Log "nn.nnn coins spent using strategy ..." on log level Debug

[sesam]

Issue #288 says that, for now, we'd want to log total amount sent.

Should I change any of

• log level = Debug
• include destination? Currently not listed for log file brevity and privacy

[ignopeverell]

I think the idea in #288 was to make this accessible to wallet info, which means a separate data file, similar to wallet.dat that captures transaction-level information. It could say something like "sent X coins on Y date to Z addres, outputs A, B, C where consumed and D change was created".

[sesam]

tl;dr roadworks. Will try adding a new and separate outputs_spent_logger or maybe better transactions_logger to get going.

Oh I see. To log (at minimum) total amount spent via util::logger, using slog, is probably cleanest done by instantiating an additional logger, completely separate from the util::logger helper.

There less clean option would be to bolt in one extra drain that is craftily filtered. But that means also terminal and file output filters must be filtered, so the filtering latency will be applied to all logging. Filtering by referencing the wanted logger instance from the beginning is of course more efficient, and a lot less messy.

slog quick review

• + nice
• + nifty drain abstraction (but "cost free", really?)
• + supports filtering by module and line number (via environment variables, so that feature is compiled in by default) as well as runtime log filtering (google: Drain for RuntimeLevelFilter)
• + key-values can be attached to each log line, and be saved machine-readable, which could be a nice way to get good data to use for batch- and CI verification of executed transactions vs final wallet.dat contents
• - likely overkill
• - any filtering latency/penalties are paid by all log! / debug! / ... calls
• - attack surface
• - release builds contain all code, whether statically filtered out (release_max_level_...) or not
• + (?) release builds contain all code, just like the core bitcoind builds also prefer to do
• - no log rotation support, nor compression. slog docs point to this being a suitable tag:easy tag:helpwanted future task)

I'm imagining we can find a simpler logging solution with smaller potential attack surface later on, or roll our own, though I'm not suggesting to refactor and disturb everyone's stashes and branches right now.

[ignopeverell]

Okay sorry, I should have been more explicit. To be easily usable by the wallet it should be some JSON data. With that the wallet could display some info but also rollback some failed transactions for example. So I didn't mean "it could say" literally, I was just trying to describe the type of information that would fit in there.

[ignopeverell]

Still going to merge this as having some minimal logging is better than nothing until we can have a more formal solution. Maybe extending the format of wallet.dat would make the most sense.