nongnu: Add unredistributable-url-fetch.

* nonguix/download.scm: New file.

nonguix/download.scm

@@ -0,0 +1,62 @@
+;;; Copyright © 2019 Julien Lepiller <julien@lepiller.eu>
+;;;
+;;; This program 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.
+;;;
+;;; This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+(define-module (nonguix download)
+  #:use-module (guix derivations)
+  #:use-module (guix monads)
+  #:use-module (guix packages)
+  #:use-module (guix store)
+  #:use-module (ice-9 match)
+  #:export (unredistributable-url-fetch))
+
+(define* (unredistributable-url-fetch url hash-algo hash
+                                      #:optional name
+                                      #:key (system (%current-system))
+                                      (guile (default-guile)))
+  "Return a fixed-output derivation that fetches URL (a string) which is expected
+to have 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.
+
+This is a simpler version of url-fetch from Guix, that doesn't support mirror://
+or file:// uris.  It is specifically designed to prevent substitution of the
+source, for the purpose of downloading copyrighted content you have access to,
+but you don't have the right to redistribute.  By marking the derivation as non
+substitutable, this fetch prevents you from giving others access to the source
+if you run a substitute server on your machine."
+  (define file-name
+    (match url
+      ((head _ ...)
+       (basename head))
+      (_
+       (basename url))))
+
+  (mlet %store-monad ()
+    (raw-derivation file-name "builtin:download" '()
+                #:system system
+                #:hash-algo hash-algo
+                #:hash hash
+
+                ;; Honor the user's proxy and locale settings.
+                #:leaked-env-vars '("http_proxy" "https_proxy"
+                                    "LC_ALL" "LC_MESSAGES" "LANG"
+                                    "COLUMNS")
+                #:env-vars `(("url" . ,(object->string url)))
+
+                ;; Do not offload because the remote daemon may not support
+                ;; the 'download' builtin.
+                #:local-build? #t
+
+                ;; Do not substitute copyrighted material
+                #:substitutable? #f)))