walletrpc: Implemented the withdrawal flow

wallet/Makefile

@@ -6,9 +6,10 @@ wallet-wrongdir:
 
 check: wallet/tests
 
-WALLET_LIB_SRC :=	\
-	wallet/db.c	\
-	wallet/wallet.c
+WALLET_LIB_SRC :=		\
+	wallet/db.c		\
+	wallet/wallet.c		\
+	wallet/walletrpc.c
 
 WALLET_LIB_OBJS := $(WALLET_LIB_SRC:.c=.o)
 WALLET_LIB_HEADERS := $(WALLET_LIB_SRC:.c=.h)

wallet/walletrpc.c

@@ -0,0 +1,189 @@
+#include <bitcoin/address.h>
+#include <bitcoin/base58.h>
+#include <bitcoin/script.h>
+#include <ccan/tal/str/str.h>
+#include <daemon/bitcoind.h>
+#include <daemon/chaintopology.h>
+#include <daemon/jsonrpc.h>
+#include <lightningd/hsm/gen_hsm_wire.h>
+#include <lightningd/key_derive.h>
+#include <lightningd/lightningd.h>
+#include <lightningd/subd.h>
+#include <lightningd/utxo.h>
+#include <lightningd/withdraw_tx.h>
+#include <permute_tx.h>
+#include <wally_bip32.h>
+
+struct withdrawal {
+	u64 amount, changesatoshi;
+	struct bitcoin_address destination;
+	const struct utxo **utxos;
+	u64 change_key_index;
+	struct command *cmd;
+	const char *hextx;
+};
+
+/**
+ * wallet_withdrawal_broadcast - The tx has been broadcast (or it failed)
+ *
+ * This is the final step in the withdrawal. We either successfully
+ * broadcast the withdrawal transaction or it failed somehow. So we
+ * report success or a broadcast failure. Upon success we also mark
+ * the used outputs as spent, and add the change output to our pool of
+ * available outputs.
+ */
+static void wallet_withdrawal_broadcast(struct bitcoind *bitcoind,
+					int exitstatus, const char *msg,
+					struct withdrawal *withdraw)
+{
+	struct command *cmd = withdraw->cmd;
+	struct lightningd *ld = ld_from_dstate(withdraw->cmd->dstate);
+
+	/* Massage output into shape so it doesn't kill the JSON serialization */
+	char *output = tal_strjoin(cmd, tal_strsplit(cmd, msg, "\n", STR_NO_EMPTY), " ", STR_NO_TRAIL);
+	if (exitstatus == 0) {
+		wallet_confirm_utxos(ld->wallet, withdraw->utxos);
+		/* TODO(cdecker) Add the change output to the database */
+		struct json_result *response = new_json_result(cmd);
+		json_object_start(response, NULL);
+		json_add_string(response, "tx", withdraw->hextx);
+		json_add_string(response, "txid", output);
+		json_object_end(response);
+		command_success(cmd, response);
+	} else {
+		command_fail(cmd, "Error broadcasting transaction: %s", output);
+	}
+}
+
+/**
+ * wallet_withdrawal_signed - The HSM has signed our withdrawal request
+ *
+ * This is the second step (2/3) of the withdrawal flow. The HSM has
+ * returned the necessary signatures for the withdrawal transaction,
+ * so now we can assemble the transaction and kick off the broadcast.
+ */
+static bool wallet_withdrawal_signed(struct subd *hsm, const u8 *reply,
+				     const int *fds,
+				     struct withdrawal *withdraw)
+{
+	struct command *cmd = withdraw->cmd;
+	struct lightningd *ld = ld_from_dstate(cmd->dstate);
+	struct ext_key ext;
+	struct pubkey changekey;
+	secp256k1_ecdsa_signature *sigs;
+	struct bitcoin_tx *tx;
+
+	if (!fromwire_hsmctl_sign_withdrawal_reply(withdraw, reply, NULL, &sigs))
+		fatal("HSM gave bad sign_withdrawal_reply %s",
+		      tal_hex(withdraw, reply));
+
+	if (bip32_key_from_parent(ld->bip32_base, withdraw->change_key_index,
+                               BIP32_FLAG_KEY_PUBLIC, &ext) != WALLY_OK) {
+             command_fail(cmd, "Changekey generation failure");
+             return true;
+	}
+
+	pubkey_from_der(ext.pub_key, sizeof(ext.pub_key), &changekey);
+	tx = withdraw_tx(withdraw, withdraw->utxos, &withdraw->destination,
+			 withdraw->amount, &changekey, withdraw->changesatoshi,
+			 ld->bip32_base);
+
+	if (tal_count(sigs) != tal_count(tx->input))
+		fatal("HSM gave %zu sigs, needed %zu",
+		      tal_count(sigs), tal_count(tx->input));
+
+	/* Create input parts from signatures. */
+	for (size_t i = 0; i < tal_count(tx->input); i++) {
+		struct pubkey key;
+
+		if (!bip32_pubkey(hsm->ld->bip32_base,
+				  &key, withdraw->utxos[i]->keyindex))
+			fatal("Cannot generate BIP32 key for UTXO %u",
+			      withdraw->utxos[i]->keyindex);
+
+		/* P2SH inputs have same witness. */
+		tx->input[i].witness
+			= bitcoin_witness_p2wpkh(tx, &sigs[i], &key);
+	}
+
+	/* Now broadcast the transaction */
+	withdraw->hextx = tal_hex(withdraw, linearize_tx(cmd, tx));
+	bitcoind_sendrawtx(ld->topology->bitcoind, withdraw->hextx,
+			   wallet_withdrawal_broadcast, withdraw);
+	return true;
+}
+
+/**
+ * json_withdraw - Entrypoint for the withdrawal flow
+ *
+ * A user has requested a withdrawal over the JSON-RPC, parse the
+ * request, select coins and a change key. Then send the request to
+ * the HSM to generate the signatures.
+ */
+static void json_withdraw(struct command *cmd,
+			      const char *buffer, const jsmntok_t *params)
+{
+	struct lightningd *ld = ld_from_dstate(cmd->dstate);
+	jsmntok_t *desttok, *sattok;
+	struct withdrawal *withdraw;
+	bool testnet;
+	/* FIXME: Read feerate and dustlimit */
+	u32 feerate_per_kw = 15000;
+	//u64 dust_limit = 600;
+	u64 fee_estimate;
+	struct utxo *utxos;
+	if (!json_get_params(buffer, params,
+			     "destination", &desttok,
+			     "satoshi", &sattok,
+			     NULL)) {
+		command_fail(cmd, "Need destination and satoshi.");
+		return;
+	}
+
+	withdraw = tal(cmd, struct withdrawal);
+	withdraw->cmd = cmd;
+
+	if (!json_tok_u64(buffer, sattok, &withdraw->amount)) {
+		command_fail(cmd, "Invalid satoshis");
+		return;
+	}
+	if (!bitcoin_from_base58(&testnet, &withdraw->destination,
+				 buffer + desttok->start,
+				 desttok->end - desttok->start)) {
+		command_fail(cmd, "Could not parse destination address");
+		return;
+	}
+
+	/* Select the coins */
+	withdraw->utxos = wallet_select_coins(cmd, ld->wallet, withdraw->amount,
+					      feerate_per_kw, &fee_estimate,
+					      &withdraw->changesatoshi);
+	if (!withdraw->utxos) {
+		command_fail(cmd, "Not enough funds available");
+		return;
+	}
+
+	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);
+
+	utxos = from_utxoptr_arr(withdraw, withdraw->utxos);
+	u8 *msg = towire_hsmctl_sign_withdrawal(cmd,
+						withdraw->amount,
+						withdraw->changesatoshi,
+						withdraw->change_key_index,
+						withdraw->destination.addr.u.u8,
+						utxos);
+	subd_req(cmd, ld->hsm, take(msg), -1, 0, wallet_withdrawal_signed,
+		 withdraw);
+	tal_free(utxos);
+}
+
+static const struct json_command withdraw_command = {
+	"withdraw",
+	json_withdraw,
+	"Send {satoshi} to the {destination} address via Bitcoin transaction",
+	"Returns the withdrawal transaction ID"
+};
+AUTODATA(json_command, &withdraw_command);

wallet/walletrpc.h

@@ -0,0 +1,11 @@
+#ifndef WALLET_WALLETRPC_H
+#define WALLET_WALLETRPC_H
+
+#include "config.h"
+
+/**
+ * Placeholder file, we aren't really exposing anything directly. RPC
+ * handlers are registered using AUTODATA.
+ */
+
+#endif /* WALLET_WALLETRPC_H */