fixed sigsegv for path as input file

python_tests/test_copy_prefix.py

@@ -271,3 +271,17 @@ def validate_copy(copy_id, expected_len = None, expected_min_len = None):
     for i in range(copy_id):
         last_len = validate_copy(i, expected_min_len = last_len)
         print(f"--- Copy {i} valid with {last_len} objects")
+
+def test_copy_prefix_throws_on_path_passed(db0_fixture):
+    path = "./invalid-dir/nonexistent/-copy/"
+    # remove path if it exists
+    if os.path.exists(path):
+        os.rmdir(path)
+
+    root = MemoTestSingleton([])
+    for _ in range(50):
+        root.value.append(MemoTestClass("a" * 1024))  # 1 KB string
+    db0.commit()
+
+    with pytest.raises(OSError) as excinfo:
+        db0.copy_prefix(path)

src/dbzero/bindings/python/PyInternalAPI.cpp

@@ -936,9 +936,15 @@ namespace db0::python
     PyObject *tryCopyPrefixImpl(BDevStorage &src_storage, const std::string &output_file_name,
         std::optional<std::uint64_t> page_io_step_size, std::optional<std::uint64_t> meta_io_step_size) 
     {
+        // make sure output is file doesn't point to a directory
+        if (output_file_name.back() == std::filesystem::path::preferred_separator) {
+            PyErr_Format(PyExc_OSError, "Output file points to a directory:  '%s'", output_file_name);
+            return nullptr;
+        }
         // make sure output file does not exist
         if (db0::CFile::exists(output_file_name)) {
-            THROWF(db0::IOException) << "Output file already exists: " << output_file_name;
+            PyErr_Format(PyExc_OSError, "Output file already exists:  '%s'", output_file_name);
+            return nullptr;
         }
 
         // use either explicit step size, input step size (if > 1) or default = 4MB
@@ -1033,6 +1039,9 @@ namespace db0::python
             auto result = Py_OWN(tryCopyPrefixImpl(*storage, output_file_name, page_io_step_size, meta_io_step_size));
             storage->close();
             return result.steal();
+            if (!result) {
+                return nullptr;
+            }
         } catch (...) {
             if (storage) {
                 storage->close();