NAME
getaddrinfo, freeaddrinfo, gaistrerror - network address and service translation SYNOPSIS
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#include
#include
int getaddrinfo(const char *node, const char *service, const struct addrinfo *hints, struct addrinfo **res); void freeaddrinfo(struct addrinfo *res); const char *gaistrerror(int errcode); Feature Test Macro Requirements for glibc (see featuretestmacros(7)): getaddrinfo(), freeaddrinfo(), gaistrerror(): POSIXCSOURCE >= 1 || XOPENSOURCE || POSIXSOURCE 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 gethostbyname(3) and getservbyname(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 aiflags; int aifamily; int aisocktype; int aiprotocol; socklent aiaddrlen; struct sockaddr *aiaddr; char *aicanonname; struct addrinfo *ainext; }; 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 aifamily, aisocktype, and aiprotocol specify crite‐ ria that limit the set of socket addresses returned by getaddrinfo(), as follows: aifamily This field specifies the desired address family for the returned addresses. Valid values for this field include AFINET and AFINET6. The value AFUNSPEC 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. aisocktype This field specifies the preferred socket type, for example SOCKSTREAM or SOCKDGRAM. Specifying 0 in this field indicates that socket addresses of any type can be returned by getaddrinfo(). aiprotocol 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(). aiflags This field specifies additional options, described below.
Multiple flags are specified by bitwise OR-ing them together. 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 aisocktype and aiprotocol to 0; aifamily to AFUNSPEC; and aiflags to (AIV4MAPPED | AIADDRCONFIG).
node specifies either a numerical network address (for IPv4, numbers-
and-dots notation as supported by inetaton(3); for IPv6, hexadecimal string format as supported by inetpton(3)), or a network hostname, whose network addresses are looked up and resolved. If hints.aiflags contains the AINUMERICHOST flag then node must be a numerical network address. The AINUMERICHOST flag suppresses any potentially lengthy network host address lookups. If the AIPASSIVE flag is specified in hints.aiflags, 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" (INADDRANY for IPv4 addresses, IN6ADDRANYINIT for IPv6 address). The wildcard address is used by applications (typically servers) that intend to accept connec‐ tions on any of the hosts's network addresses. If node is not NULL, then the AIPASSIVE flag is ignored. If the AIPASSIVE flag is not set in hints.aiflags, 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 (INADDRLOOPBACK for IPv4 addresses, IN6ADDRLOOPBACKINIT 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 AINUMERICSERV is specified in hints.aiflags 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 ainext 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 AFINET and AFINET6); or the same service is available from multiple socket types (one SOCKSTREAM address and another SOCKDGRAM 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.aiflags includes the AICANONNAME flag, then the aicanonname 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 aifamily, aisocktype, and aiprotocol fields return the socket creation parameters (i.e., these fields have the same meaning as the corresponding arguments of socket(2)). For example, aifamily might return AFINET or AFINET6; aisocktype might return SOCKDGRAM or SOCKSTREAM; and aiprotocol returns the protocol for the socket. * A pointer to the socket address is placed in the aiaddr field, and the length of the socket address, in bytes, is placed in the aiaddrlen field. If hints.aiflags includes the AIADDRCONFIG 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. If hints.aiflags specifies the AIV4MAPPED flag, and hints.aifamily was specified as AFINET6, and no matching IPv6 addresses could be
found, then return IPv4-mapped IPv6 addresses in the list pointed to by res. If both AIV4MAPPED and AIALL are specified in hints.aiflags,
then return both IPv6 and IPv4-mapped IPv6 addresses in the list pointed to by res. AIALL is ignored if AIV4MAPPED 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: AIIDN 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. AICANONIDN After a successful name lookup, and if the AICANONNAME 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 AICANONIDN flag can be passed in addition to AICANONNAME. The resulting string is encoded using the current locale's encoding. AIIDNALLOWUNASSIGNED, AIIDNUSESTD3ASCIIRULES Setting these flags will enable the IDNAALLOWUNASSIGNED (allow unassigned Unicode code points) and IDNAUSESTD3ASCIIRULES (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: EAIADDRFAMILY The specified network host does not have any network addresses in the requested address family. EAIAGAIN The name server returned a temporary failure indication. Try again later. EAIBADFLAGS hints.aiflags contains invalid flags; or, hints.aiflags included AICANONNAME and name was NULL. EAIFAIL The name server returned a permanent failure indication. EAIFAMILY The requested address family is not supported. EAIMEMORY Out of memory. EAINODATA The specified network host exists, but does not have any network addresses defined. EAINONAME The node or service is not known; or both node and service are NULL; or AINUMERICSERV was specified in hints.aiflags and ser‐
vice was not a numeric port-number string. EAISERVICE 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 ser‐ vice available only on stream sockets), and either hints.aipro‐ tocol was IPPROTOUDP, or hints.aisocktype was SOCKDGRAM; or the error could occur if service was not NULL, and hints.aisocktype was SOCKRAW (a socket type that does not sup‐ port the concept of services). EAISOCKTYPE The requested socket type is not supported. This could occur, for example, if hints.aisocktype and hints.aiprotocol are inconsistent (e.g., SOCKDGRAM and IPPROTOTCP, respectively). EAISYSTEM Other system error, check errno for details. The gaistrerror() 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. AIADDRCONFIG, AIALL, and AIV4MAPPED are available since glibc 2.3.3. AINUMERICSERV is available since glibc 2.3.4.
According to POSIX.1-2001, specifying hints as NULL should cause aiflags to be assumed as 0. The GNU C library instead assumes a value of (AIV4MAPPED | AIADDRCONFIG) for this case, since this value is considered an improvement on the specification. EXAMPLE The following programs demonstrate the use of getaddrinfo(), gaistr‐ error(), freeaddrinfo(), and getnameinfo(3). The programs are an echo server and client for UDP datagrams. Server program
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#define BUFSIZE 500 int main(int argc, char *argv[]) { struct addrinfo hints; struct addrinfo *result, *rp; int sfd, s; struct sockaddrstorage peeraddr; socklent peeraddrlen; ssizet nread; char buf[BUFSIZE]; if (argc != 2) {
fprintf(stderr, "Usage: %s port\n", argv[0]); exit(EXITFAILURE); } memset(&hints, 0, sizeof(struct addrinfo)); hints.aifamily = AFUNSPEC; /* Allow IPv4 or IPv6 */ hints.aisocktype = SOCKDGRAM; /* Datagram socket */ hints.aiflags = AIPASSIVE; /* For wildcard IP address */ hints.aiprotocol = 0; /* Any protocol */ hints.aicanonname = NULL; hints.aiaddr = NULL; hints.ainext = NULL; s = getaddrinfo(NULL, argv[1], &hints, &result); if (s != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gaistrerror(s)); exit(EXITFAILURE); } /* 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->ainext) {
sfd = socket(rp->aifamily, rp->aisocktype,
rp->aiprotocol);
if (sfd == -1) continue;
if (bind(sfd, rp->aiaddr, rp->aiaddrlen) == 0) break; /* Success */ close(sfd); } if (rp == NULL) { /* No address succeeded */ fprintf(stderr, "Could not bind\n"); exit(EXITFAILURE); } freeaddrinfo(result); /* No longer needed */ /* Read datagrams and echo them back to sender */ for (;;) { peeraddrlen = sizeof(struct sockaddrstorage); nread = recvfrom(sfd, buf, BUFSIZE, 0, (struct sockaddr *) &peeraddr, &peeraddrlen);
if (nread == -1) continue; /* Ignore failed request */ char host[NIMAXHOST], service[NIMAXSERV]; s = getnameinfo((struct sockaddr *) &peeraddr, peeraddrlen, host, NIMAXHOST, service, NIMAXSERV, NINUMERICSERV); if (s == 0)
printf("Received %ld bytes from %s:%s\n", (long) nread, host, service); else
fprintf(stderr, "getnameinfo: %s\n", gaistrerror(s)); if (sendto(sfd, buf, nread, 0, (struct sockaddr *) &peeraddr, peeraddrlen) != nread) fprintf(stderr, "Error sending response\n"); } } Client program
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#define BUFSIZE 500 int main(int argc, char *argv[]) { struct addrinfo hints; struct addrinfo *result, *rp; int sfd, s, j; sizet len; ssizet nread; char buf[BUFSIZE]; if (argc < 3) {
fprintf(stderr, "Usage: %s host port msg...\n", argv[0]); exit(EXITFAILURE); } /* Obtain address(es) matching host/port */ memset(&hints, 0, sizeof(struct addrinfo)); hints.aifamily = AFUNSPEC; /* Allow IPv4 or IPv6 */ hints.aisocktype = SOCKDGRAM; /* Datagram socket */ hints.aiflags = 0; hints.aiprotocol = 0; /* Any protocol */ s = getaddrinfo(argv[1], argv[2], &hints, &result); if (s != 0) {
fprintf(stderr, "getaddrinfo: %s\n", gaistrerror(s)); exit(EXITFAILURE); } /* 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->ainext) {
sfd = socket(rp->aifamily, rp->aisocktype,
rp->aiprotocol);
if (sfd == -1) continue;
if (connect(sfd, rp->aiaddr, rp->aiaddrlen) != -1) break; /* Success */ close(sfd); } if (rp == NULL) { /* No address succeeded */ fprintf(stderr, "Could not connect\n"); exit(EXITFAILURE); } 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 > BUFSIZE) { 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(EXITFAILURE); } nread = read(sfd, buf, BUFSIZE);
if (nread == -1) { perror("read"); exit(EXITFAILURE); }
printf("Received %ld bytes: %s\n", (long) nread, buf); } exit(EXITSUCCESS); } SEE ALSO getaddrinfoa(3), gethostbyname(3), getnameinfo(3), inet(3), gai.conf(5), hostname(7), ip(7) COLOPHON
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GNU 2013-01-15 GETADDRINFO(3)