#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
 
void error_handling(char*);
void str_left(char*);
 
int main(int argc, char *argv[]) {
 
	int i;
 
	int serv_sock;
	int clnt_sock;
 
	struct sockaddr_in serv_addr;
	struct sockaddr_in clnt_addr;
 
	socklen_t clnt_addr_size;
 
	char message[] = "Hello World!";
 
	printf("argc : %d\n", argc);
	if (argc != 2) {
		printf("Usage : %s <port>\n", argv[0]);
		exit(1);
	}
 
	// socket 생성
	if ((serv_sock = socket(PF_INET, SOCK_STREAM, 0)) == -1)
		error_handling("socket() error");
 
	memset(&serv_addr, 0, sizeof(serv_addr));
	serv_addr.sin_family = AF_INET;
	serv_addr.sin_port = htons(atoi(argv[1]));
	serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
 
	// ip와 port를 할당한다
	if (bind(serv_sock, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -1)
		error_handling("bind() error");
 
	// 연결요청 가능상태로 변경
	if (listen(serv_sock, 5) == -1)
		error_handling("listen() error");
 
	clnt_addr_size = sizeof(clnt_addr);
	if ((clnt_sock = accept(serv_sock, (struct sockaddr*) &clnt_addr, &clnt_addr_size)) == -1)
		error_handling("accept() error");
 
	for (i=0; i<100; i++) {	
		str_left(message);
		printf("%s\n", message);
		write(clnt_sock, message, sizeof(message));
	}
 
	close(clnt_sock);
	close(serv_sock);
 
	return 0;
 
}
 
 
 
void error_handling(char *message) {
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}
 
 
 
// 문자열을 한칸씩 왼쪽으로 이동!!
void str_left(char *str) {
	int i;
	int max;
	char *temp = (char*) malloc(strlen(str)+1);
	strcpy(temp, str);
	max = strlen(str);
 
	for (i=max; i>=0; i--) {
		str[i-1] = temp[i];
	}
 
	str[max-1] = temp[0];
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
 
void error_handling(char *);
 
int main(int argc, char *argv[]) {
 
	int sock, read_result, read_index = 0;
	struct sockaddr_in serv_addr;
	char message[30];
 
	if (argc != 3) {
		printf("ip, port 를 넘겨주세요");
		exit(1);
	}
 
	if ((sock = socket(PF_INET, SOCK_STREAM, 0)) == -1)
		error_handling("socket() error");
 
	memset(&serv_addr, 0, sizeof(serv_addr));
	serv_addr.sin_family = AF_INET;
	serv_addr.sin_port = htons(atoi(argv[2]));
	serv_addr.sin_addr.s_addr = inet_addr(argv[1]);
 
	if (connect(sock, (struct sockaddr*) &serv_addr, sizeof(serv_addr)) == -1)
		error_handling("connect() error");
 
	// 서버로부터 데이터 읽기
	printf("server message : \n");
	while (1) {
		if (read(sock, message, sizeof(message)) > 0) {
			printf("%s\n", message);
			memset(message, 0, sizeof(message));
		} else {
			break;
		}
	}
 
	close(sock);
	return 0;
}
 
 
 
void error_handling(char *message) {
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}