1 files changed, 113 insertions, 0 deletions
diff --git a/intl/l10n/rust/l10nregistry-ffi/src/load.rs b/intl/l10n/rust/l10nregistry-ffi/src/load.rs
new file mode 100644
index 0000000000..04a041246f
--- /dev/null
+++ b/intl/l10n/rust/l10nregistry-ffi/src/load.rs
@@ -0,0 +1,113 @@
+/* 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 futures_channel::oneshot;
+use nserror::{nsresult, NS_OK, NS_SUCCESS_ADOPTED_DATA};
+use nsstring::{nsACString, nsCStringLike};
+use std::{
+    cell::Cell,
+    ffi::c_void,
+    io::{self, Error, ErrorKind},
+    ptr,
+};
+use xpcom::{
+    interfaces::{nsIStreamLoader, nsIStreamLoaderObserver, nsISupports},
+    xpcom,
+};
+
+unsafe fn boxed_slice_from_raw(ptr: *mut u8, len: usize) -> Box<[u8]> {
+    if ptr.is_null() {
+        // It is undefined behaviour to create a `Box<[u8]>` with a null pointer,
+        // so avoid that case.
+        assert_eq!(len, 0);
+        Box::new([])
+    } else {
+        Box::from_raw(ptr::slice_from_raw_parts_mut(ptr, len))
+    }
+}
+
+#[xpcom(implement(nsIStreamLoaderObserver), nonatomic)]
+struct StreamLoaderObserver {
+    sender: Cell<Option<oneshot::Sender<Result<Box<[u8]>, nsresult>>>>,
+}
+
+impl StreamLoaderObserver {
+    #[allow(non_snake_case)]
+    unsafe fn OnStreamComplete(
+        &self,
+        _loader: *const nsIStreamLoader,
+        _ctxt: *const nsISupports,
+        status: nsresult,
+        result_length: u32,
+        result: *const u8,
+    ) -> nsresult {
+        let sender = match self.sender.take() {
+            Some(sender) => sender,
+            None => return NS_OK,
+        };
+
+        if status.failed() {
+            sender.send(Err(status)).expect("Failed to send data");
+            return NS_OK;
+        }
+
+        // safety: take ownership of the data passed in. This is OK because we
+        // have configured Rust and C++ to use the same allocator, and our
+        // caller won't free the `result` pointer if we return
+        // NS_SUCCESS_ADOPTED_DATA.
+        sender
+            .send(Ok(boxed_slice_from_raw(
+                result as *mut u8,
+                result_length as usize,
+            )))
+            .expect("Failed to send data");
+        NS_SUCCESS_ADOPTED_DATA
+    }
+}
+
+extern "C" {
+    fn L10nRegistryLoad(
+        path: *const nsACString,
+        observer: *const nsIStreamLoaderObserver,
+    ) -> nsresult;
+
+    fn L10nRegistryLoadSync(
+        aPath: *const nsACString,
+        aData: *mut *mut c_void,
+        aSize: *mut u64,
+    ) -> nsresult;
+}
+
+pub async fn load_async(path: impl nsCStringLike) -> io::Result<Box<[u8]>> {
+    let (sender, receiver) = oneshot::channel::<Result<Box<[u8]>, nsresult>>();
+    let observer = StreamLoaderObserver::allocate(InitStreamLoaderObserver {
+        sender: Cell::new(Some(sender)),
+    });
+    unsafe {
+        L10nRegistryLoad(&*path.adapt(), observer.coerce())
+            .to_result()
+            .map_err(|err| Error::new(ErrorKind::Other, err))?;
+    }
+    receiver
+        .await
+        .expect("Failed to receive from observer.")
+        .map_err(|err| Error::new(ErrorKind::Other, err))
+}
+
+pub fn load_sync(path: impl nsCStringLike) -> io::Result<Box<[u8]>> {
+    let mut data_ptr: *mut c_void = ptr::null_mut();
+    let mut data_length: u64 = 0;
+    unsafe {
+        L10nRegistryLoadSync(&*path.adapt(), &mut data_ptr, &mut data_length)
+            .to_result()
+            .map_err(|err| Error::new(ErrorKind::Other, err))?;
+
+        // The call succeeded, meaning `data_ptr` and `size` have been filled in with owning pointers to actual data payloads (or null).
+        // If we get a null, return a successful read of the empty file.
+        Ok(boxed_slice_from_raw(
+            data_ptr as *mut u8,
+            data_length as usize,
+        ))
+    }
+}