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    drop(Box::from_raw(raw_cb as *mut MergeOperatorCallback<F, PF>));
85}
86
87pub unsafe extern "C" fn delete_callback(
88    _raw_cb: *mut c_void,
89    value: *const c_char,
90    value_length: size_t,
91) {
92    if !value.is_null() {
93        drop(Box::from_raw(slice::from_raw_parts_mut(
94            value as *mut u8,
95            value_length,
96        )));
97    }
98}
99
100pub unsafe extern "C" fn name_callback<F: MergeFn, PF: MergeFn>(
101    raw_cb: *mut c_void,
102) -> *const c_char {
103    let cb = &mut *(raw_cb as *mut MergeOperatorCallback<F, PF>);
104    cb.name.as_ptr()
105}
106
107pub unsafe extern "C" fn full_merge_callback<F: MergeFn, PF: MergeFn>(
108    raw_cb: *mut c_void,
109    raw_key: *const c_char,
110    key_len: size_t,
111    existing_value: *const c_char,
112    existing_value_len: size_t,
113    operands_list: *const *const c_char,
114    operands_list_len: *const size_t,
115    num_operands: c_int,
116    success: *mut u8,
117    new_value_length: *mut size_t,
118) -> *mut c_char {
119    let cb = &mut *(raw_cb as *mut MergeOperatorCallback<F, PF>);
120    let operands = &MergeOperands::new(operands_list, operands_list_len, num_operands);
121    let key = slice::from_raw_parts(raw_key as *const u8, key_len);
122    let oldval = if existing_value.is_null() {
123        None
124    } else {
125        Some(slice::from_raw_parts(
126            existing_value as *const u8,
127            existing_value_len,
128        ))
129    };
130    (cb.full_merge_fn)(key, oldval, operands).map_or_else(
131        || {
132            *new_value_length = 0;
133            *success = 0_u8;
134            ptr::null_mut() as *mut c_char
135        },
136        |result| {
137            *new_value_length = result.len() as size_t;
138            *success = 1_u8;
139            Box::into_raw(result.into_boxed_slice()) as *mut c_char
140        },
141    )
142}
143
144pub unsafe extern "C" fn partial_merge_callback<F: MergeFn, PF: MergeFn>(
145    raw_cb: *mut c_void,
146    raw_key: *const c_char,
147    key_len: size_t,
148    operands_list: *const *const c_char,
149    operands_list_len: *const size_t,
150    num_operands: c_int,
151    success: *mut u8,
152    new_value_length: *mut size_t,
153) -> *mut c_char {
154    let cb = &mut *(raw_cb as *mut MergeOperatorCallback<F, PF>);
155    let operands = &MergeOperands::new(operands_list, operands_list_len, num_operands);
156    let key = slice::from_raw_parts(raw_key as *const u8, key_len);
157    (cb.partial_merge_fn)(key, None, operands).map_or_else(
158        || {
159            *new_value_length = 0;
160            *success = 0_u8;
161            ptr::null_mut::<c_char>()
162        },
163        |result| {
164            *new_value_length = result.len() as size_t;
165            *success = 1_u8;
166            Box::into_raw(result.into_boxed_slice()) as *mut c_char
167        },
168    )
169}
170
171pub struct MergeOperands {
172    operands_list: *const *const c_char,
173    operands_list_len: *const size_t,
174    num_operands: usize,
175}
176
177impl MergeOperands {
178    fn new(
179        operands_list: *const *const c_char,
180        operands_list_len: *const size_t,
181        num_operands: c_int,
182    ) -> MergeOperands {
183        assert!(num_operands >= 0);
184        MergeOperands {
185            operands_list,
186            operands_list_len,
187            num_operands: num_operands as usize,
188        }
189    }
190
191    pub fn len(&self) -> usize {
192        self.num_operands
193    }
194
195    pub fn is_empty(&self) -> bool {
196        self.num_operands == 0
197    }
198
199    pub fn iter(&self) -> MergeOperandsIter {
200        MergeOperandsIter {
201            operands: self,
202            cursor: 0,
203        }
204    }
205
206    fn get_operand(&self, index: usize) -> Option<&[u8]> {
207        if index >= self.num_operands {
208            None
209        } else {
210            unsafe {
211                let base = self.operands_list as usize;
212                let base_len = self.operands_list_len as usize;
213                let spacing = mem::size_of::<*const *const u8>();
214                let spacing_len = mem::size_of::<*const size_t>();
215                let len_ptr = (base_len + (spacing_len * index)) as *const size_t;
216                let len = *len_ptr;
217                let ptr = base + (spacing * index);
218                Some(slice::from_raw_parts(*(ptr as *const *const u8), len))
219            }
220        }
221    }
222}
223
224pub struct MergeOperandsIter<'a> {
225    operands: &'a MergeOperands,
226    cursor: usize,
227}
228
229impl<'a> Iterator for MergeOperandsIter<'a> {
230    type Item = &'a [u8];
231
232    fn next(&mut self) -> Option<Self::Item> {
233        let operand = self.operands.get_operand(self.cursor)?;
234        self.cursor += 1;
235        Some(operand)
236    }
237
238    fn size_hint(&self) -> (usize, Option<usize>) {
239        let remaining = self.operands.num_operands - self.cursor;
240        (remaining, Some(remaining))
241    }
242}
243
244impl<'a> IntoIterator for &'a MergeOperands {
245    type Item = &'a [u8];
246    type IntoIter = MergeOperandsIter<'a>;
247
248    fn into_iter(self) -> Self::IntoIter {
249        Self::IntoIter {
250            operands: self,
251            cursor: 0,
252        }
253    }
254}
rust_rocksdb/merge_operator.rs

rust_rocksdb/
merge_operator.rs
