rust-rocksdb/src/comparator.rs

/*
   Copyright 2014 Tyler Neely

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/
extern crate libc;
use self::libc::{c_char, c_int, c_void, size_t};
use std::ffi::CString;
use std::mem;
use std::ptr;
use std::slice;

use rocksdb_options::Options;
use rocksdb::DB;

pub struct ComparatorCallback {
    pub name: CString,
    pub f: fn(&[u8], &[u8]) -> i32,
}

pub extern "C" fn destructor_callback(raw_cb: *mut c_void) {
    // turn this back into a local variable so rust will reclaim it
    let _: Box<ComparatorCallback> = unsafe {mem::transmute(raw_cb)};
}

pub extern "C" fn name_callback(raw_cb: *mut c_void) -> *const c_char {
    unsafe {
        let cb: &mut ComparatorCallback =
            &mut *(raw_cb as *mut ComparatorCallback);
        let ptr = cb.name.as_ptr();
        ptr as *const c_char
    }
}

pub extern "C" fn compare_callback(raw_cb: *mut c_void,
                                   a_raw: *const c_char,
                                   a_len: size_t,
                                   b_raw: *const c_char,
                                   b_len: size_t)
                                   -> c_int {
    unsafe {
        let cb: &mut ComparatorCallback =
            &mut *(raw_cb as *mut ComparatorCallback);
        let a: &[u8] = slice::from_raw_parts(a_raw as *const u8, a_len as usize);
        let b: &[u8] = slice::from_raw_parts(b_raw as *const u8, b_len as usize);
        (cb.f)(a, b)
    }
}

fn test_reverse_compare(a: &[u8], b: &[u8]) -> c_int {
    if a < b {
        1
    } else if a > b {
        -1
    } else {
        0
    }
}

//#[allow(dead_code)]
//#[test]
//fn compare_works() {
//    let path = "_rust_rocksdb_comparetest";
//    let mut opts = Options::new();
//    opts.create_if_missing(true);
//    opts.add_comparator("test comparator", test_reverse_compare);
//    {
//        let db = DB::open(&opts, path).unwrap();
//        // TODO add interesting test
//    }
//    assert!(DB::destroy(&opts, path).is_ok());
//}