wallet: Implement withdrawal transaction generation

This will be used by both the master daemon and the HSM to
generate (hopefully) identical transactions for signature and
broadcast.

lightningd/Makefile

@@ -55,7 +55,8 @@ LIGHTNINGD_LIB_SRC :=				\
 	lightningd/ping.c			\
 	lightningd/sphinx.c			\
 	lightningd/status.c			\
-	lightningd/utxo.c
+	lightningd/utxo.c			\
+	lightningd/withdraw_tx.c
 
 LIGHTNINGD_LIB_OBJS := $(LIGHTNINGD_LIB_SRC:.c=.o)
 LIGHTNINGD_LIB_HEADERS := $(LIGHTNINGD_LIB_SRC:.c=.h)

lightningd/withdraw_tx.c

@@ -0,0 +1,47 @@
+#include "withdraw_tx.h"
+#include <bitcoin/pubkey.h>
+#include <bitcoin/script.h>
+#include <ccan/ptrint/ptrint.h>
+#include <lightningd/key_derive.h>
+#include <lightningd/utxo.h>
+#include <permute_tx.h>
+#include <wally_bip32.h>
+
+struct bitcoin_tx *withdraw_tx(const tal_t *ctx,
+			       const struct utxo **utxos,
+			       const struct bitcoin_address *destination,
+			       const u64 withdraw_amount,
+			       const struct pubkey *changekey,
+			       const u64 changesat,
+			       const struct ext_key *bip32_base)
+{
+	u8 *script;
+	struct bitcoin_tx *tx =
+	    bitcoin_tx(ctx, tal_count(utxos), changekey ? 2 : 1);
+	for (size_t i = 0; i < tal_count(utxos); i++) {
+		tx->input[i].txid = utxos[i]->txid;
+		tx->input[i].index = utxos[i]->outnum;
+		tx->input[i].amount = tal_dup(tx, u64, &utxos[i]->amount);
+		if (utxos[i]->is_p2sh && bip32_base) {
+			struct pubkey key;
+			bip32_pubkey(bip32_base, &key, utxos[i]->keyindex);
+			tx->input[i].script =
+				bitcoin_scriptsig_p2sh_p2wpkh(tx, &key);
+		}
+	}
+	tx->output[0].amount = withdraw_amount;
+	script = scriptpubkey_p2pkh(ctx, destination);
+	tx->output[0].script = script;
+
+	if (changesat != 0) {
+		const void *map[2];
+		map[0] = int2ptr(0);
+		map[1] = int2ptr(1);
+		tx->output[1].script = scriptpubkey_p2wpkh(tx, changekey);
+		tx->output[1].amount = changesat;
+		permute_outputs(tx->output, tal_count(tx->output), map);
+	}
+	permute_inputs(tx->input, tal_count(tx->input), (const void **)utxos);
+	return tx;
+}
+

lightningd/withdraw_tx.h

@@ -0,0 +1,33 @@
+#ifndef LIGHTNING_LIGHTNINGD_WITHDRAW_TX_H
+#define LIGHTNING_LIGHTNINGD_WITHDRAW_TX_H
+#include "config.h"
+#include <ccan/short_types/short_types.h>
+#include <ccan/tal/tal.h>
+
+struct bitcoin_tx;
+struct ext_key;
+struct privkey;
+struct pubkey;
+struct bitcoin_address;
+struct utxo;
+
+/**
+ * withdraw_tx - Create a p2pkh withdrawal transaction
+ *
+ * @ctx: context to tal from.
+ * @utxos: (in/out) tal_arr of UTXO pointers to spend (permuted to match)
+ * @destination: (in) bitcoin_address to send to.
+ * @amount: (in) satoshis to send to the destination
+ * @changekey: (in) key to send change to (only used if change_satoshis != 0).
+ * @changesa: (in) amount to send as change.
+ * @bip32_base: (in) bip32 base for key derivation, or NULL.
+ */
+struct bitcoin_tx *withdraw_tx(const tal_t *ctx,
+			       const struct utxo **utxos,
+			       const struct bitcoin_address *destination,
+			       const u64 withdraw_amount,
+			       const struct pubkey *changekey,
+			       const u64 changesat,
+			       const struct ext_key *bip32_base);
+
+#endif /* LIGHTNING_LIGHTNINGD_WITHDRAW_TX_H */