소켓 프로그래밍 질문입니다.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <sys/socket.h>
 
#define BUF_SIZE 30
void error_handling(char *message);
void read_childproc(int sig);
 
int main(int argc, char *argv[])
{
	int serv_sock, clnt_sock;
	struct sockaddr_in serv_adr, clnt_adr;
	int fds[2];
 
	pid_t pid;
	struct sigaction act;
	socklen_t adr_sz;
	int str_len, state;
	char buf[BUF_SIZE];
	if(argc!=2)
	{
		printf("Usage : %s <port>\n", argv[0]);
		exit(1);
	}
 
	act.sa_handler=read_childproc;
	sigemptyset(&act.sa_mask);
	act.sa_flags=0;
	state=sigaction(SIGCHLD, &act, 0);
 
	serv_sock=socket(PF_INET, SOCK_STREAM, 0);
	memset(&serv_adr, 0, sizeof(serv_adr));
	serv_adr.sin_family=AF_INET;
	serv_adr.sin_addr.s_addr=htonl(INADDR_ANY);
	serv_adr.sin_port=htons(atoi(argv[1]));
 
	if(bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr))==-1)
		error_handling("bind() error");
	if(listen(serv_sock, 5)==-1)
		error_handling("listen() error");
	pipe(fds);
	pid=fork();
	if(pid==0)
	{
		FILE * fp=fopen("echomsg.txt", "wt");
		char msgbuf[BUF_SIZE];
		int i, len;
 
		for (i=0; i<10; i++)
		{
			len=read(fds[0], msgbuf, BUF_SIZE);
			fwrite((void*)msgbuf, 1, len, fp);
		}
		fclose(fp);
		return 0;
	}
 
 
	while(1)
	{
		adr_sz=sizeof(clnt_adr);
		clnt_sock=accept(serv_sock, (struct sockaddr*)&clnt_adr, &adr_sz);
		if(clnt_sock==-1)
			continue;
		else
			puts("new client connected....");
 
		pid=fork();
		if(pid==0)
		{
			close(serv_sock);
			while((str_len=read(clnt_sock, buf, BUF_SIZE))!=0)
			{
				write(clnt_sock, buf, str_len);
				write(fds[1], buf, str_len);
			}
 
			close(clnt_sock);
			puts("client disconnected");
			return 0;
		}
		else
			close(clnt_sock);
	}
	close(serv_sock);
	return 0;
}
 
void read_childproc(int sig)
{
	pid_t pid;
	int status;
	pid=waitpid(-1, &status, WNOHANG);
	printf("removed proc id : %d \n", pid);
}
void error_handling(char *message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
 
#define BUF_SIZE 100
void error_handling(char *message);
void read_routine(int sock, char *buf);
void write_routine(int sock, char *buf);
 
int main(int argc, char *argv[])
{
	int sock;
	pid_t pid;
	char buf[BUF_SIZE];
	struct sockaddr_in serv_adr;
	struct s_msg{
		char name[30];
		char msg[BUF_SIZE];
	}
	if(argc!=3) {
		printf("Usage : %s <port>\n", argv[0]);
		exit(1);
	}
 
	sock=socket(PF_INET, SOCK_STREAM, 0);
	memset(&serv_adr, 0, sizeof(serv_adr));
	serv_adr.sin_family=AF_INET;
	serv_adr.sin_addr.s_addr=inet_addr(argv[1]);
	serv_adr.sin_port=htons(atoi(argv[2]));
 
	if (connect(sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr))==-1)
		error_handling("connect() error!");
 
	pid=fork();
	if(pid==0)
		write_routine(sock,buf);
	else
 
		read_routine(sock,buf);
 
	close(sock);
	return 0;
}
 
 
void read_routine(int sock, char *buf)
{
	while(1)
	{
		int str_len=read(sock, buf, BUF_SIZE);
		if(str_len==0)
			return;
 
		buf[str_len]=0;
		printf("Message from server : %s", buf);
	}
}
 
void write_routine(int sock, char *buf)
{
	while(1)
	{
		fgets(buf, BUF_SIZE, stdin);
		if(!strcmp(buf,"q\n") || !strcmp(buf,"Q\n"))
		{
			shutdown(sock, SHUT_WR);
			return;
		}
		write(sock, buf, strlen(buf));
	}
}
 
void error_handling(char *message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

struct s_msg {
       char name[30];
       char msg[BUF_SIZE]; //BUF_SIZE=100;
};