scripts: substitute: Default to fast decompression.

This changes the behaviour for the first one or few nars the substitute script
downloads, with uncompressed and zstd compressed nars prefered rather than
picking by file size.

* guix/scripts/substitute.scm: (%default-fast-decompression?): Change to #t.
* tests/substitute.scm ("substitute, preferred nar URL is 404, other is 200"):
Adjust test.

Change-Id: I89202f084cd6b9d506bcb3d46f75de690c6986b5

1 files changed, 18 insertions, 4 deletions

diff --git a/tests/substitute.scm b/tests/substitute.scm
index 33a6d6040ae..cd75d56b981 100644
--- a/tests/substitute.scm
+++ b/tests/substitute.scm
@@ -618,16 +618,30 @@ System: mips64el-linux\n")))
   (with-narinfo* (string-append %narinfo "Signature: " (signature-field %narinfo))
       %main-substitute-directory
 
+    (define (compress input output compression)
+      (call-with-output-file output
+        (lambda (port)
+          (call-with-compressed-output-port compression port
+            (lambda (port)
+              (call-with-input-file input
+                (lambda (input)
+                  (dump-port input port))))))))
+
+    ;; This test is dependent on which nar the substitute script picks to
+    ;; request first
     (with-http-server `((200 ,(string-append %narinfo "Signature: "
                                              (signature-field %narinfo)
                                              "\n"
                                              "URL: example.nar.lz\n"
                                              "Compression: lzip\n"))
                         (404 "Sorry, nar.lz is missing!")
-                        (200 ,(call-with-input-file
-                                  (string-append %main-substitute-directory
-                                                 "/example.nar")
-                                get-bytevector-all)))
+                        (200 ,(let ((nar (string-append
+                                          %main-substitute-directory
+                                          "/example.nar")))
+                                (compress nar (string-append nar ".lz") 'lzip)
+                                (call-with-input-file
+                                    (string-append nar ".lz")
+                                  get-bytevector-all))))
       (dynamic-wind
         (const #t)
         (lambda ()