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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
use nserror::{nsresult, NS_ERROR_NULL_POINTER};
/// The xpcom_method macro generates a Rust XPCOM method stub that converts
/// raw pointer arguments to references, calls a Rustic implementation
/// of the method, writes its return value into the XPCOM method's outparameter,
/// and returns an nsresult.
///
/// In other words, given an XPCOM method like:
///
/// ```ignore
/// interface nsIFooBarBaz : nsISupports {
/// nsIVariant foo(in AUTF8String bar, [optional] in bool baz);
/// }
/// ```
///
/// And a Rust implementation that uses #[xpcom] to implement it:
///
/// ```ignore
/// #[xpcom(implement(nsIFooBarBaz), atomic)]
/// struct FooBarBaz {
/// // …
/// }
/// ```
///
/// With the appropriate extern crate and use declarations
///
/// ```ignore
/// extern crate xpcom;
/// use xpcom::xpcom_method;
/// ```
///
/// Invoking the macro with the name of the XPCOM method, the name of its
/// Rustic implementation, the set of its arguments, and its return value:
///
/// ```ignore
/// impl FooBarBaz {
/// xpcom_method!(
/// foo => Foo(bar: *const nsACString, baz: bool) -> *const nsIVariant
/// );
/// }
/// ```
///
/// Results in the macro generating an XPCOM stub like the following:
///
/// ```ignore
/// unsafe fn Foo(&self, bar: *const nsACString, baz: bool, retval: *mut *const nsIVariant) -> nsresult {
/// let bar = match Ensure::ensure(bar) {
/// Ok(val) => val,
/// Err(result) => return result,
/// };
/// let baz = match Ensure::ensure(baz) {
/// Ok(val) => val,
/// Err(result) => return result,
/// };
///
/// match self.foo(bar, baz) {
/// Ok(val) => {
/// val.forget(&mut *retval);
/// NS_OK
/// }
/// Err(error) => {
/// error!("{}", error);
/// error.into()
/// }
/// }
/// }
/// ```
///
/// Which calls a Rustic implementation (that you implement) like the following:
///
/// ```ignore
/// impl FooBarBaz {
/// fn foo(&self, bar: &nsACString, baz: bool) -> Result<RefPtr<nsIVariant>, nsresult> {
/// // …
/// }
/// }
/// ```
///
/// Notes:
///
/// On error, the Rustic implementation can return an Err(nsresult) or any
/// other type that implements Into<nsresult>. So you can define and return
/// a custom error type, which the XPCOM stub will convert to nsresult.
///
/// This macro assumes that all non-null pointer arguments are valid!
/// It does ensure that they aren't null, using the `ensure_param` macro.
/// But it doesn't otherwise check their validity. That makes the function
/// unsafe, so callers must ensure that they only call it with valid pointer
/// arguments.
#[macro_export]
macro_rules! xpcom_method {
// This rule is provided to ensure external modules don't need to import
// internal implementation details of xpcom_method.
// The @ensure_param rule converts raw pointer arguments to references,
// returning NS_ERROR_NULL_POINTER if the argument is_null().
//
// Notes:
//
// This rule can be called on a non-pointer copy parameter, but there's no
// benefit to doing so. The macro will just set the value of the parameter
// to itself. (This macro does this anyway due to limitations in declarative
// macros; it isn't currently possible to distinguish between pointer and
// copy types when processing a set of parameters.)
//
// The macro currently supports only in-parameters (*const nsIFoo); It
// doesn't (yet?) support out-parameters (*mut nsIFoo). The xpcom_method
// macro itself does, however, support the return value out-parameter.
(@ensure_param $name:ident) => {
let $name = match $crate::Ensure::ensure($name) {
Ok(val) => val,
Err(result) => return result,
};
};
// `#[allow(non_snake_case)]` is used for each method because `$xpcom_name`
// is almost always UpperCamelCase, and Rust gives a warning that it should
// be snake_case. It isn't reasonable to rename the XPCOM methods, so
// silence the warning.
// A method whose return value is a *mut *const nsISomething type.
// Example: foo => Foo(bar: *const nsACString, baz: bool) -> *const nsIVariant
($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> *const $retval:ty) => {
#[allow(non_snake_case)]
unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut *const $retval) -> nsresult {
$(xpcom_method!(@ensure_param $param_name);)*
match self.$rust_name($($param_name, )*) {
Ok(val) => {
val.forget(&mut *retval);
NS_OK
}
Err(error) => {
error.into()
}
}
}
};
// A method whose return value is a *mut nsAString type.
// Example: foo => Foo(bar: *const nsACString, baz: bool) -> nsAString
($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> nsAString) => {
#[allow(non_snake_case)]
unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut nsAString) -> nsresult {
$(xpcom_method!(@ensure_param $param_name);)*
match self.$rust_name($($param_name, )*) {
Ok(val) => {
(*retval).assign(&val);
NS_OK
}
Err(error) => {
error.into()
}
}
}
};
// A method whose return value is a *mut nsACString type.
// Example: foo => Foo(bar: *const nsACString, baz: bool) -> nsACString
($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> nsACString) => {
#[allow(non_snake_case)]
unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut nsACString) -> nsresult {
$(xpcom_method!(@ensure_param $param_name);)*
match self.$rust_name($($param_name, )*) {
Ok(val) => {
(*retval).assign(&val);
NS_OK
}
Err(error) => {
error.into()
}
}
}
};
// A method whose return value is a non-nsA[C]String *mut type.
// Example: foo => Foo(bar: *const nsACString, baz: bool) -> bool
($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*) -> $retval:ty) => {
#[allow(non_snake_case)]
unsafe fn $xpcom_name(&self, $($param_name: $param_type,)* retval: *mut $retval) -> nsresult {
$(xpcom_method!(@ensure_param $param_name);)*
match self.$rust_name($($param_name, )*) {
Ok(val) => {
*retval = val;
NS_OK
}
Err(error) => {
error.into()
}
}
}
};
// A method that doesn't have a return value.
// Example: foo => Foo(bar: *const nsACString, baz: bool)
($rust_name:ident => $xpcom_name:ident($($param_name:ident: $param_type:ty),*)) => {
#[allow(non_snake_case)]
unsafe fn $xpcom_name(&self, $($param_name: $param_type,)*) -> nsresult {
$(xpcom_method!(@ensure_param $param_name);)*
match self.$rust_name($($param_name, )*) {
Ok(_) => NS_OK,
Err(error) => {
error.into()
}
}
}
};
}
/// A trait that ensures that a raw pointer isn't null and converts it to
/// a reference. Because of limitations in declarative macros, this includes an
/// implementation for types that are Copy, which simply returns the value
/// itself.
#[doc(hidden)]
pub trait Ensure<T> {
unsafe fn ensure(value: T) -> Self;
}
impl<'a, T: 'a> Ensure<*const T> for Result<&'a T, nsresult> {
unsafe fn ensure(ptr: *const T) -> Result<&'a T, nsresult> {
if ptr.is_null() {
Err(NS_ERROR_NULL_POINTER)
} else {
Ok(&*ptr)
}
}
}
impl<'a, T: 'a> Ensure<*const T> for Result<Option<&'a T>, nsresult> {
unsafe fn ensure(ptr: *const T) -> Result<Option<&'a T>, nsresult> {
Ok(if ptr.is_null() { None } else { Some(&*ptr) })
}
}
impl<T: Copy> Ensure<T> for Result<T, nsresult> {
unsafe fn ensure(copyable: T) -> Result<T, nsresult> {
Ok(copyable)
}
}
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