1 files changed, 59 insertions, 2 deletions
diff --git a/src/libstore/rust.hh b/src/libstore/rust.hh
index 4366e4723..4c7720a44 100644
--- a/src/libstore/rust.hh
+++ b/src/libstore/rust.hh
@@ -4,7 +4,8 @@ namespace rust {
 
 // Depending on the internal representation of Rust slices is slightly
 // evil...
-template<typename T> struct Slice
+template<typename T>
+struct Slice
 {
     T * ptr;
     size_t size;
@@ -37,8 +38,64 @@ struct Source
     }
 };
 
+/* C++ representation of Rust's Result<T, CppException>. */
+template<typename T>
+struct Result
+{
+    unsigned int tag;
+
+    union {
+        T data;
+        std::exception_ptr * exc;
+    };
+
+    /* Rethrow the wrapped exception or return the wrapped value. */
+    T unwrap()
+    {
+        if (tag == 0)
+            return data;
+        else if (tag == 1)
+            std::rethrow_exception(*exc);
+        else
+            abort();
+    }
+};
+
+template<typename T>
+struct CBox
+{
+    T * ptr;
+
+    T * operator ->()
+    {
+        return ptr;
+    }
+
+    CBox(T * ptr) : ptr(ptr) { }
+    CBox(const CBox &) = delete;
+    CBox(CBox &&) = delete;
+
+    ~CBox()
+    {
+        free(ptr);
+    }
+};
+
+// Grrr, this is only needed because 'extern "C"' functions don't
+// support non-POD return types (and CBox has a destructor so it's not
+// POD).
+template<typename T>
+struct CBox2
+{
+    T * ptr;
+    CBox<T> use()
+    {
+        return CBox(ptr);
+    }
+};
+
 }
 
 extern "C" {
-    void unpack_tarfile(rust::Source source, rust::StringSlice dest_dir);
+    rust::CBox2<rust::Result<std::tuple<>>> unpack_tarfile(rust::Source source, rust::StringSlice dest_dir);
 }