Server stuck in Select and Reading Continuously from Client buffer

Question

I am trying client server code with Select call. But once i send from client to server, server continously reads from the buffer send by client even though client is not sending anything after Ist packet.Where i am doing wrong ?

Below is snippet of code:

fd_set readSet,master_list_read;
FD_ZERO(&master_list_read);
FD_SET(STDIN, &master_list_read);//stdin manually trigger reading
FD_SET(sockfd, &master_list_read);//tcp socket

struct timeval tv;
int retval;
tv.tv_sec = 10;
tv.tv_usec = 0;
while(1)
{ 
bool idle=false;
char *buffer=NULL;
int n;

tv.tv_sec = 10;
readSet=master_list_read;
retval = select(sockfd+1, &readSet, NULL, NULL,&tv);
if (retval == -1) 
{
    perror("Error in select\n");
    exit(4);
}
else if(retval==0)
{ 
    printf("*********SEND SUCCESSFUL******\n");
}       
else 
{   
if(FD_ISSET(0, &readSet))
{
    bzero(buf,256);
    fgets(buf,256,stdin); 
    if (send(sockfd, buffer,n, 0) == -1) perror("error in sending MSG to server\n");
}

else  if (FD_ISSET(sockfd, &readSet))  // receives data from server,print it on StdOutput
{  
    bzero(buf,256);
    int nbytes = recv(sockfd, buf, 256,0);
    if(nbytes<=0)
    {
        perror("recv error from server \n");
        exit(0);
    }
}

} //END OF ELSE 
} //end of while
close(sockfd);          
return 0;

Answer 1

The select() call in your while(1) loop leaves the readSet unchanged. This means that later the FD_ISSET() check succeeds.

The solution is simple: clear the fd_set's on every iteration:

FD_ZERO(&master_list_read);
FD_SET(STDIN, &master_list_read);
FD_SET(sockfd, &master_list_read);
// only now the select() returns what you need
retval = select(sockfd+1, &master_list_read, NULL, NULL,&tv);

// use the master_list_read later

Simply copying the fd_set does not solve the problem.