wire: serialize the amounts for a bitcoin tx over the wire

we'll need this for calculating fees etc in onchaind

wire/fromwire.c

@@ -368,7 +368,24 @@ void derive_channel_id(struct channel_id *channel_id,
 struct bitcoin_tx *fromwire_bitcoin_tx(const tal_t *ctx,
 				       const u8 **cursor, size_t *max)
 {
-	return pull_bitcoin_tx(ctx, cursor, max);
+	struct bitcoin_tx *tx;
+	u16 input_amts_len;
+	size_t i;
+
+	tx = pull_bitcoin_tx(ctx, cursor, max);
+	input_amts_len = fromwire_u16(cursor, max);
+	/* We don't serialize the amounts if they're not *all* populated */
+	if (input_amts_len != tal_count(tx->input_amounts))
+		return tx;
+
+	for (i = 0; i < input_amts_len; i++) {
+		struct amount_sat sat;
+		sat = fromwire_amount_sat(cursor, max);
+		tx->input_amounts[i] =
+			tal_dup(tx, struct amount_sat, &sat);
+	}
+
+	return tx;
 }
 
 void fromwire_siphash_seed(const u8 **cursor, size_t *max,

wire/towire.c

@@ -226,8 +226,25 @@ void towire_wirestring(u8 **pptr, const char *str)
 
 void towire_bitcoin_tx(u8 **pptr, const struct bitcoin_tx *tx)
 {
+	size_t i;
 	u8 *lin = linearize_tx(tmpctx, tx);
 	towire_u8_array(pptr, lin, tal_count(lin));
+
+	/* We only want to 'save' the amounts if every amount
+	 * has been populated */
+	for (i = 0; i < tal_count(tx->input_amounts); i++) {
+		if (!tx->input_amounts[i]) {
+			towire_u16(pptr, 0);
+			return;
+		}
+	}
+
+	/* Otherwise, we include the input amount set */
+	towire_u16(pptr, tal_count(tx->input_amounts));
+	for (i = 0; i < tal_count(tx->input_amounts); i++) {
+		assert(tx->input_amounts[i]);
+		towire_amount_sat(pptr, *tx->input_amounts[i]);
+	}
 }
 
 void towire_siphash_seed(u8 **pptr, const struct siphash_seed *seed)