【linux】59、Internet Domain

1、网络字节序（大端）

2、主机和网络字节序之间转换整数

#include <arpa/inet.h>
uint16_t htons(uint16_t host_unint16);
uint32_t htonl(uint32_t host_unint32);
uint16_t ntohs(uint16_t host_unint16);
uint32_t ntohl(uint32_t host_unint32);

3、Internet socket 地址（ipv4、ipv6）

ipv4通配地址(0.0.0.0)：INADDR_ANY
ipv6通配地址（0::0）：IN6ADDR_ANY_INIT
ipv6环回地址（::1）: IN6ADDR_LOOPBACK_INIT

inet_pton()和inet_ntop()

#include <arpa/inet.h>
int inet_pton(int domain, const char *src_str, void *addrptr);
//success,1; error format(src_str), 0;error -1
const char *inet_ntop(int domain, const void *addrptr, char *dst_str, size_t len);
//success, *det_str; error, NULL

domain: AF_INET or AF_INET6
（1）inet_pton() 函数将src_str 中的字符串转换成网络字节序的二进制IP地址。转换得到的地址放在addrptr指向的结构中。
（2）inet_ntop()函数 执行逆向转换。addrptr：待转换的in_addr或in6_addr结构。dst_str：得到以null结尾的字符串。len：dst_str的大小
（3）ipv4和ipv6展示字符串的最大长度:

inet6_sv.c

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

#define LENGTH 30
#define PORT_NUM 31001

int main(int argc, char *argv[])
{
	struct sockaddr_in6 sv_addr, cl_addr;
	int sfd, len, j;
	ssize_t num;
	char buf[INET6_ADDRSTRLEN], msg[LENGTH];

	sfd = socket(AF_INET6, SOCK_DGRAM, 0);
	if (sfd == -1)
		exit(EXIT_FAILURE);
	memset(&sv_addr, 0, sizeof(struct sockaddr_in6));
	sv_addr.sin6_family = AF_INET6;
	sv_addr.sin6_addr = in6addr_any;
	sv_addr.sin6_port = htons(PORT_NUM);

	if (bind(sfd, (struct sockaddr *) &sv_addr, sizeof(struct sockaddr_in6)) == -1)
		exit(EXIT_FAILURE);

	len = sizeof(struct sockaddr_in6);

	for (;;) {
		memset(&msg, 0, sizeof(msg));
		num = recvfrom(sfd, msg, sizeof(msg), 0, (struct sockaddr *) &cl_addr, &len);
		if (num == -1)
			exit(EXIT_FAILURE);
		if (inet_ntop(AF_INET6, &cl_addr.sin6_addr, buf, INET6_ADDRSTRLEN) == NULL)
			exit(EXIT_FAILURE);
		else
			printf("Server received %ld bytes from (%s, %u)：%s\n", num, buf, ntohs(cl_addr.sin6_port), msg);
		for (j = 0; j < num; j++) 
			msg[j] = toupper(msg[j]);

		if (sendto(sfd, msg, num, 0, (struct sockaddr *) &cl_addr, len) != num)
			exit(EXIT_FAILURE);
	}
}

inet6_cl.c

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

#define LENGTH 30
#define PORT_NUM 31001

int main(int argc, char *argv[]) 
{
	struct sockaddr_in6 sv_addr, cl_addr;
	int sfd, j, msgLen;
	char msg[LENGTH], addrBuf[INET6_ADDRSTRLEN];
	socklen_t num;

	sfd = socket(AF_INET6, SOCK_DGRAM, 0);
	if (sfd == -1)
		exit(EXIT_FAILURE);

	memset(&sv_addr, 0, sizeof(sv_addr));
	sv_addr.sin6_family = AF_INET6;
	sv_addr.sin6_port = htons(PORT_NUM);
	if (inet_pton(AF_INET6, "::1", &sv_addr.sin6_addr) <= 0)
		exit(EXIT_FAILURE);
	num = sizeof(struct sockaddr_in6);

 	for (j = 1; j < argc; j++) {
 		msgLen = strlen(argv[j]);
 		memset(&msg, 0, sizeof(msg));
 		if (sendto(sfd, argv[j], msgLen, 0, (struct sockaddr *) &sv_addr, sizeof(struct sockaddr_in6)) != msgLen)
 			exit(EXIT_FAILURE);
 		if ((msgLen = recvfrom(sfd, msg, LENGTH, 0, (struct sockaddr *) &cl_addr, &num)) == -1)
 			exit(EXIT_FAILURE);
 		if (inet_ntop(AF_INET6, &cl_addr.sin6_addr, addrBuf, INET6_ADDRSTRLEN) == NULL)
 			exit(EXIT_FAILURE);
 		printf("Client received %d bytes from %s, the msg is %s\n", msgLen, addrBuf, msg);
 	}	
}