bug#34855: 27.0.50; url-retrieve-synchronously Bad request Error every 2nd call

[Thomas Hisch]

When I try to connect to our local gerrit server (https, using a custom
CAcert) every second request fails: (400 bad request error)
When I perform the test in emacs 26.1 (installed via the fedora package
manager) all request are successfull.

This is the script I'm using for my tests:

(require 'auth-source)
(require 'json)
(require 'url)
(require 'url-http)
(require 'url-vars)
(require 'subr-x)


(defcustom ims-gerrit-host "gerrit.ims.co.at"
  "hostname of the gerrit instance"
  :group 'ims-jira
  :type 'string)

(defun ims-gerrit-authentication ()
  "Return an encoded string with jira username and password."
  (let ((pass-entry (auth-source-user-and-password ims-gerrit-host)))

    (if-let ((username (nth 0 pass-entry))
             (password (nth 1 pass-entry)))
        (base64-encode-string
         (concat username ":" password)))))

(defun ims-gerrit--get-auth-headers ()
  "Helper function to setup auth header for gerrit url call."
  `(("Content-Type" . "application/x-www-form-urlencoded")
    ("Authorization" .
     ,(concat
       "Basic "
       (ims-gerrit-authentication)))))

(defun ims-gerrit--retrieve-page-as-json (path)
  "Shortcut for gerrit api PATH to return valid json."
  (let ((url-request-extra-headers (ims-gerrit--get-auth-headers)))
    (with-current-buffer (url-retrieve-synchronously
                          (concat "https://"; ims-gerrit-host path))
      (goto-char (point-min))
      (re-search-forward "^$")
      (delete-region (point) (point-min))

      ;; FIXME
      (buffer-string))
      ;; (json-read-from-string (buffer-string)))
))


(defun gerrit-get-server-version ()
  (interactive)
  (switch-to-buffer "*gerritests*")
  (erase-buffer)
  (insert (emacs-version))
  (insert ?\n)
  (dolist (loopvar `(0 1 2 3 4 5 6 7 8))
    (insert (format "\n##### %d\n" loopvar))
    (insert (prin1-to-string (ims-gerrit--retrieve-page-as-json
                              "/config/server/version")))))

The emacs 27.0 build, where the test fails,  was build be me locally.
Could it be that something between emacs 26.1 and the HEAD of master
broke sth?

This is the ouput I get in emcas 27.0 (as you can see every 2nd request
is empty)

GNU Emacs 27.0.50 (build 99, x86_64-pc-linux-gnu, GTK+ Version 3.24.1)
 of 2019-03-14

##### 0
""
##### 1
"
)]}'
\"2.16.2\"
"
##### 2
""
##### 3
"
)]}'
\"2.16.2\"
"
##### 4
""
##### 5
"
)]}'
\"2.16.2\"
"
##### 6
""
##### 7
"
)]}'
\"2.16.2\"
"
##### 8
""

Regards
Thomas


In GNU Emacs 27.0.50 (build 99, x86_64-pc-linux-gnu, GTK+ Version 3.24.1)
 of 2019-03-14 built on PC-16609.ims.co.at
Repository revision: 020e69d992c98fd852e835c9bd707a8d137090f2
Repository branch: master
Windowing system distributor 'Fedora Project', version 11.0.12003000
System Description: Fedora 29 (Workstation Edition)

Recent messages:
Mark set
Quit
Saving file 
/home/thomas.hisch/gitrepos/dotfiles/emacs.d/user-lisp/gerrit-urltest.el...
Wrote 
/home/thomas.hisch/gitrepos/dotfiles/emacs.d/user-lisp/gerrit-urltest.el
You can run the command ‘eval-buffer’ with M-x ev-b RET
Contacting host: gerrit.ims.co.at:443
completing-read-default: Command attempted to use minibuffer while in 
minibuffer
Quit
Making completion list... [2 times]
Scanning for dabbrevs...done

Configured using:
 'configure --prefix=/opt/emacs --with-x-toolkit=gtk3 --with-xpm
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Configured features:
XPM PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM THREADS PDUMPER LCMS2 GMP

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
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  mouse-wheel-mode: t
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Load-path shadows:
None found.

Features:
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url-auth mail-parse rfc2231 rfc2047 rfc2045 mm-util ietf-drums
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Memory information:
((conses 16 65737 7435)
 (symbols 48 7667 1)
 (strings 32 23669 1937)
 (string-bytes 1 709583)
 (vectors 16 12492)
 (vector-slots 8 153584 13038)
 (floats 8 25 80)
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 (buffers 992 32))
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