接口说明补充

getaddrinfo（3）

相关信息

network address and service translation

addrinfo

   struct addrinfo {
	   int              ai_flags;
	   int              ai_family;
	   int              ai_socktype;
	   int              ai_protocol;
	   socklen_t        ai_addrlen;
	   struct sockaddr *ai_addr;
	   char            *ai_canonname;
	   struct addrinfo *ai_next;
   };

参数	值	用途	说明
ai_flags	0：无附加选项 AI_NUMERICHOST AI_PASSIVE AI_V4MAPED AI_ADDRCONFIG	specifies additional options
ai_family	AF_INET：ipv4 AF_INET6：ipv6 AF_UNSPEC：前面两者皆可	specifies the desired address family for the returned addresses.
ai_socktype	SOCK_STREAM SOCK_DGRAM ... 0: any type	specifies the preferred socket type
ai_protocol	0: any protocol	specifies the protocol for the returned socket addresses.
ai_addrlen	0
ai_addr	NULL
ai_canonname	NULL	If hints.ai_flags includes the AI_CANONNAME flag, then the ai_canonname field of the first of the addrinfo structures in the returned list is set to point to the official name of the host.	规范名称
next	NULL

canon: a generally accepted rule, standard or principle by which sth is judged

getaddrinfo

       int getaddrinfo(const char *restrict node,
                       const char *restrict service,
                       const struct addrinfo *restrict hints,
                       struct addrinfo **restrict res);

参数	值	用途	说明
node	Server: NULL Client: 192.168.56.xxx - ip地址（numerical network address） www.baidu.com - 域名（network hostname）	identify an Internet host	ip地址（主机）
service	http 80	identity a service	端口号（服务）
hints	NULL：any type & any protocol & AF_UNSPEC & (AI_V4MAPPED | AI_ADDRCONFIG)	points to an addrinfo structure that specifies criteria for selecting the socket address structures
res			符合条件的地址信息列表
RETURN VALUE	0: succeed error code

returns one or more addrinfo structures, each of which contains an Internet address that can be specified in a call to bind(2) or connect(2)

对于Server， 通过getaddrinfo（）可以获取可用的 ip地址，然后bind
对于client，可以方便地获取服务端的地址类型 ，然后创建对应类型的socket，再与服务端进行connect

freeaddrinfo

    void freeaddrinfo(struct addrinfo *res);

相关信息

The freeaddrinfo() function frees the memory that was allocated for the dynamically allocated linked list res.

示例 - client

连接到指定upd

int main(int argc, char *argv[])
{
   int              sfd, s;
   char             buf[BUF_SIZE];
   size_t           len;
   ssize_t          nread;
   struct addrinfo  hints;
   struct addrinfo  *result, *rp;

   if (argc < 3) {
	   fprintf(stderr, "Usage: %s host port msg...\n", argv[0]);
	   exit(EXIT_FAILURE);
   }

   /* Obtain address(es) matching host/port. */

   memset(&hints, 0, sizeof(hints));
   hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
   hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
   hints.ai_flags = 0;
   hints.ai_protocol = 0;          /* Any protocol */

   s = getaddrinfo(argv[1], argv[2], &hints, &result);
   if (s != 0) {
	   fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
	   exit(EXIT_FAILURE);
   }
   
  /* getaddrinfo() returns a list of address structures.
  Try each address until we successfully connect(2).
  If socket(2) (or connect(2)) fails, we (close the socket
  and) try the next address. */

   for (rp = result; rp != NULL; rp = rp->ai_next) {
	   sfd = socket(rp->ai_family, rp->ai_socktype,
					rp->ai_protocol);
	   if (sfd == -1)
		   continue;

	   if (connect(sfd, rp->ai_addr, rp->ai_addrlen) != -1)
		   break;                  /* Success */

	   close(sfd);
   }

   freeaddrinfo(result);           /* No longer needed */

   if (rp == NULL) {               /* No address succeeded */
	   fprintf(stderr, "Could not connect\n");
	   exit(EXIT_FAILURE);
   }

   /* Send remaining command-line arguments as separate
	  datagrams, and read responses from server. */

   for (size_t j = 3; j < argc; j++) {
	   len = strlen(argv[j]) + 1;
			   /* +1 for terminating null byte */

	   if (len > BUF_SIZE) {
		   fprintf(stderr,
				   "Ignoring long message in argument %zu\n", j);
		   continue;
	   }

	   if (write(sfd, argv[j], len) != len) {
		   fprintf(stderr, "partial/failed write\n");
		   exit(EXIT_FAILURE);
	   }

	   nread = read(sfd, buf, BUF_SIZE);
	   if (nread == -1) {
		   perror("read");
		   exit(EXIT_FAILURE);
	   }

	   printf("Received %zd bytes: %s\n", nread, buf);
   }

   exit(EXIT_SUCCESS);
}

行号	功能	说明
17-21	设置服务端信息
23		result 指向列表首元素
34-44	创建udp socket，并绑定连接
46	释放

效果：

Client

./Network 192.168.56.1 10086 ni hao!

对端地址信息：192.168.56.1 10086

Server

RECV ASCII/3 from 192.168.56.101 :60243 <<<
ni

省去了手动填充地址结构体的步骤，并且可以通过域名指定服务端地址，同时支持IPV4 和 IPV6。

getnameinfo

address-to-name translation in protocol-independent manner

   #include <sys/socket.h>
   #include <netdb.h>

   int getnameinfo(const struct sockaddr *sa, socklen_t salen,
				   char *host, socklen_t hostlen,
				   char *serv, socklen_t servlen, int flags);

参数	值	用途	说明
sa		a pointer to a generic socket address structure(of type sockaddr_in or sockaddr_in6) that holds the input IP address and port number
salen		sa size
host		pointer to caller-allocated buffer, null-terminated string
hostlen		host buffer size
serv
servlen
RETURAN VALUE	0: success

flags

值	含义	说明
NI_NAMEREQD	If set, then an error is returned if the hostname cannot be determined.
NI_DGRAM	If set, then the service is datagram (UDP) based rather than stream (TCP) based. This is required for the few ports (512-514) that have different services for UDP and TCP.	通常同一个端口对应的TCP、UDP服务相同，但存在同一端口TCP、UDP服务不同的情况。 514,TCP:shell(远程shell); UDP: syslog(系统日志)
NI_NOFQDN	If set, return only the hostname part of the fully qualified domain name for local hosts.
NI_NUMERICSERV	If set, then the numeric form of the service address is returned.
NI_NUMERICHOST	If set, then the numeric form of the hostname is returned.

EXAMPLE

int main(int argc, char* argv[])
{
   int s;
   struct addrinfo *result, *rp;
   char *host = "www.baidu.com", *service = "http";
   s = getaddrinfo(host, service, NULL, &result);
   if (s != 0) {
	   fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
	   exit(EXIT_FAILURE);
   }
   char hbuf[NI_MAXHOST], sbuf[NI_MAXSERV];
   getnameinfo(result->ai_addr, result->ai_addrlen, hbuf, sizeof(hbuf), sbuf, sizeof(sbuf), NI_NUMERICSERV);
   printf("Host: %s, Service: %s\n", hbuf, sbuf);

   return 0;
}

字符数组长度宏定义：

netdb.h

#define NI_MAXHOST      1025
#define NI_MAXSERV      32

效果：

Host: 36.152.44.93, Service: 80

示例 - Server

 memset(&hints, 0, sizeof(struct addrinfo));
   hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
   hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
   hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
   hints.ai_protocol = 0;          /* Any protocol */
   hints.ai_canonname = NULL;
   hints.ai_addr = NULL;
   hints.ai_next = NULL;

   s = getaddrinfo(NULL, argv[1], &hints, &result);
   if (s != 0) {
	   fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(s));
	   exit(EXIT_FAILURE);
   }

   /* getaddrinfo() returns a list of address structures.
	  Try each address until we successfully bind(2).
	  If socket(2) (or bind(2)) fails, we (close the socket
	  and) try the next address. */

   for (rp = result; rp != NULL; rp = rp->ai_next) {
	   sfd = socket(rp->ai_family, rp->ai_socktype,
			   rp->ai_protocol);
	   if (sfd == -1)
		   continue;

	   if (bind(sfd, rp->ai_addr, rp->ai_addrlen) == 0)
		   break;                  /* Success */

	   close(sfd);
   }
   if (rp == NULL) {               /* No address succeeded */
	   fprintf(stderr, "Could not bind\n");
	   exit(EXIT_FAILURE);
   }

   freeaddrinfo(result);           /* No longer needed */

   /* Read datagrams and echo them back to sender */

   for (;;) {
	   peer_addr_len = sizeof(struct sockaddr_storage);
	   nread = recvfrom(sfd, buf, BUF_SIZE, 0,
			   (struct sockaddr *) &peer_addr, &peer_addr_len);
	   if (nread == -1)
		   continue;               /* Ignore failed request */

	   char host[NI_MAXHOST], service[NI_MAXSERV];

	   s = getnameinfo((struct sockaddr *) &peer_addr,
					   peer_addr_len, host, NI_MAXHOST,
					   service, NI_MAXSERV, NI_NUMERICSERV);
	  if (s == 0)
		   printf("Received %zd bytes from %s:%s\n",
				   nread, host, service);
	   else
		   fprintf(stderr, "getnameinfo: %s\n", gai_strerror(s));

	   if (sendto(sfd, buf, nread, 0,
				   (struct sockaddr *) &peer_addr,
				   peer_addr_len) != nread)
		   fprintf(stderr, "Error sending response\n");
   }

sockaddr(3type)

       struct sockaddr {
           sa_family_t     sa_family;      /* Address family */
           char            sa_data[];      /* Socket address */
       };
       
       struct sockaddr_storage {
           sa_family_t     ss_family;      /* Address family */
       };
       
	  Internet domain sockets
       #include <netinet/in.h>

       struct sockaddr_in {
           sa_family_t     sin_family;     /* AF_INET */
           in_port_t       sin_port;       /* Port number */
           struct in_addr  sin_addr;       /* IPv4 address */
       };

       struct sockaddr_in6 {
           sa_family_t     sin6_family;    /* AF_INET6 */
           in_port_t       sin6_port;      /* Port number */
           uint32_t        sin6_flowinfo;  /* IPv6 flow info */
           struct in6_addr sin6_addr;      /* IPv6 address */
           uint32_t        sin6_scope_id;  /* Set of interfaces for a scope */
       };
       
	   struct in_addr {
           in_addr_t s_addr;
       };

       struct in6_addr {
           uint8_t   s6_addr[16];
       };

       typedef uint32_t in_addr_t;
       typedef uint16_t in_port_t;

Type	size	DESCRIPTION	说明
sockaddr	16	Describes a socket address
sockaddr_storage	128	- at least as large as any other sockaddr * addr structures - is aligned	可以容纳任何其他类型的地址结构体 ；内存对齐，访问更快，转换为其他类型指针时不会出问题 可以用来表示任意类型地址结构，在确定了具体类型后再转换类型
sockaddr_in	16	Describes an IPv4 Internet domain socket address. The sin_port and sin_addr members are stored in network byte order.	按网络字节序存储ipv4地址
sockaddr_in6	28
in_addr	4
in6_addr	16

getpeername

#include <sys/socket.h>
int getpeername(int sockfd, struct sockaddr *addr, socklen_t *addrlen);

get name of connected of peer socket

参数	值	用途	说明
sockfd			获取连接到sockfd的对端地址信息
addr			存储peer 地址信息
addrlen		indicate the amount of space pointed to by addr	如果peer地址信息长度大于addr提供的大小，那么实际信息会被截断，但是addrlen仍然为peer实际地址大小
RETURN		0：success -1：error

getsockname

#include <sys/socket.h>
int getsockname(int sockfd, struct sockaddr *addr, socklen_t *addrlen);

get socket name

参数	值	用途	说明
sockfd			要获取地址的socket fd
addr			存储地址信息
addrlen		the actual size of the socket address
RETURN	0: success

inet_ntop

#include <arpa/inet.h>
const char *inet_ntop(int af, const void *src,
					 char *dst, socklen_t size);

convert IPv4 and IPv6 addresses from binary to text form

参数	值	用途	说明
af	AF_INET：IPv4 AF_INET6: IPv6	address family
src		network address structure
dst\output			存储结果的字符串指针, IPv4 为ddd.ddd.ddd.ddd 格式
size\input	INET_ADDRSTRLEN：IPv4 最小长度 INET6_ADDRSTRLEN	the number of bytes available in the buffer
RETURN	NULL: error a non-null pointer to dst		既然在参数中指定了输出结果，这里返回结果为什么不是bool类型？额，可以直接从返回值判断结果以及获取转换后的地址字符串？

inet_ntoa - 过时的方法