add max_total_htlc_out to listpeerchannels by Lagrang3 · Pull Request #7193 · ElementsProject/lightning

Lagrang3 · 2024-04-02T07:52:37Z

Add to listpeerchannels a couple of fields
their_max_total_htlc_out_msat and our_max_total_htlc_out_msat, the channel open configuration value specified
in BOLT02 that limits the exposure to HTLCs.

This field is relevant to renepay and askrene as discussed in #7159 (comment), since the payment plugin needs to know how much can be sent at a time through each local channel, besides spendable_msat.

vincenzopalazzo

LGTM otherwise

Lagrang3 · 2024-10-31T06:09:44Z

I noticed that to make this PR complete. I should also include this field in the gossmods_from_listpeerchannels API.

rustyrussell · 2024-11-13T07:17:30Z

Generally exposing these calculated values has proven to be a mistake. We should expose the peers' max_htlc_value_in_flight_msat (their_max_htlc_value_in_flight_msat) directly: we already expose their reserve (generally, we prefer spec names for fields, too, though some of these fields predate that policy!).

Lagrang3 · 2024-11-14T08:15:14Z

Generally exposing these calculated values has proven to be a mistake. We should expose the peers' max_htlc_value_in_flight_msat (their_max_htlc_value_in_flight_msat) directly: we already expose their reserve (generally, we prefer spec names for fields, too, though some of these fields predate that policy!).

There is already one field max_total_htlc_in_msat that exposes the equivalent of their_max_htlc_value_in_flight_msat.
I wonder what should be better, either:

to keep the name convention and add a new field max_total_htlc_out_msat to refer to our_max_htlc_value_in_flight_msat, we will have two fields

max_total_htlc_in_msat: already there that actually means our_max_htlc_value_in_flight_msat
max_total_htlc_out_msat: new field that actually means their_max_htlc_value_in_flight_msat

or to adopt a new name convention and add two new fields our_max_htlc_value_in_flight_msat and their_max_htlc_value_in_flight_msat?

max_total_htlc_in_msat: deprecate, that actually means our_max_htlc_value_in_flight_msat
our_max_htlc_value_in_flight_msat: new as in BOLT02
their_max_htlc_value_in_flight_msat: new as in BOLT02

or to have mixed name conventions

max_total_htlc_in_msat: already there that actually means our_max_htlc_value_in_flight_msat
their_max_htlc_value_in_flight_msat: new as in BOLT02

rustyrussell · 2024-11-21T04:29:55Z

Unfortunately, deprecate the old name (we usually give these things a year), and use the BOLT name. Sorry you stepped in this!

Lagrang3 · 2024-12-02T08:54:17Z

All right. Now max_total_htlc_in_msat is deprecated.

Lagrang3 · 2024-12-02T08:56:03Z

Rebased.

niftynei

something about the description text is off, but i'm not sure which it is.

niftynei · 2024-12-02T22:13:36Z

 		cb(mods, self, &dst, &scidd, capacity_msat,
 		   htlc_min[LOCAL], htlc_max[LOCAL],
-		   spendable, fee_base[LOCAL], fee_proportional[LOCAL],
+		   spendable, max_total_out_htlc, fee_base[LOCAL], fee_proportional[LOCAL],


just to confirm my understanding: max_total_out_htlc is the total amount that we can receive, so it gets added as the total max on the local receiving channel; max_total_in_htlc is the total amount we can send, so it gets added to the REMOTE set.

maybe renaming these would make this clearer? max_total_out seems to imply amount we can receive and vice versa for total_in lol

@rustyrussell: help!

From the spec BOLT02:

A sending node: - if the total value of offered HTLCs would exceed the remote's `max_htlc_value_in_flight_msat`: - MUST NOT add an HTLC. A receiving node: - if a sending node adds more than receiver `max_value_in_flight_msat` worth of offered HTLCs to its local commitment transaction: - SHOULD send a `warning` and close the connection, or send an `error` and fail the channel.

My interpretation is that our_max_value_in_flight_msat limits how much can we receive, and their_max_value_in_flight_max limits how much can we send.

niftynei · 2024-12-02T22:19:21Z

 				JSON_SCAN(json_to_msat, &spendable),
 				JSON_SCAN(json_to_msat, &receivable),
+				JSON_SCAN(json_to_msat, &max_total_in_htlc),
+				JSON_SCAN(json_to_msat, &max_total_out_htlc),


how often does this get updated?

The max_htlc_value_in_flight pair is fixed for the entire lifetime of the channel.
The gossmod_from_listpeerchannels is called to parse the response from listpeerchannels.
In askrene or renepay this is expected to happen once per rpc call.

niftynei · 2024-12-02T22:21:02Z

                  "type": "msat",
                  "description": [
-                    "Max amount accept in a single payment."
+                    "Max amount accept in a single payment. This field is deprecated, use instead our_max_htlc_value_in_flight_msat"


nit: this commit should be squashed into the commit where these fields are originally introduced/added to the RPC (the first one in the series, in this case)

It's complicated. These are autogenerated, if you ask me I wouldn't have these files into the source code cause no human wrote them. I add them as a separate commit to make it easier to rebase on the master branch in case someone else has also modified them.

My usual rebase when changing schemas is

soft reset the last commit (with the autogenerated files, very annoying),

rebase

then generate those files again and commit

niftynei · 2024-12-02T22:22:40Z

+                  "type": "msat",
+                  "added": "v24.11",
+                  "description": [
+                    "Cap on total value of outstanding HTLCs offered by the remote node. This limits the total amount in flight we can send through this channel."


suggestion to make this more readable: cap on total value of outstanding HTLCs offered to the remote node (from our balance).

though now that i've written these out, i feel like the their part of the max htlc value in flight name is confusing, since it's our balance that's in flight? something about this seems wrong. Either the modifier "this limits the total amount in flight we can send" is wrong or their max in flight is incorrect?

we can't add more HTLCs to be sent to the peer, because they don't want to let X% of their balance be committed as HTLCs?

Yes, this is weird. It is like our_max_value... is telling the peer "please don't try to send me more than this
or I will not accept it". The prefix their_ and our_ refers to who set the configuration value.

The description is a sentence taken from BOLT02.

niftynei · 2024-12-02T22:23:20Z

+                  "type": "msat",
+                  "added": "v24.11",
+                  "description": [
+                    "Cap on total value of outstanding HTLCs offered by the local node. This limits the total amount in flight we can receive through this channel."


suggestion to make this more readable: cap on total value of outstanding HTLCs offered to the local node (from peer's balance).

Could this also work?
our_max_htlc_value_in_flight_msat: Cap on total value of outstanding HTLCs we accept from the remote node.

Lagrang3 · 2024-12-03T09:08:14Z

CI is failing on tests/autogenerate-rpc-examples.py::test_generate_examples
complaining about

Error in setting up nodes: Additional properties are not allowed ('our_max_htlc_value_in_flight_msat', 'their_max_htlc_value_in_flight_msat' were unexpected)

I don't know what else, besides changing the schema, needs to be done to add new fields to RPC commands.

rustyrussell · 2025-02-11T00:37:40Z

OK, rebasing now. I actually did the deprecation, too:

Using command_deprecated_out_ok() so it won't appear if deprectest fields are disabled
Updated the deprecation start since we missed 24.11 with this
Increased deprecation end to 1 year (my preferred default), esp. since it's a neatness deprecation and not urgent.

rustyrussell · 2025-02-12T00:25:25Z

Damn, I accidentally pushed master to this branch. Now it's closed, and I can't re-push. Opening a new one :(

Lagrang3 force-pushed the max_total_htlc_out_msat branch from 181d591 to 44dd453 Compare April 2, 2024 08:49

Lagrang3 mentioned this pull request Apr 2, 2024

Renepay patch htlc_max=0 cases #7159

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Lagrang3 force-pushed the max_total_htlc_out_msat branch from fae9328 to 6e05ed4 Compare October 30, 2024 10:38

Lagrang3 added this to the v24.11 milestone Oct 30, 2024

Lagrang3 force-pushed the max_total_htlc_out_msat branch from fbd7ec6 to f5c08b9 Compare October 30, 2024 11:08

vincenzopalazzo reviewed Oct 30, 2024

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Comment thread doc/schemas/lightning-listpeerchannels.json Outdated

vincenzopalazzo reviewed Oct 30, 2024

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Lagrang3 force-pushed the max_total_htlc_out_msat branch from f5c08b9 to 1f6d416 Compare October 31, 2024 06:06

Lagrang3 force-pushed the max_total_htlc_out_msat branch from 1f6d416 to 891a176 Compare October 31, 2024 07:02

Lagrang3 force-pushed the max_total_htlc_out_msat branch 2 times, most recently from f77f0d2 to 5498491 Compare November 14, 2024 08:48

Lagrang3 force-pushed the max_total_htlc_out_msat branch from 5498491 to 436d847 Compare December 2, 2024 08:53

Lagrang3 force-pushed the max_total_htlc_out_msat branch from 436d847 to e017937 Compare December 2, 2024 08:55

Lagrang3 force-pushed the max_total_htlc_out_msat branch from e017937 to 80013e7 Compare December 2, 2024 09:09

niftynei reviewed Dec 2, 2024

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Lagrang3 force-pushed the max_total_htlc_out_msat branch from 80013e7 to ed35ad8 Compare December 3, 2024 08:48

rustyrussell modified the milestones: v24.11, v25.02 Dec 13, 2024

rustyrussell force-pushed the max_total_htlc_out_msat branch from ed35ad8 to 6b7a91e Compare February 11, 2025 01:07

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rustyrussell closed this Feb 12, 2025

rustyrussell force-pushed the max_total_htlc_out_msat branch from a01f8f5 to 1820423 Compare February 12, 2025 00:23

rustyrussell mentioned this pull request Feb 12, 2025

add max_total_htlc_out to listpeerchannels #8084

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Lagrang3 deleted the max_total_htlc_out_msat branch February 12, 2025 08:04

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