Nim Wrapper for LevelDB

(HIGH LEVEL WRAPPER STILL NEEDS TO BE WRITTEN)

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.

About efficiency of get operations

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_t pointer

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:

1. 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).

2. 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.

Project structure

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