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

[ludo@gnu.org (Ludovic Courtès)]

Hi,

Andy Patterson <ajpatter@uwaterloo.ca> skribis:

> 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.

Indeed, <https://tools.ietf.org/html/rfc7230#section-6.1> reads:

  The "close" connection option is defined for a sender to signal that
  this connection will be closed after completion of the response.

> 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.

I think you found a genuine bug and provided the right patch!

Did you observe the problem when connecting to hydra.gnu.org, or was it
another server?  Did you have a way to reproduce it?

(In my experience Nginx at hydra.gnu.org closes the connection after
~100 responses, so even if the last response is not consumed directly,
that’s OK.)

> 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.

I’ve committed a slightly edited version of the patch where I factorized
the call to PROC and changed the commit message to describe the changes
at the source code level, in GNU change log style.  (I hope this is fine
with you.)

Thank you!

Ludo’.