C Network programing

字节序

验证当前电脑是大端还是小端。

#include <stdio.h>

void byteorder() {
	union {
		short value;
		char union_bytes[sizeof(short)];
	} test;
	test.value = 0x0102;
	if((1 == test.union_bytes[0]) && (2 == test.union_bytes[1])) {
		printf("big endian\n");
	}else if((2 == test.union_bytes[0]) && (1 == test.union_bytes[1])) {
		printf("little endian\n");
	}else {
		printf("unknown\n");
	}
}

int main(void) {
	byteorder();
	return 0;
}

测试listen函数

server.c

#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <signal.h>
#include <unistd.h>
#include <assert.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

static bool stop = false;
static void handle_term(int sig) {
	stop = true;
}

int main(int argc, char **argv) {
	signal(SIGTERM, handle_term);
	if(argc <= 3) {
		printf("Usage: %s ip_address port_number backlog\n", basename(argv[0]));
		return 1;
	}
	const char *ip = argv[1];
	int port = atoi(argv[2]);
	int backlog = atoi(argv[3]);

	int sock = socket(PF_INET, SOCK_STREAM, 0);
	assert(sock >= 0);
	struct sockaddr_in address;
	bzero(&address, sizeof(address)); //清空为0
	address.sin_family = AF_INET;

	//inet_pton是一个IP地址转换函数,
	//可以在将IP地址在“点分十进制”和“二进制整数”之间转换
	//而且inet_pton和inet_ntop这2个函数能够处理ipv4和ipv6
	
	inet_pton(AF_INET, ip,  &address.sin_addr);
	address.sin_port = htons(port); //转化为网络字节序

	//绑定
	int ret = bind(sock, (struct sockaddr *)&address, sizeof(address));
	assert(-1 != ret);

	ret = listen(sock, backlog);
	assert(-1 != ret);

	//通过系统发送信号来终止程序
	while(!stop) {
		sleep(1);
	}

	close(sock);
	printf("End program\n");

	return 0;
}

获取客户端基本信息

#include <unistd.h>
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <assert.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char **argv) {
	if(argc <= 2) {
		printf("Usage: %s [ip] [port]\n", basename(argv[0]));
		return 1;
	}

	const char *ip = argv[1];
	int port = atoi(argv[2]);

	struct sockaddr_in address;
	bzero(&address, sizeof(address));

	address.sin_family = AF_INET;
	inet_pton(AF_INET, ip, &address.sin_addr);
	address.sin_port = htons(port);

	int sock = socket(PF_INET, SOCK_STREAM, 0);
	assert(sock >= 0);

	int ret = bind(sock, (struct sockaddr *)&address, sizeof(address));
	if(-1 == ret) {
		perror("bind");
		return 1;
	}

	ret = listen(sock, 5);
	assert(ret != -1);

	struct sockaddr_in client_addr;
	socklen_t client_addr_len = sizeof(client_addr);
	int c_fd = accept(sock, (struct sockaddr*)&client_addr, &client_addr_len);
	if(c_fd == -1) {
		perror("accept::");
	}else {
		char remote[INET_ADDRSTRLEN];
		printf("connected with ip: %s and port %d\n",
		inet_ntop(AF_INET, &client_addr.sin_addr, remote, INET_ADDRSTRLEN),
		ntohs(client_addr.sin_port));

		close(c_fd);
	}

	return 0;
}

Echo Server例子

客户端

client.cpp

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <string>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

using namespace std;
#define SERVER_PORT 6666
#define SERVER_IP "127.0.0.1"

int main(int argc, char **argv) {
	int sockfd;
	int n;
	struct sockaddr_in serveraddr;
	char str[256] = "Hello You guys\n";
	if(argc < 2) {
		cout << "Usage: ./clinet [message]" << endl;	
		fputs("Input error! \n", stderr);
		exit(1);
	}

	sockfd = socket(AF_INET, SOCK_STREAM, 0);
	memset(&serveraddr, 0, sizeof(struct sockaddr_in));
	serveraddr.sin_family = AF_INET;

	inet_pton(AF_INET, SERVER_IP, &serveraddr.sin_addr);
	serveraddr.sin_port = htons(SERVER_PORT); //转化为网络字节顺序
	
	connect(sockfd, (struct sockaddr *)&serveraddr, sizeof(serveraddr));
	write(sockfd, argv[1], strlen(argv[1]));
	n = read(sockfd, str, sizeof(str) - 1);
	if(n > 0) {
		str[n] = '\0';
		cout << str;
	}else {
		perror("error");
	}	

	cout << endl << "finished" << endl;
	close(sockfd);
	return 0;
}

服务端

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

#define SERVER_PORT 6666
int main(void) {
	int sock;  //信箱
	//AF_INET表示使用网络地址, SOCK_STREAM表示使用TCP协议
	sock = socket(AF_INET, SOCK_STREAM, 0);
	struct sockaddr_in server_addr; //这个结构体,头文件中已经声明
	//清空标签
	bzero(&server_addr, sizeof(server_addr));
	//设置协议家族为网络协议	
	//htonl = host to net ,选择协议族为ipv4,
	server_addr.sin_family = AF_INET;
	//监听本地所有地址
	server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
	server_addr.sin_port = htons(SERVER_PORT); //绑定端口号
	//实现标签贴到信箱上
	bind(sock, (struct sockaddr *)&server_addr, sizeof(server_addr));

	listen(sock, 128); //同时的连接数量,同时来的信件接受多少封,这里为128
	
	//万事俱备,只等来信.
	printf("等待客户连接...\n");

	while(1) {
		struct sockaddr_in client;
		int client_sock ; //客户端
		char client_ip[64];
		char buf[256];
		int buf_len;
		socklen_t client_addr_len = sizeof(client);

		 client_sock = accept(sock, (struct sockaddr *)&client, &client_addr_len);
		//打印客户端地址和端口号	
		//转化网络字节序
		printf("client ip: %s\n port: %d\n", 
		inet_ntop(AF_INET, &client.sin_addr.s_addr, client_ip, sizeof(client_ip)),
		ntohs(client.sin_port));
		
		//读取数据
		buf_len = read(client_sock, buf, sizeof(buf) - 1);
		buf[buf_len] = '\x00';
		printf("接受到消息: %s\n", buf);
		for(int i = 0; i < buf_len; i++) {
				buf[i] = toupper(buf[i]);
		}	
		write(client_sock, buf, strlen(buf));
		printf("write[%s] finished!!!\n", buf);

		close(client_sock);
	}

	return 0;
}