1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
// Copyright 2012 The Rust Project Developers.
// Copyright 2015 Guillaume Gomez
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Library to interface with chunks of memory allocated in C.
//!
//! It is often desirable to safely interface with memory allocated from C,
//! encapsulating the unsafety into allocation and destruction time.  Indeed,
//! allocating memory externally is currently the only way to give Rust shared
//! mut state with C programs that keep their own references; vectors are
//! unsuitable because they could be reallocated or moved at any time, and
//! importing C memory into a vector takes a one-time snapshot of the memory.
//!
//! This module simplifies the usage of such external blocks of memory.  Memory
//! is encapsulated into an opaque object after creation; the lifecycle of the
//! memory can be optionally managed by Rust, if an appropriate destructor
//! closure is provided.  Safety is ensured by bounds-checking accesses, which
//! are marshalled through get and set functions.
//!
//! There are three unsafe functions: the two constructors, and the
//! unwrapping method. The constructors are unsafe for the
//! obvious reason (they act on a pointer that cannot be checked inside the
//! method), but `into_inner()` is somewhat more subtle in its unsafety.
//! It returns the contained pointer, but at the same time destroys the CVec
//! without running its destructor. This can be used to pass memory back to
//! C, but care must be taken that the ownership of underlying resources are
//! handled correctly, i.e. that allocated memory is eventually freed
//! if necessary.

use std::ptr;
use std::slice;
use std::ops::{Index, IndexMut};

/// The type representing a foreign chunk of memory
pub struct CVec<T> {
    base: *mut T,
    len: usize,
    dtor: Option<Box<FnMut(*mut T)>>
}

impl<T> Drop for CVec<T> {
    fn drop(&mut self) {
        if let Some(mut f) = self.dtor.take() {
            f(self.base);
        }
    }
}

impl<T> CVec<T> {
    /// Create a `CVec` from a raw pointer to a buffer with a given length.
    ///
    /// Panics if the given pointer is null. The returned vector will not attempt
    /// to deallocate the vector when dropped.
    ///
    /// # Arguments
    ///
    /// * base - A unique pointer to a buffer
    /// * len - The number of elements in the buffer
    pub unsafe fn new(base: *mut T, len: usize) -> CVec<T> {
        assert!(base != ptr::null_mut());
        CVec {
            base: base,
            len: len,
            dtor: None,
        }
    }

    /// Create a `CVec` from a foreign buffer, with a given length,
    /// and a function to run upon destruction.
    ///
    /// Panics if the given pointer is null.
    ///
    /// # Arguments
    ///
    /// * base - A unique pointer to a buffer
    /// * len - The number of elements in the buffer
    /// * dtor - A fn to run when the value is destructed, useful
    ///          for freeing the buffer, etc. `base` will be passed
    ///          to it as an argument.
    pub unsafe fn new_with_dtor<F>(base: *mut T,
                                   len: usize,
                                   dtor: F)
                                   -> CVec<T>
        where F: FnMut(*mut T) + 'static
    {
        assert!(base != ptr::null_mut());
        let dtor = Box::new(dtor);
        CVec {
            base: base,
            len: len,
            dtor: Some(dtor)
        }
    }

    /// Retrieves an element at a given index, returning `None` if the requested
    /// index is greater than the length of the vector.
    pub fn get<'a>(&'a self, ofs: usize) -> Option<&'a T> {
        if ofs < self.len {
            Some(unsafe { &*self.base.offset(ofs as isize) })
        } else {
            None
        }
    }

    /// Retrieves a mutable element at a given index, returning `None` if the
    /// requested index is greater than the length of the vector.
    pub fn get_mut<'a>(&'a mut self, ofs: usize) -> Option<&'a mut T> {
        if ofs < self.len {
            Some(unsafe { &mut *self.base.offset(ofs as isize) })
        } else {
            None
        }
    }

    /// Unwrap the pointer without running the destructor
    ///
    /// This method retrieves the underlying pointer, and in the process
    /// destroys the CVec but without running the destructor. A use case
    /// would be transferring ownership of the buffer to a C function, as
    /// in this case you would not want to run the destructor.
    ///
    /// Note that if you want to access the underlying pointer without
    /// cancelling the destructor, you can simply call `transmute` on the return
    /// value of `get(0)`.
    pub unsafe fn into_inner(mut self) -> *mut T {
        self.dtor = None;
        self.base
    }

    /// Returns the number of items in this vector.
    pub fn len(&self) -> usize { self.len }

    /// Returns whether this vector is empty.
    pub fn is_empty(&self) -> bool { self.len() == 0 }

    /// Convert to CSlice
    pub fn as_cslice(&self) -> CSlice<T> {
        CSlice {
            base: self.base,
            len: self.len
        }
    }
}

impl<T> AsRef<[T]> for CVec<T> {
    /// View the stored data as a slice.
    fn as_ref(&self) -> &[T] {
        unsafe {
            slice::from_raw_parts(self.base as *const T, self.len)
        }
    }
}

impl<T> AsMut<[T]> for CVec<T> {
    /// View the stored data as a slice.
    fn as_mut(&mut self) -> &mut [T] {
        unsafe {
            slice::from_raw_parts_mut(self.base, self.len)
        }
    }
}

/// The type representing an 'unsafe' foreign chunk of memory
pub struct CSlice<T> {
    base: *mut T,
    len: usize
}

impl<T> CSlice<T> {
    /// Create a `CSlice` from a raw pointer to a buffer with a given length.
    ///
    /// Panics if the given pointer is null. The returned vector will not attempt
    /// to deallocate the vector when dropped.
    ///
    /// # Arguments
    ///
    /// * base - A raw pointer to a buffer
    /// * len - The number of elements in the buffer
    pub unsafe fn new(base: *mut T, len: usize) -> CSlice<T> {
        assert!(base != ptr::null_mut());
        CSlice {
            base: base,
            len: len
        }
    }

    /// Retrieves an element at a given index, returning `None` if the requested
    /// index is greater than the length of the vector.
    pub fn get<'a>(&'a self, ofs: usize) -> Option<&'a T> {
        if ofs < self.len {
            Some(unsafe { &*self.base.offset(ofs as isize) })
        } else {
            None
        }
    }

    /// Retrieves a mutable element at a given index, returning `None` if the
    /// requested index is greater than the length of the vector.
    pub fn get_mut<'a>(&'a mut self, ofs: usize) -> Option<&'a mut T> {
        if ofs < self.len {
            Some(unsafe { &mut *self.base.offset(ofs as isize) })
        } else {
            None
        }
    }

    /// Returns the number of items in this vector.
    pub fn len(&self) -> usize { self.len }

    /// Returns whether this vector is empty.
    pub fn is_empty(&self) -> bool { self.len() == 0 }
}

impl<T> AsRef<[T]> for CSlice<T> {
    /// View the stored data as a slice.
    fn as_ref(&self) -> &[T] {
        unsafe {
            slice::from_raw_parts(self.base as *const T, self.len)
        }
    }
}

impl<T> AsMut<[T]> for CSlice<T> {
    /// View the stored data as a slice.
    fn as_mut(&mut self) -> &mut [T] {
        unsafe {
            slice::from_raw_parts_mut(self.base, self.len)
        }
    }
}

impl<T> Index<usize> for CSlice<T> {
    type Output = T;

    fn index<'a>(&'a self, _index: usize) -> &'a T {
        assert!(_index < self.len);
        unsafe { &*self.base.offset(_index as isize) }
    }
}

impl<T> IndexMut<usize> for CSlice<T> {
    fn index_mut<'a>(&'a mut self, _index: usize) -> &'a mut T {
        assert!(_index < self.len);
        unsafe { &mut *self.base.offset(_index as isize) }
    }
}

impl<T: Clone> Into<Vec<T>> for CSlice<T> {
    fn into(self: CSlice<T>) -> Vec<T> {
        let mut v = Vec::with_capacity(self.len);
        v.extend_from_slice(self.as_ref());
        v
    }
}

impl<T: Clone> Into<Vec<T>> for CVec<T> {
    fn into(self: CVec<T>) -> Vec<T> {
        self.as_cslice().into()
    }
}

#[cfg(test)]
mod tests {
    extern crate libc;

    use super::{CVec, CSlice};
    use std::ptr;

    // allocation of CVec
    fn v_malloc(n: usize) -> CVec<u8> {
        unsafe {
            let mem = libc::malloc(n as libc::size_t) as *mut u8;
            CVec::new_with_dtor(mem, n, |mem| { libc::free((mem) as *mut _); })
        }
    }

    // allocation of CSlice
    fn s_malloc(n: usize) -> CSlice<u8> {
        unsafe {
            let mem: *mut u8 = libc::malloc(n as libc::size_t) as *mut _;
            CSlice::new(mem, n)
        }
    }

    #[test]
    fn vec_test_basic() {
        let mut cv = v_malloc(16);

        *cv.get_mut(3).unwrap() = 8;
        *cv.get_mut(4).unwrap() = 9;
        assert_eq!(*cv.get(3).unwrap(), 8);
        assert_eq!(*cv.get(4).unwrap(), 9);
        assert_eq!(cv.len(), 16);
    }

    #[test]
    fn slice_test_basic() {
        let mut cs = s_malloc(16);

        cs[3] = 8;
        cs[4] = 9;
        assert_eq!(cs[3], 8);
        assert_eq!(cs[4], 9);
        assert_eq!(cs.len(), 16);
    }

    #[test]
    #[should_panic]
    fn vec_test_panic_at_null() {
        unsafe {
            CVec::new(ptr::null_mut::<u8>(), 9);
        }
    }

    #[test]
    #[should_panic]
    fn slice_test_panic_at_null() {
        unsafe {
            CSlice::new(ptr::null_mut::<u8>(), 9);
        }
    }

    #[test]
    fn vec_test_overrun_get() {
        let cv = v_malloc(16);

        assert!(cv.get(17).is_none());
    }

    #[test]
    #[should_panic]
    fn slice_test_overrun_get() {
        let cs = s_malloc(16);

        assert!(cs[17] == 18);
    }

    #[test]
    fn vec_test_overrun_set() {
        let mut cv = v_malloc(16);

        assert!(cv.get_mut(17).is_none());
    }

    #[test]
    fn vec_test_unwrap() {
        unsafe {
            let cv = CVec::new_with_dtor(1 as *mut isize,
                                         0,
                                         |_| panic!("Don't run this destructor!"));
            let p = cv.into_inner();
            assert_eq!(p, 1 as *mut isize);
        }
    }

    #[test]
    fn vec_to_slice_test() {
        let mut cv = v_malloc(2);

        *cv.get_mut(0).unwrap() = 10;
        *cv.get_mut(1).unwrap() = 12;
        let cs = cv.as_cslice();

        assert_eq!(cs[0], 10);
        assert_eq!(cs[1], 12);
    }

    #[test]
    fn slice_to_vec_test() {
        let cv = v_malloc(2);
        let mut cs = cv.as_cslice();

        cs[0] = 13;
        cs[1] = 26;
        assert_eq!(*cv.get(0).unwrap(), 13);
        assert_eq!(*cv.get(1).unwrap(), 26);
    }

    #[test]
    fn convert_test() {
        let cv = v_malloc(2);
        let mut cs = cv.as_cslice();
        cs[0] = 1;
        cs[1] = 99;
        let v: Vec<_> = cs.into();
        assert_eq!(1, v[0]);
        assert_eq!(99, v[1]);
        let v: Vec<_> = cv.into();
        assert_eq!(1, v[0]);
        assert_eq!(99, v[1]);
    }
}