[Ericsson Utvecklings AB]

asn1ct

MODULE

asn1ct

MODULE SUMMARY

ASN.1 compiler and compile-time support functions

DESCRIPTION

The ASN.1 compiler takes an ASN.1 module as input and genarates a corresponding Erlang module which can encode and decode the datatypes 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]
Option = ber|per|ber_bin|per_bin|der|compact_bit_string|noobj| {outdir,Dir}|{i,IncludeDir}
Reason = term()

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 qoutation 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.hrl and SetOfFiles.asn1db.

Options is a list with some of the following available options:

ber | ber_bin | per | per_bin
The encoding rule to be used. EncodingRule is ber or per. If this option is omitted ber is the default. The per option means the aligned variant, the unaligned variant of PER is not supported in this version of the compiler. 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 ber and per options 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 list (mayby nested) with Erlang terms, including binaries. Note that the erlang virtual machine that will execute the generated code must be of version R7 or higher.
der
By this option the Distinguished Encoding Rule (DER) is chosed. DER is regarded as a specialized variant of the BER encoding rule, therefore the der option only makes sense when the ber or ber_bin option is used. This option sometimes adds sorting and value checks when encoding, which implies a slower encoding. The decoding rutines 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.
{i,IncludeDir}
Adds IncludeDir to the search-path for .asn1db files. The compiler tries to open a .asn1db file when a module imports definitions from another ASN.1 module. Several {i,IncludeDir} can be given.
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.
{out_dir,Dir}
Specifies the directory Dir where all generated files shall be placed. If omitted the files are placed in the current directory.

The compiler generates the following files:

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 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 occured.

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.

start(IncludePaths) -> ok | already_started

Types:

IncludePaths = [IncludeDirectory]
IncludeDirectory = string()

Starts the ASN.1 database server and initiates it with IncludePaths. IncludePaths is a list of directories where the data base server should search for .asn1db files when a new module should be loaded into the database.

stop() -> void

Stops the ASN.1 database server. The database server is only used by the compile-time functions.

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 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} = asn1:decode(Module,Type,Bytes). 

AUTHORS

Kenneth Lundin - support@erlang.ericsson.se

asn1 1.3.2
Copyright © 1991-2002 Ericsson Utvecklings AB