tapfreighter: set type for burn/tombstone keys correctly

In order for burn/tombstone keys to be stored with the correct type, we need to
detect them before storing the transfer outputs to the database.
We can't set the script key type before, because we're carrying around
the script key in a virtual packet, where that information isn't
available.

Author: guggero

tapfreighter/chain_porter.go

@@ -1723,6 +1723,46 @@ func (p *ChainPorter) publishSubscriberEvent(event fn.Event) {
 	}
 }
 
+// detectUnSpendableKeys checks if the script key in the virtual output is a
+// burn or tombstone key and sets the appropriate type on the output script key.
+func detectUnSpendableKeys(vOut *tappsbt.VOutput) {
+	setScriptKeyType := func(vOut *tappsbt.VOutput,
+		scriptKeyType asset.ScriptKeyType) {
+
+		if vOut.Asset.ScriptKey.TweakedScriptKey == nil {
+			vOut.Asset.ScriptKey.TweakedScriptKey = new(
+				asset.TweakedScriptKey,
+			)
+			vOut.Asset.ScriptKey.RawKey.PubKey =
+				vOut.Asset.ScriptKey.PubKey
+		}
+		if vOut.ScriptKey.TweakedScriptKey == nil {
+			vOut.ScriptKey.TweakedScriptKey = new(
+				asset.TweakedScriptKey,
+			)
+			vOut.ScriptKey.RawKey.PubKey = vOut.ScriptKey.PubKey
+		}
+
+		vOut.Asset.ScriptKey.Type = scriptKeyType
+		vOut.ScriptKey.Type = scriptKeyType
+	}
+
+	if vOut.Asset == nil {
+		return
+	}
+
+	witness := vOut.Asset.PrevWitnesses
+	scriptKey := vOut.ScriptKey
+	if len(witness) > 0 && asset.IsBurnKey(scriptKey.PubKey, witness[0]) {
+		setScriptKeyType(vOut, asset.ScriptKeyBurn)
+	}
+
+	unSpendable, _ := scriptKey.IsUnSpendable()
+	if unSpendable {
+		setScriptKeyType(vOut, asset.ScriptKeyTombstone)
+	}
+}
+
 // A compile-time assertion to make sure ChainPorter satisfies the
 // fn.EventPublisher interface.
 var _ fn.EventPublisher[fn.Event, bool] = (*ChainPorter)(nil)

tapfreighter/parcel.go

@@ -589,6 +589,13 @@ func ConvertToTransfer(currentHeight uint32, activeTransfers []*tappsbt.VPacket,
 		vPkt := activeTransfers[pIdx]
 
 		for vPktOutputIdx := range vPkt.Outputs {
+			// Burn and tombstone keys are the only keys that we
+			// don't explicitly store in the DB before this point.
+			// But we'll want them to have the correct type when
+			// creating the transfer, as they'll be inserted into
+			// the DB, assigned to this transfer.
+			detectUnSpendableKeys(vPkt.Outputs[vPktOutputIdx])
+
 			tOut, err := transferOutput(
 				vPkt, vPktOutputIdx, outputPosition, anchorTx,
 				passiveAssets, isLocalKey,