add ftp download method

[sahiljhawar]

Closes #79

[Copilot]

Pull request overview

Adds an FTP-based download implementation to el_paso.download, extending the existing download() dispatcher to support pulling files from FTP directories using a glob pattern.

Changes:

• Added "ftp" as a supported method option in download() and _download_single_step.
• Implemented FTP connection and download helpers (_ftp_connect, _ftp_download) with directory listing + fnmatch-based selection.
• Updated docstring to describe the new FTP behavior and anonymous-login fallback.

Suppressed comments (2)

el_paso/download.py:376

• FTP URLs that specify a non-default port (e.g. ftp://example.com:2121/path) are currently ignored because only parsed.hostname is used. Pass parsed.port through so these URLs work as expected.

    try:
        ftp = _ftp_connect(parsed.hostname or "", authentication_info)
    except OSError as e:
        logger.warning(f"Error connecting to FTP server for {url}: {e}")
        return

el_paso/download.py:352

• The new FTP download logic isn’t covered by tests, while other download methods have unit/system coverage (see tests/unittests/test_download.py). Add unit tests that mock ftplib.FTP (connect/login/nlst/retrbinary) to cover: pattern matching, port handling, skip_existing behavior, and .gz decompression path.

def _ftp_download(
    current_time: datetime,
    save_path: Path,
    download_url: str,
    file_name_stem: str,
    authentication_info: tuple[str, str],
    rename_file_name_stem: str | None,
    *,
    skip_existing: bool,
) -> None:

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[sahiljhawar]

@DoctorRabbit55 The tests is not running maybe because the username and password is not in my forked repo secrets. It works "on my machine"

[DoctorRabbit55]

Hi Sahil! I assume the fnmatch call is there for the version? In that case, we solved this in the past using a regex expression (see the other download methods).

It would probably be easier to add a test for an FTP server, which does not require login information (e.g. https://kp.gfz.de/daten). Otherwise, the test does not run locally for other people.