[UNIX]Sending large file socket stream in c - c

Question

I've created a Client in C that essentially sends the content of a file and a number of line to remove to the Server. The server creates a child that reads the content and then send it right back to the Client, except for the line received. The communication is made with a socket stream, and the content of the file is sent char-for-char. The problem appears when the client send a file bigger than 9.9Mb, the server reads the contents of the file but at some point it stops, and the only way for closing the server is by killing the process with CTRL-C.
This is the code of the child of the server:
if (fork() == 0){
close(listen_sd);
host = gethostbyaddr((char *)&client_addr.sin_addr, sizeof(client_addr.sin_addr), AF_INET);
if (host == NULL) {
printf("Server (figlio %d): client host non trovato.\n", getpid());
exit(8);
}
else
printf("Server (figlio %d): operazione richiesta da %s.\n", getpid(), host->h_name);
host = gethostbyaddr((char *)&client_addr.sin_addr, sizeof(client_addr.sin_addr), AF_INET);
if ((read(conn_sd, &sub_line, 1) > 0))
printf("Server (figlio %d): eliminazione della linea %d...\n", getpid(), sub_line);
line = 1;
while((nread = read(conn_sd, &c, sizeof(char))) != 0) {
if (nread < 0){
printf("Server (figlio %d): impossibile leggere il file.\n", getpid(), sub_line);
exit(EXIT_FAILURE);
}
if(line != sub_line)
write(conn_sd, &c, 1);
if(c == '\n')
line += 1;
}
close(conn_sd);
exit(0);
}
And this is the code of the client that sends the content of the file, reads the result and then write it on a file:
#define DIM_BUFF 256
[...]
write(sd, &line, sizeof(int));
char buff[DIM_BUFF];
while ((nread = read(fd_sorg, buff, DIM_BUFF)) > 0)
write(sd, buff, nread);
shutdown(sd, 1);
while ((nread = read(sd, buff, DIM_BUFF)) > 0){
write(fd_dest, buff, nread);
}