publish: Add keep-alive support when sending nar.

The default Guile web server implementation supports the keep alive
mechanism. However, in our custom http-write implementation, the connection
is unconditionally close after sending nar files.

To prevent that, when supported, add the client port to the server poll set so
that further requests can be handled without closing the connection.

* guix/scripts/publish.scm (nar-response-port): Rename it into ...
(nar-compressed-port): ... this procedure. Operate directly on a given PORT.
(http-write): Add keep-alive support when sending nar files.
* guix/scripts/substitute.scm (process-substitution): Pass the download size
to the progress-report-port procedure so that it doesn't block reading from
the input port when keep-alive is supported.

1 files changed, 5 insertions, 2 deletions

diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index 8e4eae00b3..54311c3e08 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -518,8 +518,11 @@ PORT."
                                          (current-error-port)
                                          #:abbreviation nar-uri-abbreviation))))
                      ;; Keep RAW open upon completion so we can later reuse
-                     ;; the underlying connection.
-                     (progress-report-port reporter raw #:close? #f)))
+                     ;; the underlying connection.  Pass the download size so
+                     ;; that this procedure won't block reading from RAW.
+                     (progress-report-port reporter raw
+                                           #:close? #f
+                                           #:download-size dl-size)))
                   ((input pids)
                    ;; NOTE: This 'progress' port of current process will be
                    ;; closed here, while the child process doing the