wallet_get_newindex: encapsulate routine to get a new keyindex.

We'll want this for shutdown.

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

wallet/wallet.c

@@ -2,6 +2,7 @@
 
 #include <bitcoin/script.h>
 #include <ccan/str/hex/hex.h>
+#include <lightningd/lightningd.h>
 
 struct wallet *wallet_new(const tal_t *ctx, struct log *log)
 {
@@ -221,3 +222,13 @@ bool wallet_can_spend(struct wallet *w, const u8 *script,
 	return false;
 }
 
+s64 wallet_get_newindex(struct lightningd *ld)
+{
+	u64 newidx = db_get_intvar(ld->wallet->db, "bip32_max_index", 0) + 1;
+
+	if (newidx == BIP32_INITIAL_HARDENED_CHILD)
+		return -1;
+
+	db_set_intvar(ld->wallet->db, "bip32_max_index", newidx);
+	return newidx;
+}

wallet/wallet.h

@@ -7,6 +7,8 @@
 #include <lightningd/utxo.h>
 #include <wally_bip32.h>
 
+struct lightningd;
+
 struct wallet {
 	struct db *db;
 	struct log *log;
@@ -104,4 +106,12 @@ void wallet_confirm_utxos(struct wallet *w, const struct utxo **utxos);
 bool wallet_can_spend(struct wallet *w, const u8 *script,
 		      u32 *index, bool *output_is_p2sh);
 
+/**
+ * wallet_get_newindex - get a new index from the wallet.
+ * @ld: (in) lightning daemon
+ *
+ * Returns -1 on error (key exhaustion).
+ */
+s64 wallet_get_newindex(struct lightningd *ld);
+
 #endif /* WALLET_WALLET_H */

wallet/walletrpc.c

@@ -161,10 +161,7 @@ static void json_withdraw(struct command *cmd,
 	if (withdraw->changesatoshi <= 546)
 		withdraw->changesatoshi = 0;
 
-	withdraw->change_key_index =
-	    db_get_intvar(ld->wallet->db, "bip32_max_index", 0) + 1;
-	db_set_intvar(ld->wallet->db, "bip32_max_index",
-		      withdraw->change_key_index);
+	withdraw->change_key_index = wallet_get_newindex(ld);
 
 	utxos = from_utxoptr_arr(withdraw, withdraw->utxos);
 	u8 *msg = towire_hsmctl_sign_withdrawal(cmd,
@@ -238,14 +235,15 @@ static void json_newaddr(struct command *cmd,
 	struct ripemd160 p2sh;
 	struct pubkey pubkey;
 	u8 *redeemscript;
-	u64 bip32_max_index = db_get_intvar(ld->wallet->db, "bip32_max_index", 0);
+	s64 keyidx;
 
-	if (bip32_max_index == BIP32_INITIAL_HARDENED_CHILD) {
+	keyidx = wallet_get_newindex(ld);
+	if (keyidx < 0) {
 		command_fail(cmd, "Keys exhausted ");
 		return;
 	}
 
-	if (bip32_key_from_parent(ld->bip32_base, bip32_max_index,
+	if (bip32_key_from_parent(ld->bip32_base, keyidx,
 				  BIP32_FLAG_KEY_PUBLIC, &ext) != WALLY_OK) {
 		command_fail(cmd, "Keys generation failure");
 		return;
@@ -261,8 +259,6 @@ static void json_newaddr(struct command *cmd,
 	sha256(&h, redeemscript, tal_count(redeemscript));
 	ripemd160(&p2sh, h.u.u8, sizeof(h));
 
-	db_set_intvar(ld->wallet->db, "bip32_max_index", bip32_max_index + 1);
-
 	json_object_start(response, NULL);
 	json_add_string(response, "address",
 			p2sh_to_base58(cmd, cmd->dstate->testnet, &p2sh));