SEQUENCE or SET of CHOICE types

[stevenroose]

Consider this spec:

Fulfillment ::= CHOICE {
  preimageSha256   [0] PreimageFulfillment ,
  prefixSha256     [1] PrefixFulfillment,
  thresholdSha256  [2] ThresholdFulfillment,
  rsaSha256        [3] RsaSha256Fulfillment,
  ed25519Sha256    [4] Ed25519Sha512Fulfillment
}

ThresholdFulfillment ::= SEQUENCE {
  subfulfillments      SET OF Fulfillment,
  subconditions        SET OF Condition
}

So in order to get a SET, we need the set ASN1 tag on the struct field. But we must also indicate what Go types are possible for the Fulfillment interface.

However, with the following code, asn1 tries to match the CHOICE type (some struct that implements the Fulfillment interface) against the SubFulfillments field, which of course does not match the []Fulfillment type.

type FfThresholdSha256 struct {
	SubFulfillments []Fulfillment `asn1:"tag:0,explicit,set,choice:fulfillment"`
	SubConditions   []*Condition  `asn1:"tag:1,explicit,set,choice:condition"`
}

Thus, asn1 should recognize that when a choice it put on a SET or a SEQUENCE, it should match the elements inside the set or the sequence instead of that field itself.

The specific error you get is

invalid Go type '[]cryptoconditions.Fulfillment' for choice 'fulfillment'