[bug#47897] [PATCH] substitutes: Don't cache negative lookups or transient errors.

[Christopher Baines]

Caching these responses can delay users getting substitutes, since they'll
have to wait at least as long as the cache TTL to fetch the substitute, even
if it's available sooner.

* guix/substitutes.scm (%narinfo-negative-ttl, %narinfo-transient-error-ttl):
Remove variables.
(cache-narinfo!): Adjust to not use the negative TTL.
(fetch-narinfos): Don't cache non 200 status code responses.
---
 guix/substitutes.scm | 22 +++-------------------
 1 file changed, 3 insertions(+), 19 deletions(-)

diff --git a/guix/substitutes.scm b/guix/substitutes.scm
index 08f8c24efd..55daa6c964 100644
--- a/guix/substitutes.scm
+++ b/guix/substitutes.scm
@@ -70,14 +70,6 @@
   ;; 'Cache-Control' response header.
   (* 36 3600))
 
-(define %narinfo-negative-ttl
-  ;; Likewise, but for negative lookups---i.e., cached lookup failures (404).
-  (* 1 3600))
-
-(define %narinfo-transient-error-ttl
-  ;; Likewise, but for transient errors such as 504 ("Gateway timeout").
-  (* 10 60))
-
 (define %narinfo-cache-directory
   ;; A local cache of narinfos, to avoid going to the network.  Most of the
   ;; time, 'guix substitute' is called by guix-daemon as root and stores its
@@ -104,8 +96,7 @@ entry is stored in a sub-directory specific to CACHE-URL."
 
 (define (cache-narinfo! cache-url path narinfo ttl)
   "Cache locally NARNIFO for PATH, which originates from CACHE-URL, with the
-given TTL (a number of seconds or #f).  NARINFO may be #f, in which case it
-indicates that PATH is unavailable at CACHE-URL."
+given TTL (a number of seconds or #f)."
   (define now
     (current-time time-monotonic))
 
@@ -113,8 +104,7 @@ indicates that PATH is unavailable at CACHE-URL."
     `(narinfo (version 2)
               (cache-uri ,cache-uri)
               (date ,(time-second now))
-              (ttl ,(or ttl
-                        (if narinfo %narinfo-ttl %narinfo-negative-ttl)))
+              (ttl ,(or ttl %narinfo-ttl))
               (value ,(and=> narinfo narinfo->string))))
 
   (let ((file (narinfo-cache-file cache-url path)))
@@ -214,16 +204,10 @@ if file doesn't exist, and the narinfo otherwise."
                   (cache-narinfo! url (narinfo-path narinfo) narinfo ttl)
                   (cons narinfo result))
                 result))
-          (let* ((path      (uri-path (request-uri request)))
-                 (hash-part (basename
-                             (string-drop-right path 8)))) ;drop ".narinfo"
+          (begin
             (if len
                 (get-bytevector-n port len)
                 (read-to-eof port))
-            (cache-narinfo! url (hash-part->path hash-part) #f
-                            (if (or (= 404 code) (= 202 code))
-                                ttl
-                                %narinfo-transient-error-ttl))
             result))))
 
   (define (do-fetch uri)
-- 
2.30.1