Official release 4.12.1
Module type
Class type
Library ocamlcommon
Module Misc . Magic_number
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 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.