core-lightning/lightningd/peer_htlcs.c

#include <bitcoin/tx.h>
#include <ccan/build_assert/build_assert.h>
#include <ccan/crypto/ripemd160/ripemd160.h>
#include <ccan/mem/mem.h>
#include <ccan/tal/str/str.h>
#include <channeld/gen_channel_wire.h>
#include <common/derive_basepoints.h>
#include <common/htlc_wire.h>
#include <common/overflows.h>
#include <common/sphinx.h>
#include <gossipd/gen_gossip_wire.h>
#include <lightningd/chaintopology.h>
#include <lightningd/htlc_end.h>
#include <lightningd/invoice.h>
#include <lightningd/lightningd.h>
#include <lightningd/log.h>
#include <lightningd/pay.h>
#include <lightningd/peer_control.h>
#include <lightningd/peer_htlcs.h>
#include <lightningd/subd.h>
#include <onchaind/gen_onchain_wire.h>
#include <onchaind/onchain_wire.h>
#include <wire/gen_onion_wire.h>

static bool state_update_ok(struct peer *peer,
			    enum htlc_state oldstate, enum htlc_state newstate,
			    u64 htlc_id, const char *dir)
{
	enum htlc_state expected = oldstate + 1;

	/* We never get told about RCVD_REMOVE_HTLC, so skip over that
	 * (we initialize in SENT_ADD_HTLC / RCVD_ADD_COMMIT, so those
	 * work). */
	if (expected == RCVD_REMOVE_HTLC)
		expected = RCVD_REMOVE_COMMIT;

	if (newstate != expected) {
		peer_internal_error(peer,
				    "HTLC %s %"PRIu64" invalid update %s->%s",
				    dir, htlc_id,
				    htlc_state_name(oldstate),
				    htlc_state_name(newstate));
		return false;
	}

	log_debug(peer->log, "HTLC %s %"PRIu64" %s->%s",
		  dir, htlc_id,
		  htlc_state_name(oldstate), htlc_state_name(newstate));
	return true;
}

static bool htlc_in_update_state(struct peer *peer,
				 struct htlc_in *hin,
				 enum htlc_state newstate)
{
	if (!state_update_ok(peer, hin->hstate, newstate, hin->key.id, "in"))
		return false;

	/* FIXME: db commit */
	hin->hstate = newstate;
	htlc_in_check(hin, __func__);
	return true;
}

static bool htlc_out_update_state(struct peer *peer,
				 struct htlc_out *hout,
				 enum htlc_state newstate)
{
	if (!state_update_ok(peer, hout->hstate, newstate, hout->key.id, "out"))
		return false;

	/* FIXME: db commit */
	hout->hstate = newstate;
	htlc_out_check(hout, __func__);
	return true;
}

/* This is where we write to the database the minimal HTLC info
 * required to do penalty transaction */
static void save_htlc_stub(struct lightningd *ld,
			   struct peer *peer,
			   enum side owner,
			   u32 cltv_value,
			   const struct sha256 *payment_hash)
{
	size_t n = tal_count(peer->htlcs);
	tal_resize(&peer->htlcs, n+1);
	peer->htlcs[n].owner = owner;
	peer->htlcs[n].cltv_expiry = cltv_value;
	ripemd160(&peer->htlcs[n].ripemd,
		  payment_hash->u.u8, sizeof(payment_hash->u));

	/* FIXME: save to db instead! */
}

static void fail_in_htlc(struct htlc_in *hin,
			 enum onion_type malformed,
			 const u8 *failuremsg)
{
	assert(!hin->preimage);
	if (malformed)
		assert(!failuremsg);
	else
		assert(failuremsg);

	hin->malformed = malformed;
	if (failuremsg)
		hin->failuremsg = tal_dup_arr(hin, u8, failuremsg, tal_len(failuremsg), 0);

	/* We update state now to signal it's in progress, for persistence. */
	htlc_in_update_state(hin->key.peer, hin, SENT_REMOVE_HTLC);

	/* Tell peer, if we can. */
	if (!hin->key.peer->owner)
		return;

	if (hin->malformed) {
		subd_send_msg(hin->key.peer->owner,
			      take(towire_channel_fail_htlc(hin,
							    hin->key.id,
							    hin->malformed,
							    NULL)));
	} else {
		u8 *reply;

		/* This obfuscates the message, whether local or forwarded. */
		reply = wrap_onionreply(hin, &hin->shared_secret,
					hin->failuremsg);
		subd_send_msg(hin->key.peer->owner,
			      take(towire_channel_fail_htlc(hin, hin->key.id,
							    0, reply)));
		tal_free(reply);
	}
}

static u8 *make_failmsg(const tal_t *ctx, u64 msatoshi,
			enum onion_type failcode,
			const u8 *channel_update)
{
	switch (failcode) {
	case WIRE_INVALID_REALM:
		return towire_invalid_realm(ctx);
	case WIRE_TEMPORARY_NODE_FAILURE:
		return towire_temporary_node_failure(ctx);
	case WIRE_PERMANENT_NODE_FAILURE:
		return towire_permanent_node_failure(ctx);
	case WIRE_REQUIRED_NODE_FEATURE_MISSING:
		return towire_required_node_feature_missing(ctx);
	case WIRE_TEMPORARY_CHANNEL_FAILURE:
		return towire_temporary_channel_failure(ctx, channel_update);
	case WIRE_CHANNEL_DISABLED:
		return towire_channel_disabled(ctx);
	case WIRE_PERMANENT_CHANNEL_FAILURE:
		return towire_permanent_channel_failure(ctx);
	case WIRE_REQUIRED_CHANNEL_FEATURE_MISSING:
		return towire_required_channel_feature_missing(ctx);
	case WIRE_UNKNOWN_NEXT_PEER:
		return towire_unknown_next_peer(ctx);
	case WIRE_AMOUNT_BELOW_MINIMUM:
		return towire_amount_below_minimum(ctx, msatoshi, channel_update);
	case WIRE_FEE_INSUFFICIENT:
		return towire_fee_insufficient(ctx, msatoshi, channel_update);
	case WIRE_INCORRECT_CLTV_EXPIRY:
		/* FIXME: ctlv! */
		return towire_incorrect_cltv_expiry(ctx, 0, channel_update);
	case WIRE_EXPIRY_TOO_SOON:
		return towire_expiry_too_soon(ctx, channel_update);
	case WIRE_UNKNOWN_PAYMENT_HASH:
		return towire_unknown_payment_hash(ctx);
	case WIRE_INCORRECT_PAYMENT_AMOUNT:
		return towire_incorrect_payment_amount(ctx);
	case WIRE_FINAL_EXPIRY_TOO_SOON:
		return towire_final_expiry_too_soon(ctx);
	case WIRE_FINAL_INCORRECT_CLTV_EXPIRY:
		/* FIXME: ctlv! */
		return towire_final_incorrect_cltv_expiry(ctx, 0);
	case WIRE_FINAL_INCORRECT_HTLC_AMOUNT:
		return towire_final_incorrect_htlc_amount(ctx, msatoshi);
	case WIRE_INVALID_ONION_VERSION:
	case WIRE_INVALID_ONION_HMAC:
	case WIRE_INVALID_ONION_KEY:
		fatal("Bad failmsg for %s", onion_type_name(failcode));
	}
	abort();
}

/* This is used for cases where we can immediately fail the HTLC. */
static void local_fail_htlc(struct htlc_in *hin, enum onion_type failcode)
{
	log_info(hin->key.peer->log, "failed htlc %"PRIu64" code 0x%04x (%s)",
		 hin->key.id, failcode, onion_type_name(failcode));

	if (failcode & BADONION)
		fail_in_htlc(hin, failcode, NULL);
	else {
		u8 *msg;

		if (failcode & UPDATE) {
			/* FIXME: Ask gossip daemon for channel_update. */
		}

		msg = make_failmsg(hin, hin->msatoshi, failcode, NULL);
		fail_in_htlc(hin, 0, take(create_onionreply(hin, &hin->shared_secret, msg)));
		tal_free(msg);
	}
}

/* localfail are for handing to the local payer if it's local. */
static void fail_out_htlc(struct htlc_out *hout, const char *localfail)
{
	htlc_out_check(hout, __func__);
	assert(hout->malformed || hout->failuremsg);
	assert(!hout->malformed || !hout->failuremsg);
	if (hout->in) {
		fail_in_htlc(hout->in, hout->malformed, hout->failuremsg);
	} else {
		payment_failed(hout->key.peer->ld, hout, localfail);
	}
}

/* BOLT #4:
 *
 * * `amt_to_forward` - The amount in milli-satoshi to forward to the next
 *    (outgoing) hop specified within the routing information.
 *
 *    This value MUST factor in the computed fee for this particular hop. When
 *    processing an incoming Sphinx packet along with the HTLC message it's
 *    encapsulated within, if the following inequality doesn't hold, then the
 *    HTLC should be rejected as it indicates a prior node in the path has
 *    deviated from the specified parameters:
 *
 *       incoming_htlc_amt - fee >= amt_to_forward
 *
 *    Where `fee` is calculated according to the receiving node's advertised fee
 *    schema as described in [BOLT 7](https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md#htlc-fees), or 0 if this node is the
 *    final hop.
 */
static bool check_amount(struct htlc_in *hin,
			 u64 amt_to_forward, u64 amt_in_htlc, u64 fee)
{
	if (amt_in_htlc - fee >= amt_to_forward)
		return true;
	log_debug(hin->key.peer->ld->log, "HTLC %"PRIu64" incorrect amount:"
		  " %"PRIu64" in, %"PRIu64" out, fee reqd %"PRIu64,
		  hin->key.id, amt_in_htlc, amt_to_forward, fee);
	return false;
}

/* BOLT #4:
 *
 *  * `outgoing_cltv_value` - The CLTV value that the _outgoing_ HTLC carrying
 *     the packet should have.
 *
 *        cltv_expiry - cltv_expiry_delta = outgoing_cltv_value
 *
 *     Inclusion of this field allows a node to both authenticate the information
 *     specified by the original sender and the parameters of the HTLC forwarded,
 *	 and ensure the original sender is using the current `cltv_expiry_delta`  value.
 *     If there is no next hop, `cltv_expiry_delta` is zero.
 *     If the values don't correspond, then the HTLC should be failed+rejected as
 *     this indicates the incoming node has tampered with the intended HTLC
 *     values, or the origin has an obsolete `cltv_expiry_delta` value.
 *     The node MUST be consistent in responding to an unexpected
 *     `outgoing_cltv_value` whether it is the final hop or not, to avoid
 *     leaking that information.
 */
static bool check_ctlv(struct htlc_in *hin,
		       u32 ctlv_expiry, u32 outgoing_cltv_value, u32 delta)
{
	if (ctlv_expiry - delta == outgoing_cltv_value)
		return true;
	log_debug(hin->key.peer->ld->log, "HTLC %"PRIu64" incorrect CLTV:"
		  " %u in, %u out, delta reqd %u",
		  hin->key.id, ctlv_expiry, outgoing_cltv_value, delta);
	return false;
}

static void fulfill_htlc(struct htlc_in *hin, const struct preimage *preimage)
{
	u8 *msg;

	hin->preimage = tal_dup(hin, struct preimage, preimage);
	htlc_in_check(hin, __func__);

	/* We update state now to signal it's in progress, for persistence. */
	htlc_in_update_state(hin->key.peer, hin, SENT_REMOVE_HTLC);

	/* No owner?  We'll either send to channeld in peer_htlcs, or
	 * onchaind in onchaind_tell_fulfill. */
	if (!hin->key.peer->owner) {
		log_debug(hin->key.peer->log, "HTLC fulfilled, but no owner.");
		return;
	}

	if (peer_state_on_chain(hin->key.peer->state)) {
		msg = towire_onchain_known_preimage(hin, preimage);
	} else {
		/* FIXME: fail the peer if it doesn't tell us that htlc
		 * fulfill is committed before deadline.
		 */
		msg = towire_channel_fulfill_htlc(hin, hin->key.id, preimage);
	}
	subd_send_msg(hin->key.peer->owner, take(msg));
}

static void handle_localpay(struct htlc_in *hin,
			    u32 cltv_expiry,
			    const struct sha256 *payment_hash,
			    u64 amt_to_forward,
			    u32 outgoing_cltv_value)
{
	enum onion_type failcode;
	struct invoice *invoice;
	struct lightningd *ld = hin->key.peer->ld;

	/* BOLT #4:
	 *
	 * If the `amt_to_forward` is higher than `incoming_htlc_amt` of
	 * the HTLC at the final hop:
	 *
	 * 1. type: 19 (`final_incorrect_htlc_amount`)
	 * 2. data:
	 *    * [`4`:`incoming_htlc_amt`]
	 */
	if (!check_amount(hin, amt_to_forward, hin->msatoshi, 0)) {
		failcode = WIRE_FINAL_INCORRECT_HTLC_AMOUNT;
		goto fail;
	}

	/* BOLT #4:
	 *
	 * If the `outgoing_cltv_value` does not match the `ctlv_expiry` of
	 * the HTLC at the final hop:
	 *
	 * 1. type: 18 (`final_incorrect_cltv_expiry`)
	 * 2. data:
	 *   * [`4`:`cltv_expiry`]
	 */
	if (!check_ctlv(hin, cltv_expiry, outgoing_cltv_value, 0)) {
		failcode = WIRE_FINAL_INCORRECT_CLTV_EXPIRY;
		goto fail;
	}

	invoice = find_unpaid(ld->invoices, payment_hash);
	if (!invoice) {
		failcode = WIRE_UNKNOWN_PAYMENT_HASH;
		goto fail;
	}

	/* BOLT #4:
	 *
	 * If the amount paid is less than the amount expected, the final node
	 * MUST fail the HTLC.  If the amount paid is more than twice the
	 * amount expected, the final node SHOULD fail the HTLC.  This allows
	 * the sender to reduce information leakage by altering the amount,
	 * without allowing accidental gross overpayment:
	 *
	 * 1. type: PERM|16 (`incorrect_payment_amount`)
	 */
	if (hin->msatoshi < invoice->msatoshi) {
		failcode = WIRE_INCORRECT_PAYMENT_AMOUNT;
		goto fail;
	} else if (hin->msatoshi > invoice->msatoshi * 2) {
		failcode = WIRE_INCORRECT_PAYMENT_AMOUNT;
		goto fail;
	}

	/* BOLT #4:
	 *
	 * If the `cltv_expiry` is too low, the final node MUST fail the HTLC:
	 */
	if (get_block_height(ld->topology) + ld->config.deadline_blocks
	    >= cltv_expiry) {
		log_debug(hin->key.peer->log,
			  "Expiry cltv %u too close to current %u + deadline %u",
			  cltv_expiry,
			  get_block_height(ld->topology),
			  ld->config.deadline_blocks);
		failcode = WIRE_FINAL_EXPIRY_TOO_SOON;
		goto fail;
	}

	log_info(ld->log, "Resolving invoice '%s' with HTLC %"PRIu64,
		 invoice->label, hin->key.id);
	fulfill_htlc(hin, &invoice->r);
	resolve_invoice(ld, invoice);
	return;

fail:
	local_fail_htlc(hin, failcode);
}

/*
 * A catchall in case outgoing peer disconnects before getting fwd.
 *
 * We could queue this and wait for it to come back, but this is simple.
 */
static void hout_subd_died(struct htlc_out *hout)
{
	log_debug(hout->key.peer->log,
		  "Failing HTLC %"PRIu64" due to peer death",
		  hout->key.id);

	hout->failuremsg = make_failmsg(hout, hout->msatoshi,
					WIRE_TEMPORARY_CHANNEL_FAILURE,
					NULL);
	fail_out_htlc(hout, "Outgoing subdaemon died");
}

/* This is where channeld gives us the HTLC id, and also reports if it
 * failed immediately. */
static bool rcvd_htlc_reply(struct subd *subd, const u8 *msg, const int *fds,
			    struct htlc_out *hout)
{
	u16 failure_code;
	u8 *failurestr;

	if (!fromwire_channel_offer_htlc_reply(msg, msg, NULL,
					       &hout->key.id,
					       &failure_code,
					       &failurestr)) {
		peer_internal_error(subd->peer, "Bad channel_offer_htlc_reply");
		tal_free(hout);
		return false;
	}

	if (failure_code) {
		if (!hout->in) {
			char *localfail = tal_fmt(msg, "%s: %.*s",
						  onion_type_name(failure_code),
						  (int)tal_len(failurestr),
						  (const char *)failurestr);
			payment_failed(hout->key.peer->ld, hout, localfail);
		} else
			local_fail_htlc(hout->in, failure_code);
		return true;
	}

	if (find_htlc_out(&subd->ld->htlcs_out, hout->key.peer, hout->key.id)) {
		peer_internal_error(subd->peer,
				    "Bad offer_htlc_reply HTLC id %"PRIu64
				    " is a duplicate",
				    hout->key.id);
		tal_free(hout);
		return false;
	}

	/* Add it to lookup table now we know id. */
	connect_htlc_out(&subd->ld->htlcs_out, hout);

	/* When channeld includes it in commitment, we'll make it persistent. */
	return true;
}

enum onion_type send_htlc_out(struct peer *out, u64 amount, u32 cltv,
			      const struct sha256 *payment_hash,
			      const u8 *onion_routing_packet,
			      struct htlc_in *in,
			      struct pay_command *pc,
			      struct htlc_out **houtp)
{
	struct htlc_out *hout;
	u8 *msg;

	if (!peer_can_add_htlc(out)) {
		log_info(out->log, "Attempt to send HTLC but not ready (%s)",
			 peer_state_name(out->state));
		return WIRE_UNKNOWN_NEXT_PEER;
	}

	if (!out->owner) {
		log_info(out->log, "Attempt to send HTLC but unowned (%s)",
			peer_state_name(out->state));
		return WIRE_TEMPORARY_CHANNEL_FAILURE;
	}

	/* Make peer's daemon own it, catch if it dies. */
	hout = new_htlc_out(out->owner, out, amount, cltv,
			    payment_hash, onion_routing_packet, in, pc);
	tal_add_destructor(hout, hout_subd_died);

	msg = towire_channel_offer_htlc(out, amount, cltv, payment_hash,
					onion_routing_packet);
	subd_req(out->ld, out->owner, take(msg), -1, 0, rcvd_htlc_reply, hout);

	if (houtp)
		*houtp = hout;
	return 0;
}

static void forward_htlc(struct htlc_in *hin,
			 u32 cltv_expiry,
			 const struct sha256 *payment_hash,
			 u64 amt_to_forward,
			 u32 outgoing_cltv_value,
			 const struct pubkey *next_hop,
			 const u8 next_onion[TOTAL_PACKET_SIZE])
{
	enum onion_type failcode;
	u64 fee;
	struct lightningd *ld = hin->key.peer->ld;
	struct peer *next = peer_by_id(ld, next_hop);

	if (!next) {
		failcode = WIRE_UNKNOWN_NEXT_PEER;
		goto fail;
	}

	/* BOLT #7:
	 *
	 * The node creating `channel_update` SHOULD accept HTLCs which pay a
	 * fee equal or greater than:
	 *
	 *    fee_base_msat + amount_msat * fee_proportional_millionths / 1000000
	 */
	if (mul_overflows_u64(amt_to_forward,
			      ld->config.fee_per_satoshi)) {
		failcode = WIRE_FEE_INSUFFICIENT;
		goto fail;
	}
	fee = ld->config.fee_base
		+ amt_to_forward * ld->config.fee_per_satoshi / 1000000;
	if (!check_amount(hin, amt_to_forward, hin->msatoshi, fee)) {
		failcode = WIRE_FEE_INSUFFICIENT;
		goto fail;
	}

	if (!check_ctlv(hin, cltv_expiry, outgoing_cltv_value,
			ld->config.min_htlc_expiry)) {
		failcode = WIRE_INCORRECT_CLTV_EXPIRY;
		goto fail;
	}

	/* BOLT #4:
	 *
	 * If the ctlv-expiry is too near, we tell them the the current channel
	 * setting for the outgoing channel:
	 * 1. type: UPDATE|14 (`expiry_too_soon`)
	 * 2. data:
	 *    * [`2`:`len`]
	 *    * [`len`:`channel_update`]
	 */
	if (get_block_height(next->ld->topology)
	    + next->ld->config.deadline_blocks >= outgoing_cltv_value) {
		log_debug(hin->key.peer->log,
			  "Expiry cltv %u too close to current %u + deadline %u",
			  outgoing_cltv_value,
			  get_block_height(next->ld->topology),
			  next->ld->config.deadline_blocks);
		failcode = WIRE_EXPIRY_TOO_SOON;
		goto fail;
	}

	failcode = send_htlc_out(next, amt_to_forward,
				 outgoing_cltv_value, &hin->payment_hash,
				 next_onion, hin, NULL, NULL);
	if (!failcode)
		return;

fail:
	local_fail_htlc(hin, failcode);
}

/* Temporary information, while we resolve the next hop */
struct gossip_resolve {
	struct short_channel_id next_channel;
	u64 amt_to_forward;
	u32 outgoing_cltv_value;
	u8 *next_onion;
	struct htlc_in *hin;
};

/* We received a resolver reply, which gives us the node_ids of the
 * channel we want to forward over */
static bool channel_resolve_reply(struct subd *gossip, const u8 *msg,
				  const int *fds, struct gossip_resolve *gr)
{
	struct pubkey *nodes, *peer_id;

	if (!fromwire_gossip_resolve_channel_reply(msg, msg, NULL, &nodes)) {
		log_broken(gossip->log,
			   "bad fromwire_gossip_resolve_channel_reply %s",
			   tal_hex(msg, msg));
		return false;
	}

	if (tal_count(nodes) == 0) {
		local_fail_htlc(gr->hin, WIRE_UNKNOWN_NEXT_PEER);
		return true;
	} else if (tal_count(nodes) != 2) {
		log_broken(gossip->log,
			   "fromwire_gossip_resolve_channel_reply has %zu nodes",
			   tal_count(nodes));
		return false;
	}

	/* Get the other peer matching the id that is not us */
	if (pubkey_cmp(&nodes[0], &gossip->ld->id) == 0) {
		peer_id = &nodes[1];
	} else {
		peer_id = &nodes[0];
	}

	forward_htlc(gr->hin, gr->hin->cltv_expiry, &gr->hin->payment_hash,
		     gr->amt_to_forward, gr->outgoing_cltv_value, peer_id,
		     gr->next_onion);
	tal_free(gr);
	return true;
}

/* Everyone is committed to this htlc of theirs */
static bool peer_accepted_htlc(struct peer *peer,
			       u64 id,
			       enum onion_type *failcode)
{
	struct htlc_in *hin;
	u8 *req;
	struct route_step *rs;
	struct onionpacket *op;
	const tal_t *tmpctx = tal_tmpctx(peer);

	hin = find_htlc_in(&peer->ld->htlcs_in, peer, id);
	if (!hin) {
		peer_internal_error(peer,
				    "peer_got_revoke unknown htlc %"PRIu64, id);
		return false;
	}

	if (!htlc_in_update_state(peer, hin, RCVD_ADD_ACK_REVOCATION))
		return false;

	/* BOLT #2:
	 *
	 * A sending node SHOULD fail to route any HTLC added after it
	 * sent `shutdown`. */
	if (peer->state == CHANNELD_SHUTTING_DOWN) {
		*failcode = WIRE_PERMANENT_CHANNEL_FAILURE;
		goto out;
	}

	/* channeld tests this, so it should have set ss to zeroes. */
	op = parse_onionpacket(tmpctx, hin->onion_routing_packet,
			       sizeof(hin->onion_routing_packet));
	if (!op) {
		if (!memeqzero(&hin->shared_secret, sizeof(hin->shared_secret))){
			peer_internal_error(peer,
				   "bad onion in got_revoke: %s",
				   tal_hexstr(peer, hin->onion_routing_packet,
					     sizeof(hin->onion_routing_packet)));
			tal_free(tmpctx);
			return false;
		}
		/* FIXME: could be bad version, bad key. */
		*failcode = WIRE_INVALID_ONION_VERSION;
		goto out;
	}

	/* Channeld sets this to zero if HSM won't ecdh it */
	if (memeqzero(&hin->shared_secret, sizeof(hin->shared_secret))) {
		*failcode = WIRE_INVALID_ONION_KEY;
		goto out;
	}

	/* If it's crap, not channeld's fault, just fail it */
	rs = process_onionpacket(tmpctx, op, hin->shared_secret.data,
				 hin->payment_hash.u.u8,
				 sizeof(hin->payment_hash));
	if (!rs) {
		*failcode = WIRE_INVALID_ONION_HMAC;
		goto out;
	}

	/* Unknown realm isn't a bad onion, it's a normal failure. */
	if (rs->hop_data.realm != 0) {
		*failcode = WIRE_INVALID_REALM;
		goto out;
	}

	if (rs->nextcase == ONION_FORWARD) {
		struct gossip_resolve *gr = tal(peer->ld, struct gossip_resolve);

		gr->next_onion = serialize_onionpacket(gr, rs->next);
		gr->next_channel = rs->hop_data.channel_id;
		gr->amt_to_forward = rs->hop_data.amt_forward;
		gr->outgoing_cltv_value = rs->hop_data.outgoing_cltv;
		gr->hin = hin;

		req = towire_gossip_resolve_channel_request(tmpctx,
							    &gr->next_channel);
		log_debug(peer->log, "Asking gossip to resolve channel %s",
			  type_to_string(tmpctx, struct short_channel_id,
					 &gr->next_channel));
		subd_req(hin, peer->ld->gossip, req, -1, 0,
			 channel_resolve_reply, gr);
	} else
		handle_localpay(hin, hin->cltv_expiry, &hin->payment_hash,
				rs->hop_data.amt_forward,
				rs->hop_data.outgoing_cltv);

	*failcode = 0;
out:
	log_debug(peer->log, "their htlc %"PRIu64" %s",
		  id, *failcode ? onion_type_name(*failcode) : "locked");

	tal_free(tmpctx);
	return true;
}

static void fulfill_our_htlc_out(struct peer *peer, struct htlc_out *hout,
				 const struct preimage *preimage)
{
	hout->preimage = tal_dup(hout, struct preimage, preimage);
	htlc_out_check(hout, __func__);

	/* FIXME: Save to db */

	if (hout->in)
		fulfill_htlc(hout->in, preimage);
	else
		payment_succeeded(peer->ld, hout, preimage);
}

static bool peer_fulfilled_our_htlc(struct peer *peer,
				    const struct fulfilled_htlc *fulfilled)
{
	struct htlc_out *hout;

	hout = find_htlc_out(&peer->ld->htlcs_out, peer, fulfilled->id);
	if (!hout) {
		peer_internal_error(peer,
				    "fulfilled_our_htlc unknown htlc %"PRIu64,
				    fulfilled->id);
		return false;
	}

	if (!htlc_out_update_state(peer, hout, RCVD_REMOVE_COMMIT))
		return false;

	fulfill_our_htlc_out(peer, hout, &fulfilled->payment_preimage);
	return true;
}

void onchain_fulfilled_htlc(struct peer *peer, const struct preimage *preimage)
{
	struct htlc_out_map_iter outi;
	struct htlc_out *hout;
	struct sha256 payment_hash;

	sha256(&payment_hash, preimage, sizeof(*preimage));

	/* FIXME: use db to look this up! */
	for (hout = htlc_out_map_first(&peer->ld->htlcs_out, &outi);
	     hout;
	     hout = htlc_out_map_next(&peer->ld->htlcs_out, &outi)) {
		if (hout->key.peer != peer)
			continue;

		if (!structeq(&hout->payment_hash, &payment_hash))
			continue;

		fulfill_our_htlc_out(peer, hout, preimage);
		/* We keep going: this is something of a leak, but onchain
		 * we have no real way of distinguishing HTLCs anyway */
	}
}

static bool peer_failed_our_htlc(struct peer *peer,
				 const struct failed_htlc *failed)
{
	struct htlc_out *hout;

	hout = find_htlc_out(&peer->ld->htlcs_out, peer, failed->id);
	if (!hout) {
		peer_internal_error(peer,
				    "failed_our_htlc unknown htlc %"PRIu64,
				    failed->id);
		return false;
	}

	if (!htlc_out_update_state(peer, hout, RCVD_REMOVE_COMMIT))
		return false;

	log_debug(peer->log, "Our HTLC %"PRIu64" failed (%u)", failed->id,
		  failed->malformed);
	if (failed->malformed)
		hout->malformed = failed->malformed;
	else
		hout->failuremsg = tal_dup_arr(hout, u8, failed->failreason,
					       tal_len(failed->failreason), 0);
	htlc_out_check(hout, __func__);
	return true;
}

static void remove_htlc_in(struct peer *peer, struct htlc_in *hin)
{
	htlc_in_check(hin, __func__);
	assert(hin->failuremsg || hin->preimage || hin->malformed);

	log_debug(peer->log, "Removing in HTLC %"PRIu64" state %s %s",
		  hin->key.id, htlc_state_name(hin->hstate),
		  hin->failuremsg ? "FAILED"
		  : hin->malformed ? "MALFORMED"
		  : "FULFILLED");

	/* If we fulfilled their HTLC, credit us. */
	if (hin->preimage) {
		log_debug(peer->log, "Balance %"PRIu64" -> %"PRIu64,
			  *peer->our_msatoshi,
			  *peer->our_msatoshi + hin->msatoshi);
		*peer->our_msatoshi += hin->msatoshi;
	}

	tal_free(hin);
}

static void remove_htlc_out(struct peer *peer, struct htlc_out *hout)
{
	htlc_out_check(hout, __func__);
	assert(hout->failuremsg || hout->preimage || hout->malformed);
	log_debug(peer->log, "Removing out HTLC %"PRIu64" state %s %s",
		  hout->key.id, htlc_state_name(hout->hstate),
		  hout->failuremsg ? "FAILED"
		  : hout->malformed ? "MALFORMED"
		  : "FULFILLED");

	/* If it's failed, now we can forward since it's completely locked-in */
	if (!hout->preimage) {
		fail_out_htlc(hout, NULL);
	} else {
		/* We paid for this HTLC, so deduct balance. */
		log_debug(peer->log, "Balance %"PRIu64" -> %"PRIu64,
			  *peer->our_msatoshi,
			  *peer->our_msatoshi - hout->msatoshi);
		*peer->our_msatoshi -= hout->msatoshi;
	}

	tal_free(hout);
}

static bool update_in_htlc(struct peer *peer, u64 id, enum htlc_state newstate)
{
	struct htlc_in *hin;

	hin = find_htlc_in(&peer->ld->htlcs_in, peer, id);
	if (!hin) {
		peer_internal_error(peer, "Can't find in HTLC %"PRIu64, id);
		return false;
	}

	if (!htlc_in_update_state(peer, hin, newstate))
		return false;

	if (newstate == SENT_REMOVE_ACK_REVOCATION)
		remove_htlc_in(peer, hin);

	return true;
}

static bool update_out_htlc(struct peer *peer, u64 id, enum htlc_state newstate)
{
	struct htlc_out *hout;

	hout = find_htlc_out(&peer->ld->htlcs_out, peer, id);
	if (!hout) {
		peer_internal_error(peer, "Can't find out HTLC %"PRIu64, id);
		return false;
	}

	if (!htlc_out_update_state(peer, hout, newstate))
		return false;

	/* First transition into commitment; now it outlives peer. */
	if (newstate == SENT_ADD_COMMIT) {
		tal_del_destructor(hout, hout_subd_died);
		tal_steal(peer->ld, hout);

		/* From now onwards, penalty tx might need this */
		save_htlc_stub(peer->ld, peer, LOCAL,
			       hout->cltv_expiry,
			       &hout->payment_hash);
	} else if (newstate == RCVD_REMOVE_ACK_REVOCATION) {
		remove_htlc_out(peer, hout);
	}
	return true;
}

static bool changed_htlc(struct peer *peer,
			 const struct changed_htlc *changed)
{
	if (htlc_state_owner(changed->newstate) == LOCAL)
		return update_out_htlc(peer, changed->id, changed->newstate);
	else
		return update_in_htlc(peer, changed->id, changed->newstate);
}

static bool peer_save_commitsig_received(struct peer *peer, u64 commitnum)
{
	if (commitnum != peer->next_index[LOCAL]) {
		peer_internal_error(peer,
			   "channel_got_commitsig: expected commitnum %"PRIu64
			   " got %"PRIu64,
			   peer->next_index[LOCAL], commitnum);
		return false;
	}

	peer->next_index[LOCAL]++;

	/* FIXME: Save to database, with sig and HTLCs. */
	if (!wallet_channel_save(peer->ld->wallet, peer->channel)) {
		fatal("Could not save channel to database: %s",
		      peer->ld->wallet->db->err);
	}
	return true;
}

static bool peer_save_commitsig_sent(struct peer *peer, u64 commitnum)
{
	if (commitnum != peer->next_index[REMOTE]) {
		peer_internal_error(peer,
			   "channel_sent_commitsig: expected commitnum %"PRIu64
			   " got %"PRIu64,
			   peer->next_index[REMOTE], commitnum);
		return false;
	}

	peer->next_index[REMOTE]++;

	/* FIXME: Save to database, with sig and HTLCs. */
	if (!wallet_channel_save(peer->ld->wallet, peer->channel)) {
		fatal("Could not save channel to database: %s",
		      peer->ld->wallet->db->err);
	}

	return true;
}

int peer_sending_commitsig(struct peer *peer, const u8 *msg)
{
	u64 commitnum;
	struct changed_htlc *changed_htlcs;
	size_t i, maxid = 0, num_local_added = 0;
	secp256k1_ecdsa_signature commit_sig;
	secp256k1_ecdsa_signature *htlc_sigs;

	if (!fromwire_channel_sending_commitsig(msg, msg, NULL,
						&commitnum,
						&changed_htlcs,
						&commit_sig, &htlc_sigs)) {
		peer_internal_error(peer, "bad channel_sending_commitsig %s",
				    tal_hex(peer, msg));
		return -1;
	}

	for (i = 0; i < tal_count(changed_htlcs); i++) {
		if (!changed_htlc(peer, changed_htlcs + i)) {
			peer_internal_error(peer,
				   "channel_sending_commitsig: update failed");
			return -1;
		}

		/* While we're here, sanity check added ones are in
		 * ascending order. */
		if (changed_htlcs[i].newstate == SENT_ADD_COMMIT) {
			num_local_added++;
			if (changed_htlcs[i].id > maxid)
				maxid = changed_htlcs[i].id;
		}
	}

	if (num_local_added != 0) {
		if (maxid != peer->next_htlc_id + num_local_added - 1) {
			peer_internal_error(peer,
				   "channel_sending_commitsig:"
				   " Added %"PRIu64", maxid now %"PRIu64
				   " from %"PRIu64,
				   num_local_added, maxid, peer->next_htlc_id);
			return -1;
		}
		/* FIXME: Save to db */
		peer->next_htlc_id += num_local_added;
	}

	if (!peer_save_commitsig_sent(peer, commitnum))
		return -1;

	/* Last was commit. */
	peer->last_was_revoke = false;
	tal_free(peer->last_sent_commit);
	peer->last_sent_commit = tal_steal(peer, changed_htlcs);

	/* Tell it we've got it, and to go ahead with commitment_signed. */
	subd_send_msg(peer->owner,
		      take(towire_channel_sending_commitsig_reply(msg)));
	return 0;
}

static void added_their_htlc(struct peer *peer,
			     const struct added_htlc *added,
			     const struct secret *shared_secret)
{
	struct htlc_in *hin;

	/* This stays around even if we fail it immediately: it *is*
	 * part of the current commitment. */
	hin = new_htlc_in(peer, peer, added->id, added->amount_msat,
			  added->cltv_expiry, &added->payment_hash,
			  shared_secret, added->onion_routing_packet);

	/* FIXME: Save to db */

	log_debug(peer->log, "Adding their HTLC %"PRIu64, added->id);
	connect_htlc_in(&peer->ld->htlcs_in, hin);

	/* Technically this can't be needed for a penalty transaction until
	 * after we send revoke_and_ack, then commit, then receive their
	 * revoke_and_ack.  But might as well record it while we have it:
	 * a few extra entries won't hurt */
	save_htlc_stub(peer->ld, peer, REMOTE, hin->cltv_expiry,
		       &hin->payment_hash);

}

/* The peer doesn't tell us this separately, but logically it's a separate
 * step to receiving commitsig */
static bool peer_sending_revocation(struct peer *peer,
				    struct added_htlc *added,
				    struct fulfilled_htlc *fulfilled,
				    struct failed_htlc *failed,
				    struct changed_htlc *changed)
{
	size_t i;

	for (i = 0; i < tal_count(added); i++) {
		if (!update_in_htlc(peer, added[i].id, SENT_ADD_REVOCATION))
			return false;
	}
	for (i = 0; i < tal_count(fulfilled); i++) {
		if (!update_out_htlc(peer, fulfilled[i].id,
				     SENT_REMOVE_REVOCATION))
			return false;
	}
	for (i = 0; i < tal_count(failed); i++) {
		if (!update_out_htlc(peer, failed[i].id, SENT_REMOVE_REVOCATION))
			return false;
	}
	for (i = 0; i < tal_count(changed); i++) {
		if (changed[i].newstate == RCVD_ADD_ACK_COMMIT) {
			if (!update_out_htlc(peer, changed[i].id,
					     SENT_ADD_ACK_REVOCATION))
				return false;
		} else {
			if (!update_in_htlc(peer, changed[i].id,
					    SENT_REMOVE_ACK_REVOCATION))
				return false;
		}
	}

	peer->last_was_revoke = true;
	return true;
}

/* This also implies we're sending revocation */
int peer_got_commitsig(struct peer *peer, const u8 *msg)
{
	u64 commitnum;
	secp256k1_ecdsa_signature commit_sig;
	secp256k1_ecdsa_signature *htlc_sigs;
	struct added_htlc *added;
	struct secret *shared_secrets;
	struct fulfilled_htlc *fulfilled;
	struct failed_htlc *failed;
	struct changed_htlc *changed;
	struct bitcoin_tx *tx = tal(msg, struct bitcoin_tx);
	size_t i;

	if (!fromwire_channel_got_commitsig(msg, msg, NULL,
					    &commitnum,
					    &commit_sig,
					    &htlc_sigs,
					    &added,
					    &shared_secrets,
					    &fulfilled,
					    &failed,
					    &changed,
					    tx)) {
		peer_internal_error(peer,
				    "bad fromwire_channel_got_commitsig %s",
				    tal_hex(peer, msg));
		return -1;
	}

	log_debug(peer->log,
		  "got commitsig %"PRIu64
		  ": %zu added, %zu fulfilled, %zu failed, %zu changed",
		  commitnum, tal_count(added), tal_count(fulfilled),
		  tal_count(failed), tal_count(changed));

	/* FIXME: store commit & htlc signature information. */

	/* New HTLCs */
	for (i = 0; i < tal_count(added); i++)
		added_their_htlc(peer, &added[i], &shared_secrets[i]);

	/* Save information now for fulfilled & failed HTLCs */
	for (i = 0; i < tal_count(fulfilled); i++) {
		if (!peer_fulfilled_our_htlc(peer, &fulfilled[i]))
			return -1;
	}

	for (i = 0; i < tal_count(failed); i++) {
		if (!peer_failed_our_htlc(peer, &failed[i]))
			return -1;
	}

	for (i = 0; i < tal_count(changed); i++) {
		if (!changed_htlc(peer, &changed[i])) {
			peer_internal_error(peer,
					    "got_commitsig: update failed");
			return -1;
		}
	}

	/* Since we're about to send revoke, bump state again. */
	if (!peer_sending_revocation(peer, added, fulfilled, failed, changed))
		return -1;

	if (!peer_save_commitsig_received(peer, commitnum))
		return -1;

	peer_last_tx(peer, tx, &commit_sig);
	/* FIXME: Put these straight in the db! */
	tal_free(peer->last_htlc_sigs);
	peer->last_htlc_sigs = tal_steal(peer, htlc_sigs);

	/* Tell it we've committed, and to go ahead with revoke. */
	msg = towire_channel_got_commitsig_reply(msg);
	subd_send_msg(peer->owner, take(msg));
	return 0;
}

/* Shuffle them over, forgetting the ancient one. */
void update_per_commit_point(struct peer *peer,
			     const struct pubkey *per_commitment_point)
{
	struct channel_info *ci = peer->channel_info;
	ci->old_remote_per_commit = ci->remote_per_commit;
	ci->remote_per_commit = *per_commitment_point;
}

int peer_got_revoke(struct peer *peer, const u8 *msg)
{
	u64 revokenum;
	struct sha256 per_commitment_secret;
	struct pubkey next_per_commitment_point;
	struct changed_htlc *changed;
	enum onion_type *failcodes;
	size_t i;

	if (!fromwire_channel_got_revoke(msg, msg, NULL,
					 &revokenum, &per_commitment_secret,
					 &next_per_commitment_point,
					 &changed)) {
		peer_internal_error(peer, "bad fromwire_channel_got_revoke %s",
				    tal_hex(peer, msg));
		return -1;
	}

	log_debug(peer->log,
		  "got revoke %"PRIu64": %zu changed",
		  revokenum, tal_count(changed));

	/* Save any immediate failures for after we reply. */
	failcodes = tal_arrz(msg, enum onion_type, tal_count(changed));
	for (i = 0; i < tal_count(changed); i++) {
		/* If we're doing final accept, we need to forward */
		if (changed[i].newstate == RCVD_ADD_ACK_REVOCATION) {
			if (!peer_accepted_htlc(peer, changed[i].id,
						&failcodes[i]))
				return -1;
		} else {
			if (!changed_htlc(peer, &changed[i])) {
				peer_internal_error(peer,
						    "got_revoke: update failed");
				return -1;
			}
		}
	}

	if (revokenum >= (1ULL << 48)) {
		peer_internal_error(peer, "got_revoke: too many txs %"PRIu64,
				    revokenum);
		return -1;
	}

	if (revokenum != revocations_received(&peer->their_shachain.chain)) {
		peer_internal_error(peer, "got_revoke: expected %"PRIu64
				    " got %"PRIu64,
				    revocations_received(&peer->their_shachain.chain), revokenum);
		return -1;
	}

	/* BOLT #2:
	 *
	 * A receiving node MAY fail if the `per_commitment_secret` was not
	 * generated by the protocol in [BOLT #3]
	 */
	if (!wallet_shachain_add_hash(peer->ld->wallet, &peer->their_shachain,
				      shachain_index(revokenum),
				      &per_commitment_secret)) {
		char *err = tal_fmt(peer,
				    "Bad per_commitment_secret %s for %"PRIu64,
				    type_to_string(msg, struct sha256,
						   &per_commitment_secret),
				    revokenum);
		peer_fail_permanent(peer, take((u8 *)err));
		return -1;
	}

	/* FIXME: Check per_commitment_secret -> per_commit_point */
	update_per_commit_point(peer, &next_per_commitment_point);

	/* FIXME: Commit shachain and next_per_commit_point to db */

	/* Tell it we've committed, and to go ahead with revoke. */
	msg = towire_channel_got_revoke_reply(msg);
	subd_send_msg(peer->owner, take(msg));

	/* Now, any HTLCs we need to immediately fail? */
	for (i = 0; i < tal_count(changed); i++) {
		struct htlc_in *hin;

		if (!failcodes[i])
			continue;

		hin = find_htlc_in(&peer->ld->htlcs_in, peer, changed[i].id);
		local_fail_htlc(hin, failcodes[i]);
	}
	if (!wallet_channel_save(peer->ld->wallet, peer->channel)) {
		fatal("Could not save channel to database: %s",
		      peer->ld->wallet->db->err);
	}

	return 0;
}

static void *tal_arr_append_(void **p, size_t size)
{
	size_t n = tal_len(*p) / size;
	tal_resize_(p, size, n+1, false);
	return (char *)(*p) + n * size;
}
#define tal_arr_append(p) tal_arr_append_((void **)(p), sizeof(**(p)))

static void add_htlc(struct added_htlc **htlcs,
		     enum htlc_state **htlc_states,
		     u64 id,
		     u64 amount_msat,
		     const struct sha256 *payment_hash,
		     u32 cltv_expiry,
		     const u8 onion_routing_packet[TOTAL_PACKET_SIZE],
		     enum htlc_state state)
{
	struct added_htlc *a;
	enum htlc_state *h;

	a = tal_arr_append(htlcs);
	h = tal_arr_append(htlc_states);

	a->id = id;
	a->amount_msat = amount_msat;
	a->payment_hash = *payment_hash;
	a->cltv_expiry = cltv_expiry;
	memcpy(a->onion_routing_packet, onion_routing_packet,
	       sizeof(a->onion_routing_packet));
	*h = state;
}

static void add_fulfill(u64 id, enum side side,
			const struct preimage *payment_preimage,
			struct fulfilled_htlc **fulfilled_htlcs,
			enum side **fulfilled_sides)
{
	struct fulfilled_htlc *f;
	enum side *s;

	f = tal_arr_append(fulfilled_htlcs);
	s = tal_arr_append(fulfilled_sides);
	f->id = id;
	f->payment_preimage = *payment_preimage;
	*s = side;
}

static void add_fail(u64 id, enum side side,
		     const u8 *failuremsg,
		     struct failed_htlc **failed_htlcs,
		     enum side **failed_sides)
{
	struct failed_htlc *f;
	enum side *s;

	f = tal_arr_append(failed_htlcs);
	s = tal_arr_append(failed_sides);
	f->id = id;
	f->failreason = tal_dup_arr(*failed_htlcs, u8,
				    failuremsg, tal_len(failuremsg), 0);
	*s = side;
}

/* FIXME: Load direct from db. */
void peer_htlcs(const tal_t *ctx,
		const struct peer *peer,
		struct added_htlc **htlcs,
		enum htlc_state **htlc_states,
		struct fulfilled_htlc **fulfilled_htlcs,
		enum side **fulfilled_sides,
		struct failed_htlc **failed_htlcs,
		enum side **failed_sides)
{
	struct htlc_in_map_iter ini;
	struct htlc_out_map_iter outi;
	struct htlc_in *hin;
	struct htlc_out *hout;

	*htlcs = tal_arr(ctx, struct added_htlc, 0);
	*htlc_states = tal_arr(ctx, enum htlc_state, 0);
	*fulfilled_htlcs = tal_arr(ctx, struct fulfilled_htlc, 0);
	*fulfilled_sides = tal_arr(ctx, enum side, 0);
	*failed_htlcs = tal_arr(ctx, struct failed_htlc, 0);
	*failed_sides = tal_arr(ctx, enum side, 0);

	for (hin = htlc_in_map_first(&peer->ld->htlcs_in, &ini);
	     hin;
	     hin = htlc_in_map_next(&peer->ld->htlcs_in, &ini)) {
		if (hin->key.peer != peer)
			continue;

		add_htlc(htlcs, htlc_states,
			 hin->key.id, hin->msatoshi, &hin->payment_hash,
			 hin->cltv_expiry, hin->onion_routing_packet,
			 hin->hstate);

		if (hin->failuremsg)
			add_fail(hin->key.id, REMOTE, hin->failuremsg,
				 failed_htlcs, failed_sides);
		if (hin->preimage)
			add_fulfill(hin->key.id, REMOTE, hin->preimage,
				    fulfilled_htlcs, fulfilled_sides);
	}

	for (hout = htlc_out_map_first(&peer->ld->htlcs_out, &outi);
	     hout;
	     hout = htlc_out_map_next(&peer->ld->htlcs_out, &outi)) {
		if (hout->key.peer != peer)
			continue;

		add_htlc(htlcs, htlc_states,
			 hout->key.id, hout->msatoshi, &hout->payment_hash,
			 hout->cltv_expiry, hout->onion_routing_packet,
			 hout->hstate);

		if (hout->failuremsg)
			add_fail(hout->key.id, LOCAL, hout->failuremsg,
				 failed_htlcs, failed_sides);
		if (hout->preimage)
			add_fulfill(hout->key.id, LOCAL, hout->preimage,
				    fulfilled_htlcs, fulfilled_sides);
	}
}