It was weird not to have a capacity associated with localmods channels, and
fixing it has some very nice side effects.
Now the gossmap_chan_get_capacity() call never fails (we prevented reading
of channels from gossmap in the partially-written case already), so we
make it return the capacity. We do this in msat, because that's what
all the callers want.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This is actually what we want in several places: to only override one or
two fields in a channel_update.
We add a gossmap_local_setchan() with a similar API to the old
gossmap_local_updatechan(), for the case where we want to set every
field.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
It's a u64, we should pass by copy. This is a big sweeping change,
but mainly mechanical (change one, compile, fix breakage, repeat).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
We have various functions to convert to a string, rename them all so we can
count on fmt_X being the formatter for struct X, and make them all return
`char *`.
Sometimes they existed but were private, sometimes they had a
different name. Most take a pointer, but simple types pass by copy:
short_channel_id, amount_msat and amount_sat.
The following public functions changed:
1. psbt_to_b64 -> fmt_wally_psbt.
2. pubkey_to_hexstr -> fmt_pubkey.
3. short_channel_id_to_str -> fmt_short_channel_id (scid by copy now!)
4. fmt_signature -> fmt_secp256k1_ecdsa_signature
5. fmt_amount_sat/fmt_amount_msat pass copy not pointer, return non-const char *.
6. node_id_to_hexstr -> fmt_node_id
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
I noticed that run-route-infloop chose some worse-looking paths after
routing was fixed, eg the second node:
Before:
Destination node, success, probability, hops, fees, cltv, scid...
02b3aa1e4ed31be83cca4bd367b2c01e39502cb25e282a9b4520ad376a1ba0a01a,1,0.991856,2,1004,40,2572260x39x0/1,2131897x45x0/0
After:
Destination node, success, probability, hops, fees, cltv, scid...
02b3aa1e4ed31be83cca4bd367b2c01e39502cb25e282a9b4520ad376a1ba0a01a,1,0.954540,3,1046,46,2570715x21x0/1,2346882x26x14/1,2131897x45x0/0
This is because although the final costs don't reflect it, routing was taking
into account local channels, and 2572260x39x0/1 has a base fee of 2970.
There's an easy fix: when we the pay plugin creates localmods for our
gossip graph, add all local channels with delay and fees equal to 0.
We do the same thing in our unit test. This improves things across
the board:
Linear success probability (when found): min-max(mean +/- stddev)
Before: 0.487040-0.999543(0.952548+/-0.075)
After: 0.486985-0.999750(0.975978+/-0.053)
Hops:
Before: 1-5(2.98374+/-0.77)
After: 1-5(2.09593+/-0.63)
Fees:
Before: 0-50848(922.457+/-2.7e+03)
After: 0-50041(861.621+/-2.7e+03)
Delay (blocks):
Before: 0-196(65.8081+/-60)
After: 0-190(60.3285+/-60)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Changed: Plugins: `pay` route algorithm doesn't bias against our own "expensive" channels any more.
The "path_score" callback was supposed to evaluate the *entire path*,
but that was counter-intuitive and opened the door to a cost function
bug which caused this path cost to be less than the closer path.
In particular, the capacity bias code didn't understand this at all.
1. Rename the function to `channel_score` and remove the "distance"
parameter (always "1" since you're supposed to be evaluating a
single hop).
2. Rename "cost" to the more specific "fee": "score" is our
actual cost function result (we avoid the word "cost" as it
may get confused with satoshi amounts).
3. For capacity biassing, we do want to know the amount, but
explicitly hand that as a separate parameter "total".
4. Fix a minor bug where total handed to scoring function previously
included channel fee (this is wrong: fee is paid before sending into
channel).
5. Remove the now-unused total_delay member from the dijkstra
struct.
Here are the results of our test now (routing 4194303 msat, which
didn't crash the old code, so we could compare). In both cases
we could find routes to 615 nodes:
Linear success probability (when found): min-max(mean +/- stddev)
Before: 0.484764-0.999750(0.9781+/-0.049)
After: 0.487040-0.999543(0.952548+/-0.075)
Hops:
Before: 1-5(2.13821+/-0.66)
After: 1-5(2.98374+/-0.77)
Fees:
Before: 0-50041(2173.75+/-5.3e+03)
After: 0-50848(922.457+/-2.7e+03)
Delay (blocks):
Before: 0-294(83.1642+/-68)
After: 0-196(65.8081+/-60)
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Fixes: https://github.com/ElementsProject/lightning/issues/7092
Changelog-Fixed: Plugins: `pay` would occasionally crash on routing.
Changelog-Fixed: Plugins: `pay` route algorithm fixed and refined to balance fees and capacity far better.
The amount is set not to crash by default, but run
"common/test/run-route-infloop 8388607" and you'll see a crash.
Sorry about the 7MB blob, but this testing was quite revealing and
I consider it worth adding.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
