Myujth

I have made one server and one client communicating through UDP sockets. The work that I am trying to do is that client will pass a string in the arguments and that string will be send to the server using UDP sockets. After receiving the string server will again echo(send) the string back to the client.Below are the codes for both:

code for echoClient.c :

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/socket.h>

#define MAXLINE 4096

int main(int argc, char const *argv)

 int sockfd;
 struct sockaddr_in servAddr;
 char sendLine[MAXLINE],recvLine[MAXLINE];

 if(argc!=3)
 
 printf("echoClient <Ip addr. of the server> <String to be echoed> n");
 exit(1);
 

 if((sockfd=socket(AF_INET,SOCK_DGRAM,0))<0)
 
 printf("Error in creating the socketn");
 exit(2);
 


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

 servAddr.sin_family = AF_INET;
 servAddr.sin_port = htons(6565); // setting up the port
 servAddr.sin_addr.s_addr = inet_addr(argv[1]); // using the given ip address of the server

 printf("%sn", argv[2]);

 if((sendto(sockfd,(const char *)argv[2],strlen(argv[2]), MSG_CONFIRM,(struct sockaddr *) &servAddr, sizeof(servAddr))!=-1))
 
 printf("data is sent to the servern");
 
 else
 
 printf("can't send the data to the servern");
 exit(3);
 

 int n = recvfrom(sockfd,(char * ) recvLine,MAXLINE,0,(struct sockaddr * )&servAddr,sizeof(servAddr));

 if(n==-1)
 
 printf("Can't receive the data from the servern");
 exit(4);
 

 recvLine[n] = ''; // to terminate the received string

 printf("%sn",recvLine);


 return 0;

code for echoServer.c:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>

#define MAXLINE 4096

int main(int argc, char const *argv)

 int sockfd;
 struct sockaddr_in servAddr,clientAddr;
 char sendLine[MAXLINE],recvLine[MAXLINE];

 if(argc!=1)
 
 printf("echoServern");
 exit(1);
 

 if((sockfd=socket(AF_INET,SOCK_DGRAM,0))<0)
 
 printf("Error in creating the socketn");
 exit(2);
 


 memset(&servAddr,0,sizeof(servAddr));
 memset(&clientAddr,0,sizeof(clientAddr));


 // filling the details of the server ip and port
 servAddr.sin_family = AF_INET;
 servAddr.sin_port = htons(6565);
 servAddr.sin_addr.s_addr = INADDR_ANY; // using the given ip address of the server

 if(bind(sockfd,(struct sockaddr * )&servAddr,sizeof(servAddr))<0)
 
 printf("Binding of the socket failedn");
 exit(1);
 

 printf("Server is Up... Waiting for the client...n");

 int len;
 int n = recvfrom(sockfd,(char *) recvLine,MAXLINE,MSG_WAITALL,(struct sockaddr * )&clientAddr,&len);

 if(n==-1)
 
 printf("can't get the message from the clientn");
 exit(2);
 

 recvLine[n] = '';

 printf("Message received from the client is %sn",recvLine);

 if(sendto(sockfd,(char *) recvLine,n,MSG_CONFIRM,(struct sockaddr *)&clientAddr,len)<0)
 
 printf("can't send the message to the clientn");
 exit(3);
 

 return 0;

Now the actual problen is that when I am executing the above codes client is able to send the string to the server but server is unable to send the string back to the client.Server gives the error can't send the message to the client.

I am not able to figure out the error which is stopping the server to send the message to the client.Please help me with this.

I am running the echoClient.c with the command :
./a.out 127.0.0.1 hellofromclientside

In the server, you overlooked that the argument len to recvfrom() is a value-result argument, which before the call you have to initialize to the size of the clientAddr in order to get this address, so change

 int len;

to

 int len = sizeof clientAddr;

Similarly in the client, change

 int n = recvfrom(sockfd,(char * ) recvLine,MAXLINE,0,(struct sockaddr * )&servAddr,sizeof(servAddr));

to

 int len = sizeof servAddr;
 int n = recvfrom(sockfd, recvLine, MAXLINE, 0, (struct sockaddr *)&servAddr, &len);