1 files changed, 59 insertions, 0 deletions
diff --git a/xpcom/rust/xpcom/src/base.rs b/xpcom/rust/xpcom/src/base.rs
new file mode 100644
index 0000000000..556768a179
--- /dev/null
+++ b/xpcom/rust/xpcom/src/base.rs
@@ -0,0 +1,59 @@
+/* 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 crate::interfaces::{nsIInterfaceRequestor, nsISupports};
+use crate::{GetterAddrefs, RefCounted, RefPtr};
+
+#[repr(C)]
+#[derive(Copy, Clone, Eq, PartialEq)]
+/// A "unique identifier". This is modeled after OSF DCE UUIDs.
+pub struct nsID(pub u32, pub u16, pub u16, pub [u8; 8]);
+
+/// Interface IDs
+pub type nsIID = nsID;
+/// Class IDs
+pub type nsCID = nsID;
+
+/// A type which implements XpCom must follow the following rules:
+///
+/// * It must be a legal XPCOM interface.
+/// * The result of a QueryInterface or similar call, passing IID, must return a
+///   valid reference to an object of the given type.
+/// * It must be valid to cast a &self reference to a &nsISupports reference.
+pub unsafe trait XpCom: RefCounted {
+    const IID: nsIID;
+
+    /// Perform a QueryInterface call on this object, attempting to dynamically
+    /// cast it to the requested interface type. Returns Some(RefPtr<T>) if the
+    /// cast succeeded, and None otherwise.
+    fn query_interface<T: XpCom>(&self) -> Option<RefPtr<T>> {
+        let mut ga = GetterAddrefs::<T>::new();
+        unsafe {
+            if (*(self as *const Self as *const nsISupports))
+                .QueryInterface(&T::IID, ga.void_ptr())
+                .succeeded()
+            {
+                ga.refptr()
+            } else {
+                None
+            }
+        }
+    }
+
+    /// Perform a `GetInterface` call on this object, returning `None` if the
+    /// object doesn't implement `nsIInterfaceRequestor`, or can't access the
+    /// interface `T`.
+    fn get_interface<T: XpCom>(&self) -> Option<RefPtr<T>> {
+        let ireq = self.query_interface::<nsIInterfaceRequestor>()?;
+
+        let mut ga = GetterAddrefs::<T>::new();
+        unsafe {
+            if ireq.GetInterface(&T::IID, ga.void_ptr()).succeeded() {
+                ga.refptr()
+            } else {
+                None
+            }
+        }
+    }
+}