routing: add build route functionality #3440

joostjager · 2019-08-30T07:12:35Z

This PR adds a new rpc for advanced users that allows them to build a fully specified route from a list of pubkeys. The call looks up the relevant channel policies from the graph and calculates the required fees and time lock values.

Route building is exposed via lncli. Example command to build a two hop route:

lncli buildroute --hops <pubkey1>,<pubkey2> --amt 500

It is also possible to leave out the --amt parameter. In that case, a route is built for the minimum amount that it can carry. This option is useful to execute probe payments for which the primary objective is to pick up black holes (stuck htlc). If the payment gets stuck, the time-locked amount is minimal.

lnrpc/routerrpc/router.proto

routing/router.go

cmd/lncli/routerrpc_active.go

cmd/lncli/cmd_build_route.go

cmd/lncli/commands.go

cmd/lncli/cmd_build_route.go

lnrpc/routerrpc/router.proto

routing/router.go

halseth

Looks pretty good to me :)

channeldb/graph.go

lnrpc/routerrpc/router_server.go

routing/router.go

cmd/lncli/cmd_build_route.go

routing/router.go

lnrpc/routerrpc/router_server.go

cmd/lncli/cmd_build_route.go

routing/pathfind.go

wpaulino · 2019-09-16T20:34:12Z

routing/router_test.go

+	_, err = ctx.router.BuildRoute(
+		nil, hops, nil, 40,
+	)
+	if _, ok := err.(ErrNoChannel); !ok {


Asserts fields of error as well?

lnrpc/routerrpc/router.proto

routing/router.go

joostjager · 2019-09-18T06:47:30Z

Also extended the test so that it also exercises selecting the best channel when there are multiple channels between a pair of nodes.

lnrpc/routerrpc/router.proto

routing/router.go

routing/router_test.go

halseth · 2019-09-18T08:05:39Z

routing/router.go

+
+	// Determine max htlc value.
+	maxHtlc := lnwire.NewMSatFromSatoshis(capacity)
+	if policy.MaxHTLC != 0 {


Should use HasMaxHtlc?

Changed. This is the confusion that I think we shouldn't need to have.

Hmm, looking in the link, it also checks for MaxHTLC == 0. I left the check identical to what happens in the link.

That's because the link uses ForwardingPolicy, which doesn't contain information about whether the bit is set or not. I'm in favor of adding the check for the bit being set here.

Ok, it is indeed a good idea, because this function is also used for non-local channels. Changed

routing/router.go

halseth · 2019-09-18T08:08:31Z

routing/router.go

+	// incompatible channel policies.
+	//
+	// There is possibility with pubkey addressing that we should
+	// have selected a different channel downstream, but we don't


Why don't we fix that? Should this be a TODO, or is there another reason?

It would complicate path finding while we expect this situation to be rare. The spec recommends to keep all policies towards a peer identical. If that is the case, there isn't a better channel that we should have selected.

Added this as a comment

cmd/lncli/cmd_build_route.go

halseth

Only a few nits and suggestions from me, LGTM 🏆

lnrpc/routerrpc/router.proto

halseth · 2019-09-19T10:25:54Z

routing/router.go

+	// If we have a specific amount for which we are building the route,
+	// validate it against the channel constraints and return the new
+	// running amount.
+	if !canIncreaseAmt {


maybe this had would been less confusing if the param was called findMinAmt or similar.

I purposely renamed it to canIncreaseAmt because I realized that it is a more generic function here.

Would it work to not pass this bool to the method, and instead let the caller check the returned amount? So if the amount has increased, but we cannot increase it, it will take action.

It should be equivalent, I just find the current branching within the prependChannel a bit confusing.

I understand your suggestion, but I think it may be confusing in another way. The current code has already seen a few earlier iterations. If there isn't a way that very clearly improves the readability, I'd rather leave it as is.

routing/router.go

halseth · 2019-09-19T10:35:08Z

routing/router.go

+			)
+			if err != nil {
+				log.Tracef("Skipping chan %v: %v",
+					inEdge.ChannelID, err)


Is this an expected error? If not maybe log as Warn

Yes, it can happen if channels have distinct policies. If all of them do not match, we return a proper error. Warn is definitely too heavy in this situation.

It's just that if this is expected to happen, and it leads us to not be able to build a route, the reason will likely never surface, as it's on trace.

The trace log is intended for use during development. The problem with reporting the exact reason to the caller is similar to the situation that we have in path finding. There may be multiple reasons. I am afraid that just exposing a random one of them will lead to the same incorrect assumptions that we currently have for path finding.

To be clear, even if the call succeeds in building a route, some channels may have been skipped. We can't log it on Warn, because it may really not be a warning.

cmd/lncli/cmd_build_route.go

wpaulino

LGTM 💫

wpaulino · 2019-09-24T22:02:51Z

cmd/lncli/cmd_build_route.go

+	if hasAmt {
+		amtMsat = ctx.Int64("amt") * 1000
+		if amtMsat == 0 {
+			return fmt.Errorf("non-zero amount required")


One last nit: do we still need all of this? Seems like AmtMsat can just be ctx.Uint64("amt") * 1000.

joostjager requested review from halseth and Roasbeef as code owners August 30, 2019 07:12

joostjager removed request for Roasbeef and halseth August 30, 2019 07:12

joostjager force-pushed the buildroute branch 2 times, most recently from 1158ce8 to 038d33b Compare August 30, 2019 08:55

joostjager requested review from halseth and wpaulino August 30, 2019 08:59

wpaulino added enhancement Improvements to existing features / behaviour routing rpc Related to the RPC interface v0.8.0 labels Aug 30, 2019

wpaulino added this to the 0.8.0 milestone Aug 30, 2019

wpaulino reviewed Aug 30, 2019

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halseth reviewed Sep 2, 2019

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joostjager requested review from halseth and wpaulino September 2, 2019 22:13

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joostjager force-pushed the buildroute branch from e24a703 to 24742c7 Compare September 3, 2019 11:47

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joostjager force-pushed the buildroute branch from 24742c7 to 00e13a6 Compare September 6, 2019 08:34

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joostjager added 3 commits September 17, 2019 11:10

channeldb: add ComputeFee function

8c44cf4

routing/route: add vertex constructor for hex string

fd63ed1

channeldb: add forward fee calculation function

a0e91b5

joostjager force-pushed the buildroute branch 2 times, most recently from 35ad463 to 396c5b6 Compare September 17, 2019 09:40

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halseth suggested changes Sep 18, 2019

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joostjager requested a review from halseth September 18, 2019 11:38

joostjager force-pushed the buildroute branch from 8712e88 to e05425d Compare September 18, 2019 11:38

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joostjager force-pushed the buildroute branch from e05425d to 21f3a06 Compare September 19, 2019 17:35

wpaulino removed their request for review September 24, 2019 00:28

joostjager added 3 commits September 24, 2019 10:00

routing+routerrpc: add BuildRoute function

2998211

lncli: add BuildRoute function

6328b2e

lncli: update SendToRoute to also parse new route format

03d33cb

joostjager force-pushed the buildroute branch from 21f3a06 to 03d33cb Compare September 24, 2019 08:00

wpaulino approved these changes Sep 24, 2019

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Roasbeef merged commit 18f88cb into lightningnetwork:master Sep 25, 2019

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routing: add build route functionality #3440

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routing: add build route functionality #3440

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