Movatterモバイル変換

GETADDRINFO(3)             Linux Programmer's ManualGETADDRINFO(3)NAME       getaddrinfo,  freeaddrinfo,  gai_strerror - network address and service       translationSYNOPSIS       #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 (seefeature_test_macros(7)):       getaddrinfo(), freeaddrinfo(), gai_strerror():           Since glibc 2.22: _POSIX_C_SOURCE >= 200112L           Glibc 2.21 and earlier: _POSIX_C_SOURCEDESCRIPTION       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 tobind(2)       orconnect(2).   The getaddrinfo() function combines the functionality       provided by thegethostbyname(3) andgetservbyname(3) functions into  a       single  interface,  but  unlike  the latter functions, getaddrinfo() is       reentrant and allows programs to eliminate  IPv4-versus-IPv6  dependen-       cies.       The  addrinfo  structure  used  by getaddrinfo() contains the following       fields:           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;           };       The hints argument points to an addrinfo structure that specifies  cri-       teria  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 crite-       ria that limit the set of socket addresses returned  by  getaddrinfo(),       as follows:       ai_family   This field specifies the desired address family for the re-                   turned 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  ad-                   dress family (either IPv4 or IPv6, for example) that can be                   used with node and service.       ai_socktype This field specifies the preferred socket type, for example                   SOCK_STREAM  or SOCK_DGRAM.  Specifying 0 in this field in-                   dicates that socket addresses of any type can  be  returned                   by getaddrinfo().       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().       ai_flags    This field specifies additional options,  described  below.                   Multiple  flags  are  specified  by bitwise OR-ing them to-                   gether.       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).  (POSIX specifies different defaults for       ai_flags; see NOTES.)  node specifies either a  numerical  network  ad-       dress   (for   IPv4,   numbers-and-dots   notation   as   supported  byinet_aton(3); for IPv6,  hexadecimal  string  format  as  supported  byinet_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_NUMERI-       CHOST flag suppresses any  potentially  lengthy  network  host  address       lookups.       If  the  AI_PASSIVE  flag  is  specified in hints.ai_flags, and node is       NULL,  then  the  returned  socket  addresses  will  be  suitable   forbind(2)ing  a  socket  that  willaccept(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  connec-       tions  on  any  of  the host's network addresses.  If node is not NULL,       then the AI_PASSIVE flag is ignored.       If the AI_PASSIVE flag is not set in hints.ai_flags, then the  returned       socket  addresses  will be suitable for use withconnect(2),sendto(2),       orsendmsg(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 ar-       gument is a service name (seeservices(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 re-       quired.       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, accessi-       ble 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  de-       fined  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  initial-       ized 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 ofsocket(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_ad-         drlen 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 returned       only if the local system has at least one IPv6 address configured.  The       loopback  address is not considered for this case as valid as a config-       ured address.  This flag is useful on, for example, IPv4-only  systems,       to ensure that getaddrinfo() does not return IPv6 socket addresses that       would always fail inconnect(2) orbind(2).       If hints.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 speci-       fied.       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 selec-       tively 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  reso-              lution 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 en-              coded 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 in-              cluded 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 ser-              vice 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 ex-              ample,  this error could occur if service was "shell" (a service              available only on stream sockets), and either  hints.ai_protocol              was IPPROTO_UDP, or hints.ai_socktype was SOCK_DGRAM; or the er-              ror 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 in-              consistent (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.confATTRIBUTES       For  an  explanation  of  the  terms  used  in  this  section,  see at-tributes(7).       +----------------+---------------+--------------------+       |Interface       | Attribute     | Value              |       +----------------+---------------+--------------------+       |getaddrinfo()   | Thread safety | MT-Safe env locale |       +----------------+---------------+--------------------+       |freeaddrinfo(), | Thread safety | MT-Safe            |       |gai_strerror()  |               |                    |       +----------------+---------------+--------------------+CONFORMING TO       POSIX.1-2001,  POSIX.1-2008.   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, 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  con-       sidered an improvement on the specification.EXAMPLE       The  following  programs demonstrate the use of getaddrinfo(), gai_str-       error(), freeaddrinfo(), andgetnameinfo(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 successfullybind(2).              Ifsocket(2) (orbind(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");           }       }   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 successfullyconnect(2).              Ifsocket(2) (orconnect(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 > 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 %zd bytes: %s\n", nread, buf);           }           exit(EXIT_SUCCESS);       }SEE ALSOgetaddrinfo_a(3),gethostbyname(3),getnameinfo(3),inet(3),gai.conf(5),hostname(7),ip(7)COLOPHON       This page is part of release 5.05 of the Linux  man-pages  project.   A       description  of  the project, information about reporting bugs, and the       latest    version    of    this    page,    can     be     found     at       https://www.kernel.org/doc/man-pages/.GNU                               2019-03-06GETADDRINFO(3)