How to force sending data with socket - c

Question

I'm building a Client/Server distributed application via socket in C.
Here is my server:
#include <stdio.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <netinet/tcp.h>
#define LEN 20
int main(void) {
int err, nread, status, optval=1;
int sd, ns;
char category[LEN];
struct addrinfo hints, *res;
memset(&hints, 0, sizeof(hints));
hints.ai_flags = AI_PASSIVE;
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if((err = getaddrinfo(NULL, "50000", &hints, &res)) != 0) {
printf("%s", gai_strerror(err));
exit(-1);
}
if((sd = socket(res->ai_family, res->ai_socktype, res->ai_protocol)) < 0) {
printf("Error in Socket Server\n");
exit(-1);
}
setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, &optval, sizeof(optval));
if(bind(sd, res->ai_addr, res->ai_addrlen) != 0) {
printf("Error in bind\n");
exit(-1);
}
freeaddrinfo(res);
if(listen(sd, 5) != 0) {
printf("Error in listen\n");
exit(-1);
}
for(;;) {
if((ns = accept(sd, NULL, NULL)) < 0) {
printf("Error in accept\n");
exit(-10);
}
/* I tried with this: setsockopt(ns, IPPROTO_TCP, TCP_NODELAY, (char*)&optval, sizeof(int));
but it didn't work out */
while((nread = read(ns, category, LEN)) > 0){
if(category[nread-1]=='\n') {
category[nread-1]='\0';
}
if(fork()==0) {
close(1);
dup(ns);
close(ns);
execlp("grep", "grep", category, "conto_corrente.txt", (char *)0);
perror("Error in fork\n");
exit(-100);
}
wait(&status);
}
close(ns);
}
}
And here is my client:
#include <stdio.h>
#include <sys/socket.h>
#include <netdb.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char **argv) {
int err, nread;
int sd;
char category[20];
char buff[1024];
struct addrinfo hints, *res, *ptr;
if(argc!=3) {
printf("Error in number of parameters\n");
exit(-1);
}
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_STREAM;
if((err = getaddrinfo(argv[1], argv[2], &hints, &res)) != 0) {
printf("%s\n", gai_strerror(err));
exit(-1);
}
for(ptr = res; ptr != NULL; ptr=ptr->ai_next) {
if((sd = socket(ptr->ai_family, ptr->ai_socktype, ptr->ai_protocol)) < 0) {continue;}
if((connect(sd, ptr->ai_addr, ptr->ai_addrlen)) == 0) {
break;
}
}
if(ptr==NULL) {
printf("Error in connection\n");
exit(-1);
}
freeaddrinfo(res);
printf("Category: ");
scanf("%s", category);
while(strcmp(category, "fine") != 0) {
write(sd, category, strlen(category)+1);
while((nread = read(sd, buff, 1024)) > 0) {
printf("%s", buff);
}
printf("Category: ");
scanf("%s", category);
}
close(sd);
return 0;
}
The program should take an input from the user (a string) and send it to the server which have to scan the file and select all the lines that contain that string.
I think there is a problem in the buffering because when the user enter a string then the client stops it looks like it is waiting for something, in fact if I kill the server then the client shows what it read. How is it?