主机名、服务与地址的映射——getaddrinfo(),getnameinfo(),gai_strerror()

http://blog.csdn.net/duyiwuer2009/article/details/7875206

 

/* Structure to contain information about address of a service provider.  */
struct addrinfo
{
  int ai_flags;         /* Input flags.  */
  int ai_family;        /* Protocol family for socket.  */
  int ai_socktype;      /* Socket type.  */
  int ai_protocol;      /* Protocol for socket.  */
  socklen_t ai_addrlen;     /* Length of socket address.  */
  struct sockaddr *ai_addr; /* Socket address for socket.  */
  char *ai_canonname;        /* Canonical name for service location.  */
  struct addrinfo *ai_next; /* Pointer to next in list.  */
};

/* Structure to contain information about address of a service provider.  */
struct addrinfo
{
  int ai_flags;			/* Input flags.  */
  int ai_family;		/* Protocol family for socket.  */
  int ai_socktype;		/* Socket type.  */
  int ai_protocol;		/* Protocol for socket.  */
  socklen_t ai_addrlen;		/* Length of socket address.  */
  struct sockaddr *ai_addr;	/* Socket address for socket.  */
  char *ai_canonname;		/* Canonical name for service location.  */
  struct addrinfo *ai_next;	/* Pointer to next in list.  */
};

----------getaddrinfo()

The getaddrinfo function allows us to map a host name and a service name to an address.(APUE-2e)

int getaddrinfo(const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res);
void freeaddrinfo(struct addrinfo *res);
const char *gai_strerror(int errcode);

int getaddrinfo(const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res);
void freeaddrinfo(struct addrinfo *res);
const char *gai_strerror(int errcode);

Note:

(1) getaddrinfo() sets res to point to a dynamically-allocated linked list of  addrinfo  structures, linked by the ai_next member.  There are several reasons why the linked list may have more than one addrinfo structure, including:  if  the  network host is multi-homed; or if the same service is available from multiple socket  protocols  (one SOCK_STREAM address and another SOCK_DGRAM address, for example).

(2) If getaddrinfo fails, we can't use perror or strerror to generate an error message. Instead, we need to callgai_strerrorto convert the error code returned into an error message.

下面的 getnameinfo 也用 gai_strerror 收集错误信息。

(3) 注意addrinfo.ai_flags AI_*的含义（见例子）

(4) getaddrinfo() returns 0 if it succeeds, or one of the following nonzero error codes: <see man page>

这也是不能用 perror or strerror 处理的原因，因为它没有用 errno(#include <errno.h>) 作为错误代码

----------getnameinfo()

The getnameinfo function converts an address into a host name and a service name.

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

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

Note:

(1) The  sa  argument is a pointer to a generic socket address structure (of type sockaddr_in or sockaddr_in6) of size salen thatholds the input IP address and port number

(2) addrinfo.ai_flags 和 getnameinfo的参数 flags 可以同时设置多个标志，按位与（|）；如果取一个标志，要按位或（&），下面的例子中有这两种用法。（Multiple flags are specified by bitwise OR-ing them together.）

 

/* Structure to contain information about address of a service provider.  */
struct addrinfo
{
  int ai_flags;         /* Input flags.  */
  int ai_family;       /* Protocol family for socket.  */
  int ai_socktype;      /* Socket type.  */
  int ai_protocol;     /* Protocol for socket.  */
  socklen_t ai_addrlen;     /* Length of socket address.  */
  struct sockaddr *ai_addr;/* Socket address for socket.  */
  char *ai_canonname;        /* Canonical name for service location.  */
  struct addrinfo *ai_next;/* Pointer to next in list.  */
};

/* Structure to contain information about address of a service provider.  */
struct addrinfo
{
  int ai_flags;			/* Input flags.  */
  int ai_family;		/* Protocol family for socket.  */
  int ai_socktype;		/* Socket type.  */
  int ai_protocol;		/* Protocol for socket.  */
  socklen_t ai_addrlen;		/* Length of socket address.  */
  struct sockaddr *ai_addr;	/* Socket address for socket.  */
  char *ai_canonname;		/* Canonical name for service location.  */
  struct addrinfo *ai_next;	/* Pointer to next in list.  */
};

----------getaddrinfo()

The getaddrinfo function allows us to map a host name and a service name to an address.(APUE-2e)

int getaddrinfo(constchar *node, constchar *service, conststruct addrinfo *hints, struct addrinfo **res);
void freeaddrinfo(struct addrinfo *res);
const char *gai_strerror(int errcode);

int getaddrinfo(const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res);
void freeaddrinfo(struct addrinfo *res);
const char *gai_strerror(int errcode);

Note:

(1) getaddrinfo() sets res to point to a dynamically-allocated linked list of  addrinfo  structures, linked by the ai_next member. There are several reasons why the linked list may have more than one addrinfo structure, including:  if  the  network host is multi-homed; or if the same service is available from multiple socket  protocols  (one SOCK_STREAM address and another SOCK_DGRAM address, for example).

(2) If getaddrinfo fails, we can't use perror or strerror to generate an error message. Instead, we need to callgai_strerrorto convert the error code returned into an error message.

下面的 getnameinfo 也用 gai_strerror收集错误信息。

(3) 注意addrinfo.ai_flags AI_*的含义（见例子）

(4) getaddrinfo() returns 0 if it succeeds, or one of the following nonzero error codes: <see man page>

这也是不能用 perror or strerror 处理的原因，因为它没有用 errno(#include <errno.h>) 作为错误代码

----------getnameinfo()

The getnameinfo function converts an address into a host name and a service name.

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

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

Note:

(1) The  sa  argument is a pointer to a generic socket address structure (of type sockaddr_in or sockaddr_in6) of size salen thatholds the input IP address and port number

(2) addrinfo.ai_flags 和 getnameinfo的参数flags 可以同时设置多个标志，按位与（|）；如果取一个标志，要按位或（&），下面的例子中有这两种用法。（Multiple flags are specified by bitwise OR-ing them together.）

/**
* getaddrinfo()
* OS: Ubuntu 11.04 Server
* This example is form APUE-2e
*/
#include    "print_ai.h"
#include    <stdio.h>
#include    <stdlib.h>
#include    <netdb.h>
#include    <arpa/inet.h>


int main(int argc,char *argv[])
{
    struct addrinfo *ailist = NULL;
    struct addrinfo hint;
    int err;

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

    hint.ai_flags = AI_CANONNAME;   // AI_CANONNAME | AI_NUMERICHOST | AI_NUMERICSERV
    hint.ai_family = 0;
    hint.ai_socktype = 0;
    hint.ai_protocol = 0;
    hint.ai_addrlen = 0;
    hint.ai_addr = NULL;
    hint.ai_canonname = NULL;
    hint.ai_next = NULL;


    if( (err = getaddrinfo(argv[1], argv[2], &hint, &ailist)) != 0 )
    {
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(err));
        exit(EXIT_FAILURE);
    }

    print_ai(ailist);

    freeaddrinfo(ailist);

    return 0;
}
/*
$ ./a.out baidu.com nfs
flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host: baidu.com
address: 220.181.111.86
port: 2049              # NFS程序常运行于这个端口

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 220.181.111.86
port: 2049

flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host:
address: 123.125.114.144
port: 2049

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 123.125.114.144
port: 2049

flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host:
address: 220.181.111.85
port: 2049

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 220.181.111.85
port: 2049

-------------------------------
$ ./a.out localhost nfs
flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host: localhost
address: 127.0.0.1
port: 2049

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 127.0.0.1
port: 2049

-------------------------------the function of AI_NUMERICHOST and AI_NUMERICSERV
hint.ai_flags = AI_CANONNAME | AI_NUMERICHOST | AI_NUMERICSERV
$ ./a.out baidu.com nfs
getaddrinfo: Name or service not known

$ ./a.out 220.181.111.85 nfs
getaddrinfo: Name or service not known

$ ./a.out 220.181.111.85 2049
flags: AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV
family: inet
socket type: stream
protocol: IPPROTO_TCP
host: 220.181.111.85
address: 220.181.111.85
port: 2049

flags: AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 220.181.111.85
port: 2049

flags: AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV
family: inet
socket type: raw
protocol: default
host:
address: 220.181.111.85
port: 2049

-------------------------------
FILES: /etc/gai.conf
*/

/**
 * getaddrinfo()
 * OS: Ubuntu 11.04 Server
 * This example is form APUE-2e
 */
#include	"print_ai.h"
#include	<stdio.h>
#include	<stdlib.h>
#include	<netdb.h>
#include	<arpa/inet.h>


int main(int argc, char *argv[])
{
	struct addrinfo *ailist = NULL;
	struct addrinfo hint;
	int err;
	
	if(argc != 3)
	{
		printf("usage: %s nodename service\n", argv[0]);
		exit(1);
	}
	
	hint.ai_flags = AI_CANONNAME;	// AI_CANONNAME | AI_NUMERICHOST | AI_NUMERICSERV
	hint.ai_family = 0;
	hint.ai_socktype = 0;
	hint.ai_protocol = 0;
	hint.ai_addrlen = 0;
	hint.ai_addr = NULL;
	hint.ai_canonname = NULL;
	hint.ai_next = NULL;


	if( (err = getaddrinfo(argv[1], argv[2], &hint, &ailist)) != 0 )
	{
		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(err));
		exit(EXIT_FAILURE);
	}
	
	print_ai(ailist);
	
	freeaddrinfo(ailist);
	
	return 0;
}
/*
$ ./a.out baidu.com nfs
flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host: baidu.com
address: 220.181.111.86
port: 2049				# NFS程序常运行于这个端口

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 220.181.111.86
port: 2049

flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host:
address: 123.125.114.144
port: 2049

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 123.125.114.144
port: 2049

flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host:
address: 220.181.111.85
port: 2049

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 220.181.111.85
port: 2049

-------------------------------
$ ./a.out localhost nfs
flags: AI_CANONNAME
family: inet
socket type: stream
protocol: IPPROTO_TCP
host: localhost
address: 127.0.0.1
port: 2049

flags: AI_CANONNAME
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 127.0.0.1
port: 2049

-------------------------------the function of AI_NUMERICHOST and AI_NUMERICSERV
hint.ai_flags = AI_CANONNAME | AI_NUMERICHOST | AI_NUMERICSERV
$ ./a.out baidu.com nfs
getaddrinfo: Name or service not known

$ ./a.out 220.181.111.85 nfs
getaddrinfo: Name or service not known

$ ./a.out 220.181.111.85 2049
flags: AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV
family: inet
socket type: stream
protocol: IPPROTO_TCP
host: 220.181.111.85
address: 220.181.111.85
port: 2049

flags: AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV
family: inet
socket type: datagram
protocol: IPPROTO_TCP
host:
address: 220.181.111.85
port: 2049

flags: AI_CANONNAME AI_NUMERICHOST AI_NUMERICSERV
family: inet
socket type: raw
protocol: default
host:
address: 220.181.111.85
port: 2049

-------------------------------
FILES: /etc/gai.conf
*/

----------打印 addrinfo 的函数——print_ai

print_ai.h

#ifndef _PRINT_AI_H
#define _PRINT_AI_H

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

extern void print_ai(struct addrinfo *ailist);
extern void print_flags(conststruct addrinfo *aip);
extern void print_family(conststruct addrinfo *aip);
extern void print_socktype(conststruct addrinfo *aip);
extern void print_protocol(conststruct addrinfo *aip);

#endif  /* _PRINT_AI_H */

#ifndef	_PRINT_AI_H
#define	_PRINT_AI_H

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

extern void print_ai(struct addrinfo *ailist);
extern void print_flags(const struct addrinfo *aip);
extern void print_family(const struct addrinfo *aip);
extern void print_socktype(const struct addrinfo *aip);
extern void print_protocol(const struct addrinfo *aip);

#endif	/* _PRINT_AI_H */

print_ai.c

#include    "print_ai.h"
#include    <stdio.h>
#include    <arpa/inet.h>

void print_ai(struct addrinfo *ailist)
{
    struct addrinfo     *aip = NULL;
    struct sockaddr_in  *sin_p = NULL; // socket inet address pointer
    char                addr_in_p[INET_ADDRSTRLEN];
    const char          *p = NULL;

    for(aip = ailist; aip != NULL; aip = aip->ai_next)
    {
        printf("flags: ");
        print_flags(aip);
        printf("\n");

        printf("family: ");
        print_family(aip);
        printf("\n");

        printf("socket type: ");
        print_socktype(aip);
        printf("\n");

        printf("protocol: ");
        print_protocol(aip);
        printf("\n");

        printf("host: %s\n", aip->ai_canonname ? aip->ai_canonname :"");

        if(aip -> ai_family == AF_INET)
        {
            sin_p = (struct sockaddr_in *)aip->ai_addr;
            p = inet_ntop(AF_INET, &sin_p->sin_addr, addr_in_p, INET_ADDRSTRLEN);
            printf("address: %s\n", p ? addr_in_p :"unknown");
            printf("port: %d\n", ntohs(sin_p->sin_port));   // Note:
        }

        printf("\n");
    }
}

void print_flags(conststruct addrinfo *aip)
{
    if(aip->ai_flags == 0)
    {
        printf("0");
    }
    else
    {
        if(aip->ai_flags & AI_PASSIVE)
        {
            printf("AI_PASSIVE ");
        }
        if(aip->ai_flags & AI_CANONNAME)
        {
            printf("AI_CANONNAME ");
        }
        if(aip->ai_flags & AI_NUMERICHOST)
        {
            printf("AI_NUMERICHOST ");
        }
#if defined(AI_V4MAPPED)
        if(aip->ai_flags & AI_V4MAPPED)
        {
            printf("AI_V4MAPPED ");
        }
#endif
#if defined(AI_ALL)
        if(aip->ai_flags & AI_ALL)
        {
            printf("AI_ALL ");
        }
#endif
#if defined(AI_ADDRCONFIG)
        if(aip->ai_flags & AI_ADDRCONFIG)
        {
            printf("AI_ADDRCONFIG ");
        }
#endif
#if defined(AI_NUMERICSERV)
        if(aip->ai_flags & AI_NUMERICSERV)
        {
            printf("AI_NUMERICSERV ");
        }
#endif
    }
}

void print_family(conststruct addrinfo *aip)
{
    switch(aip->ai_family)
    {
    case AF_INET:
        printf("inet");
        break;
    case AF_INET6:
        printf("inet6");
        break;
    case AF_UNIX:
        printf("unix");
        break;
    case AF_UNSPEC:
        printf("unspecified");
        break;
    default:
        printf("unknown");
    }
}

void print_socktype(conststruct addrinfo *aip)
{
    switch(aip->ai_socktype)
    {
    case SOCK_STREAM:
        printf("stream");
        break;
    case SOCK_DGRAM:
        printf("datagram");
        break;
    case SOCK_SEQPACKET:
        printf("seqpacket");
        break;
    case SOCK_RAW:
        printf("raw");
        break;
    default:
        printf("unknown (%d)", aip->ai_socktype);
    }
}

void print_protocol(conststruct addrinfo *aip)
{
    switch(aip->ai_protocol)
    {
    case 0:
        printf("default");
        break;
    case IPPROTO_TCP:
        printf("IPPROTO_TCP");
        break;
    case IPPROTO_UDP:
        printf("IPPROTO_UDP");
        break;
    case IPPROTO_RAW:
        printf("IPPROTO_RAW");
        break;
    default:
        printf("unknown (%d)", aip->ai_protocol);
    }
}

#include	"print_ai.h"
#include	<stdio.h>
#include	<arpa/inet.h>

void print_ai(struct addrinfo *ailist)
{
	struct addrinfo		*aip = NULL;
	struct sockaddr_in	*sin_p = NULL;	// socket inet address pointer
	char 				addr_in_p[INET_ADDRSTRLEN];
	const char 			*p = NULL;

	for(aip = ailist; aip != NULL; aip = aip->ai_next)
	{
		printf("flags: ");
		print_flags(aip);
		printf("\n");
		
		printf("family: ");
		print_family(aip);
		printf("\n");
		
		printf("socket type: ");
		print_socktype(aip);
		printf("\n");
		
		printf("protocol: ");
		print_protocol(aip);
		printf("\n");
		
		printf("host: %s\n", aip->ai_canonname ? aip->ai_canonname : "");
		
		if(aip -> ai_family == AF_INET)
		{
			sin_p = (struct sockaddr_in *)aip->ai_addr;
			p = inet_ntop(AF_INET, &sin_p->sin_addr, addr_in_p, INET_ADDRSTRLEN);
			printf("address: %s\n", p ? addr_in_p : "unknown");
			printf("port: %d\n", ntohs(sin_p->sin_port));	// Note: 
		}
		
		printf("\n");
	}
}

void print_flags(const struct addrinfo *aip)
{
	if(aip->ai_flags == 0)
	{
		printf("0");
	}
	else
	{
		if(aip->ai_flags & AI_PASSIVE)
		{
			printf("AI_PASSIVE ");
		}
		if(aip->ai_flags & AI_CANONNAME)
		{
			printf("AI_CANONNAME ");
		}
		if(aip->ai_flags & AI_NUMERICHOST)
		{
			printf("AI_NUMERICHOST ");
		}
#if defined(AI_V4MAPPED)
		if(aip->ai_flags & AI_V4MAPPED)
		{
			printf("AI_V4MAPPED ");
		}
#endif
#if defined(AI_ALL)
		if(aip->ai_flags & AI_ALL)
		{
			printf("AI_ALL ");
		}
#endif
#if defined(AI_ADDRCONFIG)
		if(aip->ai_flags & AI_ADDRCONFIG)
		{
			printf("AI_ADDRCONFIG ");
		}
#endif
#if defined(AI_NUMERICSERV)
		if(aip->ai_flags & AI_NUMERICSERV)
		{
			printf("AI_NUMERICSERV ");
		}
#endif
	}
}

void print_family(const struct addrinfo *aip)
{
	switch(aip->ai_family)
	{
	case AF_INET:
		printf("inet");
		break;
	case AF_INET6:
		printf("inet6");
		break;
	case AF_UNIX:
		printf("unix");
		break;
	case AF_UNSPEC:
		printf("unspecified");
		break;
	default:
		printf("unknown");
	}
}

void print_socktype(const struct addrinfo *aip)
{
	switch(aip->ai_socktype)
	{
	case SOCK_STREAM:
		printf("stream");
		break;
	case SOCK_DGRAM:
		printf("datagram");
		break;
	case SOCK_SEQPACKET:
		printf("seqpacket");
		break;
	case SOCK_RAW:
		printf("raw");
		break;
	default:
		printf("unknown (%d)", aip->ai_socktype);
	}
}

void print_protocol(const struct addrinfo *aip)
{
	switch(aip->ai_protocol)
	{
	case 0:
		printf("default");
		break;
	case IPPROTO_TCP:
		printf("IPPROTO_TCP");
		break;
	case IPPROTO_UDP:
		printf("IPPROTO_UDP");
		break;
	case IPPROTO_RAW:
		printf("IPPROTO_RAW");
		break;
	default:
		printf("unknown (%d)", aip->ai_protocol);
	}
}

/**
* getnameinfo()
* OS: Ubuntu 11.04 Server
* for other examples, see man getnameinfo page
*/
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <arpa/inet.h>

int main(int argc,char *argv[])
{
    struct sockaddr_in sa_in;
    char host[NI_MAXHOST], service[NI_MAXSERV];
    int flags;
    int err;

    sa_in.sin_family = AF_INET; // IPv4
    sa_in.sin_port = htons(2049);   // the port of NFS
    inet_pton(AF_INET, "127.0.0.1", &sa_in.sin_addr.s_addr);   // "220.181.111.86" is the address of baidu.com
    flags = 0;  // NI_NUMERICHOST | NI_NUMERICSERV

    err = getnameinfo((struct sockaddr *)(&sa_in),sizeof(struct sockaddr),
                    host, sizeof(host), service,sizeof(service), flags);
    if(err != 0)
    {
        gai_strerror(err);
        exit(EXIT_FAILURE);
    }
    printf("host=%s, serv=%s\n", host, service);

    return 0;
}
/*
$ ./a.out
host=localhost, serv=nfs

$ ./a.out
host=220.181.111.86, serv=nfs
*/

/**
 * getnameinfo()
 * OS: Ubuntu 11.04 Server
 * for other examples, see man getnameinfo page
 */
#include <stdio.h>
#include <stdlib.h>
#include <netdb.h>
#include <arpa/inet.h>

int main(int argc, char *argv[])
{
	struct sockaddr_in sa_in;
	char host[NI_MAXHOST], service[NI_MAXSERV];
	int flags;
	int err;
	
	sa_in.sin_family = AF_INET;	// IPv4
	sa_in.sin_port = htons(2049);	// the port of NFS
	inet_pton(AF_INET, "127.0.0.1", &sa_in.sin_addr.s_addr);	// "220.181.111.86" is the address of baidu.com
	flags = 0;	// NI_NUMERICHOST | NI_NUMERICSERV
	
	err = getnameinfo((struct sockaddr *)(&sa_in), sizeof(struct sockaddr),
					host, sizeof(host), service, sizeof(service), flags);
	if(err != 0)
	{
		gai_strerror(err);
		exit(EXIT_FAILURE);
	}
	printf("host=%s, serv=%s\n", host, service);
	
	return 0;
}
/*
$ ./a.out
host=localhost, serv=nfs

$ ./a.out
host=220.181.111.86, serv=nfs
*/

 

----------参考资料

APUE-2e

Linux man pages