tcp_client.c

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>

void error_handler(const char *msg);

int main(int argc, char **argv)
{
	int sock;
	struct sockaddr_in servaddr;
	char msg[30];
	int str_len = 0;
	int idx = 0, read_len = 0;

	if(argc != 3) {
		printf("usage : %s <IP> <port> \n", argv[0]);
		exit(1);
	}

	sock = socket(AF_INET, SOCK_STREAM, 0);
	if(sock < 0) {
		error_handler("socket");
	}

	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_addr.s_addr = inet_addr(argv[1]);
	servaddr.sin_port = htons(atoi(argv[2]));

	if(connect(sock, (struct sockaddr *)&servaddr, sizeof(servaddr)) < 0) {
		error_handler("connect");
	}

	while(read_len = read(sock, &msg[idx++], 1)) {
		// EOF까지 값을 읽는다. read는 EOF를 만났을 때, 0을 반환한다
      		if(read_len == 0) break;
		str_len += read_len;
	}

	printf("Message from server : %s\n", msg);
	printf("function read call count : %d\n", str_len);
	close(sock);

	return 0;
}

void error_handler(const char *msg)
{
	fputs(msg, stderr);
	fputc('\n', stderr);
	exit(1);
}

tcp_server.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>

void error_handle(char *msg);

int main(int argc, char **argv)
{
	int serv_sock, cli_sock;

	struct sockaddr_in serv_addr, cli_addr;
	socklen_t cli_addr_size;

	char msg[256] = "Hello world!";

	if(argc != 2) {
		printf("usage : %s <port>\n", argv[0]);
		exit(1);
	}

	serv_sock = socket(PF_INET, SOCK_STREAM, 0);
	if(serv_sock == -1) {
		error_handle("socket() error");
	}

	memset(&serv_addr, 0, sizeof(serv_addr));
	serv_addr.sin_family = AF_INET;
	serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	serv_addr.sin_port = htons(atoi(argv[1]));

	if(bind(serv_sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) <  0) {
		error_handle("bind() error");
	}

	if(listen(serv_sock, 5) < 0) {
		error_handle("listen() error");
	}

	cli_addr_size = sizeof(cli_addr);
	cli_sock = accept(serv_sock, (struct sockaddr *)&cli_addr, &cli_addr_size);
	if(cli_sock < 0){
		error_handle("accept() error");
	}
	
	// sizeof가 아닌 strlen을 써서 EOF까지 버퍼를 전달
	// 만일 배열을 []로 선언했다면 sizeof가 strlen과 비슷하다
	write(cli_sock, msg, strlen(msg));
	close(cli_sock);
	close(serv_sock);

	return 0;
}

void error_handle(char *msg)
{
	fputs(msg, stderr);
	fputc('\n', stderr);
	exit(1);
}