strange 400 Bad Request with Emacs 26 and GNU ELPA

[Paul Pogonyshev <pogonyshev@gmail.com>]

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Hi,

recently a bug has been reported to me (it is marked as closed
now, but only in Eldev itself, in that I added a workaround for
it):

    https://github.com/doublep/eldev/issues/52

I managed to reduce the way to reproduce it to a fairly short piece of
Elisp code that doesn't depend on Eldev, i.e. is "pure". The
workaround I used is also present in the attached script, but
commented out.

In short:
- run attached script as

    $ emacs --batch --load bad-request.el

  using Emacs 26.x (important!);

- observe that it dies with error
  "https://elpa.gnu.org/packages/org-edna-1.1.2.tar: Bad Request"

The script tries two install two packages (Org and Org-edna) from GNU
ELPA.  The second download dies with the error shown above.  If the
workaround line is uncommented, i.e. if HTTP(S) connection to GNU ELPA
is *not* reused for downloading the second package, it succeeds.

I'm not sure if it is a bug with GNU ELPA, Emacs 26 or something else.

Paul

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(require 'package)

(delete-directory "/tmp/400-bad-request" t)

(setf user-emacs-directory "/tmp/400-bad-request/.emacs"
      package-user-dir "/tmp/400-bad-request/elpa"
      package-archives '(("gnu" . "https://elpa.gnu.org/packages/")))

(package-initialize)
(package-refresh-contents)
(package-read-all-archive-contents)

(let ((inhibit-message t))
  (package-install-from-archive (cadr (assq 'org package-archive-contents)))
  ;(clrhash url-http-open-connections)  ; WORKAROUND
  (package-install-from-archive (cadr (assq 'org-edna package-archive-contents))))