[PATCH] scripts: substitute: Avoid infinite looping when updating the substitute list

[Andy Patterson <ajpatter@uwaterloo.ca>]

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Hi,

I was having trouble using substitutes, so I decided to investigate it.
I found out that when retrieving the batch of .narinfo files from the
server, my connection was always being closed after the first response.
Therefore, I would always be reconnecting to the server with every
request in the batch still to process, and this reconnecting would be
repeated infinitely, or at least until my Internet went down. Based on
the documentation for the "connection: close" header, I think that this
first response should be complete, so we can use it. Maybe I'm wrong;
I'm not totally familiar with how http works.

I also considered ensuring that a good response code was received, but
the handler deals with error response codes as well, so it seemed
superfluous.

This patch will make use of the last response from the server, before
reconnecting to try the next one. With it I was able to successfully
build and run links.

Let me know if my understanding is off, or if there's a better approach.

Thanks,

Andy

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From 633c491e2dad4c3a70eb045177c17bd2552d63f3 Mon Sep 17 00:00:00 2001
From: Andy Patterson <ajpatter@uwaterloo.ca>
Date: Sun, 5 Jul 2015 19:34:05 -0400
Subject: [PATCH] scripts: substitute: Avoid infinite looping when updating the
 substitute list

* guix/scripts/substitute.scm (http-multiple-get): Make use of the current
  response before reconnecting.
---
 guix/scripts/substitute.scm | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index 8b4fa36..e767d0f 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -468,8 +468,9 @@ to read the response body.  Return the list of results."
              ;; case we have to try again.  Check whether that is the case.
              (match (assq 'connection (response-headers resp))
                (('connection 'close)
-                (close-port p)
-                (connect requests result))        ;try again
+                (let ((first-result (proc head resp body)))
+                  (close-port p)
+                  (connect tail (cons first-result result))))     ;try again
                (_
                 (loop tail                        ;keep going
                       (cons (proc head resp body) result)))))))))))
-- 
2.4.5