utils: Support zstd compression via Guile-zstd.

* guix/utils.scm (lzip-port): Return a single value.
(zstd-port): New procedure.
(decompressed-port, compressed-output-port): Add 'zstd' case.
* tests/utils.scm (test-compression/decompression): Test 'zstd' when
the (zstd) module is available.

1 files changed, 4 insertions, 2 deletions

diff --git a/tests/utils.scm b/tests/utils.scm
index c278b2a2778..9bce446d98f 100644
--- a/tests/utils.scm
+++ b/tests/utils.scm
@@ -228,8 +228,10 @@ skip these tests."
                       get-bytevector-all)))))
 
 (for-each test-compression/decompression
-          '(gzip xz lzip)
-          (list (const #t) (const #t) (const #t)))
+          `(gzip xz lzip zstd)
+          (list (const #t) (const #t) (const #t)
+                (lambda ()
+                  (resolve-module '(zstd) #t #f #:ensure #f))))
 
 ;; This is actually in (guix store).
 (test-equal "store-path-package-name"