Feature Request: Investigate Use of Existing Impl Pathfinding

[carlaKC]

Describe desired feature

When running with a fully simulated network, it would be amazing of SimLN could use the same pathfinding as LND/CLN/Eclair. LND would be the highest priority, because it's the majority of the network.

Possible Approaches

Extern C

• Create C libraries that implement each pathfinding algorithm
  • CLN: easy, compile library in C
  • LND: use c-shared to build C shared library
  • Eclair: not possible, so far as I know
• Use extern to call C code for each pathfinding

This would require some (likely painful) investigation to figure out if the c-shared approach would work for LND. There are all sorts of caveats about C-compatible types that I haven't looked into.

IPC

• Create "stub" servers that call directly to the implementations routing code:
  • Listen on socket, accepting parameters expressed in json
  • Run pathfinding
  • Return result
• SimLN then spins up each of these small servers using Command
• Implement the Pathfinder trait in Add pathfinder trait #273 which is responsible for shooting the request into the socket

Notes:

• I don't have strong opinions on how to handle IPC (never done this myself)
• We could also define a common RPC for these mini-servers, but that's a lot of boilerplate
• Main priority is that this should be ✨ seamless ✨ for the end user, SimLN should handle all the ugly stuff.

Use case for feature

A common use case for SimLN's random payment generation is to create "background noise" payments in a network, and then take and measure some action within that busy network.

Would you like to contribute code for this feature?

I don't have capacity to take this on right now, but would be happy to participate in design discussions and review.

[carlaKC]

IPC seems like a better approach to me because:

• We can support all LN impls
• It doesn't involve painful binding voodoo

I mostly wrote up extern c because it ✨ looks cool ✨, but that's not a very strong motivation.