ERROR on gethostbyaddr: Success - c

Question

I am building a multiclient UDP server in c,but when i tried to connect to my server from a system, i get this error ERROR on gethostbyaddr: Success
Please find the below server code.I have tried the solutions from similar questions(gethostbyaddr() returns NULL but errno result in SUCCESS) but i couldn't get it working.Any help will be greatly appreciated
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <netdb.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#define BUFSIZE 1024
/*
* error - wrapper for perror
*/
void error(char *msg) {
perror(msg);
exit(1);
}
int main(int argc, char **argv) {
int sockfd; /* socket */
int portno; /* port to listen on */
int clientlen; /* byte size of client's address */
struct sockaddr_in serveraddr; /* server's addr */
struct sockaddr_in clientaddr; /* client addr */
struct hostent *hostp; /* client host info */
char buf[BUFSIZE]; /* message buf */
char *hostaddrp; /* dotted decimal host addr string */
int optval; /* flag value for setsockopt */
int n; /* message byte size */
FILE *fp; /* file variable */
char str[10];
int i = 0;
char userlist[10];
int array_size;
char line[256];
int cred,flag;
/*
* check command line arguments
*/
if (argc != 2) {
fprintf(stderr, "usage: %s <port>\n", argv[0]);
exit(1);
}
portno = atoi(argv[1]);
/*
* socket: create the parent socket
*/
sockfd = socket(AF_INET, SOCK_DGRAM, 0);
if (sockfd < 0)
error("ERROR opening socket");
/* setsockopt: Handy debugging trick that lets
* us rerun the server immediately after we kill it;
* otherwise we have to wait about 20 secs.
* Eliminates "ERROR on binding: Address already in use" error.
*/
optval = 1;
setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR,
(const void *)&optval , sizeof(int));
/*
* build the server's Internet address
*/
bzero((char *) &serveraddr, sizeof(serveraddr));
memset(&serveraddr,0,sizeof(serveraddr));
serveraddr.sin_family = AF_INET;
serveraddr.sin_addr.s_addr = htonl(INADDR_ANY);
serveraddr.sin_port = htons((unsigned short)portno);
/*
* bind: associate the parent socket with a port
*/
if (bind(sockfd, (struct sockaddr *) &serveraddr,
sizeof(serveraddr)) < 0)
error("ERROR on binding");
/*
* main loop: wait for a datagram, then echo it
*/
clientlen = sizeof(clientaddr);
while (1) {
/*
* recvfrom: receive a UDP datagram from a client
*/
bzero(buf, BUFSIZE);
n = recvfrom(sockfd, buf, BUFSIZE, 0,
(struct sockaddr *) &clientaddr, &clientlen);
if (n < 0)
error("ERROR in recvfrom");
/*
* gethostbyaddr: determine who sent the datagram
*/
hostp = gethostbyaddr((const char *)&clientaddr.sin_addr.s_addr,
sizeof(clientaddr.sin_addr.s_addr), AF_INET);
if (hostp == NULL)
error("ERROR on gethostbyaddr");
hostaddrp = inet_ntoa(clientaddr.sin_addr);
if (hostaddrp == NULL)
error("ERROR on inet_ntoa\n");
printf("server received datagram from %s (%s)\n",
hostp->h_name, hostaddrp);
printf("server received %d/%d bytes: %s\n", strlen(buf), n, buf);
fp = fopen("users.txt", "r");
while (fgets(line, sizeof(line), fp)) {
//printf("%s\n",line);
cred = strncmp(buf,line,strlen(line)-1);
//printf("%d",strlen(line)-1);
if(cred == 0){
printf("Authenticated....");
flag = 1;
break;
}
else{
printf("Invalid username/password");
}
}
fclose(fp);

Answer 1

gethostbyaddr() expects a pointer to a struct in_addr as 1st parameter, which would be &clientaddr.sin_addr for the code you show.
Form the relevant (Linux) documentation (man gethostbyaddr):
[...] The host address argument is a pointer to a struct of a type depending on the address type, for example a struct in_addr * (probably obtained via a call to inet_addr(3)) for address type AF_INET.
gethostbyaddr() sets the error code in h_errno not in errno.
Form the relevant (Linux) documentation (man gethostbyaddr):
RETURN VALUE
[...[ The gethostbyname() and gethostbyaddr() functions return the hostent structure or a null pointer if an error occurs. On error, the h_errno variable holds an error number.
The possible error code are given by the man-page as well:
ERRORS
The variable h_errno can have the following values:
HOST_NOT_FOUND
The specified host is unknown.
NO_ADDRESS or NO_DATA
The requested name is valid but does not have an IP address.
NO_RECOVERY
A nonrecoverable name server error occurred.
TRY_AGAIN
A temporary error occurred on an authoritative name server. Try again later.