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/*!
* 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 introduction forms, and the
* pointer elimination form. The introduction forms are unsafe for the
* obvious reason (they act on a pointer that cannot be checked inside the
* method), but the elimination form is somewhat more subtle in its unsafety.
* By using a pointer taken from a c_vec::t without keeping a reference to the
* c_vec::t itself around, the CVec could be garbage collected, and the
* memory within could be destroyed. There are legitimate uses for the
* pointer elimination form -- for instance, to pass memory back into C -- but
* great care must be taken to ensure that a reference to the c_vec::t is
* still held if needed.
*/
export CVec;
export CVec, c_vec_with_dtor;
export get, set;
export len;
export ptr;
/**
* The type representing a foreign chunk of memory
*
* Wrapped in a enum for opacity; FIXME #818 when it is possible to have
* truly opaque types, this should be revisited.
*/
enum CVec<T> {
CVecCtor({ base: *mut T, len: uint, rsrc: @DtorRes})
}
struct DtorRes {
dtor: Option<fn@()>,
drop {
match self.dtor {
option::None => (),
option::Some(f) => f()
}
}
}
fn DtorRes(dtor: Option<fn@()>) -> DtorRes {
DtorRes {
dtor: dtor
}
}
/*
Section: Introduction forms
*/
/**
* Create a `CVec` from a foreign buffer with a given length.
*
* # Arguments
*
* * base - A foreign pointer to a buffer
* * len - The number of elements in the buffer
*/
unsafe fn CVec<T>(base: *mut T, len: uint) -> CVec<T> {
return CVecCtor({
base: base,
len: len,
rsrc: @DtorRes(option::None)
});
}
/**
* Create a `CVec` from a foreign buffer, with a given length,
* and a function to run upon destruction.
*
* # Arguments
*
* * base - A foreign pointer to a buffer
* * len - The number of elements in the buffer
* * dtor - A function to run when the value is destructed, useful
* for freeing the buffer, etc.
*/
unsafe fn c_vec_with_dtor<T>(base: *mut T, len: uint, dtor: fn@())
-> CVec<T> {
return CVecCtor({
base: base,
len: len,
rsrc: @DtorRes(option::Some(dtor))
});
}
/*
Section: Operations
*/
/**
* Retrieves an element at a given index
*
* Fails if `ofs` is greater or equal to the length of the vector
*/
fn get<T: Copy>(t: CVec<T>, ofs: uint) -> T {
assert ofs < len(t);
return unsafe { *ptr::mut_offset((*t).base, ofs) };
}
/**
* Sets the value of an element at a given index
*
* Fails if `ofs` is greater or equal to the length of the vector
*/
fn set<T: Copy>(t: CVec<T>, ofs: uint, v: T) {
assert ofs < len(t);
unsafe { *ptr::mut_offset((*t).base, ofs) = v };
}
/*
Section: Elimination forms
*/
/// Returns the length of the vector
fn len<T>(t: CVec<T>) -> uint {
return (*t).len;
}
/// Returns a pointer to the first element of the vector
unsafe fn ptr<T>(t: CVec<T>) -> *mut T {
return (*t).base;
}
#[cfg(test)]
mod tests {
import libc::*;
fn malloc(n: size_t) -> CVec<u8> {
let mem = libc::malloc(n);
assert mem as int != 0;
return unsafe { c_vec_with_dtor(mem as *mut u8, n as uint,
||free(mem)) };
}
#[test]
fn test_basic() {
let cv = malloc(16u as size_t);
set(cv, 3u, 8u8);
set(cv, 4u, 9u8);
assert get(cv, 3u) == 8u8;
assert get(cv, 4u) == 9u8;
assert len(cv) == 16u;
}
#[test]
#[should_fail]
#[ignore(cfg(windows))]
fn test_overrun_get() {
let cv = malloc(16u as size_t);
get(cv, 17u);
}
#[test]
#[should_fail]
#[ignore(cfg(windows))]
fn test_overrun_set() {
let cv = malloc(16u as size_t);
set(cv, 17u, 0u8);
}
#[test]
fn test_and_I_mean_it() {
let cv = malloc(16u as size_t);
let p = unsafe { ptr(cv) };
set(cv, 0u, 32u8);
set(cv, 1u, 33u8);
assert unsafe { *p } == 32u8;
set(cv, 2u, 34u8); /* safety */
}
}
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