NAME

netdb.h — definitions for network database operations

SYNOPSIS

#include <netdb.h>

DESCRIPTION

The <netdb.h> header shall define the hostent structure, which shall include at least the following members:

char   *h_name       Official name of the host.
char  **h_aliases    A pointer to an array of pointers to
                     alternative host names, terminated by a
                     null pointer.
int     h_addrtype   Address type.
int     h_length     The length, in bytes, of the address.
char  **h_addr_list  A pointer to an array of pointers to network
                     addresses (in network byte order) for the host,
                     terminated by a null pointer.

The <netdb.h> header shall define the netent structure, which shall include at least the following members:

char     *n_name      Official, fully-qualified (including the
                      domain) name of the host.
char    **n_aliases   A pointer to an array of pointers to
                      alternative network names, terminated by a
                      null pointer.
int       n_addrtype  The address type of the network.
uint32_t  n_net       The network number, in host byte order.

The <netdb.h> header shall define the uint32_t type as described in <inttypes.h>.

The <netdb.h> header shall define the protoent structure, which shall include at least the following members:

char   *p_name     Official name of the protocol.
char  **p_aliases  A pointer to an array of pointers to
                   alternative protocol names, terminated by
                   a null pointer.
int     p_proto    The protocol number.

The <netdb.h> header shall define the servent structure, which shall include at least the following members:

char   *s_name     Official name of the service.
char  **s_aliases  A pointer to an array of pointers to
                   alternative service names, terminated by
                   a null pointer.
int     s_port     A value which, when converted to uint16_t,
                   yields the port number in network byte order
                   at which the service resides.
char   *s_proto    The name of the protocol to use when
                   contacting the service.

The <netdb.h> header shall define the IPPORT_RESERVED symbolic constant with the value of the highest reserved Internet port number.

Address Information Structure

The <netdb.h> header shall define the addrinfo structure, which shall include at least the following members:

int               ai_flags      Input flags.
int               ai_family     Address family of socket.
int               ai_socktype   Socket type.
int               ai_protocol   Protocol of socket.
socklen_t         ai_addrlen    Length of socket address.
struct sockaddr  *ai_addr       Socket address of socket.
char             *ai_canonname  Canonical name of service location.
struct addrinfo  *ai_next       Pointer to next in list.

The addrinfo structure shall not include any additional members which have a floating-point type if an object of that type with an all-bits-zero representation does not have the value 0.0.
^[MX] Implementations that define __STDC_IEC_559__ are required to treat the all-zero bit pattern for a floating point object as a representation of 0.0, and may therefore have floating-point type members.

The <netdb.h> header shall define the following symbolic constants that evaluate to bitwise-distinct integer constants for use in the ai_flags field of the addrinfo structure:

AI_PASSIVE

Socket address is intended for bind().

AI_CANONNAME

Request for canonical name.

AI_NUMERICHOST

Return numeric host address as name.

AI_NUMERICSERV

Inhibit service name resolution.

AI_V4MAPPED

If no IPv6 addresses are found, query for IPv4 addresses and return them to the caller as IPv4-mapped IPv6 addresses.

AI_ALL

Query for both IPv4 and IPv6 addresses.

AI_ADDRCONFIG

Query for IPv4 addresses only when an IPv4 address is configured; query for IPv6 addresses only when an IPv6 address is configured.

The <netdb.h> header shall define the following symbolic constants that evaluate to bitwise-distinct integer constants for use in the flags argument to getnameinfo():

NI_NOFQDN

Only the nodename portion of the FQDN is returned for local hosts.

NI_NUMERICHOST

The numeric form of the node's address is returned instead of its name.

NI_NAMEREQD

Return an error if the node's name cannot be located in the database.

NI_NUMERICSERV

The numeric form of the service address is returned instead of its name.

NI_NUMERICSCOPE

For IPv6 addresses, the numeric form of the scope identifier is returned instead of its name.

NI_DGRAM

Indicates that the service is a datagram service (SOCK_DGRAM).

Address Information Errors

The <netdb.h> header shall define the following symbolic constants for use as error values for getaddrinfo() and getnameinfo(). The values shall be suitable for use in #if preprocessing directives.

EAI_AGAIN

The name could not be resolved at this time. Future attempts may succeed.

EAI_BADFLAGS

The flags had an invalid value.

EAI_FAIL

A non-recoverable error occurred.

EAI_FAMILY

The address family was not recognized or the address length was invalid for the specified family.

EAI_MEMORY

There was a memory allocation failure.

EAI_NONAME

The name does not resolve for the supplied parameters.

NI_NAMEREQD is set and the host's name cannot be located, or both nodename and servname were null.

EAI_SERVICE

The service passed was not recognized for the specified socket type.

EAI_SOCKTYPE

The intended socket type was not recognized.

EAI_SYSTEM

A system error occurred. The error code can be found in errno.

EAI_OVERFLOW

An argument buffer overflowed.

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

void              endhostent(void);
void              endnetent(void);
void              endprotoent(void);
void              endservent(void);
void              freeaddrinfo(struct addrinfo *);
const char       *gai_strerror(int);
int               getaddrinfo(const char *restrict, const char *restrict,
                      const struct addrinfo *restrict,
                      struct addrinfo **restrict);
struct hostent   *gethostent(void);
int               getnameinfo(const struct sockaddr *restrict, socklen_t,
                      char *restrict, socklen_t, char *restrict,
                      socklen_t, int);
struct netent    *getnetbyaddr(uint32_t, int);
struct netent    *getnetbyname(const char *);
struct netent    *getnetent(void);
struct protoent  *getprotobyname(const char *);
struct protoent  *getprotobynumber(int);
struct protoent  *getprotoent(void);
struct servent   *getservbyname(const char *, const char *);
struct servent   *getservbyport(int, const char *);
struct servent   *getservent(void);
void              sethostent(int);
void              setnetent(int);
void              setprotoent(int);
void              setservent(int);

The <netdb.h> header shall define the socklen_t type through typedef, as described in <sys/socket.h>.

Inclusion of the <netdb.h> header may also make visible all symbols from <netinet/in.h>, <sys/socket.h>, and <inttypes.h>.

APPLICATION USAGE

The requirement that addrinfo does not include any additional members which have a floating-point type if an object of that type with an all-bits-zero representation does not have the value 0.0 is to allow initialization of an addrinfo hints structure (see XSH freeaddrinfo) using:

struct addrinfo hints;
memset(&hints, 0, sizeof hints);

as an alternative to the use of default initialization.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

<inttypes.h>, <netinet/in.h>, <sys/socket.h>

XSH bind, endhostent, endnetent, endprotoent, endservent, freeaddrinfo, gai_strerror, getnameinfo

CHANGE HISTORY

First released in Issue 6. Derived from the XNS, Issue 5.2 specification.

The Open Group Base Resolution bwg2001-009 is applied, which changes the return type for gai_strerror() from char * to const char *. This is for coordination with the IPnG Working Group.

IEEE Std 1003.1-2001/Cor 1-2002, item XBD/TC1/D6/11 is applied, adding a description of the NI_NUMERICSCOPE macro and correcting the getnameinfo() function prototype. These changes are for alignment with IPv6.

Issue 7

SD5-XBD-ERN-14 is applied, changing the description of the s_port member of the servent structure.

The obsolescent h_errno external integer, and the obsolescent gethostbyaddr() and gethostbyname() functions are removed, along with the HOST_NOT_FOUND, NO_DATA, NO_RECOVERY, and TRY_AGAIN macros.

This reference page is clarified with respect to macros and symbolic constants.

Issue 8

Austin Group Defect 940 is applied, requiring that the addrinfo structure does not include any additional members which have a floating-point type if an object of that type with an all-bits-zero representation does not have the value 0.0.

Austin Group Defect 1289 is applied, removing some redundant text from the DESCRIPTION.

Austin Group Defect 1327 is applied, changing "flags" to "ai_flags".