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GETHOSTBYNAME(3) Library Functions Manual GETHOSTBYNAME(3) NAME dnsres_init, dnsres_gethostbyname, dnsres_gethostbyname2, dnsres_gethostbyaddr, dnsres_getaddrinfo -- non blocking DNS resolving library SYNOPSIS #include <sys/types.h> #include <sys/socket.h> #include <netdb.h> #include <dnsres.h> int dnsres_init(struct dnsres *_resp); void dnsres_gethostbyname(struct dnsres *res, const char *name, void (*cb)(struct hostent *hp, int error, void *arg), void *arg); void dnsres_gethostbyname2(struct dnsres *res, const char *name, int af, void (*cb)(struct hostent *hp, int error, void *arg), void *arg); void dnsres_gethostbyaddr(struct dnsres *res, const char *addr, int len, int af, void (*cb)(struct hostent *hp, int error, void *arg), void *arg); void dnsres_getaddrinfo(struct dnsres *res, const char *hostname, const char *servname, const struct addrinfo *hints, void (*cb)(struct addrinfo *ai, int res, void *arg), void *arg); DESCRIPTION The dnsres_init() is used to initialize the dnsres library. If you are developing a multi-threaded application, you need one struct dnsres per thread. The dnsres_gethostbyname(), dnsres_gethostbyname2() and dnsres_gethostbyaddr() functions each call their provided callback function with a pointer to an object with the following structure de- scribing an internet host referenced by name or by address, respec- tively. This structure contains either information obtained from the name server (i.e., resolver(3) and named(8)), broken-out fields from a line in /etc/hosts, or database entries supplied by the yp(8) system. resolv.conf(5) describes how the particular database is chosen. struct dnsres_hostent { char *h_name; /* official name of host */ char **h_aliases; /* alias list */ int h_addrtype; /* host address type */ int h_length; /* length of address */ char **h_addr_list; /* list of addresses from name server */ }; The members of this structure are: h_name Official name of the host. h_aliases A NULL-terminated array of alternate names for the host. h_addrtype The type of address being returned. h_length The length, in bytes, of the address. h_addr_list A zero-terminated array of network addresses for the host. Host addresses are returned in network byte order. h_addr The first address in h_addr_list; this is for backward compatibility. The function dnsres_gethostbyname() will search for the named host in the current domain and its parents using the search lookup semantics detailed in resolv.conf(5) and hostname(7). dnsres_gethostbyname2() is an advanced form of gethostbyname() which allows lookups in address families other than AF_INET. Currently, the only supported address family besides AF_INET is AF_INET6. The dnsres_gethostbyaddr() function will search for the specified ad- dress of length len in the address family af. The only address family currently supported is AF_INET. The dnsres_getaddrinfo() function is used to get a list of IP addresses and port numbers for host hostname and service servname. ENVIRONMENT HOSTALIASES A file containing local host aliases. See hostname(7) for more information. RES_OPTIONS A list of options to override the resolver's internal de- faults. See resolver(3) for more information. FILES /etc/hosts /etc/resolv.conf DIAGNOSTICS Error return status from dnsres_gethostbyname(), dnsres_gethostbyname2(), and dnsres_gethostbyaddr() is indicated by a null pointer passed to the callback function. The integer dr_errno may then be checked in struct dnsres to see whether this is a temporary failure or an invalid or unknown host. The variable h_errno can have the following values: DNSRES_HOST_NOT_FOUND No such host is known. DNSRES_TRY_AGAIN This is usually a temporary error and means that the local server did not receive a response from an authoritative server. A retry at some later time may succeed. DNSRES_NO_RECOVERY Some unexpected server failure was encountered. This is a non-recoverable error. DNSRES_NO_DATA The requested name is valid but does not have an IP address; this is not a temporary error. This means that the name is known to the name server but there is no address associated with this name. Another type of request to the name server using this domain name will result in an answer; for example, a mail-forwarder may be registered for this domain. DNSRES_NETDB_INTERNAL An internal error occurred. This may occurs when an address family other than AF_INET or AF_INET6 is specified or when a resource is un- able to be allocated. DNSRES_NETDB_SUCCESS The function completed successfully. SEE ALSO getnameinfo(3), resolver(3), hosts(5), resolv.conf(5), hostname(7), named(8) HISTORY The herror() function appeared in 4.3BSD. The endhostent(), gethostbyaddr(), gethostbyname(), gethostent(), and sethostent() func- tions appeared in 4.2BSD. CAVEATS If the search routines in resolv.conf(5) decide to read the /etc/hosts file, gethostent() and other functions will read the next line of the file, re-opening the file if necessary. The sethostent() function opens and/or rewinds the file /etc/hosts. If the stayopen argument is non-zero, the file will not be closed after each call to gethostbyname(), gethostbyname2(), or gethostbyaddr(). The endhostent() function closes the file. AUTHORS The dnsres library was hacked together by Niels Provos. Heavy use was made of the exisiting BSD resolver library. FreeBSD Ports 14.quarterly March 13, 1997 GETHOSTBYNAME(3)
NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | FILES | DIAGNOSTICS | SEE ALSO | HISTORY | CAVEATS | AUTHORS
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