From bd4dbddbce7325ba74cf4c69a66ae054138fdaef Mon Sep 17 00:00:00 2001
From: Thomas Hahn <Thahn@tcbtech.com>
Date: Wed, 11 May 2022 23:38:24 -0600
Subject: [PATCH] Add config to ignore PASV host

---
 client.go                |  5 +++++
 persistent_connection.go | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/client.go b/client.go
index 779cd5e..442872b 100644
--- a/client.go
+++ b/client.go
@@ -149,6 +149,11 @@ type Config struct {
 	// hung connections.
 	DisableEPSV bool
 
+	// Ignores the returned remote host IP for PASV connections. Some FTP Servers are
+	// behind NAT, and return their internal IPs. This ignores the IP portion of the
+	// PASV response, using the control connection's IP instead.
+	IgnoreHost bool
+
 	// For testing convenience.
 	stubResponses map[string]stubResponse
 }
diff --git a/persistent_connection.go b/persistent_connection.go
index 15f5d74..886dc6d 100644
--- a/persistent_connection.go
+++ b/persistent_connection.go
@@ -418,6 +418,20 @@ func (pconn *persistentConn) prepareDataConn() (func() (net.Conn, error), error)
 			return nil, err
 		}
 
+		// Some FTP servers are behind NAT themselves, and lie about their IP address.
+		if pconn.config.IgnoreHost {
+			pconn.debug("Ignoring PASV returned host %s", host)
+			_, remotePort, err := net.SplitHostPort(host)
+			if err != nil {
+				return nil, err
+			}
+			remoteHost, _, err := net.SplitHostPort(pconn.host)
+			if err != nil {
+				return nil, err
+			}
+			host = net.JoinHostPort(remoteHost, remotePort)
+		}
+
 		pconn.debug("opening data connection to %s", host)
 		dc, netErr := net.DialTimeout("tcp", host, pconn.config.Timeout)