AngeFTP cannot parse the output of the GNU inetutils FTP client on macOS
10.14. It errors out with "FTP Error: OPEN request failed:" and the
process buffer shows the following:

ftp> open ftp.tcl.tk
open ftp.tcl.tk
cd /
cd /
cd /
cd /
cd /
cd /
cd /
cd /
cd /
cd /
cd /
cd /
Connected to ftp.tcl.tk.
421 Service not available, remote server has closed connection
ftp> Not connected.
ftp> Not connected.
ftp> Not connected.
ftp> Not connected.
ftp> Not connected.
ftp> Not connected.
ftp> 

This appears to be caused by readline being enabled for ftp and is
resolved when disabling it.

NetBSD/FreeBSD specifically mentions this in its ftp(1) for tnftp:

     -e		 Disables command line editing.	 This is useful	for Emacs
		 ange-ftp mode.

Netkit-ftp on Linux does not exhibit this problem even with readline
enabled; I could not test GNU inetutils on Linux. I tested tnftp on
macOS and it also did not exhibit this problem even with readline
enabled.

Tested versions:
ftp (GNU inetutils) 2.0 macOS 10.14.6
tnftp-20200705 macOS 10.14.6
netkit-ftp 0.17-34.1 Ubuntu 20.04.2 LTS


There is no -e option for Windows FTP and ftp will terminate when
receiving an unknown option (tested version Windows 10.0.19042.928)

There is no -e option in Solaris FTP and I cannot test how it responds
to an unknown option.

I am proposing the below patch which resolves the problem on macOS with
GNU inetutils and does no harm for Netkit-ftp/lukemftp/tnftp.

However, because of the way a Windows client would respond, I am open to
different approaches including considering this an inetutils bug
instead.