This is a wrapper for the key-value store LevelDB, and wraps the C API to provide basic support for working with LevelDB in Nim. It's been tested with LevelDB v1.15 and v1.18 in Linux x86-64. You have to have the LevelDB library installed (.so,.dll, etc.) in order for this to work.
As has been noted elsewhere, the way that LevelDB implements the C API for looking up values is to:
- Look up the value from the database as a C++ function call
- Copy this value to a non-null terminated char array
- Return the char array with length passed back as in a
size_tpointer
This is problematic because we're unavoidably doing (if using the C API which is a stable ABI) an extra copy of the value stored. On passing this back to Nim, we will probably want to do a second copy of this so that we can have it as a 'normal' string type, which is null-terminated, managed by Nim, and has all of the nice, normal library operations defined.
There's no clean way around this without either wrapping the C++ functions (and risking breakage), or having a wrapper struct for Nim and losing many of the pleasant string library functions. I've chosen to go ahead and do the extra copy anyway, for two reasons:
-
Most users will not be using LevelDB for intensive, performance-critical applications, but instead filling the same role as SQLite (prototyping and persistence for applications vs. flat files).
-
If implemented as a struct that wraps the value returned from
leveldb_get, the first thing that most people would do would be to display the value or pass it to a another function that takes a string, which would do an implicit conversion anyway.
The wrapper generated from LevelDB's C API is in the internal directory, with
tests included; to run tests, compile leveldb_wrapper.nim as the main module:
cd src/internal
nim c -r leveldb_wrapper.nim