+(define (compress-nar cache item compression)
+ "Save in directory CACHE the nar for ITEM compressed with COMPRESSION."
+ (define nar
+ (nar-cache-file cache item #:compression compression))
+
+ (mkdir-p (dirname nar))
+ (match (compression-type compression)
+ ('gzip
+ ;; Note: the file port gets closed along with the gzip port.
+ (call-with-gzip-output-port (open-output-file (string-append nar ".tmp"))
+ (lambda (port)
+ (write-file item port))
+ #:level (compression-level compression)
+ #:buffer-size (* 128 1024))
+ (rename-file (string-append nar ".tmp") nar))
+ ('lzip
+ ;; Note: the file port gets closed along with the lzip port.
+ (call-with-lzip-output-port (open-output-file (string-append nar ".tmp"))
+ (lambda (port)
+ (write-file item port))
+ #:level (compression-level compression))
+ (rename-file (string-append nar ".tmp") nar))
+ ('none
+ ;; Cache nars even when compression is disabled so that we can
+ ;; guarantee the TTL (see <https://bugs.gnu.org/28664>.)
+ (with-atomic-file-output nar
+ (lambda (port)
+ (write-file item port))))))
+