
    int sockfd, newsockfd, bindfd,portno,clilen;
    char buffer[256];
    int buf;	
    struct sockaddr_in server, cli_addr;

    if(argc<2)
    {
        perror("Not provided all the information.");
        exit(1);
    }

    sockfd=socket(AF_INET,SOCK_STREAM,0);
    if(sockfd<0)
    {
        perror("could not create socket.");
        exit(1);
    
    }

    memset((char *)&server, 0, sizeof(server));

    server.sin_family=AF_INET;
    server.sin_addr.s_addr=INADDR_ANY;

    portno=atoi(argv[1]);
    server.sin_port=htons(portno);

    bindfd=bind(sockfd, (struct sockaddr *)&server, sizeof(server));
    if(bind<0)
    {
        perror("could not bind.");
        exit(1);
    }

    listen(sockfd,5);

    clilen=sizeof(cli_addr);
    newsockfd=accept(sockfd,(struct sockaddr *)&cli_addr,&clilen);
    if(newsockfd<0)
    {
        perror("could not accept client.");
        exit(1);
    }

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

    buf=read(newsockfd,buffer,256);
    if(buf<0)
    {
        perror("reading from socket.");
        exit(1);
    }

    printf("the value is %s\n",buffer);
    buf=write(newsockfd,"this is for chapter 5",25);
    if(buf<0)
    {
        perror("error in writing.");
        exit(1);
    }
    return 0;
}

Program Execution Guide:

To compile server.c:
$gcc -o exe_filename server.c
To run exe_filename:
$./exe_filename port_number

Whatever may be the executable file name.
port_number should be the 16-bit integer number.
You have to make sure the server is in listen mode.

To compile client.c:
$gcc -o exe_filename1 client.c
To run exe_filename1:
$./exe_filename1 localhost port_number

in place of localhost, you have to mention the IP address of the server, if your server is listening in another machine.

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