rocksdb/
slice_transform.rs

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1// Copyright 2020 Tyler Neely
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15use std::ffi::CString;
16use std::slice;
17
18use libc::{c_char, c_uchar, c_void, size_t};
19
20use crate::{ffi, ffi_util::CStrLike};
21
22/// A `SliceTransform` is a generic pluggable way of transforming one string
23/// to another. Its primary use-case is in configuring rocksdb
24/// to store prefix blooms by setting prefix_extractor in
25/// ColumnFamilyOptions.
26pub struct SliceTransform {
27    pub inner: *mut ffi::rocksdb_slicetransform_t,
28}
29
30// NB we intentionally don't implement a Drop that passes
31// through to rocksdb_slicetransform_destroy because
32// this is currently only used (to my knowledge)
33// by people passing it as a prefix extractor when
34// opening a DB.
35
36impl SliceTransform {
37    pub fn create(
38        name: impl CStrLike,
39        transform_fn: TransformFn,
40        in_domain_fn: Option<InDomainFn>,
41    ) -> SliceTransform {
42        let cb = Box::into_raw(Box::new(TransformCallback {
43            name: name.into_c_string().unwrap(),
44            transform_fn,
45            in_domain_fn,
46        }));
47
48        let st = unsafe {
49            ffi::rocksdb_slicetransform_create(
50                cb as *mut c_void,
51                Some(slice_transform_destructor_callback),
52                Some(transform_callback),
53                Some(in_domain_callback),
54                // this None points to the deprecated InRange callback
55                None,
56                Some(slice_transform_name_callback),
57            )
58        };
59
60        SliceTransform { inner: st }
61    }
62
63    pub fn create_fixed_prefix(len: size_t) -> SliceTransform {
64        SliceTransform {
65            inner: unsafe { ffi::rocksdb_slicetransform_create_fixed_prefix(len) },
66        }
67    }
68
69    pub fn create_noop() -> SliceTransform {
70        SliceTransform {
71            inner: unsafe { ffi::rocksdb_slicetransform_create_noop() },
72        }
73    }
74}
75
76pub type TransformFn<'a> = fn(&'a [u8]) -> &'a [u8];
77pub type InDomainFn = fn(&[u8]) -> bool;
78
79pub struct TransformCallback<'a> {
80    pub name: CString,
81    pub transform_fn: TransformFn<'a>,
82    pub in_domain_fn: Option<InDomainFn>,
83}
84
85pub unsafe extern "C" fn slice_transform_destructor_callback(raw_cb: *mut c_void) {
86    drop(Box::from_raw(raw_cb as *mut TransformCallback));
87}
88
89pub unsafe extern "C" fn slice_transform_name_callback(raw_cb: *mut c_void) -> *const c_char {
90    let cb = &mut *(raw_cb as *mut TransformCallback);
91    cb.name.as_ptr()
92}
93
94pub unsafe extern "C" fn transform_callback(
95    raw_cb: *mut c_void,
96    raw_key: *const c_char,
97    key_len: size_t,
98    dst_length: *mut size_t,
99) -> *mut c_char {
100    let cb = &mut *(raw_cb as *mut TransformCallback);
101    let key = slice::from_raw_parts(raw_key as *const u8, key_len);
102    let prefix = (cb.transform_fn)(key);
103    *dst_length = prefix.len() as size_t;
104    prefix.as_ptr() as *mut c_char
105}
106
107pub unsafe extern "C" fn in_domain_callback(
108    raw_cb: *mut c_void,
109    raw_key: *const c_char,
110    key_len: size_t,
111) -> c_uchar {
112    let cb = &mut *(raw_cb as *mut TransformCallback);
113    let key = slice::from_raw_parts(raw_key as *const u8, key_len);
114    c_uchar::from(cb.in_domain_fn.map_or(true, |in_domain| in_domain(key)))
115}
rocksdb/slice_transform.rs

rocksdb/
slice_transform.rs
