nit: I'd prefer not to use vsnprintf here. We've purged this from the code when introducing tinyformat. Wonder if we can do something based on our strprintf. Though bridging between C varargs and C++ is likely going to be difficult, and this solution as-taken-from LevelDB should be fine. It's just fairly ugly code and should not be taken as a hint to contributors that using system v?s?n?printf is okay in other places.

Maybe just add a comment in that regard, mentioning where the code comes from and why and explaining the above.

CBitcoinLevelDBLogger maybe? The name is too general otherwise, we should reserve this class name for ourselves.

Why is this class in the .h file? It seems to be only used internally in dbwrapper.cpp.

well, h for declaration and cpp for implementation, at least that is what I always thought. You mean just putting the class directly in the cpp ?

.h is for the externally accessible parts of a cpp file. This class doesn't need to be exposed to anything, so it can just go inside the cpp file.

Right, .h is for interface declaration. Although with C++ it's not always clear what should be part of the interface and what not (especially when tests are involved), this one could just as well be private to the .cpp.

Please retain alphabetical ordering (leveldb should be between http and libevent)