Load values from ASN.1 Value Notation

[kliberty]

Is it possible to load values from a file that are written in the ASN.1 value notation? I'm working on an input deck for an application and am a fan of the ASN.1 syntax + validation.

With the schema

Prompt ::=  SEQUENCE {
    title       VisibleString    SIZE(1..100),
    message     SEQUENCE OF VisibleString    SIZE(1..7)
}

load a value from a text file into a native data structure

value Prompt ::= 
{
  title "My title",
  message 
  {
    "line 1",
    "line 2"
  }
}

[maxime-esa]

Yes you can have the values in a separate file and have it compiled with the grammar.

In practice:

• Put your grammar in a file (e.g mygrammar.asn) with an ASN.1 Module named, eg. MyGrammar:

  MyGrammar DEFINITIONS ::=
  BEGIN
  Prompt ::= ...
  END

• Use IA5String instead of VisibleString (which is not supported). ASN.1 comes with varieties of string types which are more or less similar. We chose to keep only IA5String for the sake of simplicity.

• Put bounds on your SEQUENCE OF, for instance

  message SEQUENCE (SIZE (1..10)) OF IA5String (SIZE (1..7))

• The file with the values must be a valid ASN.1 grammar, so it must start with:

  
  MyValues DEFINITIONS ::=
  BEGIN
  IMPORTS Prompt FROM MyGrammar
  
  value  Prompt ::= ....

END

* Then compile the two files together:

asn1.exe -Ada mygrammar.asn myvalues.asn

or if you target C/C++:

asn1.exe -c mygrammar.asn myvalues.asn

And you will get the source code:

const Prompt value = { .title = "Hello", .message = { .nCount = 2, .arr = { "line 1", "line 2"
} } };

[kliberty]

Thank you, I didn't actually know you could do that (still learning ASN.1). My original meaning was in a dynamic sense, so that users could provide input to an already built application.

[maxime-esa]

Ah, this is different, this is what is called GSER (Generic String Encoding Rules), a standard textual encoding which we do not have support for at the moment (in the sense that we do not generate parsers and encoders for it in the target language).