Xpay bad nodes #8608
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Xpay bad nodes #8608
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Lagrang3
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We add one more field to biases: "timestamp". With the timestamp variable old biases can be removed with the askrene-age command. Changelog-None Signed-off-by: Lagrang3 <[email protected]>
Changelog-Added: askrene-bias-node: an RPC command to set a bias on node's outgoing or incoming channels. Signed-off-by: Lagrang3 <[email protected]>
Changelog-None Signed-off-by: Lagrang3 <[email protected]>
Changelog-None Signed-off-by: Lagrang3 <[email protected]>
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rustyrussell
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Nov 10, 2025
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rustyrussell
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Minor API changes, and I need to be convinced of the xpay change.
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| for (bias = bias_hash_first(layer->biases, &biasit); bias; | ||
| bias = bias_hash_next(layer->biases, &biasit)) { | ||
| if (bias->timestamp < cutoff) { | ||
| bias_hash_delval(layer->biases, &biasit); | ||
| tal_free(bias); | ||
| num_removed++; | ||
| } | ||
| } | ||
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This is cool. but
- askrene-age needs to document this new behaviour!
- Changelog-None should be Changelog-Added: Plugins:
askrenechannel biases now have an associated timestamp, and are timed out byaskrene-age.
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| "out_direction": { | ||
| "type": "boolean", | ||
| "default": true, | ||
| "description": [ | ||
| "If true the bias applies to outgoing channels otherwise it applies to incoming channels." | ||
| ] | ||
| } |
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Prefer this be called "direction", a string "in" or "out", and a required field.
I think this makes it more explicit.
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| // FIXME: is this the correct direction? | ||
| biases[idx] += node_bias->out_bias; | ||
| biases[idx ^ 1] += node_bias->in_bias; |
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To answer your FIXME: yes, it's correct.
The direction for a node pair corresponds to the outgoing channel: that's because the node controls fees only on outgoing. So, biases[index] is indeed this node's outgoing.
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| /* We add a negative bias to this channel to penalize it for other | ||
| * payments. | ||
| * Biases are nice way to penalize or encourage the use of | ||
| * channels. But it has some limitations. For example the bias would | ||
| * have no effect if the channel already provides 0 cost routing. */ | ||
| req = payment_ignored_req(aux_cmd, attempt, "askrene-bias-channel"); | ||
| json_add_string(req->js, "layer", XPAY_GLOBAL_LAYER); | ||
| json_add_short_channel_id_dir(req->js, "short_channel_id_dir", | ||
| attempt->hops[index].scidd); | ||
| json_add_s32(req->js, "bias", -5); | ||
| json_add_bool(req->js, "relative", true); | ||
| send_payment_req(aux_cmd, attempt->payment, req); | ||
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| /* We add a negative bias to the node that owns this half channel. */ | ||
| if (index) { | ||
| req = | ||
| payment_ignored_req(aux_cmd, attempt, "askrene-bias-node"); | ||
| json_add_string(req->js, "layer", XPAY_GLOBAL_LAYER); | ||
| json_add_pubkey(req->js, "node", | ||
| &attempt->hops[index - 1].next_node); | ||
| json_add_s32(req->js, "bias", -1); | ||
| json_add_bool(req->js, "relative", true); | ||
| json_add_bool(req->js, "out_direction", true); | ||
| send_payment_req(aux_cmd, attempt->payment, req); | ||
| } | ||
| goto check_previous_success; |
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Do we have evidence to support this approach? We've effectively biased it already by lowering the capacity, after all.
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Several changes to askrene, mainly to introduce penalties (biases) on nodes and channels that
can be used across payments.
It addresses issue #8600.
- [ ] add expiration on biases,- [ ] add expiration on knowledge data,