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

use std::convert::Infallible;
use std::error::Error;
use std::marker::PhantomData;

use super::null_ptr_error;
use super::{FromForeign, InputType, ReturnType, ToForeign};

/// The `Box` marshaler is the catch-all just-throw-it-on-the-heap opaque pointer solution.
///
/// It supports the following modes of operation:
///
/// ### To the foreign interface:
///
///   - `T` → `*const/mut T`
///   - `Box<T>` → `*const/*mut T`
///
/// ### From the foreign interface:
///
///   - `*const/mut T` → `Box<T>` (owned)
///   - `*const T` → `&T` (ref)
///   - `*mut T` → `&mut T` (mut ref)
///
/// ## Freeing `T`
///
/// Your foreign code should ensure that they call `BoxMarshaler::<*mut/const T, Box<T>>::from_foreign`,
/// which will allow you to consume the boxed `T` and allow it to drop as per Rust's usual rules.
///
/// ## Example
///
/// ```rust
/// use cffi::{BoxMarshaler, FromForeign, ToForeign};
///
/// struct Something {
///     data: Vec<u8>
/// }
///
/// fn demo() {
///     let something = Something { data: vec![1, 3, 55] };
///
///     // BoxMarshaler::to_foreign is Infallible
///     let ptr: *const Something = BoxMarshaler::to_foreign(something).unwrap();
///
///     /* send `ptr` over ffi, process it in some way, etc */
///
///     // This isn't infallible though, checks for null pointers.
///     let boxed: Box<Something> = match BoxMarshaler::from_foreign(ptr) {
///         Ok(v) => v,
///         Err(e) => panic!("!")
///     };
///
///     // Let the boxed item drop and it is freed. :)
/// }
/// ```
pub struct BoxMarshaler<T: ?Sized>(PhantomData<T>);

impl<T> InputType for BoxMarshaler<T> {
    type Foreign = *const T;
}

impl<T> ReturnType for BoxMarshaler<T> {
    type Foreign = *const T;

    fn foreign_default() -> Self::Foreign {
        std::ptr::null()
    }
}

impl<T> ToForeign<Box<T>, *const T> for BoxMarshaler<T> {
    type Error = Infallible;

    #[inline(always)]
    fn to_foreign(local: Box<T>) -> Result<*const T, Self::Error> {
        log::debug!(
            "<BoxMarshaler<{ty}> as ToForeign<{ty}, {o}>>::to_foreign",
            ty = std::any::type_name::<T>(),
            o = "*const T"
        );
        Ok(Box::into_raw(local) as *const _ as *const _)
    }
}

impl<T: ?Sized> ToForeign<Result<Box<T>, Box<dyn Error>>, *const T> for BoxMarshaler<T> {
    type Error = Box<dyn Error>;

    #[inline(always)]
    fn to_foreign(local: Result<Box<T>, Box<dyn Error>>) -> Result<*const T, Self::Error> {
        local.and_then(|x| Ok(Box::into_raw(x) as *const _ as *const _))
    }
}

// impl<T> ToForeign<Box<T>, *mut T> for BoxMarshaler<T> {
//     type Error = Infallible;

//     #[inline(always)]
//     fn to_foreign(local: Box<T>) -> Result<*mut T, Self::Error> {
//         Ok(Box::into_raw(local as *mut _ as *mut _)
//     }
// }

impl<T> FromForeign<*const T, Box<T>> for BoxMarshaler<T> {
    type Error = Box<dyn Error>;

    #[inline(always)]
    unsafe fn from_foreign(foreign: *const T) -> Result<Box<T>, Self::Error> {
        log::debug!(
            "<BoxMarshaler<{ty}> as FromForeign<*const T, T>>::from_foreign({:?})",
            foreign,
            ty = std::any::type_name::<T>()
        );

        if foreign.is_null() {
            return Err(null_ptr_error());
        }

        Ok(Box::from_raw(foreign as *mut _))
    }
}

// impl<T: ?Sized> FromForeign<*mut T, Box<T>> for BoxMarshaler<T> {
//     type Error = Box<dyn Error>;

//     #[inline(always)]
//     unsafe fn from_foreign(foreign: *mut T) -> Result<Box<T>, Self::Error> {
//         log::debug!("<BoxMarshaler<{ty}> as FromForeign<*mut {ty}, &'a {ty}>>::from_foreign({:?})",
//             foreign,
//             ty = std::any::type_name::<T>()
//         );
//         if foreign.is_null() {
//             return Err(null_ptr_error());
//         }

//         Ok(unsafe { Box::from_raw(foreign) })
//     }
// }
//
// impl<'a, T: Clone> ToForeign<&'a T, *const T> for BoxMarshaler<T> {
//     type Error = Infallible;

//     #[inline(always)]
//     fn to_foreign(local: &'a T) -> Result<*const T, Self::Error> {
//         Ok(Box::into_raw(Box::new(local.clone())))
//     }
// }

// impl<'a, T: Clone> ToForeign<&'a T, *mut T> for BoxMarshaler<T> {
//     type Error = Infallible;

//     #[inline(always)]
//     fn to_foreign(local: &'a T) -> Result<*mut T, Self::Error> {
//         Ok(Box::into_raw(Box::new(local.clone())))
//     }
// }

// impl<T: ?Sized> ToForeign<Box<T>, *mut T> for BoxMarshaler<T> {
//     type Error = Infallible;

//     #[inline(always)]
//     fn to_foreign(local: Box<T>) -> Result<*mut T, Self::Error> {
//         Ok(Box::into_raw(local))
//     }
// }

// impl<'a, T: ?Sized> FromForeign<*mut T, &'a mut T> for BoxMarshaler<T> {
//     type Error = Box<dyn Error>;

//     #[inline(always)]
//     unsafe fn from_foreign(foreign: *mut T) -> Result<&'a mut T, Self::Error> {
//         if foreign.is_null() {
//             return Err(null_ptr_error());
//         }

//         Ok(unsafe { &mut *foreign })
//     }
// }