tx: add helper for extracting script from a wally_tx

the bitcoin_tx version is basically a wrapper for the wally_tx script
extraction -- here we pull it apart so we can easily get a tal'd script
for a wally_tx_output

bitcoin/tx.c

@@ -265,22 +265,26 @@ void bitcoin_tx_output_set_amount(struct bitcoin_tx *tx, int outnum,
 	}
 }
 
-const u8 *bitcoin_tx_output_get_script(const tal_t *ctx,
-				       const struct bitcoin_tx *tx, int outnum)
+const u8 *wally_tx_output_get_script(const tal_t *ctx,
+				     const struct wally_tx_output *output)
 {
-	const struct wally_tx_output *output;
-	u8 *res;
-	assert(outnum < tx->wtx->num_outputs);
-	output = &tx->wtx->outputs[outnum];
-
 	if (output->script == NULL) {
 		/* This can happen for coinbase transactions and pegin
 		 * transactions */
 		return NULL;
 	}
 
-	res = tal_dup_arr(ctx, u8, output->script, output->script_len, 0);
-	return res;
+	return tal_dup_arr(ctx, u8, output->script, output->script_len, 0);
+}
+
+const u8 *bitcoin_tx_output_get_script(const tal_t *ctx,
+				       const struct bitcoin_tx *tx, int outnum)
+{
+	const struct wally_tx_output *output;
+	assert(outnum < tx->wtx->num_outputs);
+	output = &tx->wtx->outputs[outnum];
+
+	return wally_tx_output_get_script(ctx, output);
 }
 
 u8 *bitcoin_tx_output_get_witscript(const tal_t *ctx, const struct bitcoin_tx *tx,

bitcoin/tx.h

@@ -126,6 +126,15 @@ void bitcoin_tx_output_set_amount(struct bitcoin_tx *tx, int outnum,
  */
 const u8 *bitcoin_tx_output_get_script(const tal_t *ctx, const struct bitcoin_tx *tx, int outnum);
 
+/**
+ * Helper to get the script of a script's output as a tal_arr
+ *
+ * The script attached to a `wally_tx_output` is not a `tal_arr`, so in order to keep the
+ * comfort of being able to call `tal_bytelen` and similar on a script we just
+ * return a `tal_arr` clone of the original script.
+ */
+const u8 *wally_tx_output_get_script(const tal_t *ctx,
+				     const struct wally_tx_output *output);
 /**
  * Helper to get a witness script for an output.
  */