      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;
            }
        }
    }