(*
 * BatMarshal - Extended marshaling operations
 * Copyright (C) 1997 Xavier Leroy
 *               2008 David Teller
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version,
 * with the special exception on linking described in file LICENSE.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 *)


(** Marshaling of data structures.

    This module provides functions to encode arbitrary data structures
    as sequences of bytes, which can then be written on a file or
    sent over a pipe or network connection.  The bytes can then
    be read back later, possibly in another process, and decoded back
    into a data structure. The format for the byte sequences
    is compatible across all machines for a given version of OCaml.

    Warning: marshaling is currently not type-safe. The type
    of marshaled data is not transmitted along the value of the data,
    making it impossible to check that the data read back possesses the
    type expected by the context. In particular, the result type of
    the [Marshal.from_*] functions is given as ['a], but this is
    misleading: the returned OCaml value does not possess type ['a]
    for all ['a]; it has one, unique type which cannot be determined
    at compile-type.  The programmer should explicitly give the expected
    type of the returned value, using the following syntax:
    - [(Marshal.from_channel chan : type)].
    Anything can happen at run-time if the object in the file does not
    belong to the given type.

    The representation of marshaled values is not human-readable, and
    uses bytes that are not printable characters. Therefore, input and
    output channels used in conjunction with {!Marshal.output} and
    {!Marshal.input} must be opened in binary mode, using e.g.
    {!BatPervasives.open_out_bin} or
    {!BatPervasives.open_in_bin}; channels opened in text
    mode will cause unmarshaling errors on platforms where text
    channels behave differently than binary channels, e.g. Windows.

    @author Xavier Leroy (base module)
    @author David Teller
*)


type extern_flags = Marshal.extern_flags =
    No_sharing                          (** Don't preserve sharing *)
  | Closures                            (** Send function closures *)
  | Compat_32                           (** Ensure 32-bit compatibility *)
(** The flags to the [Marshal.to_*] functions below. *)


val output: _ BatInnerIO.output -> ?sharing:bool -> ?closures:bool -> 'a -> unit
(** [output out v] writes the representation of [v] on [chan].

    @param sharing If [true] (default value), circularities
    and sharing inside the value [v] are detected and preserved
    in the sequence of bytes produced. In particular, this
    guarantees that marshaling always terminates. Sharing
    between values marshaled by successive calls to
    [output] is not detected, though. If [false], sharing is ignored.
    This results in faster marshaling if [v] contains no shared
    substructures, but may cause slower marshaling and larger
    byte representations if [v] actually contains sharing,
    or even non-termination if [v] contains cycles.

    @param closures If [false] (default value) marshaling fails when
    it encounters a functional value inside [v]: only ``pure'' data
    structures, containing neither functions nor objects, can safely
    be transmitted between different programs. If [true], functional
    values will be marshaled as a position in the code of the
    program. In this case, the output of marshaling can only be read
    back in processes that run exactly the same program, with
    exactly the same compiled code. (This is checked at
    un-marshaling time, using an MD5 digest of the code transmitted
    along with the code position.) *)

external to_string :
  'a -> extern_flags list -> string = "caml_output_value_to_string"
(** [Marshal.to_string v flags] returns a string containing
    the representation of [v] as a sequence of bytes.
    The [flags] argument has the same meaning as for
    {!Marshal.to_channel}. *)

val to_buffer : string -> int -> int -> 'a -> extern_flags list -> int
(** [Marshal.to_buffer buff ofs len v flags] marshals the value [v],
    storing its byte representation in the string [buff],
    starting at character number [ofs], and writing at most
    [len] characters.  It returns the number of characters
    actually written to the string. If the byte representation
    of [v] does not fit in [len] characters, the exception [Failure]
    is raised. *)

val input : BatInnerIO.input -> 'a
(** [input inp] reads from [inp] the
    byte representation of a structured value, as produced by
    one of the [Marshal.to_*] functions, and reconstructs and
    returns the corresponding value.*)

val from_string : string -> int -> 'a
(** [Marshal.from_string buff ofs] unmarshals a structured value
    like {!Marshal.from_channel} does, except that the byte
    representation is not read from a channel, but taken from
    the string [buff], starting at position [ofs]. *)

val header_size : int
(** The bytes representing a marshaled value are composed of
    a fixed-size header and a variable-sized data part,
    whose size can be determined from the header.
    {!Marshal.header_size} is the size, in characters, of the header.
    {!Marshal.data_size}[ buff ofs] is the size, in characters,
    of the data part, assuming a valid header is stored in
    [buff] starting at position [ofs].
    Finally, {!Marshal.total_size}[ buff ofs] is the total size,
    in characters, of the marshaled value.
    Both {!Marshal.data_size} and {!Marshal.total_size} raise [Failure]
    if [buff], [ofs] does not contain a valid header.

    To read the byte representation of a marshaled value into
    a string buffer, the program needs to read first
    {!Marshal.header_size} characters into the buffer,
    then determine the length of the remainder of the
    representation using {!Marshal.data_size},
    make sure the buffer is large enough to hold the remaining
    data, then read it, and finally call {!Marshal.from_string}
    to unmarshal the value. *)

val data_size : string -> int -> int
(** See {!Marshal.header_size}.*)

val total_size : string -> int -> int
(** See {!Marshal.header_size}.*)

(** {6 Deprecated} *)

val to_channel : _ BatInnerIO.output -> 'a -> extern_flags list -> unit
(** @deprecated Use {!output} instead *)

val from_channel : BatInnerIO.input -> 'a
  (** @deprecated Use {!input} instead *)
