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+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2014, 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2017 Mathieu Lirzin <mthl@gnu.org>
+;;; Copyright © 2017 Christopher Baines <mail@cbaines.net>
+;;; Copyright © 2020 Jakub Kądziołka <kuba@kadziolka.net>
+;;; Copyright © 2020 Hartmut Goebel <h.goebel@crazy-compilers.com>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix hexpm-download)
+  #:use-module (ice-9 match)
+  #:use-module (guix extracting-download)
+  #:use-module (guix packages) ;; for %current-system
+  #:use-module (srfi srfi-26)
+  #:export (hexpm-fetch
+
+            %hexpm-repo-url
+            hexpm-url
+            hexpm-url?
+            hexpm-uri))
+
+;;;
+;;; An <origin> method that fetches a package from the hex.pm repository,
+;;; unwrapping the actual content from the download tarball.
+;;;
+
+;; URL and paths from
+;; https://github.com/hexpm/specifications/blob/master/endpoints.md
+(define %hexpm-repo-url
+  (make-parameter "https://repo.hex.pm"))
+(define hexpm-url
+  (string-append (%hexpm-repo-url) "/tarballs/"))
+(define hexpm-url?
+  (cut string-prefix? hexpm-url <>))
+
+(define (hexpm-uri name version)
+  "Return a URI string for the package hosted at hex.pm corresponding to NAME
+and VERSION."
+  (string-append hexpm-url name "-" version ".tar"))
+
+(define* (hexpm-fetch url hash-algo hash
+                    #:optional name
+                    #:key
+                    (filename-to-extract "contents.tar.gz")
+                    (system (%current-system))
+                    (guile (default-guile)))
+  "Return a fixed-output derivation that fetches URL and extracts
+\"contents.tar.gz\".  The output is expected to have hash HASH of type
+HASH-ALGO (a symbol).  By default, the file name is the base name of URL;
+optionally, NAME can specify a different file name.  By default, the file name
+is the base name of URL with \".gz\" appended; optionally, NAME can specify a
+different file name."
+  (define file-name
+    (match url
+      ((head _ ...)
+       (basename head))
+      (_
+       (basename url))))
+
+  (http-fetch/extract url "contents.tar.gz" hash-algo hash
+                      ;; urls typically end with .tar, but contents is .tar.gz
+                      (or name (string-append file-name ".gz"))
+                      #:system system #:guile guile))