Improve logging of pathfinding behavior

[tnull]

The behavior of sending a payment can be quite confusing to users, in particular if an otherwise obvious channel choice is avoided without giving any feedback as to why.

We therefore should try to improve the logging in get_route without getting too spammy. In particular, we should find a way to give users feedback when for example a direct channel is avoided due to lacking channel reserves, its value contribution, or similar.

[Sharmalm]

Hey i,d like to try this issue.

[Sharmalm]

And i am new to opensource, so i may need guidance.

[tnull]

Welcome! The relevant parts of the code can be found in the get_route method which is part of lightning/routing/router.rs. I'd recommend first reading this method in its entirety to understand how it works (it's kind of a beast, featuring multiple sub-macros, etc).

Then you'll have to figure out for which cases it makes sense to add logging lines (probably in TRACE level). It's important to strike a balance here, as a lot of hops/paths are excluded trivially, which shouldn't spam our logs. However, it would be nice to have logging for edge cases, in particular if they result in no path being returned at all. So maybe to start you could, instead of just logging any candidate exclusion right away, remember the last failure reason and only log it when it results in no path being returned.

[Sharmalm]

Thanks

[Sharmalm]

Welcome! The relevant parts of the code can be found in the get_route method which is part of lightning/routing/router.rs. I'd recommend first reading this method in its entirety to understand how it works (it's kind of a beast, featuring multiple sub-macros, etc).

Then you'll have to figure out for which cases it makes sense to add logging lines (probably in TRACE level). It's important to strike a balance here, as a lot of hops/paths are excluded trivially, which shouldn't spam our logs. However, it would be nice to have logging for edge cases, in particular if they result in no path being returned at all. So maybe to start you could, instead of just logging any candidate exclusion right away, remember the last failure reason and only log it when it results in no path being returned.

Hey @tnull, thanks for the explanation, but I still find it hard to understand this issue. Please provide some material to understand the code.

[tnull]

Hey @tnull, thanks for the explanation, but I still find it hard to understand this issue. Please provide some material to understand the code.

Mh, could you be a bit more specific on what you're having trouble understanding? Also, feel free to find me on LDK Discord and we can discuss this a bit more interactively.

[Sharmalm]

Yeah, I am finding it hard to understand code in lightning/routing/router.rs .
and tnull#9465 is this your discord username?

[tnull]

Yeah, I am finding it hard to understand code in lightning/routing/router.rs . and tnull#9465 is this your discord username?

Yep, feel free to reach out.

[Sharmalm]

Yeah, I am finding it hard to understand code in lightning/routing/router.rs . and tnull#9465 is this your discord username?

Yep, feel free to reach out.

Ok

[Aankirz]

Hello @tnull, I have spent some time in understanding LDK and I would like to work on this issue can you pls assign this to me ?

[tnull]

Hello @tnull, I have spent some time in understanding LDK and I would like to work on this issue can you pls assign this to me ?

I think @BOLT-12 is already working on this in #2011. So please pick another "good first issue". :)