Asn annotation based parser

A Jackson inspired annotation based parser for Asn.1 BER data. Decode or encode your POJOs with annotations.

Most of the Asn.1 parser I have seen online were either using their specific classes to decode data (i.e. AsnInteger instead of using regular java int or Integer) or they came with a generator which converted Asn specifications into obscure code riddled with their internals.

This parser allows selective encoding/decoding, meaning that you don’t have to read all Asn.1 fields into your data, but selectively choose which fields to decode.

For an example, take a look at the following specification:

FooProtocol DEFINITIONS ::= BEGIN

    FooQuestion ::= SEQUENCE {
        trackingNumber INTEGER,
        question       IA5String
    }

    FooAnswer ::= SEQUENCE {
        questionNumber INTEGER,
        answer         BOOLEAN
    }

END

If you map your POJO properly, you can only decode 'answer' without decoding 'question' if you are not interested in it.

Importing into your project

Maven

Add the JitPack repository into your pom.xml.

<repositories>
  <repository>
    <id>jitpack.io</id>
    <url>https://jitpack.io</url>
  </repository>
</repositories>

Add the following under your <dependencies>:

<dependencies>
  <dependency>
    <groupId>com.github.alturkovic</groupId>
    <artifactId>asn-parser</artifactId>
    <version>[insert latest version here]</version>
  </dependency>
</dependencies>

Example

This is an example of a complex POJO class using @AsnX annotations to decode BER data and @AsnPostProcessMethod("postDecode") to call a custom method to further configure a decoded object.

@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
@AsnPostProcessMethod("postDecode")
@AsnStructure(@AsnTag(value = 16, type = Type.PRIVATE))
public class Person {

    @AsnPrimitive
    private boolean male;

    @AsnPrimitive
    private Integer age;

    @AsnCollection(elementTag = @AsnTag(5), structured = false, asnConverter = HexStringConverter.class, type = String.class)
    private Set<String> phones;

    @AsnCollection(value = @AsnTag(1), type = Address.class)
    private List<Address> addresses;

    private boolean adult;

    public Person(final boolean male, final int age, final Set<String> phones) {
        this.male = male;
        this.age = age;
        this.phones = phones;
    }

    private void postDecode() {
        adult = age >= 18;
    }

    @Data
    @NoArgsConstructor
    @AllArgsConstructor
    public static class Address {

        @AsnPrimitive
        private String street;

        @AsnPrimitive
        private int number;

        @AsnPrimitive(@AsnTag(2))
        private boolean enabled;
    }
}

Example of BER data representing a possible Person object.

F0390101FF020118311085063859980690038506385998069002A11F300D040546697273740201018201FF300E04065365636F6E64020102820100

We can simply decode this data by calling Person person = asnDecoder.decode(Person.class, byteArrayInputStream);

What this parser does and does not support (at least currently)

Only BER rules are supported.

There is no code generation tool, you will need to map the POJOs manually.

This parser reads the data as it is without validations, meaning that if the TLV structure is valid, it will be decoded/encoded. There is (currently) no support for any validations, such as SIZE(0..100).

Possible improvements

• More implementations (DER, PER, XER, …​)

• JavaDoc and documentation improvements

• Class generator?

• Asn validations (i.e. SIZE)

Last notes

I am aware that the documentation is pretty bad, if there is any interest in this parser, let me know in the Issues and I will add better documentation if needed. For starters, please check the tests for basic usage examples.