lnwallet: Add 2nd-stage htlc size constants and outgoing GenWitnessFunc

lnwallet/script_utils.go

@@ -809,6 +809,34 @@ func htlcSpendSuccess(signer Signer, signDesc *SignDescriptor,
 	return witnessStack, nil
 }
 
+// HtlcSpendSuccess exposes the public witness generation function for spending
+// an HTLC success transaction, either due to an expiring time lock or having
+// had the payment preimage.
+// NOTE: The caller MUST set the txn version, sequence number, and sign
+// descriptor's sig hash cache before invocation.
+func HtlcSpendSuccess(signer Signer, signDesc *SignDescriptor,
+	sweepTx *wire.MsgTx) (wire.TxWitness, error) {
+
+	// With the proper sequence an version set, we'll now sign the timeout
+	// transaction using the passed signed descriptor. In order to generate
+	// a valid signature, then signDesc should be using the base delay
+	// public key, and the proper single tweak bytes.
+	sweepSig, err := signer.SignOutputRaw(sweepTx, signDesc)
+	if err != nil {
+		return nil, err
+	}
+
+	// We set a zero as the first element the witness stack (ignoring the
+	// witness script), in order to force execution to the second portion
+	// of the if clause.
+	witnessStack := wire.TxWitness(make([][]byte, 3))
+	witnessStack[0] = append(sweepSig, byte(txscript.SigHashAll))
+	witnessStack[1] = nil
+	witnessStack[2] = signDesc.WitnessScript
+
+	return witnessStack, nil
+}
+
 // htlcTimeoutRevoke spends a second-level HTLC output. This function is to be
 // used by the sender or receiver of an HTLC to claim the HTLC after a revoked
 // commitment transaction was broadcast.

lnwallet/size.go

@@ -186,20 +186,29 @@ const (
 	// weight limits.
 	MaxHTLCNumber = 966
 
-	// ToLocalPenaltyScriptSize 83 bytes
+	// ToLocalScriptSize 83 bytes
 	//      - OP_IF: 1 byte
 	//              - OP_DATA: 1 byte (revocationkey length)
 	//              - revocationkey: 33 bytes
 	//              - OP_CHECKSIG: 1 byte
 	//      - OP_ELSE: 1 byte
 	//              - OP_DATA: 1 byte (localkey length)
-	//              - localkey: 33 bytes
+	//              - local_delay_key: 33 bytes
 	//              - OP_CHECKSIG_VERIFY: 1 byte
 	//              - OP_DATA: 1 byte (delay length)
 	//              - delay: 8 bytes
 	//              -OP_CHECKSEQUENCEVERIFY: 1 byte
 	//      - OP_ENDIF: 1 byte
-	ToLocalPenaltyScriptSize = 1 + 1 + 33 + 1 + 1 + 1 + 33 + 1 + 1 + 8 + 1 + 1
+	ToLocalScriptSize = 1 + 1 + 33 + 1 + 1 + 1 + 33 + 1 + 1 + 8 + 1 + 1
+
+	// ToLocalTimeoutWitnessSize x bytes
+	//     - number_of_witness_elements: 1 byte
+	//     - local_delay_sig_length: 1 byte
+	//     - local_delay_sig: 73 bytes
+	//     - zero_length: 1 byte
+	//     - witness_script_length: 1 byte
+	//     - witness_script (to_local_script)
+	ToLocalTimeoutWitnessSize = 1 + 1 + 73 + 1 + 1 + ToLocalScriptSize
 
 	// ToLocalPenaltyWitnessSize 160 bytes
 	//      - number_of_witness_elements: 1 byte
@@ -208,9 +217,9 @@ const (
 	//      - one_length: 1 byte
 	//      - witness_script_length: 1 byte
 	//      - witness_script (to_local_script)
-	ToLocalPenaltyWitnessSize = 1 + 1 + 73 + 1 + 1 + ToLocalPenaltyScriptSize
+	ToLocalPenaltyWitnessSize = 1 + 1 + 73 + 1 + 1 + ToLocalScriptSize
 
-	// AcceptedHtlcPenaltyScriptSize 139 bytes
+	// AcceptedHtlcScriptSize 139 bytes
 	//      - OP_DUP: 1 byte
 	//      - OP_HASH160: 1 byte
 	//      - OP_DATA: 1 byte (RIPEMD160(SHA256(revocationkey)) length)
@@ -245,9 +254,22 @@ const (
 	//                      - OP_CHECKSIG: 1 byte
 	//              - OP_ENDIF: 1 byte
 	//      - OP_ENDIF: 1 byte
-	AcceptedHtlcPenaltyScriptSize = 3*1 + 20 + 5*1 + 33 + 7*1 + 20 + 4*1 +
+	AcceptedHtlcScriptSize = 3*1 + 20 + 5*1 + 33 + 7*1 + 20 + 4*1 +
 		33 + 5*1 + 4 + 5*1
 
+	// AcceptedHtlcSuccessWitnessSize 325 bytes
+	//    - number_of_witness_elements: 1 byte
+	//    - nil_length: 1 byte
+	//    - sig_alice_length: 1 byte
+	//    - sig_alice: 73 bytes
+	//    - sig_bob_length: 1 byte
+	//    - sig_bob: 73 bytes
+	//    - preimage_length: 1 byte
+	//    - preimage: 32 bytes
+	//    - witness_script_length: 1 byte
+	//    - witness_script (accepted_htlc_script)
+	AcceptedHtlcSuccessWitnessSize = 1 + 1 + 73 + 1 + 73 + 1 + 32 + 1 + AcceptedHtlcScriptSize
+
 	// AcceptedHtlcPenaltyWitnessSize 249 bytes
 	//    - number_of_witness_elements: 1 byte
 	//    - revocation_sig_length: 1 byte
@@ -256,8 +278,7 @@ const (
 	//    - revocation_key: 33 bytes
 	//    - witness_script_length: 1 byte
 	//    - witness_script (accepted_htlc_script)
-	AcceptedHtlcPenaltyWitnessSize = 1 + 1 + 73 + 1 + 33 + 1 +
-		AcceptedHtlcPenaltyScriptSize
+	AcceptedHtlcPenaltyWitnessSize = 1 + 1 + 73 + 1 + 33 + 1 + AcceptedHtlcScriptSize
 
 	// OfferedHtlcScriptSize 133 bytes
 	//      - OP_DUP: 1 byte
@@ -303,6 +324,18 @@ const (
 	//    - witness_script (offered_htlc_script)
 	OfferedHtlcWitnessSize = 1 + 1 + 73 + 1 + 33 + 1 + OfferedHtlcScriptSize
 
+	// OfferedHtlcTimeoutWitnessSize 285 bytes
+	// - number_of_witness_elements: 1 byte
+	// - nil_length: 1 byte
+	// - sig_alice_length: 1 byte
+	// - sig_alice: 73 bytes
+	// - sig_bob_length: 1 byte
+	// - sig_bob: 73 bytes
+	// - nil_length: 1 byte
+	// - witness_script_length: 1 byte
+	// - witness_script (offered_htlc_script)
+	OfferedHtlcTimeoutWitnessSize = 1 + 1 + 1 + 73 + 1 + 73 + 1 + 1 + OfferedHtlcScriptSize
+
 	// OfferedHtlcPenaltyWitnessSize 243 bytes
 	//      - number_of_witness_elements: 1 byte
 	//      - revocation_sig_length: 1 byte

lnwallet/witnessgen.go

@@ -13,17 +13,18 @@ import (
 type WitnessType uint16
 
 const (
-	// CommitmentTimeLock is a witness that allows us to spend the output of a
-	// commitment transaction after a relative lock-time lockout.
+	// CommitmentTimeLock is a witness that allows us to spend the output of
+	// a commitment transaction after a relative lock-time lockout.
 	CommitmentTimeLock WitnessType = 0
 
-	// CommitmentNoDelay is a witness that allows us to spend a settled no-delay
-	// output immediately on a counterparty's commitment transaction.
+	// CommitmentNoDelay is a witness that allows us to spend a settled
+	// no-delay output immediately on a counterparty's commitment
+	// transaction.
 	CommitmentNoDelay WitnessType = 1
 
-	// CommitmentRevoke is a witness that allows us to sweep the settled output
-	// of a malicious counterparty's who broadcasts a revoked commitment
-	// transaction.
+	// CommitmentRevoke is a witness that allows us to sweep the settled
+	// output of a malicious counterparty's who broadcasts a revoked
+	// commitment transaction.
 	CommitmentRevoke WitnessType = 2
 
 	// HtlcOfferedRevoke is a witness that allows us to sweep an HTLC
@@ -33,6 +34,15 @@ const (
 	// HtlcAcceptedRevoke is a witness that allows us to sweep an HTLC
 	// output that we accepted from the counterparty.
 	HtlcAcceptedRevoke WitnessType = 4
+
+	// HtlcOfferedTimeout is a witness that allows us to sweep an HTLC
+	// output that we extended to a party, but was never fulfilled.
+	HtlcOfferedTimeout WitnessType = 5
+
+	// HtlcAcceptedSuccess is a witness that allows us to sweep an HTLC
+	// output that was offered to us, and for which we have a payment
+	// preimage.
+	HtlcAcceptedSuccess WitnessType = 6
 )
 
 // WitnessGenerator represents a function which is able to generate the final
@@ -64,6 +74,8 @@ func (wt WitnessType) GenWitnessFunc(signer Signer,
 			return ReceiverHtlcSpendRevoke(signer, desc, tx)
 		case HtlcAcceptedRevoke:
 			return SenderHtlcSpendRevoke(signer, desc, tx)
+		case HtlcOfferedTimeout:
+			return HtlcSpendSuccess(signer, desc, tx)
 		default:
 			return nil, fmt.Errorf("unknown witness type: %v", wt)
 		}