Add/remove the HTLC amount from the channel hints so concurrent getroute calls
have the correct exclusions. This can sometimes underflow, if we're unlucky
and call getroute too closely, but that's not a big issue, it can only result
in a failed MPP attempt too many, nothing fatal, and it'll get corrected based
on the result returned by the failing node.
These are primarily the fee and cltv constraints that we need to keep up to
date in order to give modifiers a correct view of what is and what isn't
allowed.
We could end up with multiple channel hints, which is a bit wasteful. We now
look for existing ones before adding a new one, and if one exists we use the
more restrictive parameters.
Suggested-by: Lisa Neigut <@niftynei>
We're lucky that we can distinguish the severity of the failure based on the
failcode, so we bubble up the one with the maximum failcode, and let callers
inspect details if they need more information.
We can have quite detailed information about our local channels, so call
`listpeers` before the `getroute` call on the root payment, to seed that
information in the channel_hints.
We were just handwaving the partid generation, which broke some tests that
expected the first payment attempt to always have partid=0, so here we just
track the partids assigned in the payment tree, starting at 0.
The status of what started as a simple JSON-RPC call is now spread across an
entire tree of partial payments and payment attempts. So we collect the status
in a single struct in order to report back success of failure.
This is just for testing for now, TLV payload computation will come next. We
stage all the payloads in deserialized form so modifiers can modify them more
easily and serialize them only before actually calling `createonion`.
This is necessary so we can build the absolute locktimes in the next step. For
now just fetch the blockheight on each (sub-)payment, later we can reuse the
root blockheight if it ends up using too much traffic.
A payment is considered finished if it is in a final state (success or
failure) or all its sub-payments are finished. If that's the case we notify
`payment_finished` and bubble up through `payment_child_finished`, eventually
bubbling up to the root, which can then report success of failure back to the
RPC command that initiated the whole process.
This is likely a bit of overkill for this type of functionality, but it is a
nice first use-case of how functionality can be compartmentalized into
modifiers. If makes swapping retry mechanisms in and out really simple.
This should make it easy for JSON-RPC functions and modifiers to get the
associated data for a given modifier name. Useful if a modifier needs to
access its parent's modifier data, or in other functions that need to access
modifier data, e.g., when passing destination pointers into the `param()`
call.
This commit can be reverted/skipped once we have implemented all the logic and
have feature parity with the normal `pay`. It's main purpose is to expose the
unfinished functionality to test it, without completely breaking the existing
`pay` command.
