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xpay: emulate maxfeepercent and exemptfee when xpay-handle-pay used #7942

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Dec 17, 2024
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xpay: emulate maxfeepercent and exemptfee when xpay-handle-pay used #7942

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107 changes: 103 additions & 4 deletions plugins/xpay/xpay.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1758,14 +1758,99 @@ static const struct plugin_notification notifications[] = {
},
};

/* xpay doesn't have maxfeepercent or exemptfee, so we convert them to
* an absolute restriction here. If we can't, fail and let pay handle
* it. */
static bool calc_maxfee(struct command *cmd,
const char **maxfeestr,
const char *buf,
const jsmntok_t *invstringtok,
const jsmntok_t *amount_msattok,
const jsmntok_t *exemptfeetok,
const jsmntok_t *maxfeepercenttok)
{
u64 maxfeepercent_ppm;
struct amount_msat amount, maxfee, exemptfee;

if (!exemptfeetok && !maxfeepercenttok)
return true;

/* Can't have both */
if (*maxfeestr)
return false;

/* If they specify amount easy, otherwise take from invoice */
if (amount_msattok) {
if (!parse_amount_msat(&amount, buf + amount_msattok->start,
amount_msattok->end - amount_msattok->start))
return false;
} else {
const struct bolt11 *b11;
char *fail;
const char *invstr;

/* We need to know total amount to calc fee */
if (!invstringtok)
return false;

invstr = json_strdup(tmpctx, buf, invstringtok);
b11 = bolt11_decode(tmpctx, invstr, NULL, NULL, NULL, &fail);
if (b11 != NULL) {
if (b11->msat == NULL)
return false;
amount = *b11->msat;
} else {
const struct tlv_invoice *b12;
b12 = invoice_decode(tmpctx, invstr, strlen(invstr),
NULL, NULL, &fail);
if (b12 == NULL || b12->invoice_amount == NULL)
return false;
amount = amount_msat(*b12->invoice_amount);
}
}

if (maxfeepercenttok) {
if (!json_to_millionths(buf,
maxfeepercenttok,
&maxfeepercent_ppm))
return false;
} else
maxfeepercent_ppm = 500000;

if (!amount_msat_fee(&maxfee, amount, 0, maxfeepercent_ppm / 100))
return false;

if (exemptfeetok) {
if (!parse_amount_msat(&exemptfee, buf + exemptfeetok->start,
exemptfeetok->end - exemptfeetok->start))
return false;
} else
exemptfee = AMOUNT_MSAT(5000);

if (amount_msat_less(maxfee, exemptfee))
maxfee = exemptfee;

*maxfeestr = fmt_amount_msat(cmd, maxfee);
plugin_log(cmd->plugin, LOG_DBG,
"Converted maxfeepercent=%.*s, exemptfee=%.*s to maxfee %s",
maxfeepercenttok ? json_tok_full_len(maxfeepercenttok) : 5,
maxfeepercenttok ? json_tok_full(buf, maxfeepercenttok) : "UNSET",
exemptfeetok ? json_tok_full_len(exemptfeetok) : 5,
exemptfeetok ? json_tok_full(buf, exemptfeetok) : "UNSET",
*maxfeestr);

return true;
}

static struct command_result *handle_rpc_command(struct command *cmd,
const char *buf,
const jsmntok_t *params)
{
struct xpay *xpay = xpay_of(cmd->plugin);
const jsmntok_t *rpc_tok, *method_tok, *params_tok, *id_tok,
*bolt11 = NULL, *amount_msat = NULL, *maxfee = NULL,
*bolt11 = NULL, *amount_msat = NULL,
*partial_msat = NULL, *retry_for = NULL;
const char *maxfee = NULL;
struct json_stream *response;

if (!xpay->take_over_pay)
Expand Down Expand Up @@ -1795,7 +1880,7 @@ static struct command_result *handle_rpc_command(struct command *cmd,
if (params_tok->size == 2)
amount_msat = json_next(bolt11);
} else if (params_tok->type == JSMN_OBJECT) {
const jsmntok_t *t;
const jsmntok_t *t, *maxfeepercent = NULL, *exemptfee = NULL;
size_t i;

json_for_each_obj(i, t, params_tok) {
Expand All @@ -1806,9 +1891,13 @@ static struct command_result *handle_rpc_command(struct command *cmd,
else if (json_tok_streq(buf, t, "retry_for"))
retry_for = t + 1;
else if (json_tok_streq(buf, t, "maxfee"))
maxfee = t + 1;
maxfee = json_strdup(cmd, buf, t + 1);
else if (json_tok_streq(buf, t, "partial_msat"))
partial_msat = t + 1;
else if (json_tok_streq(buf, t, "maxfeepercent"))
maxfeepercent = t + 1;
else if (json_tok_streq(buf, t, "exemptfee"))
exemptfee = t + 1;
else {
plugin_log(cmd->plugin, LOG_INFORM,
"Not redirecting pay (unknown arg %.*s)",
Expand All @@ -1822,6 +1911,14 @@ static struct command_result *handle_rpc_command(struct command *cmd,
"Not redirecting pay (missing bolt11 parameter)");
goto dont_redirect;
}
/* If this returns NULL, we let pay handle the weird case */
if (!calc_maxfee(cmd, &maxfee, buf,
bolt11, amount_msat,
exemptfee, maxfeepercent)) {
plugin_log(cmd->plugin, LOG_INFORM,
"Not redirecting pay (weird maxfee params)");
goto dont_redirect;
}
} else {
plugin_log(cmd->plugin, LOG_INFORM,
"Not redirecting pay (unexpected params type)");
Expand All @@ -1840,8 +1937,10 @@ static struct command_result *handle_rpc_command(struct command *cmd,
json_add_tok(response, "amount_msat", amount_msat, buf);
if (retry_for)
json_add_tok(response, "retry_for", retry_for, buf);
/* Even if this was a number token, handing it as a string is
* allowed by parse_msat */
if (maxfee)
json_add_tok(response, "maxfee", maxfee, buf);
json_add_string(response, "maxfee", maxfee);
if (partial_msat)
json_add_tok(response, "partial_msat", partial_msat, buf);
json_object_end(response);
Expand Down
18 changes: 10 additions & 8 deletions tests/test_xpay.py
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Original file line number Diff line number Diff line change
Expand Up @@ -436,18 +436,10 @@ def test_xpay_takeover(node_factory, executor):
l1.rpc.pay(inv['bolt11'], amount_msat=10000, riskfactor=1)
l1.daemon.wait_for_log(r'Not redirecting pay \(unknown arg \\"riskfactor\\"\)')

inv = l3.rpc.invoice('any', "test_xpay_takeover9", "test_xpay_takeover9")
l1.rpc.pay(inv['bolt11'], amount_msat=10000, maxfeepercent=1)
l1.daemon.wait_for_log(r'Not redirecting pay \(unknown arg \\"maxfeepercent\\"\)')

inv = l3.rpc.invoice('any', "test_xpay_takeover10", "test_xpay_takeover10")
l1.rpc.pay(inv['bolt11'], amount_msat=10000, maxdelay=200)
l1.daemon.wait_for_log(r'Not redirecting pay \(unknown arg \\"maxdelay\\"\)')

inv = l3.rpc.invoice('any', "test_xpay_takeover11", "test_xpay_takeover11")
l1.rpc.pay(inv['bolt11'], amount_msat=10000, exemptfee=1)
l1.daemon.wait_for_log(r'Not redirecting pay \(unknown arg \\"exemptfee\\"\)')

# Test that it's really dynamic.
l1.rpc.setconfig('xpay-handle-pay', False)

Expand All @@ -473,6 +465,16 @@ def test_xpay_takeover(node_factory, executor):
assert ret['amount_msat'] == 100000
assert ret['amount_sent_msat'] > 100000

# Test maxfeepercent.
inv = l3.rpc.invoice(100000, "test_xpay_takeover14", "test_xpay_takeover14")['bolt11']
with pytest.raises(RpcError, match=r"Could not find route without excessive cost"):
l1.rpc.pay(bolt11=inv, maxfeepercent=0.001, exemptfee=0)
l1.daemon.wait_for_log('plugin-cln-xpay: Converted maxfeepercent=0.001, exemptfee=0 to maxfee 1msat')

# Exemptfee default more than covers it.
l1.rpc.pay(bolt11=inv, maxfeepercent=0.25)
l1.daemon.wait_for_log('Converted maxfeepercent=0.25, exemptfee=UNSET to maxfee 5000msat')


def test_xpay_preapprove(node_factory):
l1, l2 = node_factory.line_graph(2, opts={'dev-hsmd-fail-preapprove': None})
Expand Down
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