Add new entrypoints for fetching and testing last result for FFI

Author: joemphilips

bindings/src/lib.rs

@@ -24,3 +24,50 @@ mod handle;
 
 pub use handle::*;
 pub use error::*;
+
+
+ffi_no_catch! {
+    fn ffi_last_result(
+        message_buf: Out<u8>,
+        message_buf_len: usize,
+        actual_message_len: Out<usize>,
+        result: Out<FFIResult>
+    ) -> FFIResult {
+        FFIResult::with_last_result(|last_result| {
+            let (value, error) = last_result.unwrap_or((FFIResult::ok(), None));
+
+            unsafe_block!("The out pointer is valid and not mutably aliased elsewhere" => result.init(value));
+
+            if let Some(error) = error {
+                let error = error.as_bytes();
+
+                unsafe_block!("The out pointer is valid and not mutably aliased elsewhere" => actual_message_len.init(error.len()));
+
+                if message_buf_len < error.len() {
+                    return FFIResult::buffer_too_small();
+                }
+
+                unsafe_block!("The buffer is valid for writes and the length is within the buffer" => message_buf.init_bytes(error));
+            } else {
+                unsafe_block!("The out pointer is valid and not mutably aliased elsewhere" => actual_message_len.init(0));
+            }
+
+            FFIResult::ok()
+        })
+    }
+}
+
+/// These tests should be used for asserting that the wrapper code can see the expected
+/// error messages when it fails (or succeeds).
+#[cfg(debug_assertions)]
+ffi! {
+    fn ffi_test_error() -> FFIResult {
+        use std::io;
+
+        FFIResult::internal_error().context(io::Error::new(io::ErrorKind::Other, "A test error."))
+    }
+
+    fn ffi_test_ok() -> FFIResult {
+        FFIResult::ok()
+    }
+}