Min. Cost Flow does not take into account fees when computing a flow
with liquidity constraints.
This is a work-around solution that reduces the amount on every route to
respect the liquidity bound. The deficity in the delivered amount is
solved by running MCF once again.
Changes:
1. the function `flow_complete` allocates amounts to send over the set of routes
computed by the MCF algorithm, but it does not allocate more than liquidity
bound of the route. For this reason `minflow` returns a set of routes that
satisfy the liquidity bounds but it is not guaranteed that the total payment
reaches the destination therefore there could a deficit in the delivery:
`deficit = amount_to_deliver - delivering`.
2. in the function `add_payflows` after `minflow` returns a set of routes we
call `flows_fit_amount` that tries to a allocate the `deficit` in the routes
that the MCF have computed.
3. if the resulting flows pass all payment constraints then we update
`amount_to_deliver = amount_to_deliver - delivering`, and the loop
repeats as long as `amount_to_deliver` is not zero.
In other words, the excess amount, beyond the liquidity bound,
in the routes is removed and then we try to allocate it
into known routes, otherwise we do a whole MCF again just for the
remaining amount.
Fixes issue #6599
Adds a "canonical" error handling in the module mcf.c,
adhering to the same convention we have adopted in flow.c.
So that when a function fails it signals the caller with an invalid
return value, or bool false, and it communicates an error message.
We cannot carry pointers into the gossmap across localmod addition
or removal.
We didn't notice because the map->chan_arr is not normally resized,
but if we change gossmap.c line 689 to only allocate 1 to start, we see this:
```
VALGRIND=1 valgrind -q --error-exitcode=7 --track-origins=yes --leak-check=full --show-reachable=yes --errors-for-leak-kinds=all plugins/renepay/test/run-mcf > /dev/null
==2349744== Invalid read of size 4
==2349744== at 0x1788C2: gossmap_chan_scid (gossmap.c:558)
==2349744== by 0x1872A2: get_chan_extra_half_by_chan (flow.c:346)
==2349744== by 0x187797: remove_completed_flow (flow.c:488)
==2349744== by 0x187927: remove_completed_flow_set (flow.c:518)
==2349744== by 0x18DF4D: main (run-mcf.c:393)
==2349744== Address 0x4b80f38 is 88 bytes inside a block of size 136 free'd
==2349744== at 0x4848C63: realloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==2349744== by 0x173D71: tal_resize_ (tal.c:744)
==2349744== by 0x177E36: next_free_chan (gossmap.c:336)
==2349744== by 0x177ED3: new_channel (gossmap.c:351)
==2349744== by 0x178441: add_channel (gossmap.c:458)
==2349744== by 0x1798D4: gossmap_apply_localmods (gossmap.c:904)
==2349744== by 0x18DEDB: main (run-mcf.c:388)
==2349744== Block was alloc'd at
==2349744== at 0x4848C63: realloc (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==2349744== by 0x173D71: tal_resize_ (tal.c:744)
==2349744== by 0x177E36: next_free_chan (gossmap.c:336)
==2349744== by 0x177ED3: new_channel (gossmap.c:351)
==2349744== by 0x178441: add_channel (gossmap.c:458)
==2349744== by 0x178B6D: map_catchup (gossmap.c:635)
==2349744== by 0x178F45: load_gossip_store (gossmap.c:697)
==2349744== by 0x179D71: gossmap_load (gossmap.c:978)
==2349744== by 0x18D22F: main (run-mcf.c:295)
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
The main function here is payment_reconsider:
* Each payment has a list of pay_flow.
* This is populated in try_paying(), calling add_payflows & sendpay_new_flows.
* When we get a notification, we resolve a pay_flow using one of the pay_flow_failedxxx
or pay_flow_succeeded functions.
* They call payment_reconsider() which cleans up finished flows decides what to do:
often calling try_paying again.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Avoids a gratuitous "ctx" field, and the simplified declaration
is now understood by `make update-mocks`.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
As recommended by your TODO, a bit simpler: we also make the hash function
return a ptr rather than the (now rather large) struct.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
- adopt "const <type> *"convention
- remove use_shadow option for some pyln tests
- show prob. information of flows into paynotes
- show prob. of success of entire payment flow in paynotes
- minflow: We were not releasing the memory of flow arrays when replacing
them with a new canditate.
- use memleak_scan_obj in memleak_check
- replace u64 with size_t
Signed-off-by: Lagrang3 <eduardo.quintana@pm.me>
The global is an *internal* hack because dijkstra_item_mover doesn't
take a context arg! It should be used with care.
Easy, since all the accessors exist: we just hand in the struct dijkstra.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
- remove internal gheap checks
- add check for arc_t.chanidx overflow
- remove outdated comments
- check the delta flow bounds before augmenting along a path
- get_flow_paths uses a dynamic tal array instead of a list.
- fix a unit test that depended on the order of returned flows
- fix bug: lightnind doesn't like if I reuse the partid of a failed
flow, therefore use a higher partid than any of the previous attempts.
- plugin_err instead of LOG_BROKEN if sendpay fails and we cannot get a
an error code.
- fix wrong comments.
- remove the background timer.
- This is a bugfix. Previous to this the MCF network was built using the
knowledge of the min and max liquidity but it didn't take into account
pending HTLCs.
- Also remove the min_prob_success option but hardcode a 90% value.
Removing some options that are not relevant to the user, they're kept
for developer mode only:
- base_fee_penalty
- min_prob_success
- prob_cost_factor
- remove heap.h, not used
Signed-off-by: Lagrang3 <eduardo.quintana@pm.me>
Lagrang3
Rusty Russell
Lagrang3