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fundpsbt: simplify the logic a little.

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It keeps multiple different variables around the loop, but a simple
"are we done yet?" helper makes this clearer and reduces special
cases or all-vs-target.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2020-08-07 10:58:47 +09:30
parent a6a8a40594
commit 601fc805d7
1 changed files with 52 additions and 40 deletions
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92
wallet/reservation.c
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@@ -175,6 +175,38 @@ static const struct json_command unreserveinputs_command = {
};
AUTODATA(json_command, &unreserveinputs_command);
/**
* inputs_sufficient - are we there yet?
* @input: total input amount
* @amount: required output amount
* @feerate_per_kw: feerate we have to pay
* @weight: weight of transaction so far.
* @diff: (output) set to amount over or under requirements.
*
* Returns true if inputs >= fees + amount, otherwise false. diff is
* the amount over (if returns true) or under (if returns false)
*/
static bool inputs_sufficient(struct amount_sat input,
struct amount_sat amount,
u32 feerate_per_kw,
size_t weight,
struct amount_sat *diff)
{
struct amount_sat fee;
fee = amount_tx_fee(feerate_per_kw, weight);
/* If we can't add fees, amount is huge (e.g. "all") */
if (!amount_sat_add(&amount, amount, fee))
return false;
/* One of these must work! */
if (amount_sat_sub(diff, input, amount))
return true;
if (!amount_sat_sub(diff, amount, input))
abort();
return false;
}
static struct command_result *json_fundpsbt(struct command *cmd,
const char *buffer,
@@ -185,7 +217,7 @@ static struct command_result *json_fundpsbt(struct command *cmd,
struct utxo **utxos;
u32 *feerate_per_kw;
u32 *minconf, *weight;
struct amount_sat *amount, input, needed, excess, total_fee;
struct amount_sat *amount, input, diff;
bool all, *reserve;
u32 locktime, maxheight, current_height;
struct bitcoin_tx *tx;
@@ -204,27 +236,21 @@ static struct command_result *json_fundpsbt(struct command *cmd,
current_height = get_block_height(cmd->ld->topology);
/* Can overflow if amount is "all" */
if (!amount_sat_add(amount, *amount,
amount_tx_fee(*feerate_per_kw, *weight)))
;
/* We keep adding until we meet their output requirements. */
input = AMOUNT_SAT(0);
utxos = tal_arr(cmd, struct utxo *, 0);
total_fee = amount_tx_fee(*feerate_per_kw, *weight);
while (amount_sat_sub(&needed, *amount, input)
&& !amount_sat_eq(needed, AMOUNT_SAT(0))) {
input = AMOUNT_SAT(0);
while (!inputs_sufficient(input, *amount, *feerate_per_kw, *weight,
&diff)) {
struct utxo *utxo;
utxo = wallet_find_utxo(utxos, cmd->ld->wallet,
cmd->ld->topology->tip->height,
&needed,
&diff,
*feerate_per_kw,
maxheight,
cast_const2(const struct utxo **, utxos));
if (utxo) {
struct amount_sat fee;
tal_arr_expand(&utxos, utxo);
/* It supplies more input. */
@@ -232,17 +258,8 @@ static struct command_result *json_fundpsbt(struct command *cmd,
return command_fail(cmd, LIGHTNINGD,
"impossible UTXO value");
/* But increase amount needed, to pay for new input */
/* But also adds weight */
*weight += utxo_spend_weight(utxo);
fee = amount_tx_fee(*feerate_per_kw,
utxo_spend_weight(utxo));
if (!amount_sat_add(amount, *amount, fee))
/* Either they specified "all", or we
* will fail anyway. */
*amount = AMOUNT_SAT(-1ULL);
if (!amount_sat_add(&total_fee, total_fee, fee))
return command_fail(cmd, LIGHTNINGD,
"impossible fee value");
continue;
}
@@ -263,7 +280,18 @@ static struct command_result *json_fundpsbt(struct command *cmd,
tal_count(utxos),
type_to_string(tmpctx,
struct amount_sat,
&needed));
&diff));
}
if (all) {
/* Anything above 0 is "excess" */
if (!inputs_sufficient(input, AMOUNT_SAT(0),
*feerate_per_kw, *weight,
&diff))
return command_fail(cmd, FUND_CANNOT_AFFORD,
"All %zu inputs could not afford"
" fees",
tal_count(utxos));
}
/* Setting the locktime to the next block to be mined has multiple
@@ -289,27 +317,11 @@ static struct command_result *json_fundpsbt(struct command *cmd,
false, 0, locktime,
BITCOIN_TX_RBF_SEQUENCE);
if (all) {
/* Count everything not going towards fees as excess. */
if (!amount_sat_sub(&excess, input, total_fee))
return command_fail(cmd, FUND_CANNOT_AFFORD,
"All %zu inputs could not afford"
" %s fees",
tal_count(utxos),
type_to_string(tmpctx,
struct amount_sat,
&total_fee));
} else {
/* This was the condition of exiting the loop above! */
if (!amount_sat_sub(&excess, input, *amount))
abort();
}
response = json_stream_success(cmd);
json_add_psbt(response, "psbt", tx->psbt);
json_add_num(response, "feerate_per_kw", *feerate_per_kw);
json_add_num(response, "estimated_final_weight", *weight);
json_add_amount_sat_only(response, "excess_msat", excess);
json_add_amount_sat_only(response, "excess_msat", diff);
if (*reserve)
reserve_and_report(response, cmd->ld->wallet, current_height,
utxos);