TCP Client and Servers in C - c

Question

I created a TCP client and a server in C and executed it in two terminals. But after changing and compiling the code, I could not get the output. Both server and client keep running and print nothing.
Here is my server code
/* Sample TCP server */
#include <sys/socket.h>
#include <netinet/in.h>
#include <stdio.h>
#include <string.h>
int fsize(FILE *fp){
int prev=ftell(fp);
fseek(fp, 0L, SEEK_END);
int sz=ftell(fp);
fseek(fp,prev,SEEK_SET); //go back to where we were
return sz;
}
int main(int argc, char**argv)
{
int listenfd,connfd,n, length;
struct sockaddr_in servaddr,cliaddr;
socklen_t clilen;
char* banner = "ack";
char buffer[1000];
/* one socket is dedicated to listening */
listenfd=socket(AF_INET,SOCK_STREAM,0);
/* initialize a sockaddr_in struct with our own address information for binding the socket */
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
servaddr.sin_port=htons(32000);
/* binding */
bind(listenfd,(struct sockaddr *)&servaddr,sizeof(servaddr));
listen(listenfd,0);
clilen=sizeof(cliaddr);
while(1){
/* accept the client with a different socket. */
connfd = accept(listenfd,(struct sockaddr *)&cliaddr,&clilen);
// the uninitialized cliaddr variable is filled in with the
n = recvfrom(connfd,buffer,1000,0,(struct sockaddr *)&cliaddr,&clilen);//information of the client by recvfrom function
buffer[n] = 0;
sendto(connfd,banner,strlen(banner),0,(struct sockaddr *)&cliaddr,sizeof(cliaddr));
printf("Received:%s\n",buffer);
FILE *fp = fopen("serverfile.txt", "r");
length = fsize(fp);
printf("%d\n", length);
}
return 0;
}
Here is my client code
/* Sample TCP client */
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char**argv)
{
int sockfd,n;
struct sockaddr_in servaddr;
char banner[] = "Hello TCP server! This is TCP client";
char buffer[1000];
if (argc != 2)
{
printf("usage: ./%s <IP address>\n",argv[0]);
return -1;
}
/* socket to connect */s
sockfd=socket(AF_INET,SOCK_STREAM,0);
/* IP address information of the server to connect to */
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr=inet_addr(argv[1]);
servaddr.sin_port=htons(32000);
connect(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
sendto(sockfd,banner,strlen(banner),0, (struct sockaddr*)&servaddr,sizeof(servaddr));
n=recvfrom(sockfd,buffer,10000,0,NULL,NULL);
buffer[n]=0;
printf("Received:%s\n",buffer);
return 0;
}

Answer 1

Your main problem is that you are not checking the results of any of your operations on the sockets, so it is entirely possible that the server or client is reporting an error message that makes the answer to your problem obvious.
In particular, if the server fails to bind or listen to the listen socket, it will just go into an infinite loop making failed accepts, reads and writes forever.
I suspect that, what happens is that when you restart the server, the previous socket is still in the TIME_WAIT state, so it can't bind to the port. You can get around this by using the following after creating the socket:
int reuseaddr = 1;
if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,&reuseaddr,sizeof(reuseaddr))==-1)
{
fprintf(stderr, "%s",strerror(errno));
exit(1);
}
Note how the above checks the return result and reports an error on failure. You need to do this or similar after every call to socket(), listen(), bind(), connect(), recvfrom(), sendto() and close().
Note, how I put close() in that list. You really must call it on the connect socket when you are finished with it, especially on the server or you will leak the file descriptor in connfd.