NAME

       Misc.Magic_number - no description

Module

       Module   Misc.Magic_number

Documentation

       Module Magic_number
        : sig end

       a  typical  magic  number  is "Caml1999I011"; it is formed of an alphanumeric prefix, here
       Caml1990I, followed by a version,  here  011.  The  prefix  identifies  the  kind  of  the
       versioned data: here the I indicates that it is the magic number for .cmi files.

       All  magic  numbers  have  the  same byte length, magic_length , and this is important for
       users as it gives them the number of bytes to read to obtain the byte sequence that should
       be a magic number. Typical user code will look like:
               let ic = open_in_bin path in
               let magic =
                 try really_input_string ic Magic_number.magic_length
                 with End_of_file -> ... in
               match Magic_number.parse magic with
               | Error parse_error -> ...
               | Ok info -> ...

       A  given  compiler  version expects one specific version for each kind of object file, and
       will fail if given an unsupported version. Because versions grow  monotonically,  you  can
       compare the parsed version with the expected "current version" for a kind, to tell whether
       the wrong-magic object file comes from the past or from the future.

       An example of code block that expects the "currently supported version" of a given kind of
       magic numbers, here Cmxa , is as follows:
               let ic = open_in_bin path in
               begin
                 try Magic_number.(expect_current Cmxa (get_info ic)) with
                 | Parse_error error -> ...
                 | Unexpected error -> ...
               end;
               ...

       Parse errors distinguish inputs that are Not_a_magic_number str , which are likely to come
       from the file being completely different, and Truncated str , raised by headers  that  are
       the (possibly empty) prefix of a valid magic number.

       Unexpected  errors correspond to valid magic numbers that are not the one expected, either
       because it corresponds to a different kind, or to a newer or older version.

       The helper functions explain_parse_error  and  explain_unexpected_error  will  generate  a
       textual explanation of each error, for use in error messages.

       type native_obj_config = {
        flambda : bool ;
        }

       native  object files have a format and magic number that depend on certain native-compiler
       configuration parameters. This configuration space is expressed by  the  native_obj_config
       type.

       val native_obj_config : native_obj_config

       the native object file configuration of the active/configured compiler.

       type version = int

       type kind =
        | Exec
        | Cmi
        | Cmo
        | Cma
        | Cmx of native_obj_config
        | Cmxa of native_obj_config
        | Cmxs
        | Cmt
        | Ast_impl
        | Ast_intf

       type info = {
        kind : kind ;
        version  :  version ;  (* Note: some versions of the compiler use the same version suffix
       for all kinds, but others use different versions counters for different kinds. We may only
       assume  that  versions  are  growing monotonically (not necessarily always by one) between
       compiler versions.
        *)
        }

       type raw = string

       the type of raw magic numbers, such as "Caml1999A027" for the .cma files of OCaml 4.10

   Parsing magic numbers
       type parse_error =
        | Truncated of string
        | Not_a_magic_number of string

       val explain_parse_error : kind option -> parse_error -> string

       Produces an explanation for a parse error. If no kind is provided, we  use  an  unspecific
       formulation suggesting that any compiler-produced object file would have been satisfying.

       val parse : raw -> (info, parse_error) result

       Parses a raw magic number

       val read_info : in_channel -> (info, parse_error) result

       Read a raw magic number from an input channel.

       If  the  data read str is not a valid magic number, it can be recovered from the Truncated
       str | Not_a_magic_number str payload of the Error parse_error case.

       If parsing succeeds with an Ok info result, we know that exactly magic_length  bytes  have
       been consumed from the input_channel.

       If  you  also  wish  to  enforce  that  the  magic  number  is at the current version, see
       Misc.Magic_number.read_current_info below.

       val magic_length : int

       all magic numbers take the same number of bytes

   Checking that magic numbers are current
       type 'a unexpected = {
        expected : 'a ;
        actual : 'a ;
        }

       type unexpected_error =
        | Kind of kind unexpected
        | Version of kind * version unexpected

       val check_current : kind -> info -> (unit, unexpected_error) result

       check_current kind info checks that the provided magic info is the current version of kind
       's magic header.

       val explain_unexpected_error : unexpected_error -> string

       Provides an explanation of the unexpected_error .

       type error =
        | Parse_error of parse_error
        | Unexpected_error of unexpected_error

       val read_current_info : expected_kind:kind option -> in_channel -> (info, error) result

       Read  a  magic number as read_info , and check that it is the current version as its kind.
       If the expected_kind argument is None , any kind is accepted.

   Information on magic numbers
       val string_of_kind : kind -> string

       a user-printable string for a kind, eg. "exec" or "cmo", to use in error messages.

       val human_name_of_kind : kind -> string

       a user-meaningful name for a kind, eg. "executable file" or "bytecode object file", to use
       in error messages.

       val current_raw : kind -> raw

       the current magic number of each kind

       val current_version : kind -> version

       the current version of each kind

   Raw representations
       Mainly for internal usage and testing.

       type raw_kind = string

       the type of raw magic numbers kinds, such as "Caml1999A" for .cma files

       val parse_kind : raw_kind -> kind option

       parse a raw kind into a kind

       val raw_kind : kind -> raw_kind

       the current raw representation of a kind.

       In  some  cases  the  raw  representation of a kind has changed over compiler versions, so
       other files of the same kind may have different raw kinds.  Note that all currently  known
       cases are parsed correctly by parse_kind .

       val raw : info -> raw

       A valid raw representation of the magic number.

       Due  to  past  and future changes in the string representation of magic numbers, we cannot
       guarantee that the raw strings returned for past and future versions  actually  match  the
       expectations  of those compilers. The representation is accurate for current versions, and
       it is correctly parsed back into the desired version by the parsing functions above.