Allow pay request and hop hints as input to queryroutes

[Bluetegu]

This addresses issue #2056

Two additional optional input flags were added to queryroutes cli command:
payment request (invoice)
hints (in json format)

This is useful mostly to compute routes to private destinations.

The current implementation assumes that the hints provide the last few steps towards the destination, i.e. that their final hop connects to the last node on the path. In particular, hints to cross a private edge in the middle of the network are not supported. This limitation can be lifted in future.

For testing a setup of A->B->C where B->C is private was used.

To test the use of an invoice as input to queryroutes, an invoice was generated on C. The invoice was paid using sendtoroute, with queryroutes feeding it with routes. The invoice was used as input to queryroutes. Here is a log of that command:

ubuntu@btc:~/go/dev/alice$ lncli-a queryroutes --pay_req="lnsb53220n1pd746evpp58njslvvsjfrwljr49aj4qtq8xcnghvppmv03jgmledgmlvlegdvqdzz2pexjanpw3jjq6twwehkjcm9yp6x7grzv5s8qctfvssxy7fqwdjkuer5daex7at5v5cqzysxqyjw5qrzjqf4996kagt4tku8fkpyp4acqr55e7ltmgypsjaamx7304trmhcqpyqq8gvqqqqgqqqqqqfcsqqqqqqqqjql7ga8cm06x68w5uw3glyy37xmqzpncqajprrnan8wes0fx0q8mf4s6x58dqys4fee6xmarm72f3ulhqdg6rg3aumxyg9x8pu78zwwccqnyvlyz" | lncli-a sendtoroute "3ce50fb1909246efc8752f65502c0736268bb021db1f19237fcb51bfb3f94358" -
{
"payment_error": "",
"payment_preimage": "94192fedd60bd0e31db8160aeaafac48cf79de5196af77e3bc58a6d2bde9734d",
"payment_route": {
"total_time_lock": 2016,
"total_fees": 10,
"total_amt": 5332,
"hops": [
{
"chan_id": 1540415790579712,
"chan_capacity": 1000000,
"amt_to_forward": 5322,
"fee": 10,
"expiry": 1872,
"amt_to_forward_msat": 5322000,
"fee_msat": 10000,
"pub_key": "026a52eadd42eabb70e9b0481af7001d299f7d7b41030977bb37a2faac7bbe0012"
},
{
"chan_id": 2043992116101120,
"chan_capacity": 5322,
"amt_to_forward": 5322,
"expiry": 1872,
"amt_to_forward_msat": 5322000,
"pub_key": "034a15c028970d4070c60f532018cfdb943b584ba267c83fe333ef1ad70b10feaf"
}
],
"total_fees_msat": 10000,
"total_amt_msat": 5332000
}
}

To test input of hints to queryroutes, a hint that includes the last B->C hop was used as input. This hint is identical to the hint generated when creating the invoice on C.

ubuntu@btc:~/go/dev/alice$ lncli-a queryroutes --hints='{"route_hints": [
{
"hop_hints": [
{
"node_id": "026a52eadd42eabb70e9b0481af7001d299f7d7b41030977bb37a2faac7bbe0012",
"chan_id": "2043992116101120",
"fee_base_msat": 10000,
"fee_proportional_millionths": 0,
"cltv_expiry_delta": 144
}
]
}
]}' "034a15c028970d4070c60f532018cfdb943b584ba267c83fe333ef1ad70b10feaf" 333
{
"routes": [
{
"total_time_lock": 2016,
"total_fees": "10",
"total_amt": "343",
"hops": [
{
"chan_id": "1540415790579712",
"chan_capacity": "1000000",
"amt_to_forward": "333",
"fee": "10",
"expiry": 1872,
"amt_to_forward_msat": "333000",
"fee_msat": "10000",
"pub_key": "026a52eadd42eabb70e9b0481af7001d299f7d7b41030977bb37a2faac7bbe0012"
},
{
"chan_id": "2043992116101120",
"chan_capacity": "333",
"amt_to_forward": "333",
"fee": "0",
"expiry": 1872,
"amt_to_forward_msat": "333000",
"fee_msat": "0",
"pub_key": "034a15c028970d4070c60f532018cfdb943b584ba267c83fe333ef1ad70b10feaf"
}
],
"total_fees_msat": "10000",
"total_amt_msat": "343000"
}
]
}

[halseth]

Nice, I imagine this will be a very useful addition for users doing their own custom path finding! :D

Mostly style suggestions for now, looks pretty good 👍

[halseth]

why 4?

[Bluetegu]

Lol. Fixed

[halseth]

needs a rebase to work with new method signature! 😀

[halseth]

should check if PaymentRequest is present before attempting to parse it.

[Bluetegu]

Yea. I was taking advantage of Decode handling correctly null inputs. Anyhow, I agree that this is convoluted. Rearranged code to make it more readable.

[halseth]

you can do this check before parsing the hop hints?

[Bluetegu]

Yes. Moved up (need parsing of payment first though)

[halseth]

this if is not necessary

[Bluetegu]

Removed.

[halseth]

if this is not set, shouldn't that be an error?

[Bluetegu]

Yes. Fixed. Now returning custom errors, to ensure the source of the error is known (i.e. that its from malformed hints).

[Bluetegu]

Thanks for the review!
Rebased && Fixed issues
Please see inline

[halseth]

Needs a rebase once #3054 is in.

[Roasbeef]

Superseded by #3911.