hydra: build-package-metadata: Compress JSON files.

* hydra/build-package-metadata.scm (write-json): Use
‘call-with-gzip-output-port’.
(main): Append “.gz” to JSON file names.
* hydra/modules/sysadmin/nginx.scm (guix.gnu.org-other-locations): Add
“gzip_static” and “gunzip” directives on /packages.json and
/sources.json.

hydra/build-package-metadata.scm

@@ -39,6 +39,7 @@
              (guix svn-download)
              (guix hg-download)
              (json)
+             (zlib)
              (web uri)
              (ice-9 match)
              (ice-9 vlist)
@@ -239,11 +240,21 @@ superseded packages."
   (list->vector (map package->json (all-packages))))
 
 (define (write-json json file)
-  "Serialize JSON to FILE."
-  (with-atomic-file-output file
-    (lambda (port)
-      (scm->json json port)
-      (chmod port #o644))))
+  "Serialize and compress JSON to FILE."
+  (let ((pivot (string-append file ".tmp")))
+    ;; Note: 'with-atomic-file-output' doesn't work well with
+    ;; 'call-with-gzip-output-port' since the latter closes its underlying
+    ;; port.
+    (call-with-output-file pivot
+      (lambda (port)
+        (chmod port #o644)
+        (call-with-gzip-output-port port
+          (lambda (port)
+            (set-port-encoding! port "UTF-8")
+            (scm->json json port))
+          #:buffer-size (expt 2 16)
+          #:level 9)))
+    (rename-file pivot file)))
 
 
 ;;;
@@ -258,7 +269,7 @@ superseded packages."
                  (write-json (thunk)
                              (string-append directory "/" file)))
                (list packages-json sources-json)
-               '("packages.json" "sources.json")))
+               '("packages.json.gz" "sources.json.gz")))
     ((command . _)
      (leave (G_ "Usage: ~a DIRECTORY
 

hydra/modules/sysadmin/nginx.scm

@@ -704,11 +704,13 @@ synonymous IETF language tags that should be mapped to the same $lang."
    (nginx-location-configuration
     (uri "= /packages.json")
     (body (list "if_modified_since exact;"
+                "gzip_static always; gunzip on;\n"
                 "root /srv/package-metadata;")))
 
    (nginx-location-configuration
     (uri "= /sources.json")
     (body (list "if_modified_since exact;"
+                "gzip_static always; gunzip on;\n"
                 "root /srv/package-metadata;")))
 
    (nginx-location-configuration                  ;certbot