From fa01896d676e87d27e0a6a0e0570899f46aa917d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tam=C3=A1s=20Gul=C3=A1csi?= <T.Gulacsi@unosoft.hu>
Date: Fri, 29 Jul 2022 09:09:44 +0200
Subject: [PATCH] Fix PASV address like lftp does

---
 ftp.go | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/ftp.go b/ftp.go
index abe944f..146a8fc 100644
--- a/ftp.go
+++ b/ftp.go
@@ -10,6 +10,7 @@ import (
 	"errors"
 	"io"
 	"net"
+	"net/netip"
 	"net/textproto"
 	"strconv"
 	"strings"
@@ -497,6 +498,19 @@ func (c *ServerConn) pasv() (host string, port int, err error) {
 
 	// Make the IP address to connect to
 	host = strings.Join(pasvData[0:4], ".")
+
+	if c.host != host {
+		if cmdIP, err := netip.ParseAddr(c.host); err == nil {
+			if dataIP, err := netip.ParseAddr(host); err == nil {
+				// Logic stolen from lftp (https://github.com/lavv17/lftp/blob/d67fc14d085849a6b0418bb3e912fea2e94c18d1/src/ftpclass.cc#L769)
+				if dataIP.IsMulticast() ||
+					cmdIP.IsPrivate() != dataIP.IsPrivate() ||
+					cmdIP.IsLoopback() != dataIP.IsLoopback() {
+					return c.host, port, nil
+				}
+			}
+		}
+	}
 	return host, port, nil
 }