module BatMarshal:sig..end
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.
typeextern_flags =Stdlib.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 : 'b BatInnerIO.output -> ?sharing:bool -> ?closures:bool -> 'a -> unitoutput out v writes the representation of v on chan.
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.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.)val to_bytes : 'a -> extern_flags list -> Stdlib.Bytes.tMarshal.to_bytes v flags returns a byte sequence containing
the representation of v.
The flags argument has the same meaning as for
Marshal.output.
val to_string : 'a -> extern_flags list -> stringSame as to_bytes but return the result as a string instead of
a byte sequence.
val to_buffer : Stdlib.Bytes.t -> int -> int -> 'a -> extern_flags list -> intMarshal.to_buffer buff ofs len v flags marshals the value v,
storing its byte representation in the sequence buff,
starting at index ofs, and writing at most
len bytes. It returns the number of bytes
actually written to the sequence. If the byte representation
of v does not fit in len characters, the exception Failure
is raised.
val input : BatInnerIO.input -> 'ainput 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_bytes : Stdlib.Bytes.t -> int -> 'aMarshal.from_bytes 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 byte sequence buff, starting at position ofs.
The byte sequence is not mutated.
val from_string : string -> int -> 'aSame as from_bytes but take a string as argument instead of a
byte sequence.
val header_size : intThe 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 bytes, of the header.
Marshal.data_size buff ofs is the size, in bytes,
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 bytes, 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 byte sequence, the program needs to read first
Marshal.header_size bytes into the sequence,
then determine the length of the remainder of the
representation using Marshal.data_size,
make sure the sequence is large enough to hold the remaining
data, then read it, and finally call Marshal.from_bytes
to unmarshal the value.
val data_size : Stdlib.Bytes.t -> int -> intSee Marshal.header_size.
val total_size : Stdlib.Bytes.t -> int -> intSee Marshal.header_size.
val to_channel : 'b BatInnerIO.output -> 'a -> extern_flags list -> unitBatMarshal.output insteadval from_channel : BatInnerIO.input -> 'aBatMarshal.input instead