Question

I am trying to write a UDP socket program in which there is a server program and a client program. This is what I have but I can't figure out where I am going wrong.

This is the input and expected output:

> gcc udpclient.c –o clientout
> gcc udpserver.c –o serverout
> ./serverout 52007 ‘to celebrate’ &
> ./clientout odin 52007 ‘Today is a good day’
Today is a good day to celebrate

//UDP echo client program
#include
#include
#include
#include
#include
#include
#include
#include

#define PORT 52010

int main(int argc, char* argv[])                           //Three arguments to be checked later
{
   //Declare and define variables
   int s;                                       //Socket descriptor
   int len;                                    //Length of string to be echoed
   char* servName;                                //Server name
   int servPort;                                   //Server Port
   char* string;                                   //String to be echoed
   char buffer[256+1];                               //Data buffer
   struct sockaddr_in servAddr;                           //Server socket address
   //Check and set program arguments
   if(argc != 3)
   {
       printf("Error: three arguments are needed!");
       exit(1);
   }
   servName = argv[1];
   servPort = atoi(argv[2]);
   string = argv[3];
   //Build server socket address
   memset(&servAddr, 0, sizeof(servAddr));
   servAddr.sin_family = AF_INET;
   inet_pton(AF_INET, servName, &servAddr.sin_addr);
   servAddr.sin_port = htons(PORT);
   //Create socket
   if ((s = socket(PF_INET, SOCK_DGRAM, 0) < 0));
   {
       perror("Error: Socket failed!");
       exit(1);
   }
   //Send echo string
   len = sendto(s, string, strlen(string), 0, (struct sockaddr*)&servAddr, sizeof(servAddr));
   //Receive echo string
   recvfrom(s, buffer, len, 0, NULL, NULL);
   //Print and verify echoed string
   buffer[len] = '\0';
   printf("Echo string received: ");
   fputs(buffer, stdout);
   //Close the socket
   close(s);
   //Stop the program
   exit(0);
} //End of echo client program

//UDP echo server program
#include
#include
#include
#include
#include
#include
#include
#include

#define PORT 52010

int main(void)
{
   //Declare and define variables
   int s;                                //Socket descriptor(reference)
   int len;                            //Length of string to be echoed
   char buffer[256];                       //Data buffer
   struct sockaddr_in servAddr;                   //Server (local) socket address
   struct sockaddr_in clntAddr;                   //Client (remote) socket address
   int clntAddrLen;                       //Length of client socket address
   //Build local (server) socket address
   memset(&servAddr, 0, sizeof(servAddr));               //Set socket structure to all 0
   servAddr.sin_family = AF_INET;                   //Family field
   servAddr.sin_port = htons(PORT);               //Default port number
   servAddr.sin_addr.s_addr = htonl(INADDR_ANY);           //Default IP address
   //Create socket
   if((s = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
   {
       perror("Error: socket failed!");
       exit(1);
   }
   //Bind socket to local address and port
   if((bind(s, (struct sockaddr*)&servAddr, sizeof(servAddr))) < 0);
   {
       perror("Error: bind failed!");
       exit(1);
   }
   for(;;)           //Run forever
   {
       //Receive String
       len = recvfrom(s, buffer, sizeof(buffer), 0,
               (struct sockaddr*)&clntAddr, &clntAddrLen);
       //Send String
       sendto(s, buffer, len, 0, (struct sockaddr*)&clntAddr, sizeof(clntAddr));
   } //End of for loop
}//End of echo server program

Answer 1

// Server side implementation of UDP client-server model

#include <stdio.h>

#include <stdlib.h>

#include <unistd.h>

#include <string.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <arpa/inet.h>

#include <netinet/in.h>

  

#define PORT     8080

#define MAXLINE 1024

  

// Driver code

int main() {

    int sockfd;

    char buffer[MAXLINE];

    char *celebrate = "celebrate from server";

    struct sockaddr_in servaddr, cliaddr;

      

    // Creating socket file descriptor

    if ( (sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {

        perror("socket creation failed");

        exit(EXIT_FAILURE);

    }

      

    memset(&servaddr, 0, sizeof(servaddr));

    memset(&cliaddr, 0, sizeof(cliaddr));

      

    // Filling server information

    servaddr.sin_family    = AF_INET; // IPv4

    servaddr.sin_addr.s_addr = INADDR_ANY;

    servaddr.sin_port = htons(PORT);

      

    // Bind the socket with the server address

    if ( bind(sockfd, (const struct sockaddr *)&servaddr,

            sizeof(servaddr)) < 0 )

    {

        perror("bind failed");

        exit(EXIT_FAILURE);

    }

      

    int len, n;

  

    len = sizeof(cliaddr); //len is value/resuslt

  

    n = recvfrom(sockfd, (char *)buffer, MAXLINE,

                MSG_WAITALL, ( struct sockaddr *) &cliaddr,

                &len);

    buffer[n] = '\0';

    printf("Client : %s\n", buffer);

    sendto(sockfd, (const char *)celebrate, strlen(celebrate),

        MSG_CONFIRM, (const struct sockaddr *) &cliaddr,

            len);

    printf("celebrate message sent.\n");

      

    return 0;

}