getaddrinfo (翻译 man 3) --未完

GETADDRINFO(3)                Linux Programmer's Manual                GETADDRINFO(3)

NAME

       getaddrinfo, freeaddrinfo, gai_strerror - network address and service transla-
       tion

//网络地址和服务器转化

SYNOPSIS

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

       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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       getaddrinfo(), freeaddrinfo(), gai_strerror():
           _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE

DESCRIPTION

       Given node and service, which identify an Internet host and a service,
       getaddrinfo() 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).
       The getaddrinfo() function combines the functionality provided by the
       getservbyname(3) and getservbyport(3) functions into a single interface, but
       unlike the latter functions, getaddrinfo() is reentrant and allows programs to
       eliminate IPv4-versus-IPv6 dependencies.
//给出 node 和 service 来标识Internet 主机和服务器, getaddrinfo() 返回一个或多个addrinfo 结构体,

//每个都包含了能够被 bind(2) 和 connect(2) 调用的Internet 地址.getaddrinfo() 联合由getservbyname(3)

//和getservbyport(3)提供的功能而成为一个单一的接口,但是又不像后者,getaddrinfo() 是可重入的和允许程序消除IPv4和IPv4的差异

       The addrinfo structure used by getaddrinfo() contains the following fields:

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

       The hints argument points to an addrinfo structure that specifies criteria for
       selecting the socket address structures returned in the list pointed to by
       res.  If hints is not NULL it points to an addrinfo structure whose ai_family,
       ai_socktype, and ai_protocol specify criteria that limit the set of socket
       addresses returned by getaddrinfo(), as follows:
//hints 参数指向一个 addrinfo 结构,这个结构指定了由指向res的链表返回的结构体的socket地址进行select的准则.

//如果hints 非空hints 就指向一个addrinfo 结构,此结构的ai_family, ai_socktype, 和 ai_protocol 成员指定了由getaddrinfo()

//返回的socket地址的设置限制的准则,如下:

       ai_family   This field specifies the desired address family for the returned
                   addresses.  Valid values for this field include AF_INET and
                   AF_INET6.  The value AF_UNSPEC indicates that getaddrinfo() should
                   return socket addresses for any address family (either IPv4 or
                   IPv6, for example) that can be used with node and service.
//这个域指定了返回地址想要的地址族.这个域的有效值是 AF_INET  和 AF_INET6. AF_UNSPEC 标志着 getaddrinfo() 

//应该返回任何地址族的socket地址(IPv4 或IPv6 例如),这个地址可以被用做node  和 service.
       ai_socktype This field specifies the preferred socket type, for example
                   SOCK_STREAM or SOCK_DGRAM.  Specifying 0 in this field indicates
                   that socket addresses of any type can be returned by
                   getaddrinfo().
//这个域指定socket类型,例如SOCK_STREAM 或 SOCK_DGRAM.在这个域指定0表示getaddrinfo()可以返回任意类型的socket地址.
       ai_protocol This field specifies the protocol for the returned socket
                   addresses.  Specifying 0 in this field indicates that socket
                   addresses with any protocol can be returned by getaddrinfo().
//这个域指定返回socket地址的协议,在这个域指定0表示getaddrinfo()可以返回socket地址为任意协议.
       ai_flags    This field specifies additional options, described below.
                   Multiple flags are specified by bitwise OR-ing them together.
//这个域指定附加选项,定义如下,过个标志位是通过位的与操作来实现的:
       All the other fields in the structure pointed to by hints must contain either
       0 or a null pointer, as appropriate.  Specifying hints as NULL is equivalent
       to setting ai_socktype and ai_protocol to 0; ai_family to AF_UNSPEC; and
       ai_flags to (AI_V4MAPPED | AI_ADDRCONFIG).
//在由hints指向的结构中的所有其他域要么是0要么是NULL才是恰当的.为NULL等同于设置ai_socktype 和ai_protocol 为0;ai_family 为AF_UNSPEC,ai_flags 为(AI_V4MAPPED | AI_ADDRCONFIG)
       node specifies either a numerical network address (for IPv4, numbers-and-dots
       notation as supported by inet_aton(3); for IPv6, hexadecimal string format as
       supported by inet_pton(3)), or a network hostname, whose network addresses are
       looked up and resolved.  If hints.ai_flags contains the AI_NUMERICHOST flag
       then node must be a numerical network address.  The AI_NUMERICHOST flag
       suppresses any potentially lengthy network host address lookups.
//指定要么是数字表示的网址(),要么是一个可以查找和解决网络主机名.如果hints.ai_flags包含了AI_NUMERICHOST 标志位那么node 必须是数字格式的网络地址.

//AI_NUMERICHOST 标志位隐藏任何潜在的网络地址主机长度
       If the AI_PASSIVE flag is specified in hints.ai_flags, and node is NULL, then
       the returned socket addresses will be suitable for bind(2)ing a socket that
       will accept(2) connections.  The returned socket address will contain the
       "wildcard address" (INADDR_ANY for IPv4 addresses, IN6ADDR_ANY_INIT for IPv6
       address).  The wildcard address is used by applications (typically servers)
       that intend to accept connections on any of the hosts's network addresses.  If
       node is not NULL, then the AI_PASSIVE flag is ignored.
//如果在hints.ai_flags 中指定了AI_PASSIVE 标志位,同时node 为NULL,那么返回的网络地址就会适合bind一个socket之后被accept().

//返回的socket地址包含”地址通配符”(INADDR_ANY 为 IPv4 地址, 而IN6ADDR_ANY_INIT 为 IPv6).

//通配符地址被程序(一般是服务器)用来在accept()在服务器任何地址上的连接.如果node 不为NULL,那么AI_PASSIVE 标识会被忽略.
       If the AI_PASSIVE flag is not set in hints.ai_flags, then the returned socket
       addresses will be suitable for use with connect(2), sendto(2), or sendmsg(2).
       If node is NULL, then the network address will be set to the loopback
       interface address (INADDR_LOOPBACK for IPv4 addresses, IN6ADDR_LOOPBACK_INIT
       for IPv6 address); this is used by applications that intend to communicate
       with peers running on the same host.

       service sets the port in each returned address structure.  If this argument is
       a service name (see services(5)), it is translated to the corresponding port
       number.  This argument can also be specified as a decimal number, which is
       simply converted to binary.  If service is NULL, then the port number of the
       returned socket addresses will be left uninitialized.  If AI_NUMERICSERV is
       specified in hints.ai_flags and service is not NULL, then service must point
       to a string containing a numeric port number.  This flag is used to inhibit
       the invocation of a name resolution service in cases where it is known not to
       be required.

       Either node or service, but not both, may be NULL.

       The getaddrinfo() function allocates and initializes a linked list of addrinfo
       structures, one for each network address that matches node and service,
       subject to any restrictions imposed by hints, and returns a pointer to the
       start of the list in res.  The items in the linked list are linked by the
       ai_next field.

       There are several reasons why the linked list may have more than one addrinfo
       structure, including: the network host is multihomed, accessible over multiple
       protocols (e.g. both AF_INET and AF_INET6); or the same service is available
       from multiple socket types (one SOCK_STREAM address and another SOCK_DGRAM
       address, for example).  Normally, the application should try using the
       addresses in the order in which they are returned.  The sorting function used
       within getaddrinfo() is defined in RFC 3484; the order can be tweaked for a
       particular system by editing /etc/gai.conf (available since glibc 2.5).

       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.

       The remaining fields of each returned addrinfo structure are initialized as
       follows:

       * The ai_family, ai_socktype, and ai_protocol fields return the socket
         creation parameters (i.e., these fields have the same meaning as the
         corresponding arguments of socket(2)).  For example, ai_family might return
         AF_INET or AF_INET6; ai_socktype might return SOCK_DGRAM or SOCK_STREAM; and
         ai_protocol returns the protocol for the socket.

       * A pointer to the socket address is placed in the ai_addr field, and the
         length of the socket address, in bytes, is placed in the ai_addrlen field.

       If hints.ai_flags includes the AI_ADDRCONFIG flag, then IPv4 addresses are
       returned in the list pointed to by res only if the local system has at least
       one IPv4 address configured, and IPv6 addresses are only returned if the local
       system has at least one IPv6 address configured.

       If hint.ai_flags specifies the AI_V4MAPPED flag, and hints.ai_family was
       specified as AF_INET6, and no matching IPv6 addresses could be found, then
       return IPv4-mapped IPv6 addresses in the list pointed to by res.  If both
       AI_V4MAPPED and AI_ALL are specified in hints.ai_flags, then return both IPv6
       and IPv4-mapped IPv6 addresses in the list pointed to by res.  AI_ALL is
       ignored if AI_V4MAPPED is not also specified.

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

Extensions to getaddrinfo() for Internationalized Domain Names

       Starting with glibc 2.3.4, getaddrinfo() has been extended to selectively
       allow the incoming and outgoing hostnames to be transparently converted to and
       from the Internationalized Domain Name (IDN) format (see RFC 3490,
       Internationalizing Domain Names in Applications (IDNA)).  Four new flags are
       defined:

       AI_IDN If this flag is specified, then the node name given in node is
              converted to IDN format if necessary.  The source encoding is that of
              the current locale.

              If the input name contains non-ASCII characters, then the IDN encoding
              is used.  Those parts of the node name (delimited by dots) that contain
              non-ASCII characters are encoded using ASCII Compatible Encoding (ACE)
              before being passed to the name resolution functions.

       AI_CANONIDN
              After a successful name lookup, and if the AI_CANONNAME flag was
              specified, getaddrinfo() will return the canonical name of the node
              corresponding to the addrinfo structure value passed back.  The return
              value is an exact copy of the value returned by the name resolution
              function.

              If the name is encoded using ACE, then it will contain the xn-- prefix
              for one or more components of the name.  To convert these components
              into a readable form the AI_CANONIDN flag can be passed in addition to
              AI_CANONNAME.  The resulting string is encoded using the current
              locale's encoding.

       AI_IDN_ALLOW_UNASSIGNED, AI_IDN_USE_STD3_ASCII_RULES
              Setting these flags will enable the IDNA_ALLOW_UNASSIGNED (allow
              unassigned Unicode code points) and IDNA_USE_STD3_ASCII_RULES (check
              output to make sure it is a STD3 conforming hostname) flags
              respectively to be used in the IDNA handling.

RETURN VALUE

       getaddrinfo() returns 0 if it succeeds, or one of the following nonzero error
       codes:

       EAI_ADDRFAMILY
              The specified network host does not have any network addresses in the
              requested address family.

       EAI_AGAIN
              The name server returned a temporary failure indication.  Try again
              later.

       EAI_BADFLAGS
              hints.ai_flags contains invalid flags; or, hints.ai_flags included
              AI_CANONNAME and name was NULL.

       EAI_FAIL
              The name server returned a permanent failure indication.

       EAI_FAMILY
              The requested address family is not supported.

       EAI_MEMORY
              Out of memory.

       EAI_NODATA
              The specified network host exists, but does not have any network
              addresses defined.

       EAI_NONAME
              The node or service is not known; or both node and service are NULL; or
              AI_NUMERICSERV was specified in hints.ai_flags and service was not a
              numeric port-number string.

       EAI_SERVICE
              The requested service is not available for the requested socket type.
              It may be available through another socket type.  For example, this
              error could occur if service was "shell" (a service only available on
              stream sockets), and either hints.ai_protocol was IPPROTO_UDP, or
              hints.ai_socktype was SOCK_DGRAM; or the error could occur if service
              was not NULL, and hints.ai_socktype was SOCK_RAW (a socket type that
              does not support the concept of services).

       EAI_SOCKTYPE
              The requested socket type is not supported.  This could occur, for
              example, if hints.ai_socktype and hints.ai_protocol are inconsistent
              (e.g., SOCK_DGRAM and IPPROTO_TCP, respectively).

       EAI_SYSTEM
              Other system error, check errno for details.

       The gai_strerror() function translates these error codes to a human readable
       string, suitable for error reporting.

FILES

       /etc/gai.conf

CONFORMING TO

       POSIX.1-2001.  The getaddrinfo() function is documented in RFC 2553.

NOTES

       getaddrinfo() supports the address%scope-id notation for specifying the IPv6
       scope-ID.

       AI_ADDRCONFIG, AI_ALL, and AI_V4MAPPED are available since glibc 2.3.3.
       AI_NUMERICSERV is available since glibc 2.3.4.

       According to POSIX.1-2001, specifying hints as NULL should cause ai_flags to
       be assumed as 0.  The GNU C library instead assumes a value of
       (AI_V4MAPPED | AI_ADDRCONFIG) for this case, since this value is considered an
       improvement on the specification.

EXAMPLE

       The following programs demonstrate the use of getaddrinfo(), gai_strerror(),
       freeaddrinfo(), and getnameinfo(3).  The programs are an echo server and
       client for UDP datagrams.

Server program

    #include <sys/types.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <string.h>
       #include <sys/socket.h>
       #include <netdb.h>

       #define BUF_SIZE 500

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

           if (argc != 2) 
           {
               fprintf(stderr, "Usage: %s port/n", argv[0]);
               exit(EXIT_FAILURE);
           }

           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 %ld bytes from %s:%s/n",(long) 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");
           }
       }
Client program
    
   
   
   

     
    
    
    
       #include <sys/types.h>
       #include <sys/socket.h>
       #include <netdb.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <string.h>

       #define BUF_SIZE 500

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

           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(struct addrinfo));
           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);
           }

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

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

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

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

               if (len + 1 > BUF_SIZE) 
               {
                   fprintf(stderr, "Ignoring long message in argument %d/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 %ld bytes: %s/n", (long) nread, buf);
           }

           exit(EXIT_SUCCESS);
       }
SEE ALSO
       getaddrinfo_a(3), gethostbyname(3), getnameinfo(3), inet(3), hostname(7),
       ip(7)
COLOPHON
       This page is part of release 3.31 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can be found
       at http://www.kernel.org/doc/man-pages/.

GNU                                   2010-09-27                       GETADDRINFO(3)