http: Support fetching builds by derivation.

There's a one to one mapping of build id to derivation, so allow querying by
derivation file name as well. I'm looking at this as I'm interested in getting
build information in to the Guix Data Service.

* src/cuirass/http.scm (url-handler): Support fetching builds by numeric id or
the derivation file name.

src/cuirass/http.scm

@@ -42,6 +42,7 @@
   #:use-module (sxml simple)
   #:use-module (cuirass templates)
   #:use-module (guix utils)
+  #:use-module ((guix store) #:select (%store-prefix))
   #:use-module (guix build union)
   #:export (run-cuirass-server))
 
@@ -243,11 +244,14 @@ Hydra format."
     (((or "jobsets" "specifications") . rest)
      (respond-json (object->json-string
                     (list->vector (db-get-specifications)))))
-    (("build" build-id)
-     (let ((hydra-build (handle-build-request (string->number build-id))))
+    (("build" id)
+     (let ((hydra-build (handle-build-request
+                         (if (string-suffix? ".drv" id)
+                             (string-append (%store-prefix) "/" id)
+                             (string->number id)))))
        (if hydra-build
            (respond-json (object->json-string hydra-build))
-           (respond-build-not-found build-id))))
+           (respond-build-not-found id))))
     (("build" build-id "details")
      (let ((build (db-get-build (string->number build-id))))
        (if build