fix: return ERR_PERMISSION when export fails due to permission denied

[Spockkk0225]

Summary

Fix wrong error code when COPY TO fails due to permission denied.

Problem

When exporting data to a directory without write permission, the error code returned is ERR_IO_ERROR (1014) instead of ERR_PERMISSION (1001). Additionally, the assert statement in test_export_no_permission was incorrectly indented inside the pytest.raises context manager.

See #428 for details.

Changes

• src/utils/writer/writer.cc: Detect Permission denied in OpenOutputStream error message and return ERR_PERMISSION (1001) instead of ERR_IO_ERROR (1014)
• src/compiler/function/csv_export_function.cpp: Throw PermissionDeniedException when status code is ERR_PERMISSION
• tools/python_bind/tests/test_db_import_export.py: Fix wrong indent — move assert outside the pytest.raises context manager

Closes #428

[lnfjpt]

LGTM

[longbinlai]

I think this err_msg.find() is very ambiguous. @copilot Can you help review this one? and propose possible solutions?

[Spockkk0225]

full error message:

"message": "Failed to open file stream: IOError: Failed to open local file '/tmp/pytest-of-shaoyu/pytest-25/test_export_no_permission0/no_perm/out.csv'. Detail: [errno 13] Permission denied"

[Copilot]

On the current branch this no longer relies on err_msg.find(). It now uses arrow::internal::ErrnoFromStatus(stream_result.status()) and only maps EACCES/EPERM to ERR_PERMISSION, which makes the check much more explicit than substring matching. If we want to make it even clearer, the next step would be to extract that into a small helper like ClassifyOpenOutputStreamError(status) and reuse it across export paths.

[longbinlai]

Review: err_msg.find("Permission denied") 的问题

同意 @longbinlai 的判断——用字符串匹配来分类错误码非常脆弱：

1. 依赖 Arrow 的 message 文本：如果 Arrow 升级后措辞变了（比如改成 "permission denied" 小写，或者本地化），这个检查就失效了
2. 跨平台不可靠：Windows 上的 permission error message 与 POSIX 不同
3. 误匹配风险：如果路径名恰好包含 "Permission denied" 字样也会命中

建议方案：使用 Arrow 的 ErrnoFromStatus API

Arrow 18 的 arrow::internal::ErrnoFromStatus(status) 可以直接从 status 的 StatusDetail 中提取 errno 值，无需解析字符串：

#include <arrow/util/io_util.h>

auto stream_result = fileSystem_->OpenOutputStream(schema_.paths[0]);
if (!stream_result.ok()) {
  auto& st = stream_result.status();
  int err = arrow::internal::ErrnoFromStatus(st);
  auto code = (err == EACCES || err == EPERM)
                  ? StatusCode::ERR_PERMISSION
                  : StatusCode::ERR_IO_ERROR;
  return neug::Status(code, "Failed to open file stream: " + st.ToString());
}

• EACCES (13) 覆盖文件权限拒绝
• EPERM (1) 覆盖操作不允许（如只读文件系统）
• ErrnoFromStatus 在 detail 不是 errno 类型时返回 0，安全地 fallback 到 ERR_IO_ERROR
• 跨平台友好，Arrow 在 Windows 上也有对应的 WinErrorFromStatus

这个方案是结构化的错误传播，不依赖任何字符串格式。