utils: Add 'decompressed-port' and 'compressed-port'.

* guix/utils.scm (decompressed-port, compressed-port): New procedures.
* guix/scripts/substitute-binary.scm (decompressed-port): Remove.
  (guix-substitute-binary): Pass a symbol or #f as the first argument to
  'decompress-port'.
* tests/utils.scm ("compressed-port, decompressed-port, non-file"): New
  test.

guix/scripts/substitute-binary.scm

@@ -400,16 +400,6 @@ (define last-expiry-date
     (call-with-output-file expiry-file
       (cute write (time-second now) <>))))
 
-(define (decompressed-port compression input)
-  "Return an input port where INPUT is decompressed according to COMPRESSION,
-along with a list of PIDs to wait for."
-  (match compression
-    ("none"  (values input '()))
-    ("bzip2" (filtered-port `(,%bzip2 "-dc") input))
-    ("xz"    (filtered-port `(,%xz "-dc") input))
-    ("gzip"  (filtered-port `(,%gzip "-dc") input))
-    (else    (error "unsupported compression scheme" compression))))
-
 (define (progress-report-port report-progress port)
   "Return a port that calls REPORT-PROGRESS every time something is read from
 PORT.  REPORT-PROGRESS is a two-argument procedure such as that returned by
@@ -598,7 +588,8 @@ (define (guix-substitute-binary . args)
                                                        (current-error-port))))
                          (progress-report-port progress raw)))
                       ((input pids)
-                       (decompressed-port (narinfo-compression narinfo)
+                       (decompressed-port (and=> (narinfo-compression narinfo)
+                                                 string->symbol)
                                           progress)))
           ;; Unpack the Nar at INPUT into DESTINATION.
           (restore-file input destination)

guix/utils.scm

@@ -70,7 +70,10 @@ (define-module (guix utils)
             call-with-temporary-output-file
             with-atomic-file-output
             fold2
-            filtered-port))
+
+            filtered-port
+            compressed-port
+            decompressed-port))
 
 
 ;;;
@@ -200,6 +203,26 @@ (define (filtered-port command input)
               (close-port out)
               (loop in (cons child pids)))))))))
 
+(define (decompressed-port compression input)
+  "Return an input port where INPUT is decompressed according to COMPRESSION,
+a symbol such as 'xz."
+  (match compression
+    ((or #f 'none) (values input '()))
+    ('bzip2        (filtered-port `(,%bzip2 "-dc") input))
+    ('xz           (filtered-port `(,%xz "-dc") input))
+    ('gzip         (filtered-port `(,%gzip "-dc") input))
+    (else          (error "unsupported compression scheme" compression))))
+
+(define (compressed-port compression input)
+  "Return an input port where INPUT is decompressed according to COMPRESSION,
+a symbol such as 'xz."
+  (match compression
+    ((or #f 'none) (values input '()))
+    ('bzip2        (filtered-port `(,%bzip2 "-c") input))
+    ('xz           (filtered-port `(,%xz "-c") input))
+    ('gzip         (filtered-port `(,%gzip "-c") input))
+    (else          (error "unsupported compression scheme" compression))))
+
 
 ;;;
 ;;; Nixpkgs.

tests/utils.scm

@@ -150,6 +150,17 @@ (define temp-file
       (any (compose (negate zero?) cdr waitpid)
            pids))))
 
+(test-assert "compressed-port, decompressed-port, non-file"
+  (let ((data (call-with-input-file (search-path %load-path "guix.scm")
+                get-bytevector-all)))
+    (let*-values (((compressed pids1)
+                   (compressed-port 'xz (open-bytevector-input-port data)))
+                  ((decompressed pids2)
+                   (decompressed-port 'xz compressed)))
+      (and (every (compose zero? cdr waitpid)
+                  (append pids1 pids2))
+           (equal? (get-bytevector-all decompressed) data)))))
+
 (false-if-exception (delete-file temp-file))
 (test-equal "fcntl-flock wait"
   42                                              ; the child's exit status