rust_rocksdb/
merge_operator.rs

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//
15
16//! rustic merge operator
17//!
18//! ```
19//! use rust_rocksdb::{Options, DB, MergeOperands};
20//!
21//! fn concat_merge(new_key: &[u8],
22//!                 existing_val: Option<&[u8]>,
23//!                 operands: &MergeOperands)
24//!                 -> Option<Vec<u8>> {
25//!
26//!    let mut result: Vec<u8> = Vec::with_capacity(operands.len());
27//!    existing_val.map(|v| {
28//!        for e in v {
29//!            result.push(*e)
30//!        }
31//!    });
32//!    for op in operands {
33//!        for e in op {
34//!            result.push(*e)
35//!        }
36//!    }
37//!    Some(result)
38//! }
39//!
40//!let tempdir = tempfile::Builder::new()
41//!    .prefix("_rust_path_to_rocksdb")
42//!    .tempdir()
43//!    .expect("Failed to create temporary path for the _rust_path_to_rocksdb");
44//!let path = tempdir.path();
45//!let mut opts = Options::default();
46//!
47//!opts.create_if_missing(true);
48//!opts.set_merge_operator_associative("test operator", concat_merge);
49//!{
50//!    let db = DB::open(&opts, path).unwrap();
51//!    let p = db.put(b"k1", b"a");
52//!    db.merge(b"k1", b"b");
53//!    db.merge(b"k1", b"c");
54//!    db.merge(b"k1", b"d");
55//!    db.merge(b"k1", b"efg");
56//!    let r = db.get(b"k1");
57//!    assert_eq!(r.unwrap().unwrap(), b"abcdefg");
58//!}
59//!let _ = DB::destroy(&opts, path);
60//! ```
61
62use libc::{self, c_char, c_int, c_void, size_t};
63use std::ffi::CString;
64use std::mem;
65use std::ptr;
66use std::slice;
67
68pub trait MergeFn:
69    Fn(&[u8], Option<&[u8]>, &MergeOperands) -> Option<Vec<u8>> + Send + Sync + 'static
70{
71}
72impl<F> MergeFn for F where
73    F: Fn(&[u8], Option<&[u8]>, &MergeOperands) -> Option<Vec<u8>> + Send + Sync + 'static
74{
75}
76
77pub struct MergeOperatorCallback<F: MergeFn, PF: MergeFn> {
78    pub name: CString,
79    pub full_merge_fn: F,
80    pub partial_merge_fn: PF,
81}
82
83pub unsafe extern "C" fn destructor_callback<F: MergeFn, PF: MergeFn>(raw_cb: *mut c_void) {
84    unsafe {
85        drop(Box::from_raw(raw_cb as *mut MergeOperatorCallback<F, PF>));
86    }
87}
88
89pub unsafe extern "C" fn delete_callback(
90    _raw_cb: *mut c_void,
91    value: *const c_char,
92    value_length: size_t,
93) {
94    unsafe {
95        if !value.is_null() {
96            // Use pointer form to avoid implicit cast from slice reference to raw slice pointer
97            drop(Box::from_raw(ptr::slice_from_raw_parts_mut(
98                value as *mut u8,
99                value_length,
100            )));
101        }
102    }
103}
104
105pub unsafe extern "C" fn name_callback<F: MergeFn, PF: MergeFn>(
106    raw_cb: *mut c_void,
107) -> *const c_char {
108    unsafe {
109        let cb = &mut *(raw_cb as *mut MergeOperatorCallback<F, PF>);
110        cb.name.as_ptr()
111    }
112}
113
114pub unsafe extern "C" fn full_merge_callback<F: MergeFn, PF: MergeFn>(
115    raw_cb: *mut c_void,
116    raw_key: *const c_char,
117    key_len: size_t,
118    existing_value: *const c_char,
119    existing_value_len: size_t,
120    operands_list: *const *const c_char,
121    operands_list_len: *const size_t,
122    num_operands: c_int,
123    success: *mut u8,
124    new_value_length: *mut size_t,
125) -> *mut c_char {
126    unsafe {
127        let cb = &mut *(raw_cb as *mut MergeOperatorCallback<F, PF>);
128        let operands = &MergeOperands::new(operands_list, operands_list_len, num_operands);
129        let key = slice::from_raw_parts(raw_key as *const u8, key_len);
130        let oldval = if existing_value.is_null() {
131            None
132        } else {
133            Some(slice::from_raw_parts(
134                existing_value as *const u8,
135                existing_value_len,
136            ))
137        };
138        (cb.full_merge_fn)(key, oldval, operands).map_or_else(
139            || {
140                *new_value_length = 0;
141                *success = 0_u8;
142                ptr::null_mut() as *mut c_char
143            },
144            |result| {
145                *new_value_length = result.len() as size_t;
146                *success = 1_u8;
147                Box::into_raw(result.into_boxed_slice()) as *mut c_char
148            },
149        )
150    }
151}
152
153pub unsafe extern "C" fn partial_merge_callback<F: MergeFn, PF: MergeFn>(
154    raw_cb: *mut c_void,
155    raw_key: *const c_char,
156    key_len: size_t,
157    operands_list: *const *const c_char,
158    operands_list_len: *const size_t,
159    num_operands: c_int,
160    success: *mut u8,
161    new_value_length: *mut size_t,
162) -> *mut c_char {
163    unsafe {
164        let cb = &mut *(raw_cb as *mut MergeOperatorCallback<F, PF>);
165        let operands = &MergeOperands::new(operands_list, operands_list_len, num_operands);
166        let key = slice::from_raw_parts(raw_key as *const u8, key_len);
167        (cb.partial_merge_fn)(key, None, operands).map_or_else(
168            || {
169                *new_value_length = 0;
170                *success = 0_u8;
171                ptr::null_mut::<c_char>()
172            },
173            |result| {
174                *new_value_length = result.len() as size_t;
175                *success = 1_u8;
176                Box::into_raw(result.into_boxed_slice()) as *mut c_char
177            },
178        )
179    }
180}
181
182pub struct MergeOperands {
183    operands_list: *const *const c_char,
184    operands_list_len: *const size_t,
185    num_operands: usize,
186}
187
188impl MergeOperands {
189    fn new(
190        operands_list: *const *const c_char,
191        operands_list_len: *const size_t,
192        num_operands: c_int,
193    ) -> MergeOperands {
194        assert!(num_operands >= 0);
195        MergeOperands {
196            operands_list,
197            operands_list_len,
198            num_operands: num_operands as usize,
199        }
200    }
201
202    pub fn len(&self) -> usize {
203        self.num_operands
204    }
205
206    pub fn is_empty(&self) -> bool {
207        self.num_operands == 0
208    }
209
210    pub fn iter(&'_ self) -> MergeOperandsIter<'_> {
211        MergeOperandsIter {
212            operands: self,
213            cursor: 0,
214        }
215    }
216
217    fn get_operand(&self, index: usize) -> Option<&[u8]> {
218        if index >= self.num_operands {
219            None
220        } else {
221            unsafe {
222                let base = self.operands_list as usize;
223                let base_len = self.operands_list_len as usize;
224                let spacing = mem::size_of::<*const *const u8>();
225                let spacing_len = mem::size_of::<*const size_t>();
226                let len_ptr = (base_len + (spacing_len * index)) as *const size_t;
227                let len = *len_ptr;
228                let ptr = base + (spacing * index);
229                Some(slice::from_raw_parts(*(ptr as *const *const u8), len))
230            }
231        }
232    }
233}
234
235pub struct MergeOperandsIter<'a> {
236    operands: &'a MergeOperands,
237    cursor: usize,
238}
239
240impl<'a> Iterator for MergeOperandsIter<'a> {
241    type Item = &'a [u8];
242
243    fn next(&mut self) -> Option<Self::Item> {
244        let operand = self.operands.get_operand(self.cursor)?;
245        self.cursor += 1;
246        Some(operand)
247    }
248
249    fn size_hint(&self) -> (usize, Option<usize>) {
250        let remaining = self.operands.num_operands - self.cursor;
251        (remaining, Some(remaining))
252    }
253}
254
255impl<'a> IntoIterator for &'a MergeOperands {
256    type Item = &'a [u8];
257    type IntoIter = MergeOperandsIter<'a>;
258
259    fn into_iter(self) -> Self::IntoIter {
260        Self::IntoIter {
261            operands: self,
262            cursor: 0,
263        }
264    }
265}
rust_rocksdb/merge_operator.rs

rust_rocksdb/
merge_operator.rs
