Fix for proxies in passive mode

Fixed the host address such that the actual host ip is stored and not the result of the proxy dialer (if used)

ftp.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"crypto/tls"
 	"errors"
+	"fmt"
 	"io"
 	"net"
 	"net/textproto"
@@ -144,21 +145,33 @@ func Dial(addr string, options ...DialOption) (*ServerConn, error) {
 		}
 	}
 
-	tconn, err := dialFunc("tcp", addr)
+	// Use the resolved IP address in case addr contains a domain name
+	// If we use the domain name, we might not resolve to the same IP.
+	dnsResolver := net.Resolver{
+		Dial: func(ctx context.Context, network string, address string) (net.Conn, error) {
+			return dialFunc(network, address)
+		},
+	}
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return nil, err
+	}
+	addrs, err := dnsResolver.LookupIPAddr(context.Background(), host)
 	if err != nil {
 		return nil, err
 	}
 
-	// Use the resolved IP address in case addr contains a domain name
-	// If we use the domain name, we might not resolve to the same IP.
-	remoteAddr := tconn.RemoteAddr().(*net.TCPAddr)
+	tconn, err := dialFunc("tcp", fmt.Sprintf("%s:%s", addrs[0].IP.String(), port))
+	if err != nil {
+		return nil, err
+	}
 
 	c := &ServerConn{
 		options:  do,
 		features: make(map[string]string),
 		conn:     textproto.NewConn(do.wrapConn(tconn)),
 		netConn:  tconn,
-		host:     remoteAddr.IP.String(),
+		host:     addrs[0].IP.String(),
 	}
 
 	_, _, err = c.conn.ReadResponse(StatusReady)
@@ -528,26 +541,9 @@ 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 := net.ParseIP(c.host); cmdIP != nil {
-			if dataIP := net.ParseIP(host); dataIP != nil {
-				if isBogusDataIP(cmdIP, dataIP) {
-					return c.host, port, nil
-				}
-			}
-		}
-	}
 	return host, port, nil
 }
 
-func isBogusDataIP(cmdIP, dataIP net.IP) bool {
-	// Logic stolen from lftp (https://github.com/lavv17/lftp/blob/d67fc14d085849a6b0418bb3e912fea2e94c18d1/src/ftpclass.cc#L769)
-	return dataIP.IsMulticast() ||
-		cmdIP.IsPrivate() != dataIP.IsPrivate() ||
-		cmdIP.IsLoopback() != dataIP.IsLoopback()
-}
-
 // getDataConnPort returns a host, port for a new data connection
 // it uses the best available method to do so
 func (c *ServerConn) getDataConnPort() (string, int, error) {