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xpay phoenix detect #8537

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7743075
pytest: Test that we don't try to pay too many htlcs at once through …
rustyrussell Sep 5, 2025
cccac43
xpay: restrict maxparts to 6 for non-public nodes, but remove it if w…
rustyrussell Sep 5, 2025
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51 changes: 31 additions & 20 deletions plugins/xpay/xpay.c
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Original file line number Diff line number Diff line change
Expand Up @@ -78,7 +78,7 @@ struct payment {
struct amount_msat maxfee;
/* Maximum delay on the route we're ok with */
u32 maxdelay;
/* Maximum number of payment routes that can be pending. */
/* If non-zero: maximum number of payment routes that can be pending. */
u32 maxparts;
/* Do we have to do it all in a single part? */
bool disable_mpp;
Expand Down Expand Up @@ -172,7 +172,6 @@ static struct command_result *xpay_core(struct command *cmd,
u32 retryfor,
const struct amount_msat *partial,
u32 maxdelay,
u32 dev_maxparts,
bool as_pay);

/* Wrapper for pending commands (ignores return) */
Expand Down Expand Up @@ -1287,6 +1286,16 @@ static struct command_result *getroutes_done_err(struct command *aux_cmd,
msg = json_strdup(tmpctx, buf, json_get_member(buf, error, "message"));
json_to_int(buf, json_get_member(buf, error, "code"), &code);

/* If we were restricting the number of parts, we remove that
* restriction and try again. */
if (payment->maxparts) {
payment_log(payment, LOG_INFORM,
"getroute failed with maxparts=%u, so retrying without that restriction",
payment->maxparts);
payment->maxparts = 0;
return getroutes_for(aux_cmd, payment, payment->amount_being_routed);
}

/* Simple case: failed immediately. */
if (payment->total_num_attempts == 0) {
payment_give_up(aux_cmd, payment, code, "Failed: %s", msg);
Expand Down Expand Up @@ -1319,7 +1328,6 @@ static struct command_result *getroutes_for(struct command *aux_cmd,
struct out_req *req;
const struct pubkey *dst;
struct amount_msat maxfee;
size_t count_pending;

/* I would normally assert here, but we have reports of this happening... */
if (amount_msat_is_zero(deliver)) {
Expand Down Expand Up @@ -1380,9 +1388,11 @@ static struct command_result *getroutes_for(struct command *aux_cmd,
json_add_amount_msat(req->js, "maxfee_msat", maxfee);
json_add_u32(req->js, "final_cltv", payment->final_cltv);
json_add_u32(req->js, "maxdelay", payment->maxdelay);
count_pending = count_current_attempts(payment);
assert(payment->maxparts > count_pending);
json_add_u32(req->js, "maxparts", payment->maxparts - count_pending);
if (payment->maxparts) {
size_t count_pending = count_current_attempts(payment);
assert(payment->maxparts > count_pending);
json_add_u32(req->js, "maxparts", payment->maxparts - count_pending);
}

return send_payment_req(aux_cmd, payment, req);
}
Expand Down Expand Up @@ -1693,7 +1703,7 @@ struct xpay_params {
struct amount_msat *msat, *maxfee, *partial;
const char **layers;
unsigned int retryfor;
u32 maxdelay, dev_maxparts;
u32 maxdelay;
const char *bip353;
};

Expand All @@ -1710,7 +1720,7 @@ invoice_fetched(struct command *cmd,
return xpay_core(cmd, take(to_canonical_invstr(NULL, take(inv))),
NULL, params->maxfee, params->layers,
params->retryfor, params->partial, params->maxdelay,
params->dev_maxparts, false);
false);
}

static struct command_result *
Expand Down Expand Up @@ -1771,7 +1781,7 @@ static struct command_result *json_xpay_params(struct command *cmd,
struct amount_msat *msat, *maxfee, *partial;
const char *invstring;
const char **layers;
u32 *maxdelay, *maxparts;
u32 *maxdelay;
unsigned int *retryfor;
struct out_req *req;
struct xpay_params *xparams;
Expand All @@ -1784,14 +1794,9 @@ static struct command_result *json_xpay_params(struct command *cmd,
p_opt_def("retry_for", param_number, &retryfor, 60),
p_opt("partial_msat", param_msat, &partial),
p_opt_def("maxdelay", param_u32, &maxdelay, 2016),
p_opt_dev("dev_maxparts", param_u32, &maxparts, 100),
NULL))
return command_param_failed();

if (*maxparts == 0)
return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
"maxparts cannot be zero");

/* Is this a one-shot vibe payment? Kids these days! */
if (!as_pay && bolt12_has_offer_prefix(invstring)) {
struct command_result *ret;
Expand All @@ -1810,7 +1815,6 @@ static struct command_result *json_xpay_params(struct command *cmd,
xparams->layers = layers;
xparams->retryfor = *retryfor;
xparams->maxdelay = *maxdelay;
xparams->dev_maxparts = *maxparts;
xparams->bip353 = NULL;

return do_fetchinvoice(cmd, invstring, xparams);
Expand All @@ -1825,7 +1829,6 @@ static struct command_result *json_xpay_params(struct command *cmd,
xparams->layers = layers;
xparams->retryfor = *retryfor;
xparams->maxdelay = *maxdelay;
xparams->dev_maxparts = *maxparts;
xparams->bip353 = invstring;

req = jsonrpc_request_start(cmd, "fetchbip353",
Expand All @@ -1836,7 +1839,7 @@ static struct command_result *json_xpay_params(struct command *cmd,
}

return xpay_core(cmd, invstring,
msat, maxfee, layers, *retryfor, partial, *maxdelay, *maxparts,
msat, maxfee, layers, *retryfor, partial, *maxdelay,
as_pay);
}

Expand All @@ -1848,11 +1851,12 @@ static struct command_result *xpay_core(struct command *cmd,
u32 retryfor,
const struct amount_msat *partial,
u32 maxdelay,
u32 dev_maxparts,
bool as_pay)
{
struct payment *payment = tal(cmd, struct payment);
struct xpay *xpay = xpay_of(cmd->plugin);
struct gossmap *gossmap = get_gossmap(xpay);
struct node_id dstid;
u64 now, invexpiry;
struct out_req *req;
char *err;
Expand All @@ -1875,10 +1879,8 @@ static struct command_result *xpay_core(struct command *cmd,
else
payment->layers = NULL;
payment->maxdelay = maxdelay;
payment->maxparts = dev_maxparts;

if (bolt12_has_prefix(payment->invstring)) {
struct gossmap *gossmap = get_gossmap(xpay);
struct tlv_invoice *b12inv
= invoice_decode(tmpctx, payment->invstring,
strlen(payment->invstring),
Expand Down Expand Up @@ -2004,6 +2006,15 @@ static struct command_result *xpay_core(struct command *cmd,
} else
payment->maxfee = *maxfee;

/* If we are using an unannounced channel, we assume we can
* only do 6 HTLCs at a time. This is currently true for
* Phoenix, which is a large and significant node. */
node_id_from_pubkey(&dstid, &payment->destination);
if (!gossmap_find_node(gossmap, &dstid))
payment->maxparts = 6;
else
payment->maxparts = 0;

/* Now preapprove, then start payment. */
if (command_check_only(cmd)) {
req = jsonrpc_request_start(cmd, "check",
Expand Down
24 changes: 24 additions & 0 deletions tests/test_xpay.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1011,3 +1011,27 @@ def test_xpay_bip353(node_factory):

node_factory.join_nodes([l2, l1])
l2.rpc.xpay('[email protected]', 100)


def test_xpay_limited_max_accepted_htlcs(node_factory):
"""xpay should try to reduce flows to 6 if there is an unannounced channel, and only try more if that fails"""
CHANNEL_SIZE_SATS = 10**6
CHANNEL_SIZE_MSATS = CHANNEL_SIZE_SATS * 1000
l1, l2 = node_factory.line_graph(2,
fundamount=CHANNEL_SIZE_SATS * 20,
opts=[{}, {'max-concurrent-htlcs': 6}],
announce_channels=False)

# We want 10 paths between l3 and l1.
l3 = node_factory.get_node()
nodes = node_factory.get_nodes(10)
for n in nodes:
node_factory.join_nodes([l3, n, l1], fundamount=CHANNEL_SIZE_SATS)

# This *could* fit in 6 channels...
l3.rpc.xpay(l2.rpc.invoice(f"{CHANNEL_SIZE_SATS * 5}sat",
'test_xpay_limited_max_accepted_htlcs',
'test_xpay_limited_max_accepted_htlcs')['bolt11'])

# Check that it *did* give a 7 flow answer!
l3.daemon.wait_for_log('Final answer has 7 flows')
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