bitcoin/tx: implement wally_tx_clone (badly) for now.

When libwally exposes it, we can use theirs.

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

bitcoin/tx.c

@@ -17,6 +17,21 @@
 
 #define SEGREGATED_WITNESS_FLAG 0x1
 
+/* FIXME: When wally exposes this, we will clash and can remove this one */
+int wally_tx_clone(struct wally_tx *tx, struct wally_tx **output)
+{
+	u8 *txlin = linearize_wtx(NULL, tx);
+	int flags = WALLY_TX_FLAG_USE_WITNESS;
+	int ret;
+
+	if (chainparams->is_elements)
+		flags |= WALLY_TX_FLAG_USE_ELEMENTS;
+
+	ret = wally_tx_from_bytes(txlin, tal_bytelen(txlin), flags, output);
+	tal_free(txlin);
+	return ret;
+}
+
 int bitcoin_tx_add_output(struct bitcoin_tx *tx, const u8 *script,
 			  u8 *wscript, struct amount_sat amount)
 {

bitcoin/tx.h

@@ -217,4 +217,6 @@ void towire_bitcoin_tx_output(u8 **pptr, const struct bitcoin_tx_output *output)
  * Get the base64 string encoded PSBT of a bitcoin transaction.
  */
 char *bitcoin_tx_to_psbt_base64(const tal_t *ctx, struct bitcoin_tx *tx);
+
+int wally_tx_clone(struct wally_tx *tx, struct wally_tx **output);
 #endif /* LIGHTNING_BITCOIN_TX_H */