dlib/lib.rs
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//! dlib is a small crate providing macros to make easy the use of external system libraries that
//! can or cannot be optionally loaded at runtime, depending on whether a certain feature is enabled.
//!
//! ## Usage
//!
//! dlib defines the `external_library!` macro, which can be invoked in this way:
//!
//! ```rust
//! external_library!(feature="dlopen-foo", Foo, "foo",
//! statics:
//! me: c_int,
//! you: c_float,
//! functions:
//! fn foo() -> c_int,
//! fn bar(c_int, c_float) -> (),
//! fn baz(*const c_int) -> c_int,
//! varargs:
//! fn blah(c_int, c_int ...) -> *const c_void,
//! fn bleh(c_int ...) -> (),
//! );
//! ```
//!
//! As you can see, it is required to separate static values from functions and from function
//! having variadic arguments. Each of these 3 categories is optional, but the ones used must appear
//! in this order. Return types of the functions must all be explicit (hence `-> ()` for void functions).
//!
//! If the feature named by the `feature` argument (in this example, `dlopen-foo`) is absent on your crate,
//! this macro will expand to an extern block defining each of the items, using the third argument
//! of the macro as a link name:
//!
//! ```rust
//! #[link(name = "foo")]
//! extern "C" {
//! pub static me: c_int;
//! pub static you: c_float;
//! pub fn foo() -> c_int;
//! pub fn bar(_: c_int, _: c_float) -> ();
//! pub fn baz(_: *const c_int) -> c_int;
//! pub fn blah(_: c_int, _: c_int, ...) -> *const c_void;
//! pub fn bleh(_: c_int, ...) -> ();
//! }
//!
//! ```
//!
//! If the feature named by the `feature` argument is present on your crate, it will expand to a
//! `struct` named by the second argument of the macro, with one field for each of the symbols defined;
//! and a method `open`, which tries to load the library from the name or path given as an argument.
//!
//! ```rust
//! pub struct Foo {
//! pub me: &'static c_int,
//! pub you: &'static c_float,
//! pub foo: unsafe extern "C" fn() -> c_int,
//! pub bar: unsafe extern "C" fn(c_int, c_float) -> (),
//! pub baz: unsafe extern "C" fn(*const c_int) -> c_int,
//! pub blah: unsafe extern "C" fn(c_int, c_int, ...) -> *const c_void,
//! pub bleh: unsafe extern "C" fn(c_int, ...) -> (),
//! }
//!
//!
//! impl Foo {
//! pub unsafe fn open(name: &str) -> Result<Foo, DlError> { /* ... */ }
//! }
//! ```
//!
//! This method returns `Ok(..)` if the loading was successful. It contains an instance of the defined struct
//! with all of its fields pointing to the appropriate symbol.
//!
//! If the library specified by `name` could not be openened, it returns `Err(DlError::CantOpen(e))`, with
//! `e` the error reported by `libloading` (see [LibLoadingError]);
//!
//! It will also fail on the first missing symbol, with `Err(DlError::MissingSymbol(symb))` where `symb`
//! is a `&str` containing the missing symbol name.
//!
//! Note that this method is unsafe, as loading (and unloading on drop) an external C library can run arbitrary
//! code. As such, you need to ensure that the specific library you want to load is safe to load in the context
//! you want to load it.
//!
//! ## Remaining generic in your crate
//!
//! If you want your crate to remain generic over dlopen vs. linking, simply add a feature to your `Cargo.toml`:
//!
//! ```toml
//! [dependencies]
//! dlib = "0.5"
//!
//! [features]
//! dlopen-foo = []
//! ```
//!
//! Then give the name of that feature as the `feature` argument to dlib's macros:
//!
//! ```rust
//! external_library!(feature="dlopen-foo", Foo, "foo",
//! functions:
//! fn foo() -> c_int,
//! );
//! ```
//!
//! `dlib` provides helper macros to dispatch the access to foreign symbols:
//!
//! ```rust
//! ffi_dispatch!(feature="dlopen-foo", Foo, function, arg1, arg2);
//! ffi_dispatch_static!(feature="dlopen-foo", Foo, my_static_var);
//! ```
//!
//! These will expand to the appropriate value or function call depending on the presence or absence of the
//! `dlopen-foo` feature on your crate.
//!
//! You must still ensure that the functions/statics or the wrapper struct `Foo` are in scope. For example,
//! you could use the [`lazy_static`](https://crates.io/crates/lazy_static) crate to do the initialization,
//! and store the wrapper struct in a static variable that you import wherever needed:
//!
//! ```rust
//! #[cfg(feature = "dlopen-foo")]
//! lazy_static::lazy_static! {
//! pub static ref FOO_STATIC: Foo =
//! Foo::open("libfoo.so").ok().expect("could not find libfoo");
//! }
//! ```
//!
//! Then, it can become as simple as putting this on top of all modules using the FFI:
//!
//! ```rust
//! #[cfg(feature = "dlopen-foo")]
//! use ffi::FOO_STATIC;
//! #[cfg(not(feature = "dlopen-foo"))]
//! use ffi::*;
//! ```
#![warn(missing_docs)]
extern crate libloading;
pub use libloading::Error as LibLoadingError;
#[doc(hidden)]
pub use libloading::{Library, Symbol};
/// Macro for generically invoking a FFI function
///
/// 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.
/// - A value of the handle generated by the macro [`external_library!`] when the
/// dlopen-controlling feature is enabled
/// - The name of the function to invoke
/// - The arguments to be passed to the function
///
/// The macro invocation evaluates to the return value of the FFI function.
///
/// #### Example
///
/// Assuming an FFI function of signature `fn(u32, u32) -> u32`:
///
/// ```rust,ignore
/// let sum = unsafe { ffi_dispatch!(feature="dlopen", LIBRARY_HANDLE, sum, 2, 2) };
/// ```
#[macro_export]
macro_rules! ffi_dispatch(
(feature=$feature: expr, $handle: expr, $func: ident, $($arg: expr),*) => (
{
#[cfg(feature = $feature)]
let ret = ($handle.$func)($($arg),*);
#[cfg(not(feature = $feature))]
let ret = $func($($arg),*);
ret
}
);
($handle: expr, $func: ident, $($arg: expr),*) => (
// NOTE: this "dlopen" refers to a feature on the crate *using* dlib
$crate::ffi_dispatch!(feature="dlopen", $handle, $func, $($arg),*)
);
);
/// Macro for generically accessing a FFI static
///
/// 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.
/// - A value of the handle generated by the macro [`external_library!`] when the
/// dlopen-controlling feature is enabled
/// - The name of the static
///
/// The macro invocation evaluates to a `&T` reference to the static
///
/// #### Example
///
/// ```rust,ignore
/// let my_static = unsafe { ffi_dispatch!(feature="dlopen", LIBRARY_HANDLE, my_static) };
/// ```
#[macro_export]
macro_rules! ffi_dispatch_static(
(feature=$feature: expr, $handle: expr, $name: ident) => (
{
#[cfg(feature = $feature)]
let ret = $handle.$name;
#[cfg(not(feature = $feature))]
let ret = &$name;
ret
}
);
($handle:expr, $name: ident) => (
$crate::ffi_dispatch_static!(feature="dlopen", $handle, $name)
);
);
#[doc(hidden)]
#[macro_export]
macro_rules! link_external_library(
($link: expr,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
#[link(name = $link)]
extern "C" {
$($(
pub static $sname: $stype;
)+)*
$($(
pub fn $fname($(_: $farg),*) -> $fret;
)+)*
$($(
pub fn $vname($(_: $vargs),+ , ...) -> $vret;
)+)*
}
);
);
/// An error generated when failing to load a library
#[derive(Debug)]
pub enum DlError {
/// The requested library would not be opened
///
/// Includes the error reported by `libloading` when trying to
/// open the library.
CantOpen(LibLoadingError),
/// Some required symbol was missing in the library
MissingSymbol(&'static str),
}
impl std::error::Error for DlError {
fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
match *self {
DlError::CantOpen(ref e) => Some(e),
DlError::MissingSymbol(_) => None,
}
}
}
impl std::fmt::Display for DlError {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match *self {
DlError::CantOpen(ref e) => write!(f, "Could not open the requested library: {}", e),
DlError::MissingSymbol(s) => write!(f, "The requested symbol was missing: {}", s),
}
}
}
#[doc(hidden)]
#[macro_export]
macro_rules! dlopen_external_library(
(__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 {
__lib: $crate::Library,
$($(
pub $sname: $crate::Symbol<'static, &'static $stype>,
)+)*
$($(
pub $fname: $crate::Symbol<'static, unsafe extern "C" fn($($farg),*) -> $fret>,
)+)*
$($(
pub $vname: $crate::Symbol<'static, unsafe extern "C" fn($($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;
let lib = $crate::Library::new(name).map_err($crate::DlError::CantOpen)?;
let s = $structname {
$($($sname: {
let s_name = concat!(stringify!($sname), "\0");
transmute(match lib.get::<&'static $stype>(s_name.as_bytes()) {
Ok(s) => s,
Err(_) => return Err($crate::DlError::MissingSymbol(s_name))
})
},
)+)*
$($($fname: {
let s_name = concat!(stringify!($fname), "\0");
transmute(match lib.get::<unsafe extern "C" fn($($farg),*) -> $fret>(s_name.as_bytes()) {
Ok(s) => s,
Err(_) => return Err($crate::DlError::MissingSymbol(s_name))
})
},
)+)*
$($($vname: {
let s_name = concat!(stringify!($vname), "\0");
transmute(match lib.get::<unsafe extern "C" fn($($vargs),+ , ...) -> $vret>(s_name.as_bytes()) {
Ok(s) => s,
Err(_) => return Err($crate::DlError::MissingSymbol(s_name))
})
},
)+)*
__lib: lib
};
Ok(s)
}
}
);
($structname: ident,
$(statics: $($sname: ident: $stype: ty),+,)|*
$(functions: $(fn $fname: ident($($farg: ty),*) -> $fret:ty),+,)|*
$(varargs: $(fn $vname: ident($($vargs: ty),+) -> $vret: ty),+,)|*
) => (
$crate::dlopen_external_library!(__struct,
$structname, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
$crate::dlopen_external_library!(__impl,
$structname, $(statics: $($sname: $stype),+,)|*
$(functions: $(fn $fname($($farg),*) -> $fret),+,)|*
$(varargs: $(fn $vname($($vargs),+) -> $vret),+,)|*
);
unsafe impl Sync for $structname { }
);
);
/// Main macro of this library, used to generate the the FFI bindings.
///
/// The expected arguments are, in order:
/// - (Optional) The name of the cargo feature conditioning the usage of dlopen, in the form
/// `feature="feature-name"`. If ommited, the feature `"dlopen"` will be used.
/// - The name of the struct that will be generated when the dlopen-controlling feature is
/// enabled
/// - The link name of the target library
/// - The desctription of the statics, functions, and vararg functions that should be linked
///
/// See crate-level documentation for a detailed example of use.
#[macro_export]
macro_rules! external_library(
(feature=$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),+) -> $vret),+,)|*
);
);
($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),+,)|*
);
);
);