asn1ct
ASN.1 compiler and compile-time support functions
The ASN.1 compiler takes an ASN.1 module as input and generates a corresponding Erlang module which can encode and decode the data-types specified. Alternatively the compiler takes a specification module (se below) specifying all input modules and generates one module with encode/decode functions. There are also some generic functions which can be used in during development of applications which handles ASN.1 data (encoded as BER or PER).
Functions
compile(Asn1module) -> ok | {error,Reason}
compile(Asn1module , Options) -> ok | {error,Reason}
Asn1module = atom() | string()
Options = [Option| OldOption]
Option = ber_bin | per_bin | uper_bin | der | compact_bit_string | noobj | {n2n,EnumTypeName} |{outdir,Dir} | {i,IncludeDir} | optimize | driver | asn1config | undec_rest | {inline,OutputName} | inline | {macro_name_prefix, Prefix} | {record_name_prefix, Prefix} | verbose
OldOption = ber | per
Reason = term()
Prefix = string()
Compiles the ASN.1 module Asn1module
and generates an
Erlang module Asn1module.erl
with encode and decode
functions for the types defined in Asn1module
. For each
ASN.1 value defined in the module an Erlang function which
returns the value in Erlang representation is generated.
If Asn1module
is a filename without extension first
".asn1"
is assumed, then ".asn"
and finally
".py"
(to be compatible with the old ASN.1 compiler).
Of course Asn1module
can be a full pathname (relative or
absolute) including filename with (or without) extension.
If one wishes to compile a set of Asn1 modules into one
Erlang file with encode/decode functions one has to list all
involved files in a configuration file. This configuration
file must have a double extension ".set.asn", (".asn" can
alternatively be ".asn1" or ".py"). The input files' names
must be listed, within quotation marks (""), one at each row
in the file. If the input files are File1.asn
,
File2.asn
and File3.asn
the configuration file
shall look like:
File1.asn File2.asn File3.asn
The output files will in this case get their names from the
configuration file. If the configuration file has the name
SetOfFiles.set.asn
the name of the output files will be
SetOfFiles.hrl, SetOfFiles.erl and SetOfFiles.asn1db
.
Sometimes in a system of ASN.1 modules there are different default tag modes, e.g. AUTOMATIC, IMPLICIT or EXPLICIT. The multi file compilation resolves the default tagging as if the modules were compiled separately.
Another unwanted effect that may occur in multi file compilation is name collisions. The compiler solves this problem in two ways: If the definitions are identical then the output module keeps only one definition with the original name. But if definitions only have same name and differs in the definition, then they will be renamed. The new names will be the definition name and the original module name concatenated.
If any name collision have occurred the compiler reports a "NOTICE: ..." message that tells if a definition was renamed, and the new name that must be used to encode/decode data.
Options
is a list with options specific for the asn1
compiler and options that are applied to the Erlang compiler.
The latter are those that not is recognized as asn1 specific.
For preferred option use see Preferred Option Use
section in users guide. Available options are:
ber | ber_bin | per | per_bin | uper_bin
-
The encoding rule to be used. The supported encoding rules are BER (Basic Encoding Rules), PER aligned (Packed Encoding Rules) and PER unaligned. If the encoding rule option is omitted
ber
is the default. Theper_bin
option means the aligned variant. To use the unaligned variant theuper_bin
option has to be used.The generated Erlang module always gets the same name as the ASN.1 module and as a consequence of this only one encoding rule per ASN.1 module can be used at runtime.
The
ber_bin
andper_bin
options are equivalent with theOldOptions
ber
andper
with the difference that the generated encoding/decoding functions take advantage of the bit syntax, which in most cases increases the performance considerably. The result from encoding is a binary or an iolist. der
-
By this option the Distinguished Encoding Rules (DER) is chosen. DER is regarded as a specialized variant of the BER encoding rule, therefore the
der
option only makes sense together with theber
orber_bin
option. This option sometimes adds sorting and value checks when encoding, which implies a slower encoding. The decoding routines are the same as forber
. compact_bit_string
-
Makes it possible to use a compact notation for values of the BIT STRING type in Erlang. The notation:
BitString = {Unused,Binary}, Unused = integer(), Binary = binary()
Unused
must be a number in the range 0 to 7. It tells how many bits in the least significant byte inBinary
that is unused. For details see BIT STRING type section in users guide . {n2n,EnumTypeName}
-
Tells the compiler to generate functions for conversion between names (as atoms) and numbers and vice versa for the EnumTypeName specified. There can be multiple occurrences of this option in order to specify several type names. The type names must be declared as ENUMERATIONS in the ASN.1 spec. If the EnumTypeName does not exist in the ASN.1 spec the compilation will stop with an error code. The generated conversion functions are named
name2num_EnumTypeName/1
andnum2name_EnumTypeName/1
. noobj
-
Do not compile (i.e do not produce object code) the generated
.erl
file. If this option is omitted the generated Erlang module will be compiled. {i,IncludeDir}
-
Adds
IncludeDir
to the search-path for.asn1db
and asn1 source files. The compiler tries to open a.asn1db
file when a module imports definitions from another ASN.1 module. If no.asn1db
file is found the asn1 source file is parsed. Several{i,IncludeDir}
can be given. {outdir,Dir}
-
Specifies the directory
Dir
where all generated files shall be placed. If omitted the files are placed in the current directory. optimize
-
This option is only valid together with one of the
per_bin
orber_bin
option. It gives time optimized code generated and it uses another runtime module and in theper_bin
case a linked-in driver. The result in theper_bin
case from an encode when compiled with this option will be a binary. driver
-
Option valid together with
ber_bin
andoptimize
options. It enables the use of a linked-in driver that gives considerable faster decode. Inber_bin
the driver is enabled only by explicit use of the optiondriver
. asn1config
-
When one of the specialized decodes, exclusive or selective decode, is wanted one has to give instructions in a configuration file. The option
asn1config
enables specialized decodes and takes the configuration file, which has the same name as the ASN.1 spec but with extension.asn1config
, in concern.The instructions for exclusive decode must follow the instruction and grammar in the User's Guide.
You can also find the instructions for selective decode in the User's Guide.
undec_rest
-
A buffer that holds a message, being decoded may also have some following bytes. Now it is possible to get those following bytes returned together with the decoded value. If an asn1 spec is compiled with this option a tuple
{ok,Value,Rest}
is returned.Rest
may be a list or a binary. Earlier versions of the compiler ignored those following bytes. {inline,OutputName}
-
Compiling with this option gives one output module containing all asn1 run-time functionality. The asn1 specs are provided in a target module Module.set.asn as described above. The name of the resulting module containing generated encode/decode functions and in-lined run-time functions will be
OutputName.erl
. The merging/in-lining of code is done by theigor
module ofsyntax_tools
. By default the functions generated from the first asn1 spec in the.set.asn
are exported, unless a{export,[atom()]}
or{export_all,true}
option are provided. The list of atoms are names of chosen asn1 specs from the.set.asn
file. inline
-
It is also possible to use the sole argument
inline
. It is as{inline,OutputName}
, but the output file gets the default name of the source.set.asn
file. {macro_name_prefix, Prefix}
-
All macro names generated by the compiler are prefixed with
Prefix
. This is useful when multiple protocols that contains macros with identical names are included in a single module. {record_name_prefix, Prefix}
-
All record names generated by the compiler are prefixed with
Prefix
. This is useful when multiple protocols that contains records with identical names are included in a single module. verbose
-
Causes more verbose information from the compiler describing what it is doing.
Any additional option that is applied will be passed to the final step when the generated .erl file is compiled.
The compiler generates the following files:
-
Asn1module.hrl
(if any SET or SEQUENCE is defined) -
Asn1module.erl
the Erlang module with encode, decode and value functions. -
Asn1module.asn1db
intermediate format used by the compiler when modules IMPORTS definitions from each other.
encode(Module,Type,Value)-> {ok,Bytes} | {error,Reason}
Module = Type = atom()
Value = term()
Bytes = [Int] when integer(Int), Int >= 0, Int =< 255
Reason = term()
Encodes Value
of Type
defined in the ASN.1 module
Module
. Returns a list of bytes if successful. To get as fast execution as
possible the
encode function only performs rudimentary tests that the input
Value
is a correct instance of Type
. The length of strings is for example
not always checked. Returns {ok,Bytes}
if successful or
{error,Reason}
if an error occurred.
decode(Module,Type,Bytes) -> {ok,Value}|{error,Reason}
Module = Type = atom()
Value = Reason = term()
Bytes = [Int] when integer(Int), Int >= 0, Int =< 255
Decodes Type
from Module
from the list of bytes
Bytes
. Returns {ok,Value}
if successful.
validate(Module,Type,Value) -> ok | {error,Reason}
Module = Type = atom()
Value = term()
Validates that Value
conforms to Type
from Module
. Not implemented in this version of the ASN.1 application.
value(Module ,Type) -> {ok,Value} | {error,Reason}
Module = Type = atom()
Value = term()
Reason = term()
Returns an Erlang term which is an example of a valid Erlang
representation of a value of the ASN.1 type Type
. The value
is a random value and subsequent calls to this function will for most
types return different values.
test(Module) -> ok | {error,Reason}
test(Module,Type) -> ok | {error,Reason}
test(Module,Type,Value) -> ok | {error,Reason}
Performs a test of encode and decode of all types in Module
.
The generated functions are called by this function.
This function is useful during test to secure that the generated
encode and decode functions and the general runtime support work
as expected.
test/1
iterates over all types in Module
.
test/2
tests type Type
with a random value.
test/3 tests type <c>Type
with Value
.
Schematically the following happens for each type in the module.
{ok,Value} = asn1ct:value(Module,Type), {ok,Bytes} = asn1ct:encode(Module,Type,Value), {ok,Value} = asn1ct:decode(Module,Type,Bytes).