From 71d2bdfa9fce546e8d8d5103aee4e1096ce65ecf Mon Sep 17 00:00:00 2001
From: Christopher Baines <mail@cbaines.net>
Date: Fri, 4 Feb 2022 10:00:50 +0000
Subject: services: nar-herder: Support ttl and negative-ttl options.

* gnu/services/guix.scm (<nar-herder-configuration>): Add ttl and negative-ttl
fields.
(nar-herder-shepherd-services): Pass the ttl and negative-ttl values to the
service.
* doc/guix.texi (Guix Services): Document this.
---
 doc/guix.texi         | 14 ++++++++++++++
 gnu/services/guix.scm | 18 +++++++++++++++---
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/doc/guix.texi b/doc/guix.texi
index aaa7cbb66f..0cf865a672 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -33721,6 +33721,20 @@ Each criteria is specified by a string, then an equals sign, then
 another string. Currently, only one criteria is supported, checking if a
 nar is stored on another Nar Herder instance.
 
+@item @code{ttl} (default: @code{#f})
+Produce @code{Cache-Control} HTTP headers that advertise a time-to-live
+(TTL) of @var{ttl}.  @var{ttl} must denote a duration: @code{5d} means 5
+days, @code{1m} means 1 month, and so on.
+
+This allows the user's Guix to keep substitute information in cache for
+@var{ttl}.
+
+@item @code{negative-ttl} (default: @code{#f})
+Similarly produce @code{Cache-Control} HTTP headers to advertise the
+time-to-live (TTL) of @emph{negative} lookups---missing store items, for
+which the HTTP 404 code is returned.  By default, no negative TTL is
+advertised.
+
 @end table
 @end deftp
 
diff --git a/gnu/services/guix.scm b/gnu/services/guix.scm
index 6a5b276b33..dc9bd8ad68 100644
--- a/gnu/services/guix.scm
+++ b/gnu/services/guix.scm
@@ -774,7 +774,12 @@ (define-record-type* <nar-herder-configuration>
                  (default "none"))
   (storage-nar-removal-criteria
    nar-herder-configuration-storage-nar-removal-criteria
-   (default '())))
+   (default '()))
+  (ttl           nar-herder-configuration-ttl
+                 (default #f))
+  (negative-ttl  nar-herder-configuration-negative-ttl
+                 (default #f)))
+
 
 (define (nar-herder-shepherd-services config)
   (match-record config <nar-herder-configuration>
@@ -782,7 +787,8 @@ (define (nar-herder-shepherd-services config)
              mirror
              database database-dump
              host port
-             storage storage-limit storage-nar-removal-criteria)
+             storage storage-limit storage-nar-removal-criteria
+             ttl negative-ttl)
 
     (unless (or mirror storage)
       (error "nar-herder: mirror or storage must be set"))
@@ -817,7 +823,13 @@ (define (nar-herder-shepherd-services config)
                                  (match criteria
                                    ((k . v) (simple-format #f "~A=~A" k v))
                                    (str str))))
-                              storage-nar-removal-criteria))
+                              storage-nar-removal-criteria)
+                      #$@(if ttl
+                             (list (string-append "--ttl=" ttl))
+                             '())
+                      #$@(if negative-ttl
+                             (list (string-append "--negative-ttl=" negative-ttl))
+                             '()))
                 #:user #$user
                 #:group #$group
                 #:pid-file "/var/run/nar-herder/pid"
-- 
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