asn1ct(3erl) Erlang Module Definition asn1ct(3erl)
NAME
asn1ct - ASN.1 compiler and compile-time support functions
DESCRIPTION
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).
EXPORTS
compile(Asn1module) -> ok | {error,Reason}
compile(Asn1module , Options) -> ok | {error,Reason}
Types 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 representa-
tion 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 SetOf-
Files.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. The per_bin option means the aligned variant. To
use the unaligned variant the uper_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 and per_bin options are equivalent with the OldOptions ber and per with the difference that the generated encod-
ing/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 the ber or ber_bin option. This option sometimes adds sorting and
value checks when encoding, which implies a slower encoding. The decoding routines are the same as for ber .
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 in Binary 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 and num2name_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 or ber_bin option. It gives time optimized code generated and it uses
another runtime module and in the per_bin case a linked-in driver. The result in the per_bin case from an encode when compiled
with this option will be a binary.
driver :
Option valid together with ber_bin and optimize options. It enables the use of a linked-in driver that gives considerable faster
decode. In ber_bin the driver is enabled only by explicit use of the option driver .
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 the igor module of syn-
tax_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}
Types 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 possi-
ble 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}
Types 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}
Types 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}
Types 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 ran-
dom 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).
Ericsson AB asn1 1.6.16 asn1ct(3erl)