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rust-rocksdb/src/slice_transform.rs

137 lines
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// Copyright 2018 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.
use std::ffi::CString;
use std::mem;
use std::ptr;
use std::slice;
use libc::{self, c_char, c_void, size_t};
use ffi;
/// A SliceTranform is a generic pluggable way of transforming one string
/// to another. Its primary use-case is in configuring rocksdb
/// to store prefix blooms by setting prefix_extractor in
/// ColumnFamilyOptions.
pub struct SliceTransform {
pub inner: *mut ffi::rocksdb_slicetransform_t,
}
// NB we intentionally don't implement a Drop that passes
// through to rocksdb_slicetransform_destroy because
// this is currently only used (to my knowledge)
// by people passing it as a prefix extractor when
// opening a DB.
impl SliceTransform {
pub fn create(
name: &str,
transform_fn: TransformFn,
in_domain_fn: Option<InDomainFn>,
) -> SliceTransform {
let cb = Box::new(TransformCallback {
name: CString::new(name.as_bytes()).unwrap(),
transform_fn,
in_domain_fn,
});
let st = unsafe {
ffi::rocksdb_slicetransform_create(
mem::transmute(cb),
Some(slice_transform_destructor_callback),
Some(transform_callback),
// this is ugly, but I can't get the compiler
// not to barf with "expected fn pointer, found fn item"
// without this. sorry.
if in_domain_fn.is_some() {
Some(in_domain_callback)
} else {
None
},
// this None points to the deprecated InRange callback
None,
Some(slice_transform_name_callback),
)
};
SliceTransform { inner: st }
}
pub fn create_fixed_prefix(len: size_t) -> SliceTransform {
SliceTransform {
inner: unsafe { ffi::rocksdb_slicetransform_create_fixed_prefix(len) },
}
}
pub fn create_noop() -> SliceTransform {
SliceTransform {
inner: unsafe { ffi::rocksdb_slicetransform_create_noop() },
}
}
}
pub type TransformFn = fn(&[u8]) -> Vec<u8>;
pub type InDomainFn = fn(&[u8]) -> bool;
pub struct TransformCallback {
pub name: CString,
pub transform_fn: TransformFn,
pub in_domain_fn: Option<InDomainFn>,
}
pub unsafe extern "C" fn slice_transform_destructor_callback(raw_cb: *mut c_void) {
let transform: Box<TransformCallback> = mem::transmute(raw_cb);
drop(transform);
}
pub unsafe extern "C" fn slice_transform_name_callback(raw_cb: *mut c_void) -> *const c_char {
let cb = &mut *(raw_cb as *mut TransformCallback);
cb.name.as_ptr()
}
pub unsafe extern "C" fn transform_callback(
raw_cb: *mut c_void,
raw_key: *const c_char,
key_len: size_t,
dst_length: *mut size_t,
) -> *mut c_char {
let cb = &mut *(raw_cb as *mut TransformCallback);
let key = slice::from_raw_parts(raw_key as *const u8, key_len as usize);
let mut result = (cb.transform_fn)(key);
result.shrink_to_fit();
// copy the result into a C++ destroyable buffer
let buf = libc::malloc(result.len() as size_t);
assert!(!buf.is_null());
ptr::copy(result.as_ptr() as *mut c_void, &mut *buf, result.len());
*dst_length = result.len() as size_t;
buf as *mut c_char
}
pub unsafe extern "C" fn in_domain_callback(
raw_cb: *mut c_void,
raw_key: *const c_char,
key_len: size_t,
) -> u8 {
let cb = &mut *(raw_cb as *mut TransformCallback);
let key = slice::from_raw_parts(raw_key as *const u8, key_len as usize);
if (cb.in_domain_fn.unwrap())(key) {
1
} else {
0
}
}