beam_lib
provides an interface to files created by
the BEAM compiler ("BEAM files"). The format used, a variant of
"EA IFF 1985" Standard for Interchange Format Files, divides data
into chunks.
Chunk data can be returned as binaries or as compound terms. Compound terms are returned when chunks are referenced by names (atoms) rather than identifiers (strings). The names recognized and the corresponding identifiers are:
abstract_code ("Abst")
attributes ("Attr")
compile_info ("CInf")
exports ("ExpT")
labeled_exports ("ExpT")
imports ("ImpT")
indexed_imports ("ImpT")
locals ("LocT")
labeled_locals ("LocT")
atoms ("Atom")
The abstract code can be encrypted in order to keep the source code secret, but still be able to use tools such as Xref or Debugger. See compile(3) for how to encrypt the abstract code.
To enable tools to use the abstract code, the key must be made
available for beam_lib
. There are two ways to provide
the key:
1) Use the function
crypto_key_fun/1
to register a fun that will be called whenever beam_lib
needs to decrypt the abstract code.
2) Store the key in a text file named .erlang.crypt
located in either the current directory or the home directory for
the current user. beam_lib
will search for and read
the .erlang.crypt
file if no crypto fun has been
registered using crypto_key_fun/1
. If the file exists and
contains a key, beam_lib
will implicitly create a crypto
key fun and register it.
The .erlang.crypt
file should contain a single list.
The elements of the list should be tuples looking like this:
{debug_info, Mode, Module, Key}
Mode
is the type of key; currently, the only allowed
value is des3_cbc
. Module
is either an atom, in
which case Key
will only be used for the module
Module
, or []
, in which case Key
will be
used for all modules. Key
is a non-empty string.
The Key
in the first tuple where both Mode
and
Module
matches will be used.
Here is an example of an .erlang.crypt
file that returns
the same key for all modules:
[{debug_info, des3_cbc, [], "%>7}|pc/DM6Cga*68$Mw]L#&_Gejr]G^"}].
And here is a slightly more complicated example of an
.erlang.crypt
which provides one key for the module
t
, and another key for all other modules:
[{debug_info, des3_cbc, t, "My KEY"}, {debug_info, des3_cbc, [], "%>7}|pc/DM6Cga*68$Mw]L#&_Gejr]G^"}].
Do not use any of the keys in these examples. Use your own keys. |
beam() -> Module | Filename | binary() Module = atom() Filename = string() | atom()
Each of the functions described below accept either the module name, the filename, or a binary containing the beam module.
chunkdata() = {ChunkId, DataB} | {ChunkName, DataT} ChunkId = chunkid() DataB = binary() {ChunkName, DataT} = {abstract_code, AbstractCode} | {attributes, [{Attribute, [AttributeValue]}]} | {compile_info, [{InfoKey, [InfoValue]}]} | {exports, [{Function, Arity}]} | {labeled_exports, [{Function, Arity, Label}]} | {imports, [{Module, Function, Arity}]} | {indexed_imports, [{Index, Module, Function, Arity}]} | {locals, [{Function, Arity}]}]} | {labeled_locals, [{Function, Arity, Label}]}]} | {atoms, [{integer(), atom()}]} AbstractCode = {AbstVersion, Forms} | no_abstract_code AbstVersion = atom() Attribute = atom() AttributeValue = term() Module = Function = atom() Arity = int() Label = int()
It is not checked that the forms conform to the abstract format
indicated by AbstVersion
. no_abstract_code
means
that the "Abst"
chunk is present, but empty.
The list of attributes is sorted on Attribute
, and each
attribute name occurs once in the list. The attribute values
occur in the same order as in the file. The lists of functions
are also sorted.
chunkid() = "Abst" | "Attr" | "CInf" | "ExpT" | "ImpT" | "LocT" | "Atom" chunkname() = abstract_code | attributes | compile_info | exports | labeled_exports | imports | indexed_imports | locals | labeled_locals | atoms chunkref() = chunkname() | chunkid()
chunks(Beam, [ChunkRef]) ->
{ok, {Module, [ChunkData]}} | {error, beam_lib, Reason}
Types:
Beam = beam()
ChunkRef = chunkref()
Module = atom()
ChunkData = chunkdata()
Reason = {unknown_chunk, Filename, atom()}
| {key_missing_or_invalid, Filename,
abstract_code}
| Reason1 -- see info/1
Filename = string()
Reads chunk data for selected chunks refs. The order of the returned list of chunk data is determined by the order of the list of chunks references.
version(Beam) ->
{ok, {Module, [Version]}} | {error, beam_lib, Reason}
Types:
Beam = beam()
Module = atom()
Version = term()
Reason -- see chunks/2
Returns the module version(s). A version is defined by
the module attribute -vsn(Vsn)
. If this attribute is
not specified, the version defaults to the checksum of
the module. Note that if the version Vsn
is not a list,
it is made into one, that is {ok,{Module,[Vsn]}}
is
returned. If there are several -vsn
module attributes,
the result is the concatenated list of versions. Examples:
1> beam_lib:version(a). % -vsn(1). {ok,{a,[1]}} 2> beam_lib:version(b). % -vsn([1]). {ok,{b,[1]}} 3> beam_lib:version(c). % -vsn([1]). -vsn(2). {ok,{c,[1,2]}} 4> beam_lib:version(d). % no -vsn attribute {ok,{d,[275613208176997377698094100858909383631]}}
info(Beam) -> [{Item, Info}] | {error, beam_lib, Reason1}
Types:
Beam = beam()
Item, Info -- see below
Reason1 =
{chunk_too_big, Filename, ChunkId, ChunkSize, FileSize}
| {invalid_beam_file, Filename, Pos}
| {invalid_chunk, Filename, ChunkId}
| {missing_chunk, Filename, ChunkId}
| {not_a_beam_file, Filename}
| {file_error, Filename, Posix}
Filename = string()
ChunkId = chunkid()
ChunkSize = FileSize = int()
Pos = int()
Posix = posix() -- see file(3)
Returns a list containing some information about a BEAM file
as tuples {Item, Info}
:
{file, Filename} | {binary, Binary}
{module, Module}
{chunks, [{ChunkId, Pos, Size}]}
cmp(Beam1, Beam2) -> ok | {error, beam_lib, Reason}
Types:
Beam1 = Beam2 = beam()
Reason = {modules_different, Module1, Module2}
| {chunks_different, ChunkId}
| Reason1 -- see info/1
Module1 = Module2 = atom()
ChunkId = chunkid()
Compares the contents of two BEAM files. If the module names
are the same, and the chunks with the identifiers
"Code"
, "ExpT"
, "ImpT"
, "StrT"
,
and "Atom"
have the same contents in both files,
ok
is returned. Otherwise an error message is returned.
cmp_dirs(Dir1, Dir2) ->
{Only1, Only2, Different} | {error, beam_lib, Reason1}
Types:
Dir1 = Dir2 = string() | atom()
Different = [{Filename1, Filename2}]
Only1 = Only2 = [Filename]
Filename = Filename1 = Filename2 = string()
Reason1 -- see info/1
The cmp_dirs/2
function compares the BEAM files in
two directories. Only files with extension ".beam"
are
compared. BEAM files that exist in directory Dir1
(Dir2
) only are returned in Only1
(Only2
). BEAM files that exist on both directories but
are considered different by cmp/2
are returned as
pairs {Filename1
, Filename2
} where
Filename1
(Filename2
) exists in directory
Dir1
(Dir2
).
diff_dirs(Dir1, Dir2) -> ok | {error, beam_lib, Reason1}
Types:
Dir1 = Dir2 = string() | atom()
Reason1 -- see info/1
The diff_dirs/2
function compares the BEAM files in
two directories the way cmp_dirs/2
does, but names of
files that exist in only one directory or are different are
presented on standard output.
strip(Beam1) ->
{ok, {Module, Beam2}} | {error, beam_lib, Reason1}
Types:
Beam1 = Beam2 = beam()
Module = atom()
Reason1 -- see info/1
The strip/1
function removes all chunks from a BEAM
file except those needed by the loader. In particular,
the abstract code is removed.
strip_files(Files) ->
{ok, [{Module, Beam2}]} | {error, beam_lib, Reason1}
Types:
Files = [Beam1]
Beam1 = beam()
Module = atom()
Beam2 = beam()
Reason1 -- see info/1
The strip_files/1
function removes all chunks except
those needed by the loader from BEAM files. In particular,
the abstract code is removed. The returned list contains one
element for each given file name, in the same order as in
Files
.
strip_release(Dir) ->
{ok, [{Module, Filename]}} | {error, beam_lib, Reason1}
Types:
Dir = string() | atom()
Module = atom()
Filename = string()
Reason1 -- see info/1
The strip_release/1
function removes all chunks
except those needed by the loader from the BEAM files of a
release. Dir
should be the installation root
directory. For example, the current OTP release can be
stripped with the call
beam_lib:strip_release(code:root_dir())
.
Types:
Reason -- see other functions
Chars = [char() | Chars]
Given the error returned by any function in this module,
the function format_error
returns a descriptive string
of the error in English. For file errors, the function
file:format_error(Posix)
should be called.
crypto_key_fun(CryptoKeyFun) -> ok | {error, Reason}
Types:
CryptoKeyFun = fun() -- see below
Reason = badfun | exists | term()
The crypto_key_fun/1
function registers a unary fun
that will be called if beam_lib
needs to read an
abstract_code
chunk that has been encrypted. The fun
is held in a process that is started by the function.
If there already is a fun registered when attempting to
register a fun, {error, exists}
is returned.
The fun must handle the following arguments:
CryptoKeyFun(init)
: Called when the fun is
registered, in the process that holds the fun. Here
the crypto key fun can do any necessary initializations.
Allowed return values:ok
{ok, NewCryptoKeyFun}
-
NewCryptoKeyFun
will be registered instead of
CryptoKeyFun
.
{error, Term}
- the registration will be
aborted and crypto_key_fun/1
will return
{error, Term}
, where Term
can be any term.
CryptoKeyFun({debug_info, Mode, Module, Filename})
:
Called when the key is needed for module Module
in
the file Filename
. Mode
describes
the method of encryption; currently the only allowed
value is des3_cbc
.CryptoKeyFun(clear)
: Called just before the fun
is unregistered. Do any needed cleanup here. The return
value is not important, but will be passed back to
the caller of clear_crypto_key_fun/0
.clear_crypto_key_fun() -> {ok, Result}
Types:
Result = undefined | term()
Unregisters the crypto key fun and terminates the process
holding it, started by crypto_key_fun/1
.
The clear_crypto_key_fun/1
either returns
{ok, undefined}
if there was no crypto key fun
registered, or {ok, Term}
, where Term
is
the return value from CryptoKeyFun(clear)
, see
crypto_key_fun/1
.