publish: Advertise a short TTL for "baking" 404s.

* guix/scripts/publish.scm (not-found): Add #:phrase and #:ttl
parameters and honor them.
* tests/publish.scm ("with cache"): Check the 'cache-control' header on
of the 404 response.

2 files changed, 18 insertions, 4 deletions

diff --git a/guix/scripts/publish.scm b/guix/scripts/publish.scm
index efaa549676..8da75cb825 100644
--- a/guix/scripts/publish.scm
+++ b/guix/scripts/publish.scm
@@ -300,10 +300,15 @@ References: ~a~%~a"
                       (canonical-sexp->string (signed-string info)))))
     (format #f "~aSignature: 1;~a;~a~%" info (gethostname) signature)))
 
-(define (not-found request)
+(define* (not-found request
+                    #:key (phrase "Resource not found")
+                    ttl)
   "Render 404 response for REQUEST."
-  (values (build-response #:code 404)
-          (string-append "Resource not found: "
+  (values (build-response #:code 404
+                          #:headers (if ttl
+                                        `((cache-control (max-age . ,ttl)))
+                                        '()))
+          (string-append phrase ": "
                          (uri-path (request-uri request)))))
 
 (define (render-nix-cache-info)
@@ -434,7 +439,9 @@ requested using POOL."
                                                      (file-expiration-time ttl)
                                                      #:delete-entry delete-entry
                                                      #:cleanup-period ttl))))
-           (not-found request))
+           (not-found request
+                      #:phrase "We're baking it"
+                      #:ttl 300))              ;should be available within 5m
           (else
            (not-found request)))))
 
diff --git a/tests/publish.scm b/tests/publish.scm
index 6238f37bc1..268c324551 100644
--- a/tests/publish.scm
+++ b/tests/publish.scm
@@ -355,6 +355,13 @@ FileSize: ~a~%"
                                        (basename %item) ".nar"))
               (response (http-get url)))
          (and (= 404 (response-code response))
+
+              ;; We should get an explicitly short TTL for 404 in this case
+              ;; because it's going to become 200 shortly.
+              (match (assq-ref (response-headers response) 'cache-control)
+                ((('max-age . ttl))
+                 (< ttl 3600)))
+
               (wait-for-file cached)
               (let* ((body         (http-get-port url))
                      (compressed   (http-get nar-url))