bug#46481: "guix download" with ftp URL doesn't work on IPv6 network

[宋文武]

Danny Milosavljevic <dannym@scratchpost.org> writes:

> I strongly suspect there to be some problem with the ftp client since
> that's the second file that doesn't work using guix download but does work
> using wget, on the same computer.
>
> $ guix download ftp://ftp.denx.de/pub/u-boot/u-boot-2021.01.tar.bz2
>
> Starting download of /tmp/guix-file.tORPhj
> From ftp://ftp.denx.de/pub/u-boot/u-boot-2021.01.tar.bz2...
> Throw to key `ftp-error' with args `(#<input-output: socket 16> "PASV" 425 
> "You cannot use PASV on IPv6 connections. Use EPSV instead.\r")'.
> failed to download "/tmp/guix-file.tORPhj" from 
> "ftp://ftp.denx.de/pub/u-boot/u-boot-2021.01.tar.bz2";
> guix download: error: ftp://ftp.denx.de/pub/u-boot/u-boot-2021.01.tar.bz2: 
> download failed

Yes, with this patch I can get it work:

>From 568ea9cc0e07eab24c7d24e228d7d391f191feca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=AE=8B=E6=96=87=E6=AD=A6?= <iyzsong@member.fsf.org>
Date: Sun, 14 Feb 2021 12:02:57 +0800
Subject: [PATCH] ftp-client: Before 'PASV', try 'EPSV' first for IPv6.

This fixes <https://bugs.gnu.org/46481>.

* guix/ftp-client.scm (ftp-epsv, ftp-passive): New procedure.
(ftp-list, ftp-retr): Replace call to 'ftp-pasv' with 'ftp-passive'.
---
 guix/ftp-client.scm | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/guix/ftp-client.scm b/guix/ftp-client.scm
index 8d5adcb8ed..a72057d3f5 100644
--- a/guix/ftp-client.scm
+++ b/guix/ftp-client.scm
@@ -216,6 +216,19 @@ TIMEOUT, an ETIMEDOUT error is raised."
           (else
            (throw 'ftp-error conn "PASV" 227 message)))))
 
+(define (ftp-epsv conn)
+  (let* ((message (%ftp-command "EPSV" 229 (ftp-connection-socket conn))))
+    (string->number
+     (match:substring
+      (string-match "\\(...([0-9]+).\\)" message) 1))))
+
+(define (ftp-passive conn)
+  "Enter passive mode using EPSV or PASV, return a data connection port on
+success."
+  ;; IPv6 only works with EPSV, so try it first.
+  (or (false-if-exception (ftp-epsv conn))
+      (ftp-pasv conn)))
+
 (define (address-with-port sa port)
   "Return a socket-address object based on SA, but with PORT."
   (let ((fam  (sockaddr:fam sa))
@@ -232,7 +245,7 @@ TIMEOUT, an ETIMEDOUT error is raised."
   (if directory
       (ftp-chdir conn directory))
 
-  (let* ((port (ftp-pasv conn))
+  (let* ((port (ftp-passive conn))
          (ai   (ftp-connection-addrinfo conn))
          (s    (socket (addrinfo:fam ai) (addrinfo:socktype ai)
                        (addrinfo:protocol ai))))
@@ -281,7 +294,7 @@ must be closed before CONN can be used for other purposes."
   ;; Ask for "binary mode".
   (%ftp-command "TYPE I" 200 (ftp-connection-socket conn))
 
-  (let* ((port (ftp-pasv conn))
+  (let* ((port (ftp-passive conn))
          (ai   (ftp-connection-addrinfo conn))
          (s    (with-fluids ((%default-port-encoding #f))
                  (socket (addrinfo:fam ai) (addrinfo:socktype ai)
-- 
2.30.0

Okay to push?