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#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
The hostname and servname arguments are either pointers to NUL-terminated strings or the null pointer. An acceptable value for hostname is either a valid host name or a numeric host address string consisting of a dotted decimal IPv4 address, an IPv6 address, or a UNIX-domain address. The servname is either a decimal port number or a service name listed in services(5). At least one of hostname and servname must be non-null.
hints is an optional pointer to a struct addrinfo, as defined by < netdb.h>:
struct addrinfo { int ai_flags; /* AI_PASSIVE, AI_CANONNAME, .. */ int ai_family; /* AF_xxx */ int ai_socktype; /* SOCK_xxx */ int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */ socklen_t ai_addrlen; /* length of ai_addr */ char *ai_canonname; /* canonical name for hostname */ struct sockaddr *ai_addr; /* binary address */ struct addrinfo *ai_next; /* next structure in linked list */ };
This structure can be used to provide hints concerning the type of socket that the caller supports or wishes to use. The caller can supply the following structure elements in hints:
ai_family | |
The address family that should be used. When ai_family is set to AF_UNSPEC, it means the caller will accept any address family supported by the operating system. | |
ai_socktype | |
Denotes the type of socket that is wanted: SOCK_STREAM, SOCK_DGRAM, SOCK_SEQPACKET, or SOCK_RAW. When ai_socktype is zero the caller will accept any socket type. | |
ai_protocol | |
Indicates which transport protocol is desired, IPPROTO_UDP, IPPROTO_TCP, IPPROTO_SCTP, or IPPROTO_UDPLITE. If ai_protocol is zero the caller will accept any protocol. | |
ai_flags | |
The ai_flags field to which the hints parameter points shall be set to zero or be the bitwise-inclusive OR of one or more of the values AI_ADDRCONFIG, AI_ALL, AI_CANONNAME, AI_NUMERICHOST, AI_NUMERICSERV, AI_PASSIVE and AI_V4MAPPED. For a UNIX-domain address, ai_flags is ignored. | |
AI_ADDRCONFIG | If the AI_ADDRCONFIG bit is set, IPv4 addresses shall be returned only if an IPv4 address is configured on the local system, and IPv6 addresses shall be returned only if an IPv6 address is configured on the local system. |
AI_ALL |
If the
AI_ALL
flag is used with the
AI_V4MAPPED
flag, then
getaddrinfo()
shall return all matching IPv6 and IPv4 addresses.
For example, when using the DNS, queries are made for both AAAA records and A records, and getaddrinfo() returns the combined results of both queries. Any IPv4 addresses found are returned as IPv4-mapped IPv6 addresses. The AI_ALL flag without the AI_V4MAPPED flag is ignored. |
AI_CANONNAME | If the AI_CANONNAME bit is set, a successful call to getaddrinfo() will return a NUL-terminated string containing the canonical name of the specified hostname in the ai_canonname element of the first addrinfo structure returned. |
AI_NUMERICHOST | |
If the AI_NUMERICHOST bit is set, it indicates that hostname should be treated as a numeric string defining an IPv4 or IPv6 address and no name resolution should be attempted. | |
AI_NUMERICSERV | |
If the AI_NUMERICSERV bit is set, then a non-null servname string supplied shall be a numeric port string. Otherwise, an EAI_NONAME error shall be returned. This bit shall prevent any type of name resolution service (for example, NIS+) from being invoked. | |
AI_PASSIVE |
If the
AI_PASSIVE
bit is set it indicates that the returned socket address structure
is intended for use in a call to
bind(2).
In this case, if the
hostname
argument is the null pointer, then the IP address portion of the
socket address structure will be set to
INADDR_ANY
for an IPv4 address or
IN6ADDR_ANY_INIT
for an IPv6 address.
If the AI_PASSIVE bit is not set, the returned socket address structure will be ready for use in a call to connect(2) for a connection-oriented protocol or connect(2), sendto(2), or sendmsg(2) if a connectionless protocol was chosen. The IP address portion of the socket address structure will be set to the loopback address if hostname is the null pointer and AI_PASSIVE is not set. |
AI_V4MAPPED |
If the
AI_V4MAPPED
flag is specified along with an ai_family of
AF_INET6,
then
getaddrinfo()
shall return IPv4-mapped IPv6 addresses on finding no matching IPv6 addresses (
ai_addrlen
shall be 16).
For example, when using the DNS, if no AAAA records are found then a query is made for A records and any found are returned as IPv4-mapped IPv6 addresses. The AI_V4MAPPED flag shall be ignored unless ai_family equals AF_INET6. |
All other elements of the addrinfo structure passed via hints must be zero or the null pointer.
If hints is the null pointer, getaddrinfo() behaves as if the caller provided a struct addrinfo with ai_family set to AF_UNSPEC and all other elements set to zero or NULL.
After a successful call to getaddrinfo(), *res is a pointer to a linked list of one or more addrinfo structures. The list can be traversed by following the ai_next pointer in each addrinfo structure until a null pointer is encountered. Each returned addrinfo structure contains three members that are suitable for a call to socket(2): ai_family, ai_socktype, and ai_protocol. For each addrinfo structure in the list, the ai_addr member points to a filled-in socket address structure of length ai_addrlen.
This implementation of getaddrinfo() allows numeric IPv6 address notation with scope identifier, as documented in chapter 11 of RFC 4007. By appending the percent character and scope identifier to addresses, one can fill the sin6_scope_id field for addresses. This would make management of scoped addresses easier and allows cut-and-paste input of scoped addresses.
At this moment the code supports only link-local addresses with the format. The scope identifier is hardcoded to the name of the hardware interface associated with the link ( such as ne0 ). An example is "fe80::1%ne0", which means " fe80::1 on the link associated with the ne0 interface ".
The current implementation assumes a one-to-one relationship between the interface and link, which is not necessarily true from the specification.
All of the information returned by getaddrinfo() is dynamically allocated: the addrinfo structures themselves as well as the socket address structures and the canonical host name strings included in the addrinfo structures.
Memory allocated for the dynamically allocated structures created by a successful call to getaddrinfo() is released by the freeaddrinfo() function. The ai pointer should be a addrinfo structure created by a call to getaddrinfo().
struct addrinfo hints, *res, *res0; int error; int s; const char *cause = NULL;memset(&hints, 0, sizeof(hints)); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_STREAM; error = getaddrinfo("www.kame.net", "http", &hints, &res0); if (error) { errx(1, "%s", gai_strerror(error)); /* NOTREACHED */ } s = -1; for (res = res0; res; res = res->ai_next) { s = socket(res->ai_family, res->ai_socktype, res->ai_protocol); if (s < 0) { cause = "socket"; continue; }
if (connect(s, res->ai_addr, res->ai_addrlen) < 0) { cause = "connect"; close(s); s = -1; continue; }
break; /* okay we got one */ } if (s < 0) { err(1, "%s", cause); /* NOTREACHED */ } freeaddrinfo(res0);
The following example tries to open a wildcard listening socket onto service "http", for all the address families available.
struct addrinfo hints, *res, *res0; int error; int s[MAXSOCK]; int nsock; const char *cause = NULL;memset(&hints, 0, sizeof(hints)); hints.ai_family = AF_UNSPEC; hints.ai_socktype = SOCK_STREAM; hints.ai_flags = AI_PASSIVE; error = getaddrinfo(NULL, "http", &hints, &res0); if (error) { errx(1, "%s", gai_strerror(error)); /* NOTREACHED */ } nsock = 0; for (res = res0; res && nsock < MAXSOCK; res = res->ai_next) { s[nsock] = socket(res->ai_family, res->ai_socktype, res->ai_protocol); if (s[nsock] < 0) { cause = "socket"; continue; }
if (bind(s[nsock], res->ai_addr, res->ai_addrlen) < 0) { cause = "bind"; close(s[nsock]); continue; } (void) listen(s[nsock], 5);
nsock++; } if (nsock == 0) { err(1, "%s", cause); /* NOTREACHED */ } freeaddrinfo(res0);
RFC 3493, Basic Socket Interface Extensions for IPv6, February 2003.
, , , , ,RFC 4007, IPv6 Scoped Address Architecture, March 2005.
, , , , ,Proceedings of the freenix track: 2000 USENIX annual technical conference, Protocol Independence Using the Sockets API, June 2000.
,GETADDRINFO (3) | February 10, 2019 |
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