Add (guix cache) and use it in (guix scripts substitute).

* guix/cache.scm, tests/cache.scm: New files.
* Makefile.am (MODULES, SCM_TESTS): Add them.
* guix/scripts/substitute.scm (obsolete?): Remove.
(remove-expired-cached-narinfos): Rename to...
(cached-narinfo-expiration-time): ... this.  Remove the removal part and
only keep the expiration time part.
(narinfo-cache-directories): Add optional 'directory' parameter and
honor it.
(maybe-remove-expired-cached-narinfo): Remove.
(cached-narinfo-files): New procedure.
(guix-substitute): Use 'maybe-remove-expired-cache-entries' instead of
'maybe-remove-expired-cached-narinfo'.

2 files changed, 142 insertions, 61 deletions

diff --git a/guix/cache.scm b/guix/cache.scm
new file mode 100644
index 0000000000..077b0780bd
--- /dev/null
+++ b/guix/cache.scm
@@ -0,0 +1,106 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013, 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (guix cache)
+  #:use-module (srfi srfi-19)
+  #:use-module (srfi srfi-26)
+  #:use-module (ice-9 match)
+  #:export (obsolete?
+            delete-file*
+            file-expiration-time
+            remove-expired-cache-entries
+            maybe-remove-expired-cache-entries))
+
+;;; Commentary:
+;;;
+;;; This module provides tools to manage a simple on-disk cache consisting of
+;;; individual files.
+;;;
+;;; Code:
+
+(define (obsolete? date now ttl)
+  "Return #t if DATE is obsolete compared to NOW + TTL seconds."
+  (time>? (subtract-duration now (make-time time-duration 0 ttl))
+          (make-time time-monotonic 0 date)))
+
+(define (delete-file* file)
+  "Like 'delete-file', but does not raise an error when FILE does not exist."
+  (catch 'system-error
+    (lambda ()
+      (delete-file file))
+    (lambda args
+      (unless (= ENOENT (system-error-errno args))
+        (apply throw args)))))
+
+(define (file-expiration-time ttl)
+  "Return a procedure that, when passed a file, returns its \"expiration
+time\" computed as its last-access time + TTL seconds."
+  (lambda (file)
+    (match (stat file #f)
+      (#f 0)                       ;FILE may have been deleted in the meantime
+      (st (+ (stat:atime st) ttl)))))
+
+(define* (remove-expired-cache-entries entries
+                                       #:key
+                                       (now (current-time time-monotonic))
+                                       (entry-expiration
+                                        (file-expiration-time 3600))
+                                       (delete-entry delete-file*))
+  "Given ENTRIES, a list of file names, remove those whose expiration time,
+as returned by ENTRY-EXPIRATION, has passed.  Use DELETE-ENTRY to delete
+them."
+  (for-each (lambda (entry)
+              (when (<= (entry-expiration entry) (time-second now))
+                (delete-entry entry)))
+            entries))
+
+(define* (maybe-remove-expired-cache-entries cache
+                                             cache-entries
+                                             #:key
+                                             (entry-expiration
+                                              (file-expiration-time 3600))
+                                             (delete-entry delete-file*)
+                                             (cleanup-period (* 24 3600)))
+  "Remove expired narinfo entries from the cache if deemed necessary.  Call
+CACHE-ENTRIES with CACHE to retrieve the list of cache entries.
+
+ENTRY-EXPIRATION must be a procedure that, when passed an entry, returns the
+expiration time of that entry in seconds since the Epoch.  DELETE-ENTRY is a
+procedure that removes the entry passed as an argument.  Finally,
+CLEANUP-PERIOD denotes the minimum time between two cache cleanups."
+  (define now
+    (current-time time-monotonic))
+
+  (define expiry-file
+    (string-append cache "/last-expiry-cleanup"))
+
+  (define last-expiry-date
+    (catch 'system-error
+      (lambda ()
+        (call-with-input-file expiry-file read))
+      (const 0)))
+
+  (when (obsolete? last-expiry-date now cleanup-period)
+    (remove-expired-cache-entries (cache-entries cache)
+                                  #:now now
+                                  #:entry-expiration entry-expiration
+                                  #:delete-entry delete-entry)
+    (call-with-output-file expiry-file
+      (cute write (time-second now) <>))))
+
+;;; cache.scm ends here
diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index d3bccf4ddb..748c334e3c 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -28,6 +28,7 @@
   #:use-module (guix hash)
   #:use-module (guix base32)
   #:use-module (guix base64)
+  #:use-module (guix cache)
   #:use-module (guix pk-crypto)
   #:use-module (guix pki)
   #:use-module ((guix build utils) #:select (mkdir-p dump-port))
@@ -440,12 +441,6 @@ or is signed by an unauthorized key."
 the cache STR originates form."
   (call-with-input-string str (cut read-narinfo <> cache-uri)))
 
-(define (obsolete? date now ttl)
-  "Return #t if DATE is obsolete compared to NOW + TTL seconds."
-  (time>? (subtract-duration now (make-time time-duration 0 ttl))
-          (make-time time-monotonic 0 date)))
-
-
 (define (narinfo-cache-file cache-url path)
   "Return the name of the local file that contains an entry for PATH.  The
 entry is stored in a sub-directory specific to CACHE-URL."
@@ -718,43 +713,28 @@ was found."
     ((answer) answer)
     (_        #f)))
 
-(define (remove-expired-cached-narinfos directory)
-  "Remove expired narinfo entries from DIRECTORY.  The sole purpose of this
-function is to make sure `%narinfo-cache-directory' doesn't grow
-indefinitely."
-  (define now
-    (current-time time-monotonic))
+(define (cached-narinfo-expiration-time file)
+  "Return the expiration time for FILE, which is a cached narinfo."
+  (catch 'system-error
+    (lambda ()
+      (call-with-input-file file
+        (lambda (port)
+          (match (read port)
+            (('narinfo ('version 2) ('cache-uri uri)
+                       ('date date) ('ttl ttl) ('value #f))
+             (+ date %narinfo-negative-ttl))
+            (('narinfo ('version 2) ('cache-uri uri)
+                       ('date date) ('ttl ttl) ('value value))
+             (+ date ttl))
+            (x
+             0)))))
+    (lambda args
+      ;; FILE may have been deleted.
+      0)))
 
-  (define (expired? file)
-    (catch 'system-error
-      (lambda ()
-        (call-with-input-file file
-          (lambda (port)
-            (match (read port)
-              (('narinfo ('version 2) ('cache-uri _)
-                         ('date date) ('ttl _) ('value #f))
-               (obsolete? date now %narinfo-negative-ttl))
-              (('narinfo ('version 2) ('cache-uri _)
-                         ('date date) ('ttl ttl) ('value _))
-               (obsolete? date now ttl))
-              (_ #t)))))
-      (lambda args
-        ;; FILE may have been deleted.
-        #t)))
-
-  (for-each (lambda (file)
-              (let ((file (string-append directory "/" file)))
-                (when (expired? file)
-                  ;; Wrap in `false-if-exception' because FILE might have been
-                  ;; deleted in the meantime (TOCTTOU).
-                  (false-if-exception (delete-file file)))))
-            (scandir directory
-                     (lambda (file)
-                       (= (string-length file) 32)))))
-
-(define (narinfo-cache-directories)
+(define (narinfo-cache-directories directory)
   "Return the list of narinfo cache directories (one per cache URL.)"
-  (map (cut string-append %narinfo-cache-directory "/" <>)
+  (map (cut string-append directory "/" <>)
        (scandir %narinfo-cache-directory
                 (lambda (item)
                   (and (not (member item '("." "..")))
@@ -762,25 +742,15 @@ indefinitely."
                         (string-append %narinfo-cache-directory
                                        "/" item)))))))
 
-(define (maybe-remove-expired-cached-narinfo)
-  "Remove expired narinfo entries from the cache if deemed necessary."
-  (define now
-    (current-time time-monotonic))
-
-  (define expiry-file
-    (string-append %narinfo-cache-directory "/last-expiry-cleanup"))
-
-  (define last-expiry-date
-    (or (false-if-exception
-         (call-with-input-file expiry-file read))
-        0))
-
-  (when (obsolete? last-expiry-date now
-                   %narinfo-expired-cache-entry-removal-delay)
-    (for-each remove-expired-cached-narinfos
-              (narinfo-cache-directories))
-    (call-with-output-file expiry-file
-      (cute write (time-second now) <>))))
+(define* (cached-narinfo-files #:optional
+                               (directory %narinfo-cache-directory))
+  "Return the list of cached narinfo files under DIRECTORY."
+  (append-map (lambda (directory)
+                (map (cut string-append directory "/" <>)
+                     (scandir directory
+                              (lambda (file)
+                                (= (string-length file) 32)))))
+              (narinfo-cache-directories directory)))
 
 (define (progress-report-port report-progress port)
   "Return a port that calls REPORT-PROGRESS every time something is read from
@@ -1013,7 +983,12 @@ default value."
 (define (guix-substitute . args)
   "Implement the build daemon's substituter protocol."
   (mkdir-p %narinfo-cache-directory)
-  (maybe-remove-expired-cached-narinfo)
+  (maybe-remove-expired-cache-entries %narinfo-cache-directory
+                                      cached-narinfo-files
+                                      #:entry-expiration
+                                      cached-narinfo-expiration-time
+                                      #:cleanup-period
+                                      %narinfo-expired-cache-entry-removal-delay)
   (check-acl-initialized)
 
   ;; Starting from commit 22144afa in Nix, we are allowed to bail out directly