libc/net/getservent.3

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.\"     From: @(#)getservent.3	8.3 (Berkeley) 1/12/94
.\" $FreeBSD: src/lib/libc/net/getservent.3,v 1.15 2007/01/09 00:28:02 imp Exp $
.\"
.Dd May 4, 2019
.Dt GETSERVENT 3
.Os
.Sh NAME
.Nm getservent ,
.Nm getservent_r ,
.Nm getservbyport ,
.Nm getservbyport_r ,
.Nm getservbyname ,
.Nm getservbyname_r ,
.Nm setservent ,
.Nm endservent
.Nd get service entry
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In netdb.h
.Ft struct servent *
.Fn getservent void
.Ft int
.Fn getservent_r "struct servent *" "char *" "size_t" "struct servent **"
.Ft struct servent *
.Fn getservbyname "const char *name" "const char *proto"
.Ft int
.Fn getservbyname_r "const char *" "const char *" "struct servent *" "char *" "size_t" "struct servent **"
.Ft struct servent *
.Fn getservbyport "int port" "const char *proto"
.Ft int
.Fn getservbyport_r "int" "const char *" "struct servent *" "char *" "size_t" "struct servent **"
.Ft void
.Fn setservent "int stayopen"
.Ft void
.Fn endservent void
.Sh DESCRIPTION
The
.Fn getservent ,
.Fn getservbyname ,
and
.Fn getservbyport
functions
each return a pointer to an object with the
following structure
containing the broken-out
fields of a line in the network services data base,
.Pa /etc/services .
.Bd -literal -offset indent
struct	servent {
	char	*s_name;	/* official name of service */
	char	**s_aliases;	/* alias list */
	int	s_port;		/* port service resides at */
	char	*s_proto;	/* protocol to use */
};
.Ed
.Pp
The members of this structure are:
.Bl -tag -width s_aliases
.It Fa s_name
The official name of the service.
.It Fa s_aliases
A zero terminated list of alternate names for the service.
.It Fa s_port
The port number at which the service resides.
Port numbers are returned in network byte order.
.It Fa s_proto
The name of the protocol to use when contacting the
service.
.El
.Pp
The
.Fn getservent
function
reads the next line of the file, opening the file if necessary.
.Pp
The
.Fn setservent
function
opens and rewinds the file.
If the
.Fa stayopen
flag is non-zero,
the net data base will not be closed after each call to
.Fn getservbyname
or
.Fn getservbyport .
.Pp
The
.Fn endservent
function
closes the file.
.Pp
The
.Fn getservbyname
and
.Fn getservbyport
functions
sequentially search from the beginning
of the file until a matching
protocol name or
port number (which must be specified in
network byte order) is found,
or until
.Dv EOF
is encountered.
If a protocol name is also supplied (non-
.Dv NULL ) ,
searches must also match the protocol.
.Pp
The
.Fn getservent_r ,
.Fn getservbyport_r ,
and
.Fn getservbyname_r
functions are reentrant versions of the above functions that take a
pointer to a
.Fa servent
structure which is used to store state information.
The structure must be zero-filled before it is used
and should be considered opaque for the sake of portability.
These functions also take a pointer to another
.Fa servent
structure which is used to store the results of the database lookup.
.Sh RETURN VALUES
The
.Fn getservent ,
.Fn getservbyport ,
and
.Fn getservbyname
functions return a pointer to a
.Vt servent
structure on success or a null pointer if end-of-file
is reached or an error occurs.
.Pp
The
.Fn getservent_r ,
.Fn getservbyport_r ,
and
.Fn getservbyname_r
functions return 0 on success or \-1 if end-of-file
is reached or an error occurs.
.Sh FILES
.Bl -tag -width ".Pa /etc/services" -compact
.It Pa /etc/services
.El
.Sh SEE ALSO
.Xr getprotoent 3 ,
.Xr services 5
.Sh STANDARDS
The
.Fn getservent ,
.Fn getservbyport ,
.Fn getservbyname ,
.Fn setservent ,
and
.Fn endservent
functions conform to
.St -p1003.1-2004 .
.Pp
The
.Fn getservent_r ,
.Fn getservbyport_r ,
and
.Fn getservbyname_r
functions are not currently standardized.
.Sh HISTORY
The
.Fn getservent ,
.Fn getservbyport ,
.Fn getservbyname ,
.Fn setservent ,
and
.Fn endservent
functions appeared in
.Bx 4.2 .
.Pp
The
.Fn getservent_r ,
.Fn getservbyport_r ,
and
.Fn getservbyname_r
functions appeared in
.Dx 2.1 .
.Sh BUGS
These functions use a thread-specific data storage;
if the data is needed for future use, it should be
copied before any subsequent calls overwrite it.
Expecting port numbers to fit in a 32 bit
quantity is probably naive.