How to compare data sent by client in server C programing - c

Question

I want to send a option from the client to a server. The server have to do some comparisons and send a string back to the client. I can receive the data from the client, but my server crashes in the moment of comparison (it gets to the else with the "error input" and ends the connection). Can someone tell me what I'm doing wrong?
Incorrect Inputclose error: Bad file descriptor
Program exited with code 01.
Server:
void
result(int sockfd)
{
ssize_t n;
char buf[MAXLINE];
int temp;
time_t ticks;
again:
while ((n =read(sockfd, buf, MAXLINE)> 0))
{
temp = rand() % 22;
if (buf=="A\n" || buf=="a\n")
{
snprintf(buf, sizeof(buf), "You option is number is -%i, time is %.24s\r\n", temp,ctime(&ticks));
Writen(sockfd, buf, n);
}
if (buf=="B\n" || buf=="f\")
{
snprintf(buf, sizeof(buf), "You option is number is -%i, time is %.24s\r\n", temp,ctime(&ticks));
Writen(sockfd, buf, n);
}
else
{
printf("Incorrect Input");
Close(sockfd);
}
}
if (n < 0 && errno == EINTR)
goto again;
else if (n < 0)
err_sys("read error");
}
int
main(int argc, char **argv)
{
int listenfd, connfd;
socklen_t len;
struct sockaddr_in servaddr, cliaddr;
char buff[MAXLINE];
char recvline[MAXLINE + 1];
listenfd = Socket(AF_INET, SOCK_STREAM, 0);
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_addr.s_addr = htonl(INADDR_ANY);/*----------------------------------------------------*/
servaddr.sin_port = htons(5678);
Bind(listenfd, (SA *) &servaddr, sizeof(servaddr));
Listen(listenfd, LISTENQ);
printf("EDMTS is running on 129.128.4.80, listening on port 5678\n");
printf("\n");
printf("Waiting for incoming connections...Press Ctrl+C to end server\n");
for ( ; ; )
{
len = sizeof(cliaddr);
connfd = Accept(listenfd, (SA *) &cliaddr, &len);
/*Client connects to server*/
printf("\n");
printf("Connection from %s, port %d\n",
Inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)),
ntohs(cliaddr.sin_port));
result(connfd);
Close(connfd);
printf("Conexion cerrada...Esperando siguiente cliente\n");
}
}
Client
void
get_temp(FILE *fp, int sock)
{
char sendline[MAXLINE], recvline[MAXLINE];
while (Fgets(sendline, MAXLINE, fp) != NULL) {
Writen(sock, sendline, strlen(sendline));
if (Readline(sock, recvline, MAXLINE) == 0)
err_quit("Server Terminated Prematurely");
Fputs(recvline, stdout);
}
}
int
main(int argc, char **argv)
{
int sockfd, n;
socklen_t len;
char recvline[MAXLINE + 1];
struct sockaddr_in servaddr, cliaddr;
char scale[2];
if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
err_sys("socket error");
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(atoi(argv[2]));
if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
err_quit("inet_pton error for %s", argv[1]);
printf("Connect...\n");
if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)
err_sys("connect error");
len = sizeof(cliaddr);
Getsockname(sockfd, (SA *) &cliaddr, &len);
printf("Local Address is: %s\n",
Sock_ntop((SA *) &cliaddr, sizeof(cliaddr)));
printf("Enter option A or B): ");
get_temp(stdin, sockfd);
exit(0);
}
When I run the debugger to find out my variables, I find:
Breakpoint 1, result (sockfd=7) at servertest.c:236 236
printf("Random es %i\n",temp);
(gdb) p buf
$1 = "A\n", '\0' , "\203\217��", '\0' ,
"h\206��h\206��\204\210������#���\000\000\000\000�\206����߷\020\207��#���",
'\0' ,
"������������\000\000\000\000\000\000\000\000�\017��", '\0' , "h\206��", '\0' ,
"\001\000\000\000\000\000\000\000�\207��", '\0' ,
"����\t\000\000\000#���\030���\000\000\000\000h\206��\003", '\0'
, "\n\000\000\000g\206��", '\0' ,
" "...
(gdb) p temp
$2 = 17
Thank you very much

Answer 1

First of all, you can't compare C strings using == (you will compare pointer adresses, and the address of buf[0] and the address of your static string "a\n" will certainly not be equal. To compare the strings, use strncmp().
Your crash happens because after you call Close(), the read() function is called again on the socket file descriptor. To remove the crash, put a break; after the Close(), like so:
else
{
printf("Incorrect Input");
Close(sockfd);
break;
}

Answer 2

Also, you are closing the socket twice. First here:
// void result(int sockfd)
else
{
printf("Incorrect Input");
Close(sockfd); // <<<
}
Then here:
// int main(int argc, char **argv)
Inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)),
ntohs(cliaddr.sin_port));
result(connfd);
Close(connfd); // <<<
printf("Conexion cerrada...Esperando siguiente cliente\n");