wally: Add accessor methods for script and amount

These are handled internally in the `wally_tx` and do not conform to our usual
tallocated strings that can by inspected using `tal_bytelen`, and we don't
really want to litter our code with whitelisting comments for the
`amount_sat.satoshis` access, so these just do read-only on the fly conversions.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

bitcoin/tx.c

@@ -93,6 +93,27 @@ void bitcoin_tx_output_set_amount(struct bitcoin_tx *tx, int outnum,
 	tx->wtx->outputs[outnum].satoshi = amount->satoshis; /* Raw: low-level helper */
 }
 
+const u8 *bitcoin_tx_output_get_script(const tal_t *ctx,
+				       const struct bitcoin_tx *tx, int outnum)
+{
+	const struct wally_tx_output *output;
+	u8 *res;
+	assert(outnum < tx->wtx->num_outputs);
+	output = &tx->wtx->outputs[outnum];
+	res = tal_arr(ctx, u8, output->script_len);
+	memcpy(res, output->script, output->script_len);
+	return res;
+}
+
+struct amount_sat bitcoin_tx_output_get_amount(const struct bitcoin_tx *tx,
+					       int outnum)
+{
+	struct amount_sat amount;
+	assert(outnum < tx->wtx->num_outputs);
+	amount.satoshis = tx->wtx->outputs[outnum].satoshi; /* Raw: helper */
+	return amount;
+}
+
 void bitcoin_tx_input_set_witness(struct bitcoin_tx *tx, int innum,
 				  u8 **witness)
 {
@@ -120,6 +141,29 @@ void bitcoin_tx_input_set_script(struct bitcoin_tx *tx, int innum, u8 *script)
 	wally_tx_set_input_script(tx->wtx, innum, script, tal_bytelen(script));
 }
 
+const u8 *bitcoin_tx_input_get_witness(const tal_t *ctx,
+				       const struct bitcoin_tx *tx, int innum,
+				       int witnum)
+{
+	const u8 *witness_item;
+	struct wally_tx_witness_item *item;
+	assert(innum < tx->wtx->num_inputs);
+	assert(witnum < tx->wtx->inputs[innum].witness->num_items);
+	item = &tx->wtx->inputs[innum].witness->items[witnum];
+	witness_item =
+	    tal_dup_arr(ctx, u8, item->witness, item->witness_len, 0);
+	return witness_item;
+}
+
+void bitcoin_tx_input_get_txid(const struct bitcoin_tx *tx, int innum,
+			       struct bitcoin_txid *out)
+{
+	assert(innum < tx->wtx->num_inputs);
+	assert(sizeof(struct bitcoin_txid) ==
+	       sizeof(tx->wtx->inputs[innum].txhash));
+	memcpy(out, tx->wtx->inputs[innum].txhash, sizeof(struct bitcoin_txid));
+}
+
 /* BIP 141:
  * It is followed by stack items, with each item starts with a var_int
  * to indicate the length. */

bitcoin/tx.h

@@ -95,6 +95,22 @@ int bitcoin_tx_add_input(struct bitcoin_tx *tx, const struct bitcoin_txid *txid,
 void bitcoin_tx_output_set_amount(struct bitcoin_tx *tx, int outnum,
 				  struct amount_sat *amount);
 
+/**
+ * Helper to get the script of a script's output as a tal_arr
+ *
+ * Internally we use a `wally_tx` to represent the transaction. 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 *bitcoin_tx_output_get_script(const tal_t *ctx, const struct bitcoin_tx *tx, int outnum);
+
+/**
+ * Helper to just get an amount_sat for the output amount.
+ */
+struct amount_sat bitcoin_tx_output_get_amount(const struct bitcoin_tx *tx,
+					       int outnum);
+
 /**
  * Set the input witness.
  *
@@ -109,6 +125,19 @@ void bitcoin_tx_input_set_witness(struct bitcoin_tx *tx, int innum,
  */
 void bitcoin_tx_input_set_script(struct bitcoin_tx *tx, int innum, u8 *script);
 
+/**
+ * Helper to get a witness as a tal_arr array.
+ */
+const u8 *bitcoin_tx_input_get_witness(const tal_t *ctx,
+				       const struct bitcoin_tx *tx, int innum,
+				       int witnum);
+
+/**
+ * Wrap the raw txhash in the wally_tx_input into a bitcoin_txid
+ */
+void bitcoin_tx_input_get_txid(const struct bitcoin_tx *tx, int innum,
+			       struct bitcoin_txid *out);
+
 /**
  * Check a transaction for consistency.
  *