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
//! A framework for Rust wrappers over C APIs.
//!
//! Ownership is as important in C as it is in Rust, but the semantics are often implicit. In
//! particular, pointer-to-value is commonly used to pass C values both when transferring ownership
//! or a borrow.
//!
//! This crate provides a framework to define a Rust wrapper over these kinds of raw C APIs in a way
//! that allows ownership semantics to be expressed in an ergonomic manner. The framework takes a
//! dual-type approach similar to APIs in the standard library such as `PathBuf`/`Path` or `String`/
//! `str`. One type represents an owned value and references to the other represent borrowed
//! values.
//!
//! # Examples
//!
//! ```
//! use foreign_types::{ForeignType, ForeignTypeRef, Opaque};
//! use std::ops::{Deref, DerefMut};
//!
//! mod foo_sys {
//! pub enum FOO {}
//!
//! extern {
//! pub fn FOO_free(foo: *mut FOO);
//! }
//! }
//!
//! // The borrowed type is a newtype wrapper around an `Opaque` value.
//! //
//! // `FooRef` values never exist; we instead create references to `FooRef`s
//! // from raw C pointers.
//! pub struct FooRef(Opaque);
//!
//! impl ForeignTypeRef for FooRef {
//! type CType = foo_sys::FOO;
//! }
//!
//! // The owned type is simply a newtype wrapper around the raw C type.
//! //
//! // It dereferences to `FooRef`, so methods that do not require ownership
//! // should be defined there.
//! pub struct Foo(*mut foo_sys::FOO);
//!
//! impl Drop for Foo {
//! fn drop(&mut self) {
//! unsafe { foo_sys::FOO_free(self.0) }
//! }
//! }
//!
//! impl ForeignType for Foo {
//! type CType = foo_sys::FOO;
//! type Ref = FooRef;
//!
//! unsafe fn from_ptr(ptr: *mut foo_sys::FOO) -> Foo {
//! Foo(ptr)
//! }
//!
//! fn as_ptr(&self) -> *mut foo_sys::FOO {
//! self.0
//! }
//! }
//!
//! impl Deref for Foo {
//! type Target = FooRef;
//!
//! fn deref(&self) -> &FooRef {
//! unsafe { FooRef::from_ptr(self.0) }
//! }
//! }
//!
//! impl DerefMut for Foo {
//! fn deref_mut(&mut self) -> &mut FooRef {
//! unsafe { FooRef::from_ptr_mut(self.0) }
//! }
//! }
//! ```
//!
//! The `foreign_type!` macro can generate this boilerplate for you:
//!
//! ```
//! #[macro_use]
//! extern crate foreign_types;
//!
//! mod foo_sys {
//! pub enum FOO {}
//!
//! extern {
//! pub fn FOO_free(foo: *mut FOO);
//! pub fn FOO_duplicate(foo: *mut FOO) -> *mut FOO; // Optional
//! }
//! }
//!
//! foreign_type! {
//! type CType = foo_sys::FOO;
//! fn drop = foo_sys::FOO_free;
//! fn clone = foo_sys::FOO_duplicate; // Optional
//! /// A Foo.
//! pub struct Foo;
//! /// A borrowed Foo.
//! pub struct FooRef;
//! }
//!
//! # fn main() {}
//! ```
//!
//! If `fn clone` is specified, then it must take `CType` as an argument and return a copy of it as `CType`.
//! It will be used to implement `ToOwned` and `Clone`.
//!
//! `#[derive(…)] is permitted before the lines with `pub struct`.
//! `#[doc(hidden)]` before the `type CType` line will hide the `foreign_type!` implementations from documentation.
//!
//! Say we then have a separate type in our C API that contains a `FOO`:
//!
//! ```
//! mod foo_sys {
//! pub enum FOO {}
//! pub enum BAR {}
//!
//! extern {
//! pub fn FOO_free(foo: *mut FOO);
//! pub fn BAR_free(bar: *mut BAR);
//! pub fn BAR_get_foo(bar: *mut BAR) -> *mut FOO;
//! }
//! }
//! ```
//!
//! The documentation for the C library states that `BAR_get_foo` returns a reference into the `BAR`
//! passed to it, which translates into a reference in Rust. It also says that we're allowed to
//! modify the `FOO`, so we'll define a pair of accessor methods, one immutable and one mutable:
//!
//! ```
//! #[macro_use]
//! extern crate foreign_types;
//!
//! use foreign_types::ForeignTypeRef;
//!
//! mod foo_sys {
//! pub enum FOO {}
//! pub enum BAR {}
//!
//! extern {
//! pub fn FOO_free(foo: *mut FOO);
//! pub fn BAR_free(bar: *mut BAR);
//! pub fn BAR_get_foo(bar: *mut BAR) -> *mut FOO;
//! }
//! }
//!
//! foreign_type! {
//! #[doc(hidden)]
//! type CType = foo_sys::FOO;
//! fn drop = foo_sys::FOO_free;
//! /// A Foo.
//! pub struct Foo;
//! /// A borrowed Foo.
//! pub struct FooRef;
//! }
//!
//! foreign_type! {
//! type CType = foo_sys::BAR;
//! fn drop = foo_sys::BAR_free;
//! /// A Foo.
//! pub struct Bar;
//! /// A borrowed Bar.
//! pub struct BarRef;
//! }
//!
//! impl BarRef {
//! fn foo(&self) -> &FooRef {
//! unsafe { FooRef::from_ptr(foo_sys::BAR_get_foo(self.as_ptr())) }
//! }
//!
//! fn foo_mut(&mut self) -> &mut FooRef {
//! unsafe { FooRef::from_ptr_mut(foo_sys::BAR_get_foo(self.as_ptr())) }
//! }
//! }
//!
//! # fn main() {}
//! ```
#![no_std]
#![warn(missing_docs)]
#![doc(html_root_url="https://docs.rs/foreign-types/0.3")]
extern crate foreign_types_shared;
#[doc(inline)]
pub use foreign_types_shared::*;
/// A macro to easily define wrappers for foreign types.
///
/// # Examples
///
/// ```
/// #[macro_use]
/// extern crate foreign_types;
///
/// # mod openssl_sys { pub type SSL = (); pub unsafe fn SSL_free(_: *mut SSL) {} pub unsafe fn SSL_dup(x: *mut SSL) -> *mut SSL {x} }
/// foreign_type! {
/// type CType = openssl_sys::SSL;
/// fn drop = openssl_sys::SSL_free;
/// fn clone = openssl_sys::SSL_dup;
/// /// Documentation for the owned type.
/// pub struct Ssl;
/// /// Documentation for the borrowed type.
/// pub struct SslRef;
/// }
///
/// # fn main() {}
/// ```
#[macro_export]
macro_rules! foreign_type {
(
$(#[$impl_attr:meta])*
type CType = $ctype:ty;
fn drop = $drop:expr;
$(fn clone = $clone:expr;)*
$(#[$owned_attr:meta])*
pub struct $owned:ident;
$(#[$borrowed_attr:meta])*
pub struct $borrowed:ident;
) => {
$(#[$owned_attr])*
pub struct $owned(*mut $ctype);
$(#[$impl_attr])*
impl $crate::ForeignType for $owned {
type CType = $ctype;
type Ref = $borrowed;
#[inline]
unsafe fn from_ptr(ptr: *mut $ctype) -> $owned {
$owned(ptr)
}
#[inline]
fn as_ptr(&self) -> *mut $ctype {
self.0
}
}
impl Drop for $owned {
#[inline]
fn drop(&mut self) {
unsafe { $drop(self.0) }
}
}
$(
impl Clone for $owned {
#[inline]
fn clone(&self) -> $owned {
unsafe {
let handle: *mut $ctype = $clone(self.0);
$crate::ForeignType::from_ptr(handle)
}
}
}
impl ::std::borrow::ToOwned for $borrowed {
type Owned = $owned;
#[inline]
fn to_owned(&self) -> $owned {
unsafe {
let handle: *mut $ctype = $clone($crate::ForeignTypeRef::as_ptr(self));
$crate::ForeignType::from_ptr(handle)
}
}
}
)*
impl ::std::ops::Deref for $owned {
type Target = $borrowed;
#[inline]
fn deref(&self) -> &$borrowed {
unsafe { $crate::ForeignTypeRef::from_ptr(self.0) }
}
}
impl ::std::ops::DerefMut for $owned {
#[inline]
fn deref_mut(&mut self) -> &mut $borrowed {
unsafe { $crate::ForeignTypeRef::from_ptr_mut(self.0) }
}
}
impl ::std::borrow::Borrow<$borrowed> for $owned {
#[inline]
fn borrow(&self) -> &$borrowed {
&**self
}
}
impl ::std::convert::AsRef<$borrowed> for $owned {
#[inline]
fn as_ref(&self) -> &$borrowed {
&**self
}
}
$(#[$borrowed_attr])*
pub struct $borrowed($crate::Opaque);
$(#[$impl_attr])*
impl $crate::ForeignTypeRef for $borrowed {
type CType = $ctype;
}
}
}