The commit "Avoid unnecessary rounding errors in timestamps" (3aee7b)
introduces a regression in the network stack. This can be seen while
using org-caldav and I managed to reproduce with emacs -Q (see attached
files).

Among the attached files, script.el is of the most importance. The first
call to `contact-server' works fine whereas the second triggers a
server-side error: 503 Service Unavailable. Unfortunately, you can't
directly reuse this script as it depends on a personal nextcloud
instance.

Reverting the commit fixes the bug. I added its author on CC.

commit 3aee7be62eaf8caef6f2fab31bee79674b3abbb7
Author: Paul Eggert <eggert@cs.ucla.edu>
Date:   Sun Oct 22 01:04:36 2017 -0700

    Avoid unnecessary rounding errors in timestamps
    
    Avoid the rounding errors of float-time when it’s easy.  E.g.,
    replace (< (float-time a) (float-time b)) with (time-less-p a b).
    * lisp/desktop.el (desktop-save):
    * lisp/ecomplete.el (ecomplete-add-item):
    * lisp/epg.el (epg-wait-for-completion):
    * lisp/files.el (dir-locals-find-file, dir-locals-read-from-dir):
    * lisp/image-dired.el (image-dired-get-thumbnail-image)
    (image-dired-create-thumb-1):
    * lisp/info.el (info-insert-file-contents):
    * lisp/ls-lisp.el (ls-lisp-format-time):
    * lisp/net/ange-ftp.el (ange-ftp-file-newer-than-file-p)
    (ange-ftp-verify-visited-file-modtime):
    * lisp/net/rcirc.el (rcirc-ctcp-sender-PING):
    * lisp/textmodes/remember.el (remember-store-in-mailbox):
    * lisp/url/url-cookie.el (url-cookie-expired-p):
    Bypass float-time to avoid rounding errors.
    
    * lisp/files.el (dir-locals-find-file):



In GNU Emacs 26.0.90 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.21)
 of 2017-11-09 built on luz4
Repository revision: b23adf48bfe03332f508f088265a0c8162747cae
Windowing system distributor 'Fedora Project', version 11.0.11903000
System Description:	Fedora release 26 (Twenty Six)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --cache-file=/tmp/emacs.config.cache'

Configured features:
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Memory information:
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-- 
Damien Cassou
http://damiencassou.seasidehosting.st

"Success is the ability to go from one failure to another without
losing enthusiasm." --Winston Churchill