substitute-binary: Try hard to avoid port buffering.

* guix/scripts/substitute-binary.scm (fetch): In the `file' case, open
  with the `b' flag, so that the coding cookie reading thing doesn't
  lead to buffering some of the data (on 2.0.5).
* tests/utils.scm ("filtered-port, file"): Open with `r0b'.  Fixes a
  test failure with Guile 2.0.5 whereby the first byte of FILE would be
  missing from DECOMPRESSED.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/utils.scm b/tests/utils.scm
index e8549204d07..3be60e443d3 100644
--- a/tests/utils.scm
+++ b/tests/utils.scm
@@ -103,7 +103,7 @@
 
 (test-assert "filtered-port, file"
   (let* ((file  (search-path %load-path "guix.scm"))
-         (input (open-file file "r0")))
+         (input (open-file file "r0b")))
     (let*-values (((compressed pids1)
                    (filtered-port `(,%gzip "-c" "--fast") input))
                   ((decompressed pids2)