.\"	$OpenBSD: xdr.3,v 1.14 2003/02/18 07:47:00 jmc Exp $
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.Dd February 16, 1988
.Dt XDR 3
.Os
.Sh NAME
.Nm xdr_array ,
.Nm xdr_bool ,
.Nm xdr_bytes ,
.Nm xdr_char ,
.Nm xdr_destroy ,
.Nm xdr_double ,
.Nm xdr_enum ,
.Nm xdr_float ,
.Nm xdr_free ,
.Nm xdr_getpos ,
.Nm xdr_inline ,
.Nm xdr_int ,
.Nm xdr_long ,
.Nm xdrmem_create ,
.Nm xdr_opaque ,
.Nm xdr_pointer ,
.Nm xdrrec_create ,
.Nm xdrrec_endofrecord ,
.Nm xdrrec_eof ,
.Nm xdrrec_skiprecord ,
.Nm xdr_reference ,
.Nm xdr_setpos ,
.Nm xdr_short ,
.Nm xdrstdio_create ,
.Nm xdr_string ,
.Nm xdr_u_char ,
.Nm xdr_u_int ,
.Nm xdr_u_long ,
.Nm xdr_u_short ,
.Nm xdr_union ,
.Nm xdr_vector ,
.Nm xdr_void ,
.Nm xdr_wrapstring
.Nd library routines for external data representation
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <rpc/xdr.h>
.Ft int
.Fn xdr_array "XDR *xdrs" "char **arrp" "u_int *sizep" "u_int maxsize" "u_int elsize" "xdrproc_t elproc"
.Ft int
.Fn xdr_bool "XDR *xdrs" "bool_t *bp"
.Ft int
.Fn xdr_bytes "XDR *xdrs" "char **sp" "u_int *sizep" "u_int maxsize"
.Ft int
.Fn xdr_char "XDR *xdrs" "char *cp"
.Ft void
.Fn xdr_destroy "XDR *xdrs"
.Ft int
.Fn xdr_double "XDR *xdrs" "double *dp"
.Ft int
.Fn xdr_enum "XDR *xdrs" "enum_t *ep"
.Ft int
.Fn xdr_float "XDR *xdrs" "float *fp"
.Ft void
.Fn xdr_free "xdrproc_t proc" "char *objp"
.Ft u_int
.Fn xdr_getpos "XDR *xdrs"
.Ft long *
.Fn xdr_inline "XDR *xdrs" "int len"
.Ft int
.Fn xdr_int "XDR *xdrs" "int *ip"
.Ft int
.Fn xdr_long "XDR *xdrs" "long *lp"
.Ft void
.Fn xdrmem_create "XDR *xdrs" "char *addr" "u_int size" "enum xdr_op op"
.Ft int
.Fn xdr_opaque "XDR *xdrs" "char *cp" "u_int cnt"
.Ft int
.Fn xdr_pointer "XDR *xdrs" "char **objpp" "u_int objsize" "xdrproc_t xdrobj"
.Ft void
.Fn xdrrec_create "XDR *xdrs" "u_int sendsize" "u_int recvsize" "char *handle" "int (*readit)()" "int (*writeit)()"
.Ft int
.Fn xdrrec_endofrecord "XDR *xdrs" "int sendnow"
.Ft int
.Fn xdrrec_eof "XDR *xdrs" "int empty"
.Ft int
.Fn xdrrec_skiprecord "XDR *xdrs"
.Ft int
.Fn xdr_reference "XDR *xdrs" "char **pp" "u_int size" "xdrproc_t proc"
.Ft int
.Fn xdr_setpos "XDR *xdrs" "u_int pos"
.Ft int
.Fn xdr_short "XDR *xdrs" "short *sp"
.Ft void
.Fn xdrstdio_create "XDR *xdrs" "FILE *file" "enum xdr_op op"
.Ft int
.Fn xdr_string "XDR *xdrs" "char **sp" "u_int maxsize"
.Ft int
.Fn xdr_u_char "XDR *xdrs" "unsigned char *ucp"
.Ft int
.Fn xdr_u_int "XDR *xdrs" "unsigned int *up"
.Ft int
.Fn xdr_u_long "XDR *xdrs" "unsigned long *ulp"
.Ft int
.Fn xdr_u_short "XDR *xdrs" "unsigned short *usp"
.Ft int
.Fn xdr_union "XDR *xdrs" "int *dscmp" "char *unp" "struct xdr_discrim *choices" "bool_t (*defaultarm)()"
.Ft int
.Fn xdr_vector "XDR *xdrs" "char *arrp" "u_int size" "u_int elsize" "xdrproc_t elproc"
.Ft int
.Fn xdr_void "void"
.Ft int
.Fn xdr_wrapstring "XDR *xdrs" "char **sp"
.Sh DESCRIPTION
These routines allow C programmers to describe
arbitrary data structures in a machine-independent fashion.
Data for remote procedure calls are transmitted using these
routines.
.Pp
.Fn xdr_array
is a filter primitive that translates between variable-length arrays
and their corresponding external representations.
The parameter
.Fa arrp
is the address of the pointer to the array, while
.Fa sizep
is the address of the element count of the array;
this element count cannot exceed
.Fa maxsize .
The parameter
.Fa elsize
is the size of each of the array's elements, and
.Fa elproc
is an
.Tn XDR
filter that translates between
the array elements' C form, and their external
representation.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_bool
is a filter primitive that translates between booleans (C integers)
and their external representations.
When encoding data, this
filter produces values of either one or zero.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_bytes
is a filter primitive that translates between counted byte
strings and their external representations.
The parameter
.Fa sp
is the address of the string pointer.
The length of the string is located at address
.Fa sizep ;
strings cannot be longer than
.Fa maxsize .
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_char
is a filter primitive that translates between C characters
and their external representations.
This routine returns one if it succeeds, zero otherwise.
Note: encoded characters are not packed, and occupy 4 bytes each.
For arrays of characters, it is worthwhile to consider
.Fn xdr_bytes ,
.Fn xdr_opaque ,
or
.Fn xdr_string .
.Pp
.Fn xdr_destroy
is a macro that invokes the destroy routine associated with the
.Tn XDR
stream
.Fa xdrs .
Destruction usually involves freeing private data structures
associated with the stream.
Using
.Fa xdrs
after invoking
.Fn xdr_destroy
is undefined.
.Pp
.Fn xdr_double
is a filter primitive that translates between C
.Li double
precision numbers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_enum
is a filter primitive that translates between the C
.Li enum
type (actually an integer) and its external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_float
is a filter primitive that translates between the C
.Li float
type and its external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_free
is a generic freeing routine.
The first argument is the
.Tn XDR
routine for the object being freed.
The second argument
is a pointer to the object itself.
Note: the pointer passed to this routine is
.Fa not
freed, but what it points to is freed (recursively).
.Pp
.Fn xdr_getpos
is a macro that invokes the get-position routine associated with the
.Tn XDR
stream
.Fa xdrs .
The routine returns an unsigned integer,
which indicates the position of the
.Tn XDR
byte stream.
A desirable feature of
.Tn XDR
streams is that simple arithmetic works with this number,
although the
.Tn XDR
stream instances need not guarantee this.
.Pp
.Fn xdr_inline
is a macro that invokes the in-line routine associated with the
.Tn XDR
stream
.Fa xdrs .
The routine returns a pointer
to a contiguous piece of the stream's buffer;
.Fa len
is the byte length of the desired buffer.
Note: pointer is cast to
.Li long * .
Warning:
.Fn xdr_inline
may return
.Dv NULL
if it cannot allocate a contiguous piece of a buffer.
Therefore the behavior may vary among stream instances;
it exists for the sake of efficiency.
.Pp
.Fn xdr_int
is a filter primitive that translates between C integers
and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_long
is a filter primitive that translates between C
.Li long
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdrmem_create
is a routine which initializes the
.Tn XDR
stream object pointed to by
.Fa xdrs .
The stream's data is written to, or read from,
a chunk of memory at location
.Fa addr
whose length is no more than
.Fa size
bytes long.
The
.Fa op
determines the direction of the
.Tn XDR
stream
(either
.Dv XDR_ENCODE ,
.Dv XDR_DECODE ,
or
.Dv XDR_FREE Ns ).
.Pp
.Fn xdr_opaque
is a filter primitive that translates between fixed size opaque
data
and its external representation.
The parameter
.Fa cp
is the address of the opaque object, and
.Fa cnt
is its size in bytes.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_pointer
is like
.Fn xdr_reference
execpt that it serializes
.Dv NULL
pointers, whereas
.Fn xdr_reference
does not.
Thus,
.Fn xdr_pointer
can represent
recursive data structures, such as binary trees or
linked lists.
.Pp
.Fn xdrrec_create
is a routine which initializes the
.Tn XDR
stream object pointed to by
.Fa xdrs .
The stream's data is written to a buffer of size
.Fa sendsize ;
a value of zero indicates the system should use a suitable
default.
The stream's data is read from a buffer of size
.Fa recvsize ;
it too can be set to a suitable default by passing a zero
value.
When a stream's output buffer is full,
.Fn (*writeit)
is called.
Similarly, when a stream's input buffer is empty,
.Fn (*readit)
is called.
The behavior of these two routines is similar to the system calls
.Fn read
and
.Fn write ,
except that
.Fa handle
is passed to the former routines as the first parameter.
Note: the
.Tn XDR
stream's
.Fa op
field must be set by the caller.
Warning: this
.Tn XDR
stream implements an intermediate record stream.
Therefore there are additional bytes in the stream
to provide record boundary information.
.Pp
.Fn xdrrec_endofrecord
is a routine which can be invoked only on
streams created by
.Fn xdrrec_create .
The data in the output buffer is marked as a completed record,
and the output buffer is optionally written out if
.Fa sendnow
is non-zero.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdrrec_eof
is a routine which can be invoked only on
streams created by
.Fn xdrrec_create .
After consuming the rest of the current record in the stream,
this routine returns one if the stream has no more input,
zero otherwise.
.Pp
.Fn xdrrec_skiprecord
is a routine which can be invoked only on
streams created by
.Fn xdrrec_create .
It tells the
.Tn XDR
implementation that the rest of the current record
in the stream's input buffer should be discarded.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_reference
is a primitive that provides pointer chasing within structures.
The parameter
.Fa pp
is the address of the pointer;
.Fa size
is the size of the structure that
.Fa *pp
points to; and
.Fa proc
is an
.Tn XDR
procedure that filters the structure
between its C form and its external representation.
This routine returns one if it succeeds, zero otherwise.
Warning: this routine does not understand
.Dv NULL
pointers.
Use
.Fn xdr_pointer
instead.
.Pp
.Fn xdr_setpos
is a macro that invokes the set position routine associated with the
.Tn XDR
stream
.Fa xdrs .
The parameter
.Fa pos
is a position value obtained from
.Fn xdr_getpos .
This routine returns one if the
.Tn XDR
stream could be repositioned,
and zero otherwise.
Warning: it is difficult to reposition some types of
.Tn XDR
streams, so this routine may fail with one
type of stream and succeed with another.
.Pp
.Fn xdr_short
is a filter primitive that translates between C
.Li short
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdrstdio_create
is a routine which initializes the
.Tn XDR
stream object pointed to by
.Fa xdrs .
The
.Tn XDR
stream data is written to, or read from, the Standard I/O
stream
.Fa file .
The parameter
.Fa op
determines the direction of the
.Tn XDR
stream (either
.Dv XDR_ENCODE ,
.Dv XDR_DECODE ,
or
.Dv XDR_FREE Ns ).
Warning: the destroy routine associated with such
.Tn XDR
streams calls
.Fn fflush
on the
.Fa file
stream, but never
.Fn fclose .
.Pp
.Fn xdr_string
is a filter primitive that translates between C strings and their
corresponding external representations.
Strings cannot be longer than
.Fa maxsize .
Note:
.Fa sp
is the address of the string's pointer.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_u_char
is a filter primitive that translates between
.Li unsigned
C characters and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_u_int
is a filter primitive that translates between C
.Li unsigned
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_u_long
is a filter primitive that translates between C
.Li unsigned long
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_u_short
is a filter primitive that translates between C
.Li unsigned short
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_union
is a filter primitive that translates between a discriminated C
.Li union
and its corresponding external representation.
It first translates the discriminant of the union located at
.Fa dscmp .
This discriminant is always an
.Li enum_t .
Next the union located at
.Fa unp
is translated.
The parameter
.Fa choices
is a pointer to an array of
.Li struct xdr_discrim
structures.
Each structure contains an ordered pair of
.Ft [ value , proc ].
If the union's discriminant is equal to the associated
.Fa value ,
then the
.Fa proc
is called to translate the union.
The end of the
.Li struct xdr_discrim
structure array is denoted by a routine of value
.Dv NULL .
If the discriminant is not found in the
.Fa choices
array, then the
.Fn (*defaultarm)
procedure is called (if it is not
.Dv NULL Ns ).
Returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_vector
is a filter primitive that translates between fixed-length arrays
and their corresponding external representations.
The parameter
.Fa arrp
is the address of the pointer to the array, while
.Fa size
is the element count of the array.
The parameter
.Fa elsize
is the size of each of the array's elements, and
.Fa elproc
is an
.Tn XDR
filter that translates between the array elements' C form, and their
external representation.
This routine returns one if it succeeds, zero otherwise.
.Pp
.Fn xdr_void
is a routine which always returns one.
It may be passed to
.Tn RPC
routines that require a function parameter, but where nothing is to be done.
.Pp
.Fn xdr_wrapstring
is a primitive that calls
.Pa "xdr_string(xdrs, sp, MAXUN.UNSIGNED );"
where
.Tn MAXUN.UNSIGNED
is the maximum value of an unsigned integer.
.Fn xdr_wrapstring
is handy because the
.Tn RPC
package passes a maximum of two
.Tn XDR
routines as parameters, and
.Fn xdr_string ,
one of the most frequently used primitives, requires three.
Returns one if it succeeds, zero otherwise.
.Sh SEE ALSO
.Xr rpc 3
.Rs
.%T eXternal Data Representation Standard: Protocol Specification
.Re
.Rs
.%T eXternal Data Representation: Sun Technical Notes
.Re
.Rs
.%A "Sun Microsystems, Inc."
.%T "XDR: External Data Representation Standard"
.%R "RFC1014, USC-ISI"
.Re