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"),
and atoms
("Atom").
The syntax of the compound term (ChunkData
) is as follows:
ChunkData = {ChunkId, binary()}
| {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()}]}
ChunkRef = ChunkId | ChunkName
ChunkName = abstract_code | attributes | compile_info
| exports | labeled_exports | imports | indexed_imports | locals
| labeled_locals | atoms
ChunkId = string()
AbstractCode = {AbstVersion, forms()}
| no_abstract_code
AbstVersion = atom()
Attribute = atom()
AttributeValue = term()
Module = Function = atom()
Arity = integer() >= 0
Label = integer() >= 0
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 on the file. The lists of
functions are also sorted. 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.
Each of the functions described below accept either a filename or a binary containing a beam module.
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 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.
Use the function crypto_key_fun/1
to register a fun that will be called whenever beam_lib
needs to
decrypt the abstract code.
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 define 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 list.
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. |
chunks(FileNameOrBinary, [ChunkRef]) ->
{ok, {Module, [ChunkData]}} | {error, Module, Reason}
Types:
FileNameOrBinary = string() | atom() | binary()
Reason = {unknown_chunk, FileName, atom()}
| {key_missing_or_invalid, FileName, abstract_code}
| - see info/1 -
The chunks/2
function reads chunk data for selected
chunks. The order of the returned list of chunk data is determined
by the order of the list of chunks references; if each
chunk data were replaced by the tag, the result would be the
given list.
version(FileNameOrBinary) ->
{ok, {Module, Version}} | {error, Module, Reason}
Types:
FileNameOrBinary = string() | atom() | binary()
Version = [term()]
Reason = - see chunks/2 -
The version/1
function returns the module version(s)
found in a BEAM file.
Types:
FileName = string() | atom()
FileNameOrBinary = FileName | binary()
SourceRef = {file, FileName} | {binary, binary()}
ChunkInfo = {ChunkId, StartPosition, Size}
StartPosition = integer() > 0
Size = integer() >= 0
Reason = {chunk_too_big, FileName, ChunkId, ChunkSize, FileSize}
| {invalid_beam_file, FileName, FilePosition}
| {invalid_chunk, FileName, ChunkId}
| {missing_chunk, FileName, ChunkId}
| {not_a_beam_file, FileName}
| {file_error, FileName, FileError}
The info/1
function extracts some information about
a BEAM file: the file name, the module name, and
for each chunk the identifier as well as the position and size
in bytes of the chunk data.
cmp(FileNameOrBinary, FileNameOrBinary) ->
ok | {error, Module, Reason}
Types:
FileName = string() | atom()
FileNameOrBinary = FileName | binary()
Reason = {modules_different, Module, Module}
| {chunks_different, ChunkId}
| - see info/1 -
The cmp/2
function 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(Directory1, Directory2) ->
{Only1, Only2, Different} | {error, Module, Reason}
Types:
Directory1 = Directory2 = string() | atom()
Different = [{FileName1, FileName2}]
Only1 = Only2 = [FileName]
FileName = FileName1 = FileName2 = string()
Reason = - 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
Directory1
(Directory2
) 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
Directory1
(Directory2
).
diff_dirs(Directory1, Directory2) ->
ok | {error, Module, Reason}
Types:
Directory1 = Directory2 = string() | atom()
Reason = - 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(FileNameOrBinary) ->
{ok, {Module, FileNameOrBinary}} | {error, Module, Reason}
Types:
FileName = string() | atom()
FileNameOrBinary = FileName | binary()
Reason = - 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. The module name found in the file
and the file name, possibly with the ".beam" extension
added, are returned.
strip_files(Files) ->
{ok, [{Module, FileNameOrBinary]}} | {error, Module, Reason}
Types:
Files = [FileNameOrBinary]
FileName = string() | atom()
FileNameOrBinary = FileName | binary()
Reason = - 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, ordered as the given
list. The list element is a pair of the module name found in
the file and the file name, the latter possibly with the
".beam" extension added.
strip_release(Directory) ->
{ok, [{Module, FileName]}} | {error, Module, Reason}
Types:
Directory = string() | atom()
FileName = string()
Reason = - see info/1 -
The strip_release/1
function removes all chunks
except those needed by the loader from the BEAM files of a
release. Directory
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())
. The returned
list contains module names and file names of stripped files.
format_error(Error) -> character_list()
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
format_error/1
in the file
module is called.
crypto_key_fun(CryptoKeyFun) ->
ok | {error, Reason}
Types:
CryptoKeyFun = fun()
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 will be held in a process that will be started
by crypto_key_fun/1
.)
If there already is a fun registered when attempting
to register a fun, {error,exists}
will be returned.
The fun will be called with one argument. The fun must be prepared to be called with the following arguments:
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
),
or {error,Reason}
(the registration will be aborted
and crypto_key_fun/1
will return {error,Reason}
,
where Reason
can be any term).
{debug_info, Mode, Module, Filename}
: Called
when the key is needed for module Module
in file Filename
.
Mode
describes the method of encryption; currently the
only allowed value is des3_cbc
.
The fun should return the key as list of characters or fail
if there is no key available.
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 that was 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 the crypto key fun called with
the argument clear
.