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Implement universal dlopen-style API #25

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138 changes: 138 additions & 0 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -127,6 +127,26 @@
//! #[cfg(not(feature = "dlopen-foo"))]
//! use ffi::*;
//! ```
//!
//! Alternatively to using `ffi_dispatch!` and `ffi_dispatch_static!` or directly calling
//! module-level functions in non-dlopen code, you can use the dlopen-style API (ie. `Foo::open`)
//! on non-dlopen builds. This allows using the same API regardless of whether the `dlopen-foo`
//! feature flag is set. To enable this, use `external_library_universal!` instead of
//! `external_library!`.
//!
//! ```rust
//! external_library_universal!(feature="dlopen-foo", Foo, "foo",
//! functions:
//! fn foo() -> c_int,
//! );
//!
//! // This works both with and without dlopen-foo. The argument to `File::open` is ignored in
//! // non-dlopen builds, and the function can fail only on dlopen builds.
//! lazy_static::lazy_static! {
//! pub static ref FOO_STATIC: Foo =
//! Foo::open("libfoo.so").ok().expect("couldn ot find libfoo");
//! }
//! ```
#![warn(missing_docs)]

extern crate libloading;
Expand Down Expand Up @@ -228,6 +248,71 @@ macro_rules! link_external_library(
);
);

#[doc(hidden)]
#[macro_export]
macro_rules! link_external_library_dlopen_compat(
(__struct, $structname: ident,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
pub struct $structname {
$($(
pub $sname: &'static $stype,
)+)*
$($(
pub $fname: unsafe extern "C" fn($($farg),*) -> $fret,
)+)*
$($(
pub $vname: unsafe extern "C" fn($($vargs),+ , ...) -> $vret,
)+)*
}
);
(__impl, $structname: ident,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
impl $structname {
pub unsafe fn open(_name: &str) -> Result<$structname, $crate::DlError> {
// we use it to ensure the 'static lifetime
use std::mem::transmute;
Ok($structname {
$($($sname: {
$sname
},
)+)*
$($($fname: {
$fname
},
)+)*
$($($vname: {
transmute($vname)
},
)+)*
})
}
}
);
($structname: ident,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
$crate::link_external_library_dlopen_compat!(__struct,
$structname, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
$crate::link_external_library_dlopen_compat!(__impl,
$structname, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
unsafe impl Sync for $structname { }
);
);

/// An error generated when failing to load a library
#[derive(Debug)]
pub enum DlError {
Expand Down Expand Up @@ -371,6 +456,59 @@ macro_rules! external_library(
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
);
($structname: ident, $link: expr,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
$crate::external_library!( feature="dlopen", $structname, $link,
$(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
);
);

/// Main macro of this library, used to generate the the FFI bindings that are universal in both
/// dlopen and non-dlopen form.
///
/// The expected arguments are, in order:
/// - (Optional) The name of the cargo feature conditioning the usage of dlopen, in the form
/// `feature="feature-name"`. If ommited, the feature `"dlopen"` will be used.
/// - The name of the struct that will be generated when the dlopen-controlling feature is
/// enabled
/// - The link name of the target library
/// - The desctription of the statics, functions, and vararg functions that should be linked
///
/// See crate-level documentation for a detailed example of use.
#[macro_export]
macro_rules! external_library_universal(
(feature=$feature: expr, $structname: ident, $link: expr,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
#[cfg(feature = $feature)]
$crate::dlopen_external_library!(
$structname, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);

#[cfg(not(feature = $feature))]
$crate::link_external_library!(
$link, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);

#[cfg(not(feature = $feature))]
$crate::link_external_library_dlopen_compat!(
$structname, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
);
($structname: ident, $link: expr,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
Expand Down