publish: Add '--compression'.

* guix/scripts/publish.scm (show-help, %options): Add '--compression'.
(<compression>): New record type.
(%no-compression, %default-gzip-compression): New variables.
(%default-options): Add 'compression' key.
(narinfo-string): Add #:compression parameter and honor it.
(render-narinfo): Likewise.
(render-nar): Likewise.
<top level>: Add call to 'declare-header!'.
(swallow-zlib-error): New macro.
(nar-response-port): New procedure.
(http-write): Add call to 'force-output'.  Use 'nar-response-port'
instead of 'response-port'.  Use 'swallow-zlib-error'.
(make-request-handler): Add #:compression parameter and honor it.  Add
"nar/gzip" URL handler.
(run-publish-server): Add #:compression parameter and honor it.
(guix-publish): Honor --compression.
* tests/publish.scm (http-get-port, wait-until-ready): New procedures.
<top level>: Run main server with "-C0".  Call 'wait-until-ready'.
("/nar/gzip/*", "/*.narinfo with compression"): New tests.
* doc/guix.texi (Invoking guix publish): Document it.

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index a2732deded..6e8fb483f2 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -5644,6 +5644,18 @@ accept connections from any interface.
 Change privileges to @var{user} as soon as possible---i.e., once the
 server socket is open and the signing key has been read.
 
+@item --compression[=@var{level}]
+@itemx -C [@var{level}]
+Compress data using the given @var{level}.  When @var{level} is zero,
+disable compression.  The range 1 to 9 corresponds to different gzip
+compression levels: 1 is the fastest, and 9 is the best (CPU-intensive).
+The default is 3.
+
+Note compression occurs on the fly and the compressed streams are not
+cached.  Thus, to reduce load on the machine that runs @command{guix
+publish}, it may be a good idea to choose a low compression level, or to
+run @command{guix publish} behind a caching proxy.
+
 @item --ttl=@var{ttl}
 Produce @code{Cache-Control} HTTP headers that advertise a time-to-live
 (TTL) of @var{ttl}.  @var{ttl} must denote a duration: @code{5d} means 5