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#include <assert.h>
#include <bitcoin/block.h>
#include <bitcoin/chainparams.h>
#include <bitcoin/psbt.h>
#include <bitcoin/script.h>
#include <bitcoin/tx.h>
#include <ccan/cast/cast.h>
#include <ccan/crypto/sha256/sha256.h>
#include <ccan/endian/endian.h>
#include <ccan/mem/mem.h>
#include <ccan/read_write_all/read_write_all.h>
#include <ccan/str/hex/hex.h>
#include <common/type_to_string.h>
#include <stdio.h>
#include <wire/wire.h>
#define SEGREGATED_WITNESS_FLAG 0x1
/* FIXME: When wally exposes this, we will clash and can remove this one */
int wally_tx_clone(struct wally_tx *tx, struct wally_tx **output)
{
u8 *txlin = linearize_wtx(NULL, tx);
int flags = WALLY_TX_FLAG_USE_WITNESS;
int ret;
if (chainparams->is_elements)
flags |= WALLY_TX_FLAG_USE_ELEMENTS;
ret = wally_tx_from_bytes(txlin, tal_bytelen(txlin), flags, output);
tal_free(txlin);
return ret;
}
struct bitcoin_tx_output *new_tx_output(const tal_t *ctx,
struct amount_sat amount,
const u8 *script)
{
struct bitcoin_tx_output *output = tal(ctx, struct bitcoin_tx_output);
output->amount = amount;
output->script = tal_dup_arr(output, u8, script, tal_count(script), 0);
return output;
}
int bitcoin_tx_add_output(struct bitcoin_tx *tx, const u8 *script,
u8 *wscript, struct amount_sat amount)
{
size_t i = tx->wtx->num_outputs;
struct wally_tx_output *output;
struct wally_psbt_output *psbt_out;
int ret;
u64 satoshis = amount.satoshis; /* Raw: low-level helper */
const struct chainparams *chainparams = tx->chainparams;
assert(i < tx->wtx->outputs_allocation_len);
assert(tx->wtx != NULL);
assert(chainparams);
if (chainparams->is_elements) {
u8 value[9];
ret = wally_tx_confidential_value_from_satoshi(satoshis, value,
sizeof(value));
assert(ret == WALLY_OK);
ret = wally_tx_elements_output_init_alloc(
script, tal_bytelen(script), chainparams->fee_asset_tag, 33,
value, sizeof(value), NULL, 0, NULL, 0, NULL, 0, &output);
assert(ret == WALLY_OK);
/* Cheat a bit by also setting the numeric satoshi value,
* otherwise we end up converting a number of times */
output->satoshi = satoshis;
} else {
ret = wally_tx_output_init_alloc(satoshis, script,
tal_bytelen(script), &output);
assert(ret == WALLY_OK);
}
ret = wally_tx_add_output(tx->wtx, output);
assert(ret == WALLY_OK);
psbt_out = psbt_add_output(tx->psbt, output, i);
if (wscript) {
ret = wally_psbt_output_set_witness_script(psbt_out,
wscript,
tal_bytelen(wscript));
assert(ret == WALLY_OK);
}
wally_tx_output_free(output);
bitcoin_tx_output_set_amount(tx, i, amount);
return i;
}
int bitcoin_tx_add_multi_outputs(struct bitcoin_tx *tx,
struct bitcoin_tx_output **outputs)
{
for (size_t j = 0; j < tal_count(outputs); j++)
bitcoin_tx_add_output(tx, outputs[j]->script,
NULL, outputs[j]->amount);
return tx->wtx->num_outputs;
}
bool elements_tx_output_is_fee(const struct bitcoin_tx *tx, int outnum)
{
assert(outnum < tx->wtx->num_outputs);
return chainparams->is_elements &&
tx->wtx->outputs[outnum].script_len == 0;
}
struct amount_sat bitcoin_tx_compute_fee_w_inputs(const struct bitcoin_tx *tx,
struct amount_sat input_val)
{
struct amount_asset asset;
bool ok;
for (size_t i = 0; i < tx->wtx->num_outputs; i++) {
asset = bitcoin_tx_output_get_amount(tx, i);
if (elements_tx_output_is_fee(tx, i) ||
!amount_asset_is_main(&asset))
continue;
ok = amount_sat_sub(&input_val, input_val,
amount_asset_to_sat(&asset));
if (!ok)
return AMOUNT_SAT(0);
}
return input_val;
}
/**
* Compute how much fee we are actually sending with this transaction.
*/
struct amount_sat bitcoin_tx_compute_fee(const struct bitcoin_tx *tx)
{
struct amount_sat input_total = AMOUNT_SAT(0), input_amt;
bool ok;
for (size_t i = 0; i < tx->psbt->num_inputs; i++) {
input_amt = psbt_input_get_amount(tx->psbt, i);
ok = amount_sat_add(&input_total, input_total, input_amt);
assert(ok);
}
return bitcoin_tx_compute_fee_w_inputs(tx, input_total);
}
/*
* Add an explicit fee output if necessary.
*
* An explicit fee output is only necessary if we are using an elements
* transaction, and we have a non-zero fee. This method may be called multiple
* times.
*
* Returns the position of the fee output, or -1 in the case of non-elements
* transactions.
*/
static int elements_tx_add_fee_output(struct bitcoin_tx *tx)
{
struct amount_sat fee = bitcoin_tx_compute_fee(tx);
int pos;
/* If we aren't using elements, we don't add explicit fee outputs */
if (!chainparams->is_elements || amount_sat_eq(fee, AMOUNT_SAT(0)))
return -1;
/* Try to find any existing fee output */
for (pos = 0; pos < tx->wtx->num_outputs; pos++) {
if (elements_tx_output_is_fee(tx, pos))
break;
}
if (pos == tx->wtx->num_outputs)
return bitcoin_tx_add_output(tx, NULL, NULL, fee);
else {
bitcoin_tx_output_set_amount(tx, pos, fee);
return pos;
}
}
void bitcoin_tx_set_locktime(struct bitcoin_tx *tx, u32 locktime)
{
tx->wtx->locktime = locktime;
tx->psbt->tx->locktime = locktime;
}
int bitcoin_tx_add_input(struct bitcoin_tx *tx, const struct bitcoin_txid *txid,
u32 outnum, u32 sequence, const u8 *scriptSig,
struct amount_sat amount, const u8 *scriptPubkey,
const u8 *input_wscript)
{
struct wally_tx_input *input;
int wally_err;
size_t i;
assert(tx->wtx != NULL);
i = tx->wtx->num_inputs;
wally_err = wally_tx_input_init_alloc(txid->shad.sha.u.u8,
sizeof(struct bitcoin_txid),
outnum, sequence,
scriptSig, tal_bytelen(scriptSig),
NULL /* Empty witness stack */,
&input);
assert(wally_err == WALLY_OK);
input->features = chainparams->is_elements ? WALLY_TX_IS_ELEMENTS : 0;
wally_tx_add_input(tx->wtx, input);
psbt_add_input(tx->psbt, input, i);
if (input_wscript) {
/* Add the prev output's data into the PSBT struct */
psbt_input_set_prev_utxo_wscript(tx->psbt, i, input_wscript, amount);
} else if (scriptPubkey) {
if (is_p2wsh(scriptPubkey, NULL) || is_p2wpkh(scriptPubkey, NULL) ||
/* FIXME: assert that p2sh inputs are witness/are accompanied by a redeemscript+witnessscript */
is_p2sh(scriptPubkey, NULL)) {
/* the only way to get here currently with a p2sh script is via a p2sh-p2wpkh script
* that we've created ...*/
/* Relevant section from bip-0174, emphasis mine:
* ** Value: The entire transaction output in network serialization which the current input spends from.
* This should only be present for inputs which spend segwit outputs, _including P2SH embedded ones._
*/
psbt_input_set_prev_utxo(tx->psbt, i, scriptPubkey, amount);
}
}
wally_tx_input_free(input);
return i;
}
bool bitcoin_tx_check(const struct bitcoin_tx *tx)
{
u8 *newtx;
size_t written;
int flags = WALLY_TX_FLAG_USE_WITNESS;
if (wally_tx_get_length(tx->wtx, flags, &written) != WALLY_OK)
return false;
newtx = tal_arr(tmpctx, u8, written);
if (wally_tx_to_bytes(tx->wtx, flags, newtx, written, &written) !=
WALLY_OK)
return false;
if (written != tal_bytelen(newtx))
return false;
return true;
}
void bitcoin_tx_output_set_amount(struct bitcoin_tx *tx, int outnum,
struct amount_sat amount)
{
u64 satoshis = amount.satoshis; /* Raw: low-level helper */
struct wally_tx_output *output = &tx->wtx->outputs[outnum];
assert(outnum < tx->wtx->num_outputs);
if (chainparams->is_elements) {
int ret = wally_tx_confidential_value_from_satoshi(
satoshis, output->value, output->value_len);
assert(ret == WALLY_OK);
} else {
output->satoshi = satoshis;
/* update the global tx for the psbt also */
output = &tx->psbt->tx->outputs[outnum];
output->satoshi = satoshis;
}
}
const u8 *wally_tx_output_get_script(const tal_t *ctx,
const struct wally_tx_output *output)
{
if (output->script == NULL) {
/* This can happen for coinbase transactions and pegin
* transactions */
return NULL;
}
return tal_dup_arr(ctx, u8, output->script, output->script_len, 0);
}
const u8 *bitcoin_tx_output_get_script(const tal_t *ctx,
const struct bitcoin_tx *tx, int outnum)
{
const struct wally_tx_output *output;
assert(outnum < tx->wtx->num_outputs);
output = &tx->wtx->outputs[outnum];
return wally_tx_output_get_script(ctx, output);
}
u8 *bitcoin_tx_output_get_witscript(const tal_t *ctx, const struct bitcoin_tx *tx,
int outnum)
{
struct wally_psbt_output *out;
assert(outnum < tx->psbt->num_outputs);
out = &tx->psbt->outputs[outnum];
if (out->witness_script_len == 0)
return NULL;
return tal_dup_arr(ctx, u8, out->witness_script, out->witness_script_len, 0);
}
struct amount_asset bitcoin_tx_output_get_amount(const struct bitcoin_tx *tx,
int outnum)
{
assert(tx->chainparams);
assert(outnum < tx->wtx->num_outputs);
return wally_tx_output_get_amount(&tx->wtx->outputs[outnum]);
}
void bitcoin_tx_output_get_amount_sat(struct bitcoin_tx *tx, int outnum,
struct amount_sat *amount)
{
struct amount_asset asset_amt;
asset_amt = bitcoin_tx_output_get_amount(tx, outnum);
assert(amount_asset_is_main(&asset_amt));
*amount = amount_asset_to_sat(&asset_amt);
}
void bitcoin_tx_input_set_witness(struct bitcoin_tx *tx, int innum,
u8 **witness)
{
struct wally_tx_witness_stack *stack = NULL;
size_t stack_size = tal_count(witness);
/* Free any lingering witness */
if (witness) {
wally_tx_witness_stack_init_alloc(stack_size, &stack);
for (size_t i = 0; i < stack_size; i++)
wally_tx_witness_stack_add(stack, witness[i],
tal_bytelen(witness[i]));
}
wally_tx_set_input_witness(tx->wtx, innum, stack);
/* Also add to the psbt */
if (stack)
wally_psbt_input_set_final_witness(&tx->psbt->inputs[innum], stack);
else {
/* FIXME: libwally-psbt doesn't allow 'unsetting' of witness via
* the set method at the moment, so we do it manually*/
struct wally_psbt_input *in = &tx->psbt->inputs[innum];
if (in->final_witness)
wally_tx_witness_stack_free(in->final_witness);
in->final_witness = NULL;
}
if (stack)
wally_tx_witness_stack_free(stack);
if (taken(witness))
tal_free(witness);
}
void bitcoin_tx_input_set_script(struct bitcoin_tx *tx, int innum, u8 *script)
{
struct wally_psbt_input *in;
wally_tx_set_input_script(tx->wtx, innum, script, tal_bytelen(script));
/* Also add to the psbt */
assert(innum < tx->psbt->num_inputs);
in = &tx->psbt->inputs[innum];
wally_psbt_input_set_final_script_sig(in, script, tal_bytelen(script));
}
const u8 *bitcoin_tx_input_get_witness(const tal_t *ctx,
const struct bitcoin_tx *tx, int innum,
int witnum)
{
const u8 *witness_item;
struct wally_tx_witness_item *item;
assert(innum < tx->wtx->num_inputs);
assert(witnum < tx->wtx->inputs[innum].witness->num_items);
item = &tx->wtx->inputs[innum].witness->items[witnum];
witness_item =
tal_dup_arr(ctx, u8, item->witness, item->witness_len, 0);
return witness_item;
}
void bitcoin_tx_input_get_txid(const struct bitcoin_tx *tx, int innum,
struct bitcoin_txid *out)
{
assert(innum < tx->wtx->num_inputs);
wally_tx_input_get_txid(&tx->wtx->inputs[innum], out);
}
void wally_tx_input_get_txid(const struct wally_tx_input *in,
struct bitcoin_txid *txid)
{
BUILD_ASSERT(sizeof(struct bitcoin_txid) == sizeof(in->txhash));
memcpy(txid, in->txhash, sizeof(struct bitcoin_txid));
}
/* BIP144:
* If the witness is empty, the old serialization format should be used. */
static bool uses_witness(const struct wally_tx *wtx)
{
size_t i;
for (i = 0; i < wtx->num_inputs; i++) {
if (wtx->inputs[i].witness)
return true;
}
return false;
}
u8 *linearize_tx(const tal_t *ctx, const struct bitcoin_tx *tx)
{
return linearize_wtx(ctx, tx->wtx);
}
u8 *linearize_wtx(const tal_t *ctx, const struct wally_tx *wtx)
{
u8 *arr;
u32 flag = 0;
size_t len, written;
int res;
if (uses_witness(wtx))
flag |= WALLY_TX_FLAG_USE_WITNESS;
res = wally_tx_get_length(wtx, flag, &len);
assert(res == WALLY_OK);
arr = tal_arr(ctx, u8, len);
res = wally_tx_to_bytes(wtx, flag, arr, len, &written);
assert(len == written);
return arr;
}
size_t bitcoin_tx_weight(const struct bitcoin_tx *tx)
{
size_t weight;
int ret = wally_tx_get_weight(tx->wtx, &weight);
assert(ret == WALLY_OK);
return weight;
}
void wally_txid(const struct wally_tx *wtx, struct bitcoin_txid *txid)
{
u8 *arr;
size_t len, written;
int res;
/* Never use BIP141 form for txid */
res = wally_tx_get_length(wtx, 0, &len);
assert(res == WALLY_OK);
arr = tal_arr(NULL, u8, len);
res = wally_tx_to_bytes(wtx, 0, arr, len, &written);
assert(len == written);
sha256_double(&txid->shad, arr, len);
tal_free(arr);
}
/* We used to have beautiful, optimal code which fed the tx parts directly
* into sha256_update(). But that was before libwally; but now we don't have
* to maintain our own transaction code, so there's that. */
void bitcoin_txid(const struct bitcoin_tx *tx, struct bitcoin_txid *txid)
{
wally_txid(tx->wtx, txid);
}
/* Use the bitcoin_tx destructor to also free the wally_tx */
static void bitcoin_tx_destroy(struct bitcoin_tx *tx)
{
wally_tx_free(tx->wtx);
}
struct bitcoin_tx *bitcoin_tx(const tal_t *ctx,
const struct chainparams *chainparams,
varint_t input_count, varint_t output_count,
u32 nlocktime)
{
struct bitcoin_tx *tx = tal(ctx, struct bitcoin_tx);
assert(chainparams);
/* If we are constructing an elements transaction we need to
* explicitly add the fee as an extra output. So allocate one more
* than the outputs we need internally. */
if (chainparams->is_elements)
output_count += 1;
wally_tx_init_alloc(WALLY_TX_VERSION_2, 0, input_count, output_count,
&tx->wtx);
tal_add_destructor(tx, bitcoin_tx_destroy);
tx->wtx->locktime = nlocktime;
tx->wtx->version = 2;
tx->chainparams = chainparams;
tx->psbt = new_psbt(tx, tx->wtx);
return tx;
}
void bitcoin_tx_finalize(struct bitcoin_tx *tx)
{
elements_tx_add_fee_output(tx);
assert(bitcoin_tx_check(tx));
}
struct bitcoin_tx *bitcoin_tx_with_psbt(const tal_t *ctx, struct wally_psbt *psbt STEALS)
{
struct bitcoin_tx *tx = bitcoin_tx(ctx, chainparams,
psbt->tx->num_inputs,
psbt->tx->num_outputs,
psbt->tx->locktime);
wally_tx_free(tx->wtx);
tx->wtx = psbt_finalize(psbt, false);
if (!tx->wtx && wally_tx_clone(psbt->tx, &tx->wtx) != WALLY_OK)
return NULL;
tal_free(tx->psbt);
tx->psbt = tal_steal(tx, psbt);
return tx;
}
struct bitcoin_tx *pull_bitcoin_tx(const tal_t *ctx, const u8 **cursor,
size_t *max)
{
size_t wsize;
int flags = WALLY_TX_FLAG_USE_WITNESS;
struct bitcoin_tx *tx = tal(ctx, struct bitcoin_tx);
if (chainparams->is_elements)
flags |= WALLY_TX_FLAG_USE_ELEMENTS;
if (wally_tx_from_bytes(*cursor, *max, flags, &tx->wtx) != WALLY_OK) {
fromwire_fail(cursor, max);
return tal_free(tx);
}
tal_add_destructor(tx, bitcoin_tx_destroy);
/* For whatever reason the length computation gets upset if we tell it
* that we are using elements. It wants to discover it on its own, NO
* CLUES! (Ms. Doyle)
*
* https://github.com/ElementsProject/libwally-core/issues/139
*/
wally_tx_get_length(tx->wtx, flags & ~WALLY_TX_FLAG_USE_ELEMENTS,
&wsize);
tx->chainparams = chainparams;
tx->psbt = new_psbt(tx, tx->wtx);
*cursor += wsize;
*max -= wsize;
return tx;
}
struct bitcoin_tx *bitcoin_tx_from_hex(const tal_t *ctx, const char *hex,
size_t hexlen)
{
const char *end;
u8 *linear_tx;
const u8 *p;
struct bitcoin_tx *tx;
size_t len;
end = memchr(hex, '\n', hexlen);
if (!end)
end = hex + hexlen;
len = hex_data_size(end - hex);
p = linear_tx = tal_arr(ctx, u8, len);
if (!hex_decode(hex, end - hex, linear_tx, len))
goto fail;
tx = pull_bitcoin_tx(ctx, &p, &len);
if (!tx)
goto fail;
if (len)
goto fail_free_tx;
tal_free(linear_tx);
return tx;
fail_free_tx:
tal_free(tx);
fail:
tal_free(linear_tx);
return NULL;
}
/* <sigh>. Bitcoind represents hashes as little-endian for RPC. */
static void reverse_bytes(u8 *arr, size_t len)
{
unsigned int i;
for (i = 0; i < len / 2; i++) {
unsigned char tmp = arr[i];
arr[i] = arr[len - 1 - i];
arr[len - 1 - i] = tmp;
}
}
bool bitcoin_txid_from_hex(const char *hexstr, size_t hexstr_len,
struct bitcoin_txid *txid)
{
if (!hex_decode(hexstr, hexstr_len, txid, sizeof(*txid)))
return false;
reverse_bytes(txid->shad.sha.u.u8, sizeof(txid->shad.sha.u.u8));
return true;
}
bool bitcoin_txid_to_hex(const struct bitcoin_txid *txid,
char *hexstr, size_t hexstr_len)
{
struct sha256_double rev = txid->shad;
reverse_bytes(rev.sha.u.u8, sizeof(rev.sha.u.u8));
return hex_encode(&rev, sizeof(rev), hexstr, hexstr_len);
}
static char *fmt_bitcoin_tx(const tal_t *ctx, const struct bitcoin_tx *tx)
{
u8 *lin = linearize_tx(ctx, tx);
char *s = tal_hex(ctx, lin);
tal_free(lin);
return s;
}
static char *fmt_bitcoin_txid(const tal_t *ctx, const struct bitcoin_txid *txid)
{
char *hexstr = tal_arr(ctx, char, hex_str_size(sizeof(*txid)));
bitcoin_txid_to_hex(txid, hexstr, hex_str_size(sizeof(*txid)));
return hexstr;
}
REGISTER_TYPE_TO_STRING(bitcoin_tx, fmt_bitcoin_tx);
REGISTER_TYPE_TO_STRING(bitcoin_txid, fmt_bitcoin_txid);
void fromwire_bitcoin_txid(const u8 **cursor, size_t *max,
struct bitcoin_txid *txid)
{
fromwire_sha256_double(cursor, max, &txid->shad);
}
struct bitcoin_tx *fromwire_bitcoin_tx(const tal_t *ctx,
const u8 **cursor, size_t *max)
{
struct bitcoin_tx *tx;
tx = pull_bitcoin_tx(ctx, cursor, max);
if (!tx)
return fromwire_fail(cursor, max);
/* pull_bitcoin_tx sets the psbt */
tal_free(tx->psbt);
tx->psbt = fromwire_wally_psbt(tx, cursor, max);
return tx;
}
void towire_bitcoin_txid(u8 **pptr, const struct bitcoin_txid *txid)
{
towire_sha256_double(pptr, &txid->shad);
}
void towire_bitcoin_tx(u8 **pptr, const struct bitcoin_tx *tx)
{
u8 *lin = linearize_tx(tmpctx, tx);
towire_u8_array(pptr, lin, tal_count(lin));
towire_wally_psbt(pptr, tx->psbt);
}
struct bitcoin_tx_output *fromwire_bitcoin_tx_output(const tal_t *ctx,
const u8 **cursor, size_t *max)
{
struct bitcoin_tx_output *output = tal(ctx, struct bitcoin_tx_output);
output->amount = fromwire_amount_sat(cursor, max);
u16 script_len = fromwire_u16(cursor, max);
output->script = fromwire_tal_arrn(output, cursor, max, script_len);
if (!*cursor)
return tal_free(output);
return output;
}
void towire_bitcoin_tx_output(u8 **pptr, const struct bitcoin_tx_output *output)
{
towire_amount_sat(pptr, output->amount);
towire_u16(pptr, tal_count(output->script));
towire_u8_array(pptr, output->script, tal_count(output->script));
}
bool wally_tx_input_spends(const struct wally_tx_input *input,
const struct bitcoin_txid *txid,
int outnum)
{
/* Useful, as tx_part can have some NULL inputs */
if (!input)
return false;
BUILD_ASSERT(sizeof(*txid) == sizeof(input->txhash));
if (memcmp(txid, input->txhash, sizeof(*txid)) != 0)
return false;
return input->index == outnum;
}
/* FIXME(cdecker) Make the caller pass in a reference to amount_asset, and
* return false if unintelligible/encrypted. (WARN UNUSED). */
struct amount_asset
wally_tx_output_get_amount(const struct wally_tx_output *output)
{
struct amount_asset amount;
be64 raw;
if (chainparams->is_elements) {
assert(output->asset_len == sizeof(amount.asset));
memcpy(&amount.asset, output->asset, sizeof(amount.asset));
/* We currently only support explicit value asset tags, others
* are confidential, so don't even try to assign a value to
* it. */
if (output->asset[0] == 0x01) {
memcpy(&raw, output->value + 1, sizeof(raw));
amount.value = be64_to_cpu(raw);
} else {
amount.value = 0;
}
} else {
/* Do not assign amount.asset, we should never touch it in
* non-elements scenarios. */
amount.value = output->satoshi;
}
return amount;
}
/* Various weights of transaction parts. */
size_t bitcoin_tx_core_weight(size_t num_inputs, size_t num_outputs)
{
size_t weight;
/* version, input count, output count, locktime */
weight = (4 + varint_size(num_inputs) + varint_size(num_outputs) + 4)
* 4;
/* Add segwit fields: marker + flag */
weight += 1 + 1;
/* A couple of things need to change for elements: */
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;
/* An elements transaction has 1 additional output for fees */
weight += bitcoin_tx_output_weight(0);
}
return weight;
}
size_t bitcoin_tx_output_weight(size_t outscript_len)
{
size_t weight;
/* amount, len, scriptpubkey */
weight = (8 + varint_size(outscript_len) + outscript_len) * 4;
if (chainparams->is_elements) {
/* Each output additionally has an asset_tag (1 + 32), value
* is prefixed by a version (1 byte), an empty nonce (1
* byte), two empty proofs (2 bytes). */
weight += (32 + 1 + 1 + 1) * 4;
}
return weight;
}
/* We grind signatures to get them down to 71 bytes (+1 for sighash flags) */
size_t bitcoin_tx_input_sig_weight(void)
{
return 1 + 71 + 1;
}
/* We only do segwit inputs, and we assume witness is sig + key */
size_t bitcoin_tx_simple_input_weight(bool p2sh)
{
size_t weight;
/* Input weight: txid + index + sequence */
weight = (32 + 4 + 4) * 4;
/* We always encode the length of the script, even if empty */
weight += 1 * 4;
/* P2SH variants include push of <0 <20-byte-key-hash>> */
if (p2sh)
weight += 23 * 4;
/* Account for witness (1 byte count + sig + key) */
weight += 1 + (bitcoin_tx_input_sig_weight() + 1 + 33);
/* Elements inputs have 6 bytes of blank proofs attached. */
if (chainparams->is_elements)
weight += 6;
return weight;
}
struct amount_sat change_amount(struct amount_sat excess, u32 feerate_perkw)
{
size_t outweight;
/* Must be able to pay for its own additional weight */
outweight = bitcoin_tx_output_weight(BITCOIN_SCRIPTPUBKEY_P2WPKH_LEN);
if (!amount_sat_sub(&excess,
excess, amount_tx_fee(feerate_perkw, outweight)))
return AMOUNT_SAT(0);
/* Must be non-dust */
if (!amount_sat_greater_eq(excess, chainparams->dust_limit))
return AMOUNT_SAT(0);
return excess;
}