module Xdr:External Data Representationsig
..end
XDR values must be formed according to an XDR type. Such types are usually written in a notation that is close to the C notation of structured types. There are some important details where XDR is better than C:
*t
is allowed, but means something
different, namely "t option" in O'Caml notation. struct *list {
int value;
next list;
}
is a list of integer values and equivalent to
type intlist = intlist_el option
and intlist_el = { value : int; next : intlist }
This module defines:
A "type system" is a collection of several types that have names and that can refer to previously defined types (i.e. a sequence of "typedef"s). As with simple types, there is an extensive and an opaque representation.
A typical way of using this module is to define an "XDR type term system"
by simply writing an O'Caml expression. After that, this system is validated
and you get the "type system". From now on, you can refer to the types
defined in the system by name and get the corresponding "XDR types".
Once you have an XDR type you can use it to pack or unpack an XDR value.
Terms that describe possible XDR types:
X_int
: integer (32 bit)X_uint
: unsigned integerX_hyper
: hyper (64 bit signed integer)X_uhyper
: unsigned hyperX_enum [x1,i1; ...]
: enum { x1 = i1, ... }
X_float
: float (32 bit fp number)X_double
: double (64 bit fp number)X_opaque_fixed n
: opaque[n]
X_opaque n
: opaque<n>
X_string n
: string<n>
X_array_fixed (t,n)
: t[n]
X_array (t,n)
: t<n>
X_struct [x1,t1;...]
: struct { t1 x1; ...}
X_union_over_int
([n1,t1;...], None)
: union switch(int) {case n1: t1; ...}
X_union_over_int
([n1,t1;...], Some t)
: union switch(int) {case n1: t1; ...; default t}
X_union_over_uint
([n1,t1;...], None)
: union switch(unsigned int) {case n1: t1; ...}
X_union_over_uint
([n1,t1;...], Some t)
: union switch(unsigned int)
{case n1: t1; ...; default t}
X_union_over_enum
(e, [n1,t1;...], None)
: union switch(e) {case n1:t1; ...}
where e is an enumeration typeX_union_over_enum
(e, [n1,t1;...], Some t)
: union switch(e) {case n1:t1; ...; default t}
where e is an enumeration typeX_void
: voidX_type
constructor is only useful for types interpreted relative to
a type system. Then it refers to a named type in this system.
The X_param
constructor includes a reference to an arbitrary type
which must only be given while packing or unpacking values.
(A "lazy" type reference.)
Example how to define a recursive type:
X_rec ("a", X_array ( X_struct ["value", X_int; "next", X_refer "a"], 1))
type
xdr_type_term =
| |
X_int |
| |
X_uint |
| |
X_hyper |
| |
X_uhyper |
| |
X_enum of |
| |
X_float |
| |
X_double |
| |
X_opaque_fixed of |
| |
X_opaque of |
| |
X_string of |
| |
X_array_fixed of |
| |
X_array of |
| |
X_struct of |
| |
X_union_over_int of |
| |
X_union_over_uint of |
| |
X_union_over_enum of |
| |
X_void |
| |
X_type of |
| |
X_param of |
| |
X_rec of |
| |
X_refer of |
type
xdr_type
xdr_type_term
. Note that it does not
contain X_type
constructors, i.e. is completely expanded.
It is allowed that an xdr_type
contains X_param
constructors (parameters).
The set of occurring parameters can be determined very quickly for an
xdr_type
.typexdr_type_term_system =
(string * xdr_type_term) list
n
must be defined
in the list before it can be used via X_type n
.
It is possible to use this module without the means of type
systems, but often code is more readable if types are defined
in an environment allowing bindings to names.type
xdr_type_system
val x_bool : xdr_type_term
xv_true
and xv_false
.val x_optional : xdr_type_term -> xdr_type_term
xv_none
and
xv_some v
.val x_opaque_max : xdr_type_term
val x_string_max : xdr_type_term
val x_array_max : xdr_type_term -> xdr_type_term
type
xdr_value =
| |
XV_int of |
|||
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XV_uint of |
|||
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XV_hyper of |
|||
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XV_uhyper of |
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XV_enum of |
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XV_float of |
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XV_double of |
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XV_opaque of |
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XV_string of |
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XV_array of |
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XV_struct of |
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XV_union_over_int of |
|||
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XV_union_over_uint of |
|||
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XV_union_over_enum of |
|||
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XV_void |
|||
| |
XV_enum_fast of |
(* | The integer is the _position_ in the X_enum list, sorted by
enum values (ascending). For example, if we have
X_enum [ "A", 4; "B", 2; "C", 6 ]
the element "B" has the position 0, because 2 is the lowest
number | *) |
| |
XV_struct_fast of |
(* | The array elements are in the same order as declared in X_struct | *) |
| |
XV_union_over_enum_fast of |
(* | The integer is the _position_ in the X_enum list. "position"
means the same as for XV_enum_fast | *) |
| |
XV_array_of_string_fast of |
(* | To be used with an X_array or X_array_fixed with an inner
type of X_string | *) |
val xv_true : xdr_value
val xv_false : xdr_value
x_bool
val xv_none : xdr_value
val xv_some : xdr_value -> xdr_value
x_optional
exception Dest_failure
val dest_xv_int : xdr_value -> Rtypes.int4
val dest_xv_uint : xdr_value -> Rtypes.uint4
val dest_xv_hyper : xdr_value -> Rtypes.int8
val dest_xv_uhyper : xdr_value -> Rtypes.uint8
val dest_xv_enum : xdr_value -> string
val dest_xv_enum_fast : xdr_value -> int
val dest_xv_float : xdr_value -> Rtypes.fp4
val dest_xv_double : xdr_value -> Rtypes.fp8
val dest_xv_opaque : xdr_value -> string
val dest_xv_string : xdr_value -> string
val dest_xv_array : xdr_value -> xdr_value array
val dest_xv_array_of_string_fast : xdr_value -> string array
val dest_xv_struct : xdr_value -> (string * xdr_value) list
val dest_xv_struct_fast : xdr_value -> xdr_value array
val dest_xv_union_over_int : xdr_value -> Rtypes.int4 * xdr_value
val dest_xv_union_over_uint : xdr_value -> Rtypes.uint4 * xdr_value
val dest_xv_union_over_enum : xdr_value -> string * xdr_value
val dest_xv_union_over_enum_fast : xdr_value -> int * xdr_value
val dest_xv_void : xdr_value -> unit
val map_xv_enum_fast : xdr_type -> xdr_value -> int32
XV_enum
and XV_enum_fast
val map_xv_struct_fast : xdr_type -> xdr_value -> xdr_value array
XV_struct
and XV_struct_fast
val map_xv_union_over_enum_fast : xdr_type -> xdr_value -> int * int32 * xdr_value
XV_union_over_enum
and XV_union_over_enum_fast
.
Returns the triple (k,i,x)
:k
: Position of the selected value in the T_enum
arrayi
: value of the enumx
: selected arm of the unionexception Xdr_format of string
exception Xdr_format_message_too_long of xdr_value
val validate_xdr_type : xdr_type_term -> xdr_type
val validate_xdr_type_system : xdr_type_term_system -> xdr_type_system
X_type
constructions are always resolvedval xdr_type_term : xdr_type -> xdr_type_term
val xdr_type_term_system : xdr_type_system -> xdr_type_term_system
expanded_xdr_type sys1 (X_type "xy")
extracts the type called "xy" defined in sys1.
Expansion removes all X_type constructions in a type term.val expanded_xdr_type : xdr_type_system -> xdr_type_term -> xdr_type
val expanded_xdr_type_term : xdr_type_term_system -> xdr_type_term -> xdr_type_term
val are_compatible : xdr_type -> xdr_type -> bool
val value_matches_type : xdr_value -> xdr_type -> (string * xdr_type) list -> bool
pack_xdr_value v t p print
: Serialize v into a string conforming to
the XDR standard where v matches t. In p the parameter instances are
given. All parameters must be given, the parameters must not contain
parameters themselves. The fourth argument, print, is a function
which is evaluated for the pieces of the resultant string. You can use
pack_xdr_value_as_string to get the whole string at once.
unpack_xdr_value s t p
: Unserialize a string to a value
matching t. If this operation fails you get an Xdr_format
exception explaining what the reason for the failure is.
Mostly the cause for failures is that t isn't the type
of the value.
Note that there are some implementation restrictions limiting
the number of elements in array, strings and opaque fields.
If you get such an error this normally still means that
the value is not of the expected type, because these limits
have no practical meaning (they are still higher than the
usable address space).
val pack_xdr_value : xdr_value ->
xdr_type -> (string * xdr_type) list -> (string -> unit) -> unit
val pack_xdr_value_as_string : ?rm:bool ->
xdr_value -> xdr_type -> (string * xdr_type) list -> string
val unpack_xdr_value : ?pos:int ->
?len:int ->
?fast:bool ->
?prefix:bool ->
string -> xdr_type -> (string * xdr_type) list -> xdr_value
val unpack_xdr_value_l : ?pos:int ->
?len:int ->
?fast:bool ->
?prefix:bool ->
string -> xdr_type -> (string * xdr_type) list -> xdr_value * int
fast
: whether to prefer the new "fast" values (default: false)
prefix
: whether it is ok that the string is longer than the message
(default: false)
The variant unpack_xdr_value_l
returns not only the decoded value,
but also the actual length in bytes.