publish: Preserve the request connection header.

The Guile web server is reading the response connection header to decide
whether to close the connection. However, as the request connection header is
not forwarded to the response, this mechanism cannot work.

* guix/scripts/publish.scm (add-extra-headers): New procedure.
(make-request-handler): Use it to forward the request connection header to the
response.

guix/scripts/publish.scm

@@ -33,6 +33,7 @@
   #:use-module (srfi srfi-2)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-9 gnu)
+  #:use-module (srfi srfi-11)
   #:use-module (srfi srfi-19)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
@@ -980,6 +981,18 @@ methods, return the applicable compression."
             compressions)
       (default-compression requested-type)))
 
+(define (preserve-connection-headers request response)
+  "Add REQUEST's 'connection' header, if any, to HEADERS, a list of response
+headers."
+  (if (pair? response)
+      (let ((connection
+             (assq 'connection (request-headers request))))
+        (append response
+                (if connection
+                    (list connection)
+                    '())))
+      response))
+
 (define* (make-request-handler store
                                #:key
                                cache pool
@@ -993,7 +1006,7 @@ methods, return the applicable compression."
     (let ((expected (split-and-decode-uri-path nar-path)))
       (cut equal? expected <>)))
 
-  (lambda (request body)
+  (define (handle request body)
     (format #t "~a ~a~%"
             (request-method request)
             (uri-path (request-uri request)))
@@ -1065,7 +1078,15 @@ methods, return the applicable compression."
                (not-found request)))
 
           (x (not-found request)))
-        (not-found request))))
+        (not-found request)))
+
+  ;; Preserve the request's 'connection' header in the response, so that the
+  ;; server can close the connection if this is requested by the client.
+  (lambda (request body)
+    (let-values (((response response-body)
+                  (handle request body)))
+      (values (preserve-connection-headers request response)
+              response-body))))
 
 (define (service-name)
   "Return the Avahi service name of the server."