DER data object decoder in Solidity

[SmartLayer]

Produce the code represented in the ellipsis, which parses a data object.

pragma experimental ABIEncoderV2
struct Ticket {
  uint match;     // from 01 to 51
  uint class;     // club(0), lounge(1), silver(2), gold(3)
  uint admission; // how many people can enter
}

function decodeTicket(bytes der) internal view returns(Ticket) {
  [...]
}

function testDecoder() public view returns(bool) {
  bytes constant der = "0x30090201010a0101020101";
  Ticket ticket =  decodeTicket(bytes der);
  return ticket.match ==1 && ticket.class == 1 && ticket.admission == 01;
}

Testify that shows the bytes being correctly construted DER:

$ echo -n 30090201010a0101020101 | xxd -r -p | openssl asn1parse -inform DER -i
    0:d=0  hl=2 l=   9 cons: SEQUENCE          
    2:d=1  hl=2 l=   1 prim:  INTEGER           :01
    5:d=1  hl=2 l=   1 prim:  ENUMERATED        :01
    8:d=1  hl=2 l=   1 prim:  INTEGER           :01

This is the python3 code to generate the DER-encoded data:

from pyasn1.codec.der import decoder, encoder
from pyasn1.type.univ import Sequence, OctetString, ObjectIdentifier, Integer, Enumerated
from pyasn1.type.namedtype import NamedTypes, NamedType
from pyasn1.type.namedval import NamedValues

class Class(Enumerated):
    namedValues = NamedValues(
        ('The Club', 0), ('The Lounge', 1),
        ('Gold', 2), ('Silver', 3)
    )

class Ticket(Sequence):
   componentType = NamedTypes(
	NamedType('match', Integer()),
	NamedType('class', Class()),
	NamedType('admission',Integer())
   )

ticket = Ticket()
ticket['match'] = 1
ticket['class'] = 1
ticket['admission'] = 1
print(encoder.encode(ticket).hex())

As you may have noticed I made everything INTEGER to make the work easier to start. Can't avoid the ENUMERATED type though.

---

An earlier decoder written by James Brown is attached

DerDecode.sol.gz

with the following comments from him:

It has limitations in that any IA5 string decoded has to be 32 bytes or less, and it can only handle up to 40 translation objects. I can fix this in future.