Keysend using gRPC lnrpc.Lightning.SendPayment fails if PaymentAddr is empty

[bjarnemagnussen]

Background

Using the lnrpc.Lightning.SendPayment gRPC fails with the error incorrect_payment_details if PaymentAddr in the SendRequest is empty using keysend.

Your environment

• version of lnd: 0.13.0

Steps to reproduce

Calling lnrpc.Lightning.SendPayment with e.g. the SendRequest used for a keysend:

{
  "dest": DestPubKey,
  "amt": Amount,
  "payment_hash": PayHash,
  "final_cltv_delta": 40,
  "dest_custom_records": {
    "5482373484": Preimage
  }
}

Expected behaviour

Keysend should be successful.

Actual behaviour

It seems that 46c9140 which fixed a nil-panic regarding not defining the PaymentAddr did not address the case that when it is not specified an empty bytearray is used instead of its nil value.

Hence

lnd/rpcserver.go

Line 4353 in f9a5188

copy(payIntent.paymentAddr[:], rpcPayReq.PaymentAddr)

copies per default the empty bytearray, which will later down in the function call cause an incorrect_payment_details as a correct Payment Address is expected.

[bjarnemagnussen]

I will take a closer look at it to find a fix for it.