lwres_getaddrinfo

Name

lwres_getaddrinfo, lwres_freeaddrinfo -- socket address structure to host and service name

Synopsis

#include <lwres/netdb.h>

int lwres_getaddrinfo(const char *hostname, const char *servname, const struct addrinfo *hints, struct addrinfo **res);

void lwres_freeaddrinfo(struct addrinfo *ai);

If the operating system does not provide a struct addrinfo, the following structure is used: 

struct  addrinfo {
        int             ai_flags;       /* AI_PASSIVE, AI_CANONNAME */
        int             ai_family;      /* PF_xxx */
        int             ai_socktype;    /* SOCK_xxx */
        int             ai_protocol;    /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
        size_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 */
};

DESCRIPTION

lwres_getaddrinfo() is used to get a list of IP addresses and port numbers for host hostname and service servname. The function is the lightweight resolver's implementation of getaddrinfo() as defined in RFC2133. hostname and servname are pointers to null-terminated strings or NULL. hostname is either a host name or a numeric host address string: a dotted decimal IPv4 address or an IPv6 address. servname is either a decimal port number or a service name as listed in /etc/services.

hints is an optional pointer to a struct addrinfo. 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 protocol family that should be used. When ai_family is set to PF_UNSPEC, it means the caller will accept any protocol family supported by the operating system.

ai_socktype

denotes the type of socket — SOCK_STREAM, SOCK_DGRAM or SOCK_RAW — that is wanted. When ai_socktype is zero the caller will accept any socket type.

ai_protocol

indicates which transport protocol is wanted: IPPROTO_UDP or IPPROTO_TCP. If ai_protocol is zero the caller will accept any protocol.

ai_flags

Flag bits. If the AI_CANONNAME bit is set, a successful call to lwres_getaddrinfo() will return a null-terminated string containing the canonical name of the specified hostname in ai_canonname of the first addrinfo structure returned. Setting the AI_PASSIVE bit indicates that the returned socket address structure is intended for used in a call to bind(2). In this case, if the hostname argument is a 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.

When ai_flags does not set the AI_PASSIVE bit, 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 a NULL pointer and AI_PASSIVE is not set in ai_flags.

If ai_flags is set to AI_NUMERICHOST it indicates that hostname should be treated as a numeric string defining an IPv4 or IPv6 address and no name resolution should be attempted.

All other elements of the struct addrinfo passed via hints must be zero.

A hints of NULL is treated as if the caller provided a struct addrinfo initialized to zero with ai_familyset to PF_UNSPEC.

After a successful call to lwres_getaddrinfo(), *res is a pointer to a linked list of one or more addrinfo structures. Each struct addrinfo in this list cn be processed by following the ai_next pointer, until a NULL pointer is encountered. The three members ai_family, ai_socktype, and ai_protocol in each returned addrinfo structure contain the corresponding arguments for a call to socket(2). For each addrinfo structure in the list, the ai_addr member points to a filled-in socket address structure of length ai_addrlen.

All of the information returned by lwres_getaddrinfo() is dynamically allocated: the addrinfo structures, and the socket address structures and canonical host name strings pointed to by the addrinfostructures. Memory allocated for the dynamically allocated structures created by a successful call to lwres_getaddrinfo() is released by lwres_freeaddrinfo(). ai is a pointer to a struct addrinfo created by a call to lwres_getaddrinfo().

RETURN VALUES

lwres_getaddrinfo() returns zero on success or one of the error codes listed in gai_strerror(3) if an error occurs. If both hostname and servname are NULL lwres_getaddrinfo() returns EAI_NONAME.

SEE ALSO

lwres(3), lwres_getaddrinfo(3), lwres_freeaddrinfo(3), lwres_gai_strerror(3), RFC2133, getservbyname(3), bind(2), connect(2), sendto(2), sendmsg(2), socket(2).