137 lines
4.4 KiB
Markdown
137 lines
4.4 KiB
Markdown
|
[](https://crates.io/crates/dlib)
|
||
|
|
[](https://docs.rs/dlib)
|
||
|
|
|
||
|
|
# dlib
|
||
|
|
|
||
|
|
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::*;
|
||
|
|
```
|
||
|
|
|
||
|
|
License: MIT
|