script: make "sig_and_empty" more generic, make htlc tx witness fns clearer.

For non-delayed HTLC success spends, we have a similar pattern ("<sig>
<preimage> <wscript>") so a we want to use the same function.

The other routines don't say "witness" in them, and should.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

bitcoin/script.c

@@ -422,14 +422,15 @@ bool is_p2wpkh(const u8 *script)
 	return true;
 }
 
-u8 **bitcoin_witness_sig_and_empty(const tal_t *ctx,
+u8 **bitcoin_witness_sig_and_element(const tal_t *ctx,
 				     const secp256k1_ecdsa_signature *sig,
+				     const void *elem, size_t elemsize,
 				     const u8 *witnessscript)
 {
 	u8 **witness = tal_arr(ctx, u8 *, 3);
 
 	witness[0] = stack_sig(witness, sig);
-	witness[1] = NULL;
+	witness[1] = tal_dup_arr(witness, u8, elem, elemsize, 0);
 	witness[2] = tal_dup_arr(witness, u8,
 				 witnessscript, tal_count(witnessscript), 0);
 
@@ -662,7 +663,7 @@ u8 *bitcoin_wscript_htlc_receive(const tal_t *ctx,
  *...
  *   * `txin[0]` witness stack: `0 <remotesig> <localsig>  <payment_preimage>` for HTLC-Success, `0 <remotesig> <localsig> 0` for HTLC-Timeout.
  */
-u8 **bitcoin_htlc_offer_spend_timeout(const tal_t *ctx,
+u8 **bitcoin_witness_htlc_timeout_tx(const tal_t *ctx,
 				     const secp256k1_ecdsa_signature *localsig,
 				     const secp256k1_ecdsa_signature *remotesig,
 				     const u8 *wscript)
@@ -678,7 +679,7 @@ u8 **bitcoin_htlc_offer_spend_timeout(const tal_t *ctx,
 	return witness;
 }
 
-u8 **bitcoin_htlc_receive_spend_preimage(const tal_t *ctx,
+u8 **bitcoin_witness_htlc_success_tx(const tal_t *ctx,
 				     const secp256k1_ecdsa_signature *localsig,
 				     const secp256k1_ecdsa_signature *remotesig,
 				     const struct preimage *preimage,
@@ -694,7 +695,6 @@ u8 **bitcoin_htlc_receive_spend_preimage(const tal_t *ctx,
 
 	return witness;
 }
-
 u8 *bitcoin_wscript_htlc_tx(const tal_t *ctx,
 			    u16 to_self_delay,
 			    const struct pubkey *revocation_pubkey,

bitcoin/script.h

@@ -66,9 +66,10 @@ u8 **bitcoin_witness_p2wpkh(const tal_t *ctx,
 			    const secp256k1_ecdsa_signature *sig,
 			    const struct pubkey *key);
 
-/* Create a witness which contains sig, an empty entry, and the witnessscript */
-u8 **bitcoin_witness_sig_and_empty(const tal_t *ctx,
+/* Create a witness which contains sig, another entry, and the witnessscript */
+u8 **bitcoin_witness_sig_and_element(const tal_t *ctx,
 				     const secp256k1_ecdsa_signature *sig,
+				     const void *elem, size_t elemsize,
 				     const u8 *witnessscript);
 
 /* BOLT #3 to-local output */
@@ -86,7 +87,7 @@ u8 *bitcoin_wscript_htlc_offer(const tal_t *ctx,
 			       const struct pubkey *remotekey,
 			       const struct sha256 *payment_hash,
 			       const struct pubkey *revocationkey);
-u8 **bitcoin_htlc_offer_spend_timeout(const tal_t *ctx,
+u8 **bitcoin_witness_htlc_timeout_tx(const tal_t *ctx,
 				     const secp256k1_ecdsa_signature *localsig,
 				     const secp256k1_ecdsa_signature *remotesig,
 				     const u8 *wscript);
@@ -96,7 +97,7 @@ u8 *bitcoin_wscript_htlc_receive(const tal_t *ctx,
 				 const struct pubkey *remotekey,
 				 const struct sha256 *payment_hash,
 				 const struct pubkey *revocationkey);
-u8 **bitcoin_htlc_receive_spend_preimage(const tal_t *ctx,
+u8 **bitcoin_witness_htlc_success_tx(const tal_t *ctx,
 				     const secp256k1_ecdsa_signature *localsig,
 				     const secp256k1_ecdsa_signature *remotesig,
 				     const struct preimage *preimage,

common/htlc_tx.c

@@ -109,7 +109,7 @@ void htlc_success_tx_add_witness(struct bitcoin_tx *htlc_success,
 					       &hash, revocationkey);
 
 	htlc_success->input[0].witness
-		= bitcoin_htlc_receive_spend_preimage(htlc_success->input,
+		= bitcoin_witness_htlc_success_tx(htlc_success->input,
 						  localsig, remotesig,
 						  payment_preimage,
 						  wscript);
@@ -150,7 +150,7 @@ void htlc_timeout_tx_add_witness(struct bitcoin_tx *htlc_timeout,
 						 payment_hash, revocationkey);
 
 	htlc_timeout->input[0].witness
-		= bitcoin_htlc_offer_spend_timeout(htlc_timeout->input,
+		= bitcoin_witness_htlc_timeout_tx(htlc_timeout->input,
 						  localsig, remotesig,
 						  wscript);
 	tal_free(wscript);

onchaind/onchain.c

@@ -659,8 +659,10 @@ static struct bitcoin_tx *tx_to_us(const tal_t *ctx,
 		tx->output[0].amount -= fee;
 
 	sign_tx_input(tx, 0, NULL, wscript, privkey, pubkey, &sig);
-	tx->input[0].witness = bitcoin_witness_sig_and_empty(tx->input,
-							     &sig, wscript);
+	tx->input[0].witness = bitcoin_witness_sig_and_element(tx->input,
+							       &sig,
+							       NULL, 0,
+							       wscript);
 	return tx;
 }
 
@@ -711,7 +713,7 @@ static void resolve_our_htlc_ourcommit(struct tracked_output *out,
 		      &keyset->self_payment_key, &localsig);
 
 	tx->input[0].witness
-		= bitcoin_htlc_offer_spend_timeout(tx->input,
+		= bitcoin_witness_htlc_timeout_tx(tx->input,
 						  &localsig,
 						  remotesig,
 						  wscript);