lightning/openingd/common.c

#include <ccan/ccan/tal/str/str.h>
#include <common/amount.h>
#include <common/channel_config.h>
#include <common/features.h>
#include <common/initial_commit_tx.h>
#include <common/type_to_string.h>
#include <openingd/common.h>

/*~ This is the key function that checks that their configuration is reasonable:
 * it applied for both the case where they're trying to open a channel, and when
 * they've accepted our open. */
bool check_config_bounds(const tal_t *ctx,
			 struct amount_sat funding,
			 u32 feerate_per_kw,
			 u32 max_to_self_delay,
			 struct amount_msat min_effective_htlc_capacity,
			 const struct channel_config *remoteconf,
			 const struct channel_config *localconf,
			 bool am_opener,
			 bool option_anchor_outputs,
			 char **err_reason)
{
	struct amount_sat capacity;
	struct amount_sat reserve;
	struct amount_sat fee;

	/* BOLT #2:
	 *
	 * The receiving node MUST fail the channel if:
	 *...
	 *  - `to_self_delay` is unreasonably large.
	 */
	if (remoteconf->to_self_delay > max_to_self_delay) {
		*err_reason = tal_fmt(ctx,
				      "to_self_delay %u larger than %u",
				      remoteconf->to_self_delay,
				      max_to_self_delay);
		return false;
	}

	/* BOLT #2:
	 *
	 * The receiving node MAY fail the channel if:
	 *...
	 *   - `funding_satoshis` is too small.
	 *   - it considers `htlc_minimum_msat` too large.
	 *   - it considers `max_htlc_value_in_flight_msat` too small.
	 *   - it considers `channel_reserve_satoshis` too large.
	 *   - it considers `max_accepted_htlcs` too small.
	 */
	/* We accumulate this into an effective bandwidth minimum. */

	/* Add both reserves to deduct from capacity. */
	if (!amount_sat_add(&reserve,
			    remoteconf->channel_reserve,
			    localconf->channel_reserve)) {
		*err_reason = tal_fmt(ctx,
				      "channel_reserve_satoshis %s"
				      " too large",
				      type_to_string(ctx, struct amount_sat,
						     &remoteconf->channel_reserve));
		return false;
	}

	/* BOLT-a12da24dd0102c170365124782b46d9710950ac1 #2:
	 *  - if `option_anchor_outputs` applies to this commitment
	 *    transaction and the sending node is the funder:
	 *   - MUST be able to additionally pay for `to_local_anchor` and
	 *    `to_remote_anchor` above its reserve.
	 */
	/* (We simply include in "reserve" here if they opened). */
	if (option_anchor_outputs
	    && !amount_sat_add(&reserve, reserve, AMOUNT_SAT(660))) {
		*err_reason = tal_fmt(ctx,
				      "cannot add anchors to reserve %s",
				      type_to_string(ctx, struct amount_sat,
						     &reserve));
		return false;
	}

	/* If reserves are larger than total sat, we fail. */
	if (!amount_sat_sub(&capacity, funding, reserve)) {
		*err_reason = tal_fmt(ctx, "channel_reserve_satoshis %s"
				      " and %s too large for funding %s",
				      type_to_string(ctx, struct amount_sat,
						     &remoteconf->channel_reserve),
				      type_to_string(ctx, struct amount_sat,
						     &localconf->channel_reserve),
				      type_to_string(ctx, struct amount_sat,
						     &funding));
		return false;
	}

	/* They have to pay for fees, too.  Assuming HTLC is dust, though,
	 * we don't account for an HTLC output. */
	fee = commit_tx_base_fee(feerate_per_kw, 0, option_anchor_outputs);
	if (!amount_sat_sub(&capacity, capacity, fee)) {
		*err_reason = tal_fmt(ctx, "channel_reserve_satoshis %s"
				      " and %s plus fee %s too large for "
				      "funding %s",
				      type_to_string(tmpctx, struct amount_sat,
					      	     &remoteconf->channel_reserve),
				      type_to_string(tmpctx, struct amount_sat,
						     &localconf->channel_reserve),
				      type_to_string(tmpctx, struct amount_sat,
						     &fee),
				      type_to_string(tmpctx, struct amount_sat,
						     &funding));
		return false;
	}

	/* If they set the max HTLC value to less than that number, it caps
	 * the channel capacity. */
	if (amount_sat_greater(capacity,
			       amount_msat_to_sat_round_down(remoteconf->max_htlc_value_in_flight)))
		capacity = amount_msat_to_sat_round_down(remoteconf->max_htlc_value_in_flight);

	/* If the minimum htlc is greater than the capacity, the channel is
	 * useless. */
	if (amount_msat_greater_sat(remoteconf->htlc_minimum, capacity)) {
		*err_reason = tal_fmt(ctx, "htlc_minimum_msat %s"
				      " too large for funding %s"
				      " capacity_msat %s",
				      type_to_string(ctx, struct amount_msat,
						     &remoteconf->htlc_minimum),
				      type_to_string(ctx, struct amount_sat,
						     &funding),
				      type_to_string(ctx, struct amount_sat,
						     &capacity));
		return false;
	}

	/* If the resulting channel doesn't meet our minimum "effective capacity"
	 * set by lightningd, don't bother opening it. */
	if (amount_msat_greater_sat(min_effective_htlc_capacity,
				    capacity)) {
		*err_reason = tal_fmt(ctx,
				      "channel capacity with funding %s,"
				      " reserves %s/%s,"
				      " max_htlc_value_in_flight_msat is %s,"
				      " channel capacity is %s, which is below %s",
				      type_to_string(ctx, struct amount_sat,
						     &funding),
				      type_to_string(ctx, struct amount_sat,
						     &remoteconf->channel_reserve),
				      type_to_string(ctx, struct amount_sat,
						     &localconf->channel_reserve),
				      type_to_string(ctx, struct amount_msat,
						     &remoteconf->max_htlc_value_in_flight),
				      type_to_string(ctx, struct amount_sat,
						     &capacity),
				      type_to_string(ctx, struct amount_msat,
						     &min_effective_htlc_capacity));
		return false;
	}

	/* We don't worry about how many HTLCs they accept, as long as > 0! */
	if (remoteconf->max_accepted_htlcs == 0) {
		*err_reason = tal_fmt(ctx,
				      "max_accepted_htlcs %u invalid",
				      remoteconf->max_accepted_htlcs);
		return false;
	}

	/* BOLT #2:
	 *
	 * The receiving node MUST fail the channel if:
	 *...
	 *  - `max_accepted_htlcs` is greater than 483.
	 */
	if (remoteconf->max_accepted_htlcs > 483) {
		*err_reason = tal_fmt(ctx,
				      "max_accepted_htlcs %u too large",
				      remoteconf->max_accepted_htlcs);
		return false;
	}

	/* BOLT #2:
	 *
	 * The receiving node MUST fail the channel if:
	 *...
	 *  - `dust_limit_satoshis` is greater than `channel_reserve_satoshis`.
	 */
	if (amount_sat_greater(remoteconf->dust_limit,
			       remoteconf->channel_reserve)) {
		*err_reason = tal_fmt(ctx,
				      "dust_limit_satoshis %s"
				      " too large for channel_reserve_satoshis %s",
				      type_to_string(ctx, struct amount_sat,
						     &remoteconf->dust_limit),
				      type_to_string(ctx, struct amount_sat,
						     &remoteconf->channel_reserve));
		return false;
	}

	return true;
}

u8 *no_upfront_shutdown_script(const tal_t *ctx,
			       struct feature_set *our_features,
			       const u8 *their_features)
{
#if DEVELOPER
	/* This is a hack, for feature testing */
	const char *e = getenv("DEV_OPENINGD_UPFRONT_SHUTDOWN_SCRIPT");
	if (e)
		return tal_hexdata(ctx, e, strlen(e));
#endif

	/* BOLT #2:
	 *
	 * - if both nodes advertised the `option_upfront_shutdown_script`
	 *   feature:
	 *   - MUST include `upfront_shutdown_script` with either a valid
	 *     `shutdown_scriptpubkey` as required by `shutdown`
	 *     `scriptpubkey`, or a zero-length `shutdown_scriptpubkey`
	 *     (ie. `0x0000`).
	 */
	if (feature_negotiated(our_features, their_features,
			       OPT_UPFRONT_SHUTDOWN_SCRIPT))
		return tal_arr(ctx, u8, 0);

	return NULL;
}