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initial_commit_tx.h
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/* Commit tx without HTLC support; needed for openingd. */
#ifndef LIGHTNING_COMMON_INITIAL_COMMIT_TX_H
#define LIGHTNING_COMMON_INITIAL_COMMIT_TX_H
#include "config.h"
#include <bitcoin/chainparams.h>
#include <bitcoin/pubkey.h>
#include <common/amount.h>
#include <common/htlc.h>
#include <common/utils.h>
struct bitcoin_txid;
struct keyset;
/* BOLT #3:
*
* This obscures the number of commitments made on the channel in the
* case of unilateral close, yet still provides a useful index for
* both nodes (who know the `payment_basepoint`s) to quickly find a
* revoked commitment transaction.
*/
u64 commit_number_obscurer(const struct pubkey *opener_payment_basepoint,
const struct pubkey *accepter_payment_basepoint);
/* Helper to calculate the base fee if we have this many htlc outputs */
static inline struct amount_sat commit_tx_base_fee(u32 feerate_per_kw,
size_t num_untrimmed_htlcs)
{
u64 weight;
/* BOLT #3:
*
* The base fee for a commitment transaction:
* - MUST be calculated to match:
* 1. Start with `weight` = 724.
*/
weight = 724;
/* BOLT #3:
*
* 2. For each committed HTLC, if that output is not trimmed as
* specified in [Trimmed Outputs](#trimmed-outputs), add 172
* to `weight`.
*/
weight += 172 * num_untrimmed_htlcs;
if (chainparams->is_elements) {
/* Each transaction has surjection and rangeproof (both empty
* for us as long as we use unblinded L-BTC transactions). */
weight += 2 * 4;
/* Inputs have 6 bytes of blank proofs attached. This TX only
* has a single input. */
weight += 6;
/* Each direct output has a bit more weight to it */
weight += (32 + 1 + 1 + 1) * 4 * 2; /* Elements added fields */
/* Each HTLC output also carries a bit more weight */
weight += (32 + 1 + 1 + 1) * 4 * num_untrimmed_htlcs;
/* For elements we also need to add the fee output and the
* overhead for rangeproofs into the mix. */
weight += (8 + 1) * 4; /* Bitcoin style output */
weight += (32 + 1 + 1 + 1) * 4; /* Elements added fields */
}
/* BOLT #3:
*
* 3. Multiply `feerate_per_kw` by `weight`, divide by 1000 (rounding
* down).
*/
return amount_tx_fee(feerate_per_kw, weight);
}
/**
* initial_commit_tx: create (unsigned) commitment tx to spend the funding tx output
* @ctx: context to allocate transaction and @htlc_map from.
* @funding_txid, @funding_out, @funding: funding outpoint.
* @funding_wscript: scriptPubkey of the funding output
* @opener: is the LOCAL or REMOTE paying the fee?
* @keyset: keys derived for this commit tx.
* @feerate_per_kw: feerate to use
* @dust_limit: dust limit below which to trim outputs.
* @self_pay: amount to pay directly to self
* @other_pay: amount to pay directly to the other side
* @self_reserve: reserve the other side insisted we have
* @obscured_commitment_number: number to encode in commitment transaction
* @direct_outputs: If non-NULL, fill with pointers to the direct (non-HTLC) outputs (or NULL if none).
* @side: side to generate commitment transaction for.
* @err_reason: When NULL is returned, this will point to a human readable reason.
*
* We need to be able to generate the remote side's tx to create signatures,
* but the BOLT is expressed in terms of generating our local commitment
* transaction, so we carefully use the terms "self" and "other" here.
*/
struct bitcoin_tx *initial_commit_tx(const tal_t *ctx,
const struct bitcoin_txid *funding_txid,
unsigned int funding_txout,
struct amount_sat funding,
u8 *funding_wscript,
enum side opener,
u16 to_self_delay,
const struct keyset *keyset,
u32 feerate_per_kw,
struct amount_sat dust_limit,
struct amount_msat self_pay,
struct amount_msat other_pay,
struct amount_sat self_reserve,
u64 obscured_commitment_number,
struct wally_tx_output *direct_outputs[NUM_SIDES],
enum side side,
char** err_reason);
/* try_subtract_fee - take away this fee from the opener (and return true), or all if insufficient (and return false). */
bool try_subtract_fee(enum side opener, enum side side,
struct amount_sat base_fee,
struct amount_msat *self,
struct amount_msat *other);
/* Generate the witness script for the to-self output:
* scriptpubkey_p2wsh(ctx, wscript) gives the scriptpubkey */
u8 *to_self_wscript(const tal_t *ctx,
u16 to_self_delay,
const struct keyset *keyset);
/* To-other is simply: scriptpubkey_p2wpkh(tx, keyset->other_payment_key) */
#endif /* LIGHTNING_COMMON_INITIAL_COMMIT_TX_H */