We were previously directly creating onion payloads inside the various
payment state machines and manipulating tlv fields. This was a layering
violation that was somewhat ok because in most cases we only needed to
create the onion payload for the recipient at the beginning of the payment
flow and didn't need to modify it, except for a small change in the MPP
case.
This forced us to handle trampoline onions directly in the payment
initiator and will not work for blinded payments, where we can only build
the onion payload for the recipient after we've chosen the routes and how
to split the amount.
We clean this up by introducing payment recipients that abstract away the
creation of onion payloads. This makes it much easier to integrate blinded
payments. It also allows us to clean up the way we do trampoline payments
and potentially support splitting across multiple trampoline routes (not
included in this PR as this change isn't immediately needed).
It also lets us simplify the MultiPartPaymentLifecycle FSM, by moving the
logic of computing how much remains to be sent and what fee can be used
to the route calculation component.
Created new files for pages that were in the wiki, but not already in the docs directory. Also made following fixes to README.md and existing files in the docs directory:
* update bolt links to avoid redirect
* link to logging guide from logging section (README.md)
* fixed typo in Backup section and capitalization of Bitcoin Core (README.md)
* Alice does not need trampoline feature enabled (TrampolinePayments.md)
* link to 2021 edition of Trampoline PR (TrampolinePayments.md)
* fixed API examples and removed quotes from password (API.md)
* use --nodeIds for sendtoroute examples (TrampolinePayments.md and MultipartPayments.md)
* update CLI example 3 to use jq (Usage.md)
* fix typo in docs/FAQ.md
* updated Guide.md to point to all pages that are guides
