lwres_gethostent

+ + + + + + + +

Name

+ lwres_gethostbyname, + lwres_gethostbyname2, + lwres_gethostbyaddr, + lwres_gethostent, + lwres_sethostent, + lwres_endhostent, + lwres_gethostbyname_r, + lwres_gethostbyaddr_r, + lwres_gethostent_r, + lwres_sethostent_r, + lwres_endhostent_r + — lightweight resolver get network host entry +

Synopsis

#include <lwres/netdb.h>

+ + + +

+struct hostent * +lwres_gethostbyname( const char *name);

+ + + + + + + + + +

`+struct hostent * +lwres_gethostbyname2(`	const char *`name`,
	int `af)`;

+ + + + + + + + + + + + + +

`+struct hostent * +lwres_gethostbyaddr(`	const char *`addr`,
	int `len`,
	int `type)`;

+ + + +

+struct hostent * +lwres_gethostent( void);

+ + + +

+void +lwres_sethostent( int stayopen);

+ + + +

+void +lwres_endhostent( void);

+ + + + + + + + + + + + + + + + + + + + + +

`+struct hostent * +lwres_gethostbyname_r(`	const char *`name`,
	struct hostent *`resbuf`,
	char *`buf`,
	int `buflen`,
	int *`error)`;

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

`+struct hostent * +lwres_gethostbyaddr_r(`	const char *`addr`,
	int `len`,
	int `type`,
	struct hostent *`resbuf`,
	char *`buf`,
	int `buflen`,
	int *`error)`;

+ + + + + + + + + + + + + + + + + +

`+struct hostent * +lwres_gethostent_r(`	struct hostent *`resbuf`,
	char *`buf`,
	int `buflen`,
	int *`error)`;

+ + + +

+void +lwres_sethostent_r( int stayopen);

+ + + +

+void +lwres_endhostent_r( void);

+ +

DESCRIPTION

+ +

+ These functions provide hostname-to-address and + address-to-hostname lookups by means of the lightweight resolver. + They are similar to the standard + + gethostent(3) + + functions provided by most operating systems. + They use a + struct hostent + which is usually defined in + <namedb.h>. +

+struct  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 */
+};
+#define h_addr  h_addr_list[0]  /* address, for backward compatibility */
+

+ The members of this structure are: +

h_name: +
+ The official (canonical) name of the host. +
+
h_aliases: +
+ A NULL-terminated array of alternate names (nicknames) for the + host. +
+
h_addrtype: +
+ The type of address being returned — + PF_INET + or + PF_INET6. +
+
h_length: +
+ The length of the address in bytes. +
+
h_addr_list: +
+ A NULL + terminated array of network addresses for the host. + Host addresses are returned in network byte order. +
+

+ For backward compatibility with very old software, + h_addr + is the first address in + h_addr_list. +

lwres_gethostent(), + lwres_sethostent(), + lwres_endhostent(), + lwres_gethostent_r(), + lwres_sethostent_r() + and + lwres_endhostent_r() + provide iteration over the known host entries on systems that + provide such functionality through facilities like + /etc/hosts + or NIS. The lightweight resolver does not currently implement + these functions; it only provides them as stub functions that always + return failure. +

+ +

lwres_gethostbyname() + and lwres_gethostbyname2() look up the + hostname name. + lwres_gethostbyname() always looks for an + IPv4 address while lwres_gethostbyname2() + looks for an address of protocol family + af: either PF_INET or + PF_INET6 — IPv4 or IPV6 addresses + respectively. Successful calls of the functions return a + struct hostentfor the name that was looked up. + NULL is returned if the lookups by + lwres_gethostbyname() or + lwres_gethostbyname2() fail. +

+ +

+ Reverse lookups of addresses are performed by + lwres_gethostbyaddr(). + addr is an address of length + len bytes and protocol family + type — PF_INET or + PF_INET6. + lwres_gethostbyname_r() is a + thread-safe function + for forward lookups. If an error occurs, an error code is returned in + *error. + resbuf is a pointer to a + struct hostent which is initialised by a successful call to + lwres_gethostbyname_r(). + buf is a buffer of length + len bytes which is used to store the + h_name, h_aliases, and + h_addr_list elements of the + struct hostent returned in resbuf. + Successful calls to lwres_gethostbyname_r() + return resbuf, + which is a pointer to the struct hostent it created. +

+ +

lwres_gethostbyaddr_r() + is a thread-safe function + that performs a reverse lookup of address addr + which is len bytes long and is of + protocol + family type — PF_INET or + PF_INET6. If an error occurs, the error code is returned + in *error. The other function + parameters are + identical to those in lwres_gethostbyname_r(). + resbuf is a pointer to a + struct hostent which is initialised by a successful call to + lwres_gethostbyaddr_r(). + buf is a buffer of length + len bytes which is used to store the + h_name, h_aliases, and + h_addr_list elements of the + struct hostent returned in resbuf. + Successful calls to lwres_gethostbyaddr_r() return + resbuf, which is a pointer to the + struct hostent() it created. +

+ +

RETURN VALUES

+ +

+ The functions + lwres_gethostbyname(), + lwres_gethostbyname2(), + lwres_gethostbyaddr(), + and + lwres_gethostent() + return NULL to indicate an error. In this case the global variable + lwres_h_errno + will contain one of the following error codes defined in + <lwres/netdb.h>: + +

HOST_NOT_FOUND: +
+ The host or address was not found. +
+
TRY_AGAIN: +
+ A recoverable error occurred, e.g., a timeout. + Retrying the lookup may succeed. +
+
NO_RECOVERY: +
+ A non-recoverable error occurred. +
+
NO_DATA: +
+ The name exists, but has no address information + associated with it (or vice versa in the case + of a reverse lookup). The code NO_ADDRESS + is accepted as a synonym for NO_DATA for backwards + compatibility. +
+

+ +

+ lwres_hstrerror(3) + + translates these error codes to suitable error messages. +

+ +

lwres_gethostent() + and lwres_gethostent_r() + always return NULL. +

+ +

+ Successful calls to lwres_gethostbyname_r() and + lwres_gethostbyaddr_r() return + resbuf, a pointer to the + struct hostent that was initialised by these functions. They return + NULL if the lookups fail or if buf + was too small to hold the list of addresses and names referenced by + the h_name, h_aliases, and + h_addr_list elements of the + struct hostent. + If buf was too small, both + lwres_gethostbyname_r() and + lwres_gethostbyaddr_r() set the global + variable + errno to ERANGE. +

+ +

BUGS

+ +

lwres_gethostbyname(), + lwres_gethostbyname2(), + lwres_gethostbyaddr() + and + lwres_endhostent() + are not thread safe; they return pointers to static data and + provide error codes through a global variable. + Thread-safe versions for name and address lookup are provided by + lwres_gethostbyname_r(), + and + lwres_gethostbyaddr_r() + respectively. +

+ The resolver daemon does not currently support any non-DNS + name services such as + /etc/hosts + or + NIS, + consequently the above functions don't, either. +

Name

Synopsis

DESCRIPTION

RETURN VALUES

SEE ALSO

BUGS