FileZilla IPv6 PASV Parsing: Zone Identifier Support

FileZilla IPv6 PASV Parsing: Zone Identifier Support

Goal: verify how the client processes the PASV response when the returned IPv6 address includes a zone identifier or an IPv4‑mapped notation. The documented feature states that FileZilla supports passive mode for IPv6, but the parsing logic for zone identifiers is not fully documented.

Constraints: older releases (<3.52) may omit zone handling; servers sometimes return non‑standard formats. Uncertainty exists whether the client strips the zone or retains it, and whether the port number is interpreted correctly in those cases.

1. Does FileZilla correctly parse IPv6 PASV responses that contain a zone identifier (e.g., fe80::1%eth0)?
2. How does the client handle IPv4‑mapped IPv6 addresses in the PASV reply?
3. Are there version‑specific differences in zone‑identifier support?